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CLASS: II YEAR / VI SEMESTER ECE

SUBJECT CODE AND NAME: EC 2254 – LINEAR INTEGRATED CIRCUITS

UNIT I – IC FABRICATION AND CIRCUIT CONFIGURATION FOR LINEAR IC

1. Mention the advantages of integrated circuits.                                                     (Apr/May 2007)

*Miniaturization and hence increased equipment density.

*Cost reduction due to batch processing.

*Increased system reliability due to the elimination of soldered joints. *Improved functional performance.*Matched devices. *Increased operating speeds.*Reduction in power consumption.

2. Write down the various processes used to fabricate IC’s using silicon planar technology. (Nov/Dec-2011)

*Silicon wafer preparation.* Epitaxial growth *Oxidation.*Photolithography.

*Diffusion*Ion implantation.*Isolation.*Metallization.*Assembly processing and packaging.

3. What is the purpose of oxidation?  Apr/May 2007)

*SiO2 is an extremely hard protective coating and is unaffected by almost all reagents.*By selective etching of SiO2, diffusion of impurities through carefully defined windows can be accomplished to fabricate various components.

4. What is meant by ion implantation? (Nov/Dec 2011)

Ion implantation is performed at low temperatures and is used to introduce impurities into a silicon wafer.By increasing voltage,the depth of penetration of any particular type of ion increases.

5. Differentiate between thin flim and thick flim technology in IC fabrication. (Nov/Dec-2007)

Generally thick –thin flim ICs are used to produce only passive elements.The thick flim technology is comparatively easier and inexpensive while the thin flim technology is slightly complicated and expensively.The thin flim technology produces components with greater precision as compared to Those produced by the thick flim technology.

6. Define an operational amplifier. (Nov/Dec-2004)

An operational amplifier is a direct-coupled, high gain amplifier consisting of one or more differential amplifier. By properly selecting the external components, it can be used to perform a variety of mathematical operations.

7. Give the different type of IC packages? (Nov/Dec-2006)

(i)Metal can package.

(ii)Dual in line package.

(iii)Flat package

8. State the applications of band gap reference circuit. (Nov/Dec-2008)

(i)Voltage regulators

(ii)D/A and A/D convertors.

(iii)Voltage to frequency and frequency to voltage convertors.

(iv)power supply supervisory circuit.

(v)Bar graph meter.

9. Define the following parameters as applied to an op-amp:                                 (Apr/May 2005)

 i) Input bias current.

Input bias current IB is the average of the currents that flow into the inverting and non-inverting input erminals of the op-amp.i.e. IB = (IB1+IB2)/2

ii) Input offset current

The algebraic difference between the current into the inverting and non-inverting terminals is referred to as input offset current Iio. Mathematically it is represented as I_io = |I_B - I_B | WhereI _B+is the current into the non-inverting input terminals.I_B- is the current into the inverting input terminals.

iii) Input offset voltage

This is the voltage required to be amplified at the input for making output voltage to zero volts

iv) C.M.R.R

The common mode rejection ratio (CMRR) can be defined as the ratio of differential gain to common mode gain.CMRR = |Ad/Ac|

v) P.S.R.R

Power Supply Rejection Ratio (PSRR) is the ability of an amplifier to maintain its output voltage as its DC power-supply voltage is varied.PSRR = (change in Vcc)/(change in Vout)

vi) Slew rate

Slew rate can be defined as the maximum rate of change of output voltage of op-amp with respect to time. It is expressed as S = (dVo / dt) max in V/Sec.Where slew rate S = 2П f Vm in V/Sec.

 

11. What is CMRR? State its ideal value.  (Apr/May 2011)

The ability of a differential amplifier to reject common mode signal is expressed by the ratio of differential gain to the common node gain which is called its common mode rejection ratio CMRR.The ideal value of the CMRR is infinite.

12. Determine the slew rate of the op-amp. (Nov/Dec-2008)

Slew rate can be defined as the maximum rate of change of output voltage of op-amp with respect to time. It is expressed as S = (dVo / dt) max in V/Sec.Where slew rate S = 2П f Vm in V/Sec.

13. What is active load? Where it is used and why?      (Nov/Dec-2007)

In circuit design, an active load is a circuit component made up of active devices, such as transistors, intended to present high small-signal impedance yet not requiring a large DC Voltage drop, as would occur if a large resistor were used instead. Such large AC load impedances may be desirable, for example, to increase the AC gain of some types of amplifier. Most commonly the active load is the output part of a current mirror and is represented in an idealized manner as a current source. Usually, it is only a constant-current resistor that is a part of the whole current source including a constant voltage source as well.

14. What causes slew rate?      (Apr/May 2008)

He rate at which the internal or external capacitance of an op-amp charges causes slew rate.

15. What do you mean by monolithic process?          (Apr/May 2006)
Monolithic process means a circuit fabricated from a single stone or a single crystal. The origin of the word ‘monolithic’ is from the Greek word monos meaning ‘single’ and litho meaning ‘stone’, so monolithic integrated circuits are, in fact, macle in a single piece of single crystal silicon.

16. List the advantages of integrated circuits over discrete component circuit.(Apr/May2010)
1. Practically size of an IC is thousands of times smaller than the discrete circuits.2.ICsoperateatlowvoltages3.ThecostofICisveryless4.Thepowerconsumption is less

17. What is meant by epitaxial growth?   (Apr/May 2008)

The epitaxial means arranged upon’. In epitaxial a monocrystallifle film is formed on the top of a monocrystalline surface. The epitaxial is crystalline growth process in which the foundation layer, i.e. substrate works as seed crystal. The epitaxial layer formed on the substrate may be either n-doped or p-doped or intrinsic.

18. Define current mirror circuit.  (Apr/May 2010)

The circuit in which the output is forced to equal the input current is called as current mirror circuit. In a current mirror circuit, the output current is the mirror image of input current.

19. What are the limitations of integrated circuits?   (Apr/May 2010)

i)Does not with stand higher voltages ii) it generates heat while running, but does not withstand in higher temperature. So heat sink (or / and) fan must be placed.

20. What is meant by integrated circuit?     (Apr/May 2010)

An integrated circuit is a miniature of electronic circuit that consisting of active and passive components together on the same silicon substrate. On the single silicon substrate the active and passive elements are fabricated by diffusing the electronics and holes where necessary.

21. Define current mirror with magnification.      (May 2008)

In this circuit sometimes it is necessary to have a circuit in which ratio of biasing currents in two transistors is required to be fixed. Such a circuit is called as current mirror circuit with magnification.

22. Define unity gain bandwidth of an Op-amp.   (May/Jun 2008)

At a certain frequency, the open loop gain reduces to 0db.This indicates that 20log│A_OL(f)│ is 0db.i.e.│A_OL(f)│=1.such a frequency at which magnitude of the open loop gain is unity is called gain cross –over frequency or unity gain bandwidth.

23. What is PSRR? What should be its ideal value? (May 2003)
PSRR is power supply rejection ratio. It is defined as the change in the input offset voltage due to the change in one of the two supply voltages when other voltage is maintained constant.lt ideal value should be zero.

24. Name the parameters which govern the thickness of the film in the oxidationprocess.        (Nov/Dec-2008)
The main parameter which governs the thickness of the film in the oxidation process is temperature. Because to grow the oxide layer high temperature is to be maintained, the other important parameters governing oxide film thickness are time up to which process is to be carried out and the moisture contents.

25. What is common mode gain of a differential amplifier? State its ideal value.

If the two input signals to a differential amplifier are same, then its output should be zero. But practically it produces a small output which is proportional to the average common level of the two input signals.

26. Why aluminum is preferred for metallization?

*It is a good conductor.*it is easy to deposit aluminum films using vacuum deposition.*It makes good mechanical bonds with silicon.*It forms a low resistance contact.

27. List out various configurations of a differential amplifier.

(i)Dual input balanced output.

(ii) Dual input unbalanced output.

(iii)Single input balanced output.(iv) Single input unbalanced output.

28. Why practically Re cannot be selected very high?

Practically Re cannot be selected very high because

(i)   Large Re requires higher biasing voltages to set the proper operating point of the transistor.

(ii)  This increases the overall chip area.

(iii) Smaller number of components can be installed on the same chip which is undesirable from integrated circuit point of view.

29. Why constant current source is used instead of Re?

Without physically increasing the value of Re,the Reis replaced by a transistor operated at a constant current. Such a constant current source circuit gives the effect of a very high resistance as the internal resistance of a constant current source is infinite.

30. What is a voltage reference circuit?

A voltage reference circuit is a constant d.c voltage source which acts as a reference or a standard for other circuits and is independent of changes in parameters like temperature, line voltage, load current etc.

31. List the performance parameters of a voltage reference circuit.

(i) Line regulation.

(ii) load regulation

(iii)Long term stability.

(iv)Ripple rejection ratio.

32. Why an open loop op-amp configuration is not used in linear applications?

a.  The open loop gain of the op-amp is very high. Therefore only the smaller signals having low frequency may be amplified accurately without distortion.

b. Open loop Voltage gain of the op-amp is not a constant voltage gain varies with changes in temperature and power supply as well as mass production techniques. This makes op-amp unsuitable for many linear applications

Bandwidth of most open loop op-amps is negligibly small or almost zero therefore op-amp is impractical in ac applications.

33. What is a differential amplifier? What is the ideal value of its gain?

 A differential amplifier is one which amplifies the difference between its two input signals. The gain with which it amplifies the difference is called is differential gain and ideally it should be infinite.

34. Define Virtual ground property of an OP-AMP.

A virtual ground is a ground which acts like a ground. It may not have physical connection to ground. This property of an ideal op-amp indicates that the inverting and non-inverting terminals of op-amp are at the same potentials. The non-inverting input is grounded for the inverting amplifier circuit. This means that the inverting input of the op-amp is also at ground potential.

35. Mention some applications of op-amp?

Op-amp can be used for a variety of applications such as ac and dc signal amplification, active filters, comparators, oscillators, regulators and other applications.

36. What are the limitations of monolithic ICs?

(i)The large value of resistances and capacitances that ae required in some linear circuits cannot de formed using this type of ICs.

(ii) There is no method available to fabricate transformers or to form large values of inductors in integrated circuit form.

37. What are the two compensating techniques used in frequency compensation?

(i) External compensation

(ii) Internal compensation.

38. What is an compensated op-amp?

Op-amp,which uses a capacitor nternally for compensation is called a compensated op-amp.this op-amp has a high gain stability and low band width.

39. What are methods used in external compensation technique?

(i) Dominant pole compensation

(ii) pole-zero compensation.

40.What is an internally compensated op-amp?

(i) These are used where a relatively broad bandwidth is not needed.

(ii) These are sometimes called compensated op-amps.

(iv)  The type 741 op-amp is compensated and has an open loop gain Vs frequency response.

41. What is a Hybrid Ic?

A hybrid Ic consists of a combination of two or more IC types.

42. Define wafer.

It is the basic physical unit used in processing. It consists of large number of identical Ics.

43. What are the limitations of ICs?

The limitations of integrated circuits are since ICs are small and unable to dissipate large amount of power,the heat produced by large currents may destroy the Ic.

44. List out the ideal characteristics, and draw the equivalent diagram of an OP-AMP.

* Open loop voltage gain is infinity.*Input impedance is infinity.*Output impedance is zero. *Bandwidth is infinity.*Zero offset.

45. Define Etching. What are the different types?

It’s a process of removing a flim or layer form the substrate in those areas not coverd with photo resist.There are two types of etching i)Wet etching and ii)Dry etching.

46.What are the properties of the chemicals used for etching?

(a) It should react with the flim etched in a smooth manner producing suitable products that can be carried away form the surface.

(b) It should not react with photoresist.

(c) It should be act with flim to be etched and not with other microelectronic materials.

47.What is the purpose of formation of SiO2 layer?

(a) It service as a diffusion mask and allow diffusion impurities through carefully defined windows etched into oxide.

(b) It serves as an insulators in the wafer surface.

(c) It protects the junction the junction from moisture and other atmospheric contaminants.

48.What is meant by metallization?

After device have been fabricated in the silicon substrate,interconnections must be made to link all the components on the chip.this process is called metallization.

49.Why aluminum is most preferred for metallization?

(a) It is a good conductor.

(b) it makes good mechanical bonds with silicon.

(c) It is cheap.

(d) It easy to deposit aluminum films using vacuum decomposition.

50. What is photolithography?

Photolithography is a process used in semiconductor device fabricating to transfer a pattern form a photomask to the surface of a wafer.

51. What are the popular IC packages available?

a.  Metal can package.b.Dual-in-line package. c. Ceramic flat package

.

PART B

1.  With neat diagram explain the steps involved in the fabrication of the ICtechnology.(10)                (Nov/Dec-2004)

2.     Explain how a monolithic capacitor can be fabricated.

3.     Explain how monolithic diode can be fabricated.   (8)(Apr/May 2007)

4.    Design a Widlar current source and obtain the expression for output current. Also prove That widlar current source has better sensitivity than constant current source.(16)                      (Nov/Dec-2008)

5.     Explain the working of current mirror with circuit diagram. (8)

6.     Explain in detail of a basic differential amplifier. (6)

7.     Design a Wilson current source and obtain the expression for output current. (10)            (Nov/Dec-2009)

8.   Write notes on

            (i) Epitaxial growth (8)

            (ii) Masking & Etching Process. (8)     (Nov/Dec 2008)                                (Apr/May 2007)

      9.   What is a Voltage reference? Explain with example. 

10.    Define slew rate. What are the methods to improve slew rate.(8)             (Apr/May 2009 )

11.    With a neat block diagram, explain the general stages of an OP-AMP IC. (6)        (Nov/Dec-2011)

  UNIT II – APPLICATIONS OF OPERATIONAL AMPLIFIE

1. Give some applications of Comparator. (Apr/ May 2003)

a. Zero crossing detector b. Window detector

c. Time marker generator d. Phase detector

2. What is a window detector?  (Apr/ May 2004)

A device, usually consisting of a pair of voltage comparators, in which output indicates whether the measured signal is within the voltage range bounded by two different thresholds (an "upper" threshold and a "lower" threshold).

3. List the Various applications of comparators. (May/Jun 2008)

1. Zero crossing detector 2.Window detector 3.Level detector.

4. Differentiate Schmitt trigger and comparator. (Apr/ May 2007)

A Schmitt trigger is a comparator with a small amount of positive feedback applied to create a hysteresis for the input level.

5. What are the limitations of an ideal active differentiator?                             (Nov/Dec-2004)

At high frequency, differentiators may become unstable and break into oscillation. The input impedance i.e. (1/ωC1) decreases with increase in frequency, thereby making the circuit sensitive to high frequency noise.

6. State the important features of an instrumentation amplifier. (Nov/Dec-2003,04)

a. high gain accuracy b. high CMRR c. high gain stability with low temperature co-efficient d. low dc offset e. low output impedance.

7. How does the precision rectifier differ from the conventional rectifier? (Nov/Dec-2009)

These rectifiers are used to rectify very small voltages or currents for which the diode never gets forward biased in the conventional one. i.e. voltage or currents are always less than .7V which can not be rectified by normal rectifiers.This rectifier doesn’t give any kind of drop in output since diodes are previously biased using op-amp.

8. What are the advantages of active filters over the passive filters?                (Nov/Dec-2005)

Active filters use amplifying elements, especially op amps, with resistors and capacitors in their feedback loops, to synthesize the desired filter characteristics. Active filters can have high input impedance, low output impedance, and virtually any arbitrary gain.They are also usually easier to design than passive filters. Possibly their most important attribute is that they lack inductors, thereby reducing the problems associated with those components.

9. Draw the freq. response of the LPF.        (Apr/May 2009)

10. What is an antilog amplifier? Draw the circuit of an antilog amplifier.       (Nov/Dec-2007)

Antilog amplifier is a decoding circuit to convert a logarithmically encoded signal back to the real signal. such op-amp antilog amplifier produces the output proportional to the exponential of the input which is nothing but antilog.

11. What is a V to C convertor?             (Nov/Dec-2008)

A transconductance amplifier (gm amplifier) puts out a current proportional to its input voltage. In network analysis, the transconductance amplifier is defined as a voltage controlled current source (VCCS) For direct current, transconductance is defined as follows:

 

 

13. What are the applications of an integrator?       (Nov/Dec-2006)

(i) Analog computers (ii)ADC (iii) Signal wave shaping circuit.

14. What is a Schmitt trigger?   Nov/Dec-2008)

Schmitt trigger is a regenerative comparator. It converts sinusoidal input into a square Wave output. The output of Schmitt trigger swings between upper and lower threshold voltages. Which are the reference voltages of the input waveform.

15. Mention two linear and two non-linear applications performed by an operationalamplifier.   (Nov/Dec-2005)

The linear applications are inverting amplifier, non-inverting amplifier, voltage follower, integrator, differentiator, instrumentation amplifier etc.The non-linear applications are comparator , Schmitt trigger , Zera crossing detector , log amplifier.etc

16. How to obtain the average circuit from the inverting summer?              (Nov/Dec-2009)

In an inverting summer if the values of resistances are selected such that R1=R2=R and Rf=R/2 then the output is the average of the two inputs applied to the circuit..

17. Mention the advantages of Butterworth approximation.                               (Apr/May 2006)

*Good amplitude response near Zero frequency.

*It provides flat pass band and stop band response

*Maximally flat amplitude response

*phase response is more linear with frequency

*The sharpness of the transition frequency increases with order of filter  

18. Why integrators are preferred over differentiators in analog computers? (May/Jun-2009)

1. Gain of the integrators decreases as frequency increases hence easy to stabilize with respect to spurious oscillations. Gain of the differentiator increases with frequency.2. The differentiator has a tendency to amplify noise and drifts which may cause oscillations. The integrator is less sensitive to noise voltages.

19. What is zero crossing detector? (May/Jun-2009)

A circuit which detects the crossing of zero level by the input signal is called a zero crossing detector. An op-amp comparator is used as a zero crossing detector.

20. What is V to I converter? (Nov/Dec-2008)

The circuit in which the output load current is pro portional to the input voltage is called V to I converter.Mathematically it is given by IL αVin.

21. An a.c signal has got a magnitude of0.1 volt peak to peak. Suggest a suitable half wave rectifier for this signal.       (May/Jun-2009)

0.1 V peak to peak is less than0.7 V which is cut in voltage of diode hence conventional rectifier is not suitable.for such a case precision rectifier using op-amp and diode is suitable.

22. State the disadvantages of passive filters. (Nov/Dec-2003)

i)number of elements required are more. ii) The filter gain and frequency adjustments can not be easily obtained.iii)Cause loading effect. iv) Without inductors high value of Q cannot be achieved.  

23. What is the roll off rate for a third order low pass filter? (Nov/Dec-2004)

The roll off rate of first order filter is -20db/decade hence the roll off rate of third order filter is -20*3=60db/decade.

24. What is a multivibrator?

Multivibrator is a wave shaping circuit which gives symmetric or asymmetric square output.It has two states.They may be either stable or quasi stable depending upon the type of the multivibrator.

25.What is an astable multivibrator?

An Astable multivibrator is a square wave circuit. It has two quasi stable states.It is also referred as free running multivibrator.

26.What is a monostable multivibrator?

A monostable multivibrator is a square wave shaping circuit having one stable state and a one quasi stable state.It is often referred to as a shot multivibrator.It is also used as gating circuit and delay circiuit.

27.Explain the merit of a regenerative comparator?

In the regenerative comparator the feedback enhances the comparator input the phase difference or out of phase condition is not visualized due to positive feedback.

28. Distinguish between triangular wave generator and sawtooth wave generator.

The difference between the triangular and sawtooth waveforms is that the rise time of the triangular wave is always equal to its fall time whereas the sawtooth waveform has unequal rise and fall times.

29.Mention a few applications of a differentiator?

Differentiators are used in wave shapping circuits to detect high frequency components in an input signal.It is also used as a rate of change in FM modulators.

30. Waht is the characteristics of a comparator?

(i) Speed of operation (ii) Accuracy (iii) Compatibility of the output.

31. What do you mean by linear circuits?

Linear circuits are the circuits in which the output signal varies with the input signal in a linear manner.(i)Adder (ii)subtractor (iii) power amplifier (iv) voltage to current converter.

32. What do you mean by non-linear circuits?

Non-linear circuits are the circuits in which the output signal do not vary linearly with the input signal.

(i)   Rectifier (ii)peakdetector (iii) Log and antilog amplifier (iv) clipper and clampers.

33. Define non-inverting amplifier?

The input is applied to the non-inverting input terminal and the inverting terminal connected to ground.

34. List the linear applications of an op-amp.

Adder, sub tractor, sign/phase changer, voltage to current convertor, current to voltage convertors, instrumentation amplifier, analog computation, power amplifier

35. What is an inverting amplifier?

Inverting amplifier is one,which amplifies the givensignal with negative gain since the input is applied at inverting terminal.

36.State the errors in an ideal integrator.

(i)The output is likely to saturate in absence of input.

(ii) The output may be distorted due to error voltage.

(iii)The bandwidth is very small.

(iv)It can be used only for small range of frequencies.

37. State the applications of voltage to current convertor.

(i) low voltage d.c voltmeter (ii) low voltage A.c voltmeter (iii) Diode tester and match finder (iv) Zener diode tester.

38. State the applications of current to voltage convertor.

(i) Photo diode detector  (ii) PhotoFET detector.

39. State the three applications of Schmitt trigger?

1. For eliminating comparator chatter 2. In ON/OFF controllers 3. FOR Square wave generation.

40. What is an antilog amplifier? Draw the circuit diagram of antilog amplifier using transistor and write its output expression.

The circuit which produces the output which is proportional to the antilog of the input is called antilog amplifier.such op-amp antilog amplifier produces the output proportional to the exponential of the input which is nothing but its antilog.ref fig.4.89 on page no4.103 .its output expression is Vo=-Vref e ^vin/nvt.

41. List the applications of instrumentation amplifier.

(i) Temperature indicator

(ii) temperature controller

(iii) light intensity meters

(iv) water flow meter.

42. List the design steps of low pass filter.

*Choose the value of cut off frequency(fc)

*select the value of capacitor less than or equal to 1µf

*Find the value of resistor R3 using the formula,

*Then, select the inverting input resistor R1 and feedback resistor R2 depends on the desired pass band gain Af.

43. What is meant by comparator?

It is a circuit which compares a signal voltage on one input of an op-amp with a known voltage called the reference voltage on the other input.

44.What is I to V converter?

The circuit in which the output voltage  is pro portional to the input current  is called  I to V converter.Mathematically it is given by Vin α.IL.

45. What are the basic requirements of an instrumentation amplifier?

(i) high gain,(ii)high CMRR (iii) High gain stability (iv) Low dc offset (v) Low power loss.

46. Mention the drawbacks of using large RC in differential amplifiers.

Main drawbacks:

1. A large value of resistance requires a large chip area

2. For large RC quiescent drop, a large power supply will be required toMaintain a given quiescent collector current.

47. How is the gain stabilized by negative feedback?

Negative feedback is used mainly to stabilize the overall voltage gain. If the open loop voltage gain AOL increases for any reason, the output voltage will increase and feeds back more voltage to the inverting input. This opposing feedback voltage reduces inverting input voltage V2. Therefore even though AOL has increased, inverting input voltage V2 has decreased and the final output increases much less that it would be without the negative feedback.

48. What is voltage follower?

Voltage follower is the circuit in which the output voltage follows the input

voltage both in magnitude as well as in phase. The circuit diagram of voltage follower isgiven below:

49. List the drawbacks of ideal integrator.

Drawbacks of ideal integrator:

1. At low frequencies (dc), gain becomes infinity.

2. When the op-amp saturates, ideal integrator behaves like an open circuit.

50. Define frequency scaling.

Frequency scaling is defined as the procedure used to convert an Original cut-off Frequency fh to a new cut-off frequency fh.

PART B (8 & 16 marks)

1.     Discuss in detail the operation of bistable multivibrator.(10)             (Apr/May    2007 )

2.     Draw the circuit diagram of Differentiator & integrator circuit &Explain.(16)

3.     Write short notes on

i)    Voltage to current converter(8)

ii)   Current to voltage converter    (8) (Apr/May    2007 )

4.     Explain the working of antilog amplifier

5.     Discuss the need for an instrumentation amplifier? Give a detailed analysis for the same.(16)            (Nov-Dec 2008).

6.     Discuss in detail the operation of Astable multivibrator. (8)

7.     Discuss in detail the operation of monostable multivibrator.(8)           (Apr/May    2008 )

8.     With the help of neat diagram explain full wave precision rectifier (8)            (Apr/May    2007 )

9.     Draw he circuit diagram of Schmitt trigger & explain                                    (Apr/May    2007 )

10.  Explain frequency compensation of op-amp.(6)

11.  Explain the working of summer, subtract or circuit of amplifier.(10)

UNIT III – ANALOG MULTIPLIER AND PLL

1. List out the blocks of PLL.  (Apr/May 2005)

b.  Phase detector/comparator 

c.  Low pass filter

d. Error amplifier

e.  Voltage controlled oscillator.

2. Define the following terms related to PLL,  (Apr/May 2005) (Nov/Dec 2003, 08)

a) Capture range

The range of frequencies over which the PLL can acquire lock with an input signal is called the capture range. It is expressed as a percentage of the VCO free running frequency.

b) Lock range

The range of frequencies over which the PLL can maintain lock with the incoming signal is called the lock-in range or tracking range. It is expressed as a percentage of the VCO free running frequency.

3. Write the expression of a) capture range b) lock range (Apr/May 2005)

Lock in range ∆fL = +/- 7.8 fo / V fo is free running frequency

Capture range = +/- = [∆fL / (2*∏*R*C)] ½

4. Define voltage to frequency conversion factor of VCO.(Nov/Dec 2004, 10)

Voltage to Frequency conversion factor is defined as,Kv= ∆fo / ∆Vc = 8fo /Vcc

where, ∆Vc is the modulation voltage required to produce the frequency shift ∆fo.

5. Mention the applications of analog multipliers.   (Nov/Dec 2008)

c.  Voltage squarer

d.  Frequency doubler

e.  Voltage divider

f.   Square rooter

g.  Phase angle detector

h.  Rectifier

6. List out the applications of PLL.          (Apr/May 2004)

a.  Frequency multiplication/division

b.  Frequency translation c. AM detection

d.  FM demodulation e.FSK demodulation.

7. What is modulation? ( Apr/May 2003)

The process of modifying the amplitude,frequency or phase of the original signal according to the amplitude of other signal is called modulation.

8. Briefly write on frequency synthesizers.  (Nov/Dec 2005)

A frequency synthesizer is an electronic system for generating any of a range of frequencies from a single fixed time base or oscillator. They are found in many modern devices, including radio receivers, mobile telephones, radiotelephones, walkie-talkies, CB radios, satellite receivers, GPS systems, etc. A frequency synthesizer can combine frequency multiplication, frequency division, and frequency mixing (the frequency mixing process generates sum and difference frequencies) operations to produce the desired output signal.

9. What is Gillbert cel? (May/Jun 2009)

A circuit which uses emitter coupled pair in series with a cross coupled emitter coupled pairs is called a Gillbert cel.

10. What is a compander IC?         (Nov/Dec 2010)

The term companding means compressing and expanding. In a communication system, the audio signal is compressed in the transmitter and expanded in the receiver. Examples: LM 2704-LM 2707; NE 570/571.

11. What are the limitations of using emitter coupled pair in multipliers? (Apr 2011)

The advantage of using emitter coupled pair in multiplier is that transistor transconductance depends on the emitter current bias which in turn can be easily controlled by applying external voltage to the base of transistor in series with the emitter of the differential amplifier.

12. Discuss the effect of having large capture range.  (Apr/May 2011)

The PLL cannot acquire a signal outside the capture range, but once captured, it will hold on till the frequency goes beyond the lock-in-range. Thus to increase the ability lock range, large capture range is required.

13. What is one quadrant,two quadrant and four quadrant multipliers? (Dec 2003,04)

In one quadrant multiplier the polarities of both the inputs must always be positive.In two quadrant multiplier theone input must be held positive and other is allowed to swing in both positive and negative.While in four quadrant multiplier both the inputs are allowed to swing in both positive and negative directions.

14. What is an operational transconductance amplifier? Draw the schematic. (Nov/Dec 2007)

The symmetric differential amplifier which uses the principle of the dependence of the transistor transconductance on the emitter bias is called operational transconductance amplifier.

15. What is voltage controlled oscillator?         (Apr/May 2004,10)

  Voltage controlled oscillator is a free running multi-vibrator operating at a set frequency called the free running frequency. This frequency can be shifted to either side by applying a D.C control voltage and the frequency deviation is proportional to the D.C control voltage.

16. What is PLL? Where are used?                      (Apr/May 2009)

  Phase locked loop is a closed loop frequency selective circuit that functions depends on the sensitive phase detection. It controls the phase difference between the input and output signals.PLLs are used in AM, FM demodulators, FSK decoder, frequency synthesizers, motor speed controls etc.

17. What is voltage multiplier?                          (Nov/Dec 2011)

  Voltage multiplier accepts voltages as inputs while current multiplier accepts currents as inputs. The schematic symbol of general two input voltage multiplier that the output can be expressed as, Vo=KV1V2

Where, K->multiplier scaling factor, usually 1/10v-1.

18. State why the phase detector output in a PLL should be followed by a low pass filter.                                                             (May/Jun 2006)

The output of phase detector is applied to low pass filter to remove high frequency noise from the dc voltage.The output of low pass filter without high frequency noise is often referred to as error voltage or control voltage for VCO.

19. What is a switch type phase detector? (Nov/Dec 2007)

  An electronic switch is opened and closed by signal coming from VCO and the input signal is chopped at a repetition rate determined by the VCO frequency. This type of phase detector is called a half wave detector since the phase information for only one half of the input signal is detected and averaged.

20. Draw the relation between the capture ranges and lock range in a PLL. (MAY 2010)

Refer Fig no.7.18

21. List the applications of OTA.

  OTA can be used in

·         Programmable gain voltage amplifier

·         Sample and hold circuits

·         Voltage controlled state variable filter

·         Current controlled relaxation oscillator.

22.What is a transconductance multiplier?

Log-amps require the input and reference voltages to be of the same polarity.This restricts log-antilog multipliers to one quadrant operation. A technique that provides four-quadrant multiplication is transconductance multiplier.

23. Give the expression for the VCO free running frequency.

 Fo = 0.25/RTCT     where RT=External timing resistor, CT= External timing capacitor.

24. What is the unique feature of Operational Transconductance Amplifier (OTA)?

The unique feature of OTA is that, it is possible to vary gm (transconductance) over a wide range, by means of an external control current and OTA is an inherently fast device.

25. List the basic limitations of Operational Transconductance Amplifier (OTA).

The basic limitations of Operational Transconductance Amplifier:

1. Output current is non linear when the input voltage exceeds 20mV

2. As the control current IC is varied to adjust gain or resistance, offset voltage, input bias current and slew rate are also affected

3. Temperature affects the performance of OTA.

26. Draw the general block diagram of phase locked loop.

Where Vs and fs are the signal voltage and signal frequency respectively,

Vc and fc are the control voltage and frequency of the control signal respectively,Ve is the error voltage,Vo is the output voltage.

27. What is the basic function of phase detector?

The basic function of the phase detector is, to compare the phase and frequency of the incoming signal with the output of VCO in PLL. If the two signals differ in frequency and/or phase, an error signal is generated, it is basically a multiplier.

28. What is a voltage controlled oscillator?

The voltage controlled oscillator is defined as the one in which the frequency of the output signal (Vo) is controlled by the control voltage (Vc).

29. List out some examples of digital phase detectors.

Examples of digital phase detectors:

1. Exclusive OR phase detector

2. Edge- triggered phase detector

3. Monolithic phase detector.

30. How can FM signal demodulated using PLL?

If PLL is locked to a FM signal, the VCO tracks the instantaneous frequency of  the input signal. The filtered error voltage which controls VCO and maintains lock with the input signal is the demodulated FM output. The VCO transfer characteristics determine the linearity of the demodulated output.

31. What is frequency shift keying technique?

Frequency Shift Keying (FSK) technique is a type of the data transmission in

which, binary data is transmitted by means of a carrier frequency which is shifted between two preset frequencies.

32. What is frequency shift?

The difference between the two preset input frequencies of Frequency Shift Keying (FSK) demodulator is called frequency shift.

33. What are the main advantages of using low pass filter in PLL circuits?

Main advantages of using low pass filter:

1. The low pass filter used in PLL not only removes the high frequency

components and noise, but also controls the dynamic characteristics of  PLL.

2. The charge on the filter capacitor gives a short time memory to the PLL. Thus, even if the signal becomes less than the noise for a few cycles, the dc voltage on the capacitor continues to shift the frequency of the VCO till it picks up the signal again.

34. Why is the capture range of PLL dependent upon low pass filter (LPF) characteristics?

The capture range of PLL depends on low pass filter characteristics because it removes the high frequency components and noise ,as the bandwidth reduces the capture range of PLL is also get reduced.

35. Give an example of a digital phase detector?

(i) Exclusive or phase detector

(ii) Edge-triggered phase detector

(iii) monolithic phase detector.

36. What is companding?

The combination of words compression and expanding in a communication system is called companding.The compression is done in the transmitter and expanded in the receiver.

37. Define scale factor of multiplier?

Scale factor isthe proportionally constant (k) relating the output voltage and the product of two input voltage.   K=Vo/v1 v2.

38. What are the performance parameters of a multiplier?

(i)   Bandwidth  (ii) accuracy (iii) linearity  (iv) zero trim (v) absolute error bandwidth.

39. State the various techniques used for the multipliers.

1.logarithmic summing technique

2.quarter square technique

3.pulse width modulation

4. triangle averaging technique.

40. Define Pull-in time.

The total time taken by the PLL to establish lock is called pull-in time. It depends on the initial phase and frequency difference between the two signals as well as on the overall loop gain and loop filter characteristics.

41. What is a peak detector?

A peak detector is a series connection of a diode and a capacitor outputting a DC voltage equal to the peak value of the applied AC signal.

42. What are the applications of Gillbert cel?

1. As a four quadrant linear multiplier which can be used as square and square root extractor,frequency doubler,RMS detector,Phase angle detector etc.

2.Mixers  3.Automatic gain control amplifiers  4.In switching applications.

43.With reference to a VCO,define voltage to frequency conversion factor Kv.

The voltage to frequency conversion factor is denoted as Kv and defined as Kv=Δfo/Δvc.Here Δvc is the change in control voltage producing corresponding change of Δfo in the frequency.

44. How VCO different from oscillators?

An oscillator is circuit that generates the frequency output of fixed frequency on the other hand, a voltage controlled oscillator is an oscillator circuit un which the frequency of oscillations can be controlled by an externally applied voltage.

45. What is analog multiplier? Classify.       

  Analog multiplier is an active network which is produces an output proportional to the multiplication of two inputs v1 and v2. Based on the input it is divided into two types: voltage multiplier and current multiplier.

46. Explain how a frequency doubler can be realized using analog multiplier.

The multiplication of two sine waves of the same frequency, but of possibly different amplitudes and phase allows doubling a frequency using an analog multiplier.

47. Define phase transfer conversion coefficient of PLL.

The covertion ratio Kd of phase detector is given by Kd = Vcc/π.

48. What is frequency synthesizer?

The frequency synthesizer is a circuit that can produce a precise series of frequencies derived from a stable crystal controlled oscillator.

49. What is frequency shift keying demodulation?

The binary data which is shifted by a carrier frequency between two preset frequencies are retrieved by using Frequency Shift Keying ( FSK) demodulator.

50. Explain the necessity of companding?

The purpose of the companding process is to preserve the signal to noise ratio of the original signal and to avoid  non-linear distortion of the signal when input amplitude is large.

Part B (8 & 16 marks)

1.     What is precision rectifier? Explain the working of half wave & full wave precision rectifier.(10)

2.     What is Comparator? Explain with its applications.(6)                                    Nov/Dec 2010

3.     With the help of circuits explain the working of logarithmic amplifier. (8)        May/June 2011

4.     Explain the Clipper & Clamper circuit using op-amp. (8)                                  Apr/May 2010

5.     Draw a neat sketch showing a second order OTA (operational transconductance amplifier) & derive expression for its transfer function.(16)                                                      (Nov/Dec 2008)

6.      Explain the working of Voltage Divider , Phase angle detection & Squaring circuit using Multiplier.(16)    (Apr/May 2011)

7.     Explain the working of frequency double & Squaring root circuit using Multiplier. (Apr/May 2011)

8.     Explain Gilbert multiplier cell. Under what condition Gilbert multiplier cell will work as modulator.     (Nov/Dec 2009)

9.     Explain in detail about the working of Four quadrant multiplier.(Apr/May 2005)

10.  Explain the working of PLL with Block diagram.(8)

11.  Explain the working of frequency multiplier & frequency synthesizer in PLL.(10) Nov/Dec 2008

12.  Explain the working of FSK Demodulator & AM detector in PLL .(16)                         (Apr/May 2007)

13.  Explain working of VCO. Give expression for Voltage to frequency factor K_D   (Nov/Dec 2010)

UNIT IV – ANALOG TO DIGITAL AND DIGITAL TO ANALOG CONVERTORS

1. Explain the operation of basic sample and hold circuit.  (Nov/Dec 2007)

A typical sample and hold circuit stores electric charge in a capacitor and contains at least one fast FET switch and at least one operational amplifier. To sample the input signal the switch connects the capacitor to the output of a buffer amplifier. The buffer amplifier charges or discharges the capacitor so that the voltage across the capacitor is practically equal, or proportional to, input voltage. In hold mode the switch disconnects the capacitor from the buffer. The capacitor is invariably discharged by its own leakage currents and useful load currents, which makes the circuit inherently volatile, but the loss of voltage (voltage droop) within a specified hold time remains within an acceptable error margin.

2. State the advantages and applications of sample and hold circuits. (Nov/Dec 2007)

A sample and hold circuit is one which samples an input signal and holds on to its last sampled value until the input is sampled again. This circuit is mainly used in digital interfacing, analog to digital systems, and pulse code modulation systems

3. List the drawbacks of binary weighted resistor technique of D/A conversion. (Apr/May   2003)

a) Wide range of resistor values needed b) Difficulty in achieving and maintaining accurate ratios over a wide range of variations.

4. What is the advantage and disadvantages of flash type ADC?  (Apr/May 2005)

Flash type ADC is the fastest as well as the most expensive. The disadvantage is the number of comparators needed almost doubles for each added bit (For a n-bit convertor 2(n-1) comparators, 2n resistors are required).

5. What is quantization noise? (Apr/May 2003)

The coding of different anlog signal values with the same digital word,depending on the intrinsic finite resolution of a converter implies an error called the quantization error or quantization noise.

6. What is adaptive delta modulation? May/Jun 2008)

Adaptive delta modulation is a delta modulation system where the step size of the DAC is automatically varied depending on the amplitude characteristics of analog input signal..

7. What are the advantages and disadvantages of Dual slope ADC? (May/Jun 2010)

These are particularly suitable for accurate measurement of slowly varying signal, such as thermocouples and weighing scales.These are also used in digital panel meters and multimeters. The main disadvantage of this type is yhe long conversion time.

8. What is granular noise? (Nov/Dec 2005)

When the original analog input signal has a relatively constant amplitude, the reconstructed signal has variations that were not present in the original signal. This is called as granular noise.

9. What are the types of ADC and DAC? (Nov/Dec 2007)

Types of ADC:

1. Flash (comparator) type converter

2. Counter type converter

3. Tracking or servo converter

4. Successive approximation type converter

Types of DAC:

1. Weighted resistor DAC

2. R-2R Ladder

3. Inverted R-2R Ladder

10. What is slope overload? (Nov/Dec 2005)

When the analog input signal changes at a faster rate than DAC can maintain, the analog signal is greater than the delta modular can maintain, and this is called as the slope overload.

11. Define following performance parameters of D/A converters:           (Apr/May 2007)

 a) Resolution

  The resolution of a converter is the smallest change in voltage which may be produced at the output or input of the converter.

Resolution (in volts)= VFS/2n-1=1 LSB increment. The resolution of an ADC is defined as the smallest change in analog input for a one bit change at the output.

b) Absolute accuracy:

It is the maximum deviation between the actual converter output & the ideal converter output. Relative accuracy:  It is the maximum deviation after gain & offset errors have been removed. The accuracy of a converter is also specified in form of LSB increments or % of full scale voltage

c) Monotonicity

  A monotonic DAC is one whose analog output increases for an increase in digital input.

d) Conversion time

  It is defined as the total time required converting an analog signal into its digital output. It depends on the conversion technique used & the propagation delay of circuit components. The conversion time of a successive approximation type ADC is given byT (n+1) where T---clock period Tc--- conversion time n----no. of bits.

12. How do you measure the accuracy of D/A converter? (Nov/Dec 2008)

  The accuracy of D/A converter is measured by the maximum deviation of actual output from the ideal value. It is expressed in fraction of 1LSB.

14.  Define offset error of D/A converter.                  (Nov/Dec 2006)

  Offset error is a difference between the ideal and the actual characteristic curve at origin. The deviation of actual output from ideal output, when the ideal output at zero, Is also called as Offset error. It is nulled by translating the actual signal to up or down until it goes through the origin.

14. What is meant by delta modulation?                        (Apr/May 2004)

  Delta modulation is a technique capable of performing analog signal quantization with smaller bandwidth requirements. Here, the binary output representing the most recent sampled amplitude will be determined on the basic of previous sampled amplitude levels

15. Define settling time and sampling rate.                  (Apr/May 2009)

The settling time is defined as the time it takes for the D/A converter to settle within some specified amount of the final value (usually 0.5LSB). The sampling rate is the rate at which samples can be continuously converted and is typically the inverse of the conversion time.

16. Define Differential Non-linearity (DNL) error.  (Nov/Dec 2007)

The largest deviation (d) between the actual differences of two adjacent threshold voltages and the ideal difference value (V_LSB). Mathematically, DNL=d-V_LSB.

17. Which is fastest A/D converter? Give reason. (Nov/Dec 2006,09)

Flash type A/D converters are the standard approach for realizing very high speed converters compare to other types. Because it processes the input in parallel form with the help of reference voltage generating resistor string and 2ⁿ parallel comparators.

18. What is Voltage to Time (V/T) converter?                (Apr/May 2008)

 Voltage to Time converter is a circuit which produces pulse train of time is inversely proportional to an analog input voltage. T=K/V_in

  Where, K->sensitivity constant, in hertz/volts.

19. Which type of ADC is used in all digital voltmeters? (Nov/Dec 2003)

  Dual slope a/d converter.        

20. Where is the successive approximation type ADC’s used? (May/Jun 2007)

  The successive approximation type ADC’s are used in applications such as data loggers and instrumentation were conversion speed is important.

21. Find the resolution of a 12 bit DAC converter. 

Resolution (volts) = VFS/(212-1) = I LSB incrementVFS – Full scale voltage22. 22. Give a few areas of applications where a dual slope ADC is used.

Dual slope ADC is suitable for precise measurement of slow varying signals like the output of thermocouples and weighting scales. Hence they are used in digital panel meters, multimeters and monitoring systems.

23. What is DAC?

A digital to anlog converter is used to covert a digital signal to an anlog signal.hence the input is an n-bit binary word D and is combined with a reference voltage Vr to give an anlog output signal.the output of DAC is Either A voltage or a current.

24. What is ADC?

A anlog to digital converter is used to convert a anlog signal to an digital signal.Hence the input is an anlog signal,to give and digital output in an binary form.

25. What is meant by direct type ADC?

Direct type ADC compares a given analog signal with the internally generated equivalent signal.

26. What are the advantages of integrating ADC technique?

(i) It is possible to transmit frequency even in a noisy environment

(ii)Used for precision measurement of slow varying signal.

27. Give some sample and hold circuit ICs.

Harris semiconductor HA 2420,National semiconductor such as LF198,LF398are used as sample and hold ICs.

28. What is sample period?

The time period during which the voltage across the capacitor is equal to input

voltage is called sample period.

29. What is hold period?

The time period during which the voltage across the capacitor is held constant iscalled hold period.

30. List out some integrating type converters.

Most widely used integrating type converters:

1. Charge balancing ADC

2. Dual slope ADC

31. Name the various types of electronic switches used in DAC.

Various types of electronic switches used in DAC:

1. Single pole double throw switch

2. Totem pole MOSFET switch

3. CMOS inverter switch

32. Mention the main disadvantage of flash type ADC?

The main disadvantage of flash type A/D converter is that, the number of

Comparators required almost doubles for each added bit.

For example: A 2-bit ADC Requires 3 comparators, 3-bit ADC requires 7 comparators.

33. How many total number of clock pulses required for 8-bit successiveapproximation

Type A/D converter?

The total number of clock pulses required for 8-bit successive-approximation A/D Converter is 8.

34. Define relative accuracy.

Relative accuracy is the maximum deviation between the actual converter output and ideal converter output after gain and offset errors have been removed.

35. What is monotonic DAC?

A monotonic DAC is the one whose analog output increases for an increase in digital input.

36. Mention the main function of comparator in delta modulation transmitter.

The comparator compares the pulse analog signal and the previous signal and

gives output as logic 1(+V) or logic 0(-V).

37. Write the two problems associated with DM.

Problems associated with DM:

1. Slope overload

2. Granular noise

38. Where are analog switches used?

Analog switches are used in chopper amplifiers, D/A converters, function generators, S/M amplifiers and switching power supplies.

39. Define Integral Non-linearity (INL) error.

  INL is defined as the worst case deviation of the transfer curve from an ideal straight line between zero and full scale value.

40. What is the difference between direct ADC and integrating type ADC?

a) The integrating type of ADC’s do not need a sample/Hold circuit at the input.

b) It is possible to transmit frequency even in noisy environment or in an isolated form.

41. What are the advantages and disadvantages of R-2R ladder DAC?

Advantages:

e.   Easier to build accurately as only two precision metal films are required.

f.   Number of bits can be expanded by adding more sections of same R/2R values.

Disadvantage:

a)     In this type of DAC, when there is a change in the input, changes the current flow in the resistor which causes more power dissipation which creates non-linearity in DAC.

42. Define start of conversion and end of conversion.

Start of Conversion in ADC (SOC): This is the control signal for start of conversion which initiates A/D conversion process.

End of Conversion in ADC (EOC): This is the control signal which is activated when the conversion is completed.

43. What are the switches used in DAC?

The switches used in DAC are in series with resistors and therefore, a resistance must be very low. Bipolar transistors do not perform as well as voltage switch due to the inherent offset voltage when in saturation. However by using MOSFET, this can be achieved.

44. What is the acquisition time of a S/H circuit?

The acquisition time of a S/H circuit of a S/H circuit is the time required for the holding capacitor Ch to charge up to a level close to the input voltage during sampling. The acquisition time of a S/H circuit should be as low as possible.

45. The basic step of a 9 bit DAC is 10.3 mV. If 000000000 represents 0Volts, what is the output for an input of 101101111?

The output voltage for input of 101101111 is

i.   10.3 mV (1*28+0*27+1*26+1*25+0*24+1*23+1*22+1*21+1*20)

10.3 * 10-3 * 367 = 3.78 V

46. Which is the fastest A/d converter?Give reson.

Flash ADC is the fastest ADC technique since its output is available immediately after the time equal to propagation delay of a comparator.

47. State the basic types of VFC.

According to the method of conversion there are two types of VFCs

• Wide sweep multivibrators and
• Charge-balancing VFCs.

48. Which factors control the acquisition time of a S/H circuit?

The acquisition time of a S/H circuit depends on three factors:

• RC time constant
• Maximum output current of op-amp
• Slew rate of op-amp.

49. What is feedthrough?

In the hold mode because of stray capacitance across the switch there is a small amount of ac coupling between Vo and Vi.This ac coupling causes output voltage to vary with variation in the input voltage.

50. Find the resolution of a 12-bit D/A converter.

Resolution=2ⁿ=2¹²=4096

            PART B - (8 &16 MARKS)

1.     Explain the working of Binary weighted resistor D/A converter.(10)               (Nov/Dec-2009)

2.     Using OP AMP, draw the successive approximation ADC & explain its working. (Apr/May 11)

3.     Explain the working of single & dual slope A/D converter.(16)          (Nov/Dec-2009)

4.     Explain the working of counter type A/D converter.(8)

5.     Explain the working of flash type A/D converter. (8)                                       (Apr/May 2011)

6.     Explain the working of R-2R ladder D/A converter both in Voltage & current mode. (16)                  (Apr/May’11)

7.     Explain the working principle of high sped sample & hold circuit.(16)                         (Nov/Dec-2011)

8.     Explain the working of delta sigma modulation. State its advantages & disadvantages.(12)     (Nov/Dec-2009)

9.     List the different types of switches used in D/A converters.(8)

UNIT V – WAVE FORM GENERATORS AND SPECIAL FUNCTION ICs

1. What is need for voltage regulator? (Apr/May 2003)

In an unregulated power supply the d.c output varies as the input voltage changes and the load changes. This is undesirable hence to get smooth constant d.c voltage, which is independent of changes in the supply voltage and the load the voltage regulator is necessary.

2. List out the applications of 555 timer?        (Nov/Dec-2009)

a)Oscillator b) pulse generator c)ramp and square wave generator d. mono-shot multivibrator e)burglar alarm f) traffic light control.

3. Define sink current and source current?  (Nov/Dec-2005)

Sink current: When the output is low, the load current that flows through the load connected between Vcc and o/p terminal is called sink current.

Source current: When the output is high, the load current that flows through the load connected between ground and o/p terminal is called source current.

4. List the characteristics of opto coupler.(May/Jun 2008)

i)Current transfer ratio ii)Isolation voltage iii)Response time iv)Common mode rejection v)Bandwidth.

5. What is the use of reset pin of 555 timer?  (Apr 2011)

This is an interrupt for the timing device when pin 4 is grounded; it stops the working of device and makes it off.

6. What is the purpose of control voltage pin (5) of 555 timer?       (Apr/May 2011)

This pin is the inverting input terminal of comparator. This is reference level for comparator with which threshold is compared. If reference level is other than 2/3 VCC, then external input is to be given to pin 5. Pulse width modulation is possible due to pin 5.

7. List out the major blocks of 555 timer functional diagram?   (Apr/May 2007)

The IC 555 timer combines the following elements.

g.  A relaxation oscillator

h.   RS flip-flop

i.    Two comparators

j.    Discharge transistor

8. What is thermal shutdown applied to voltage regulators? (Nov/Dec-2010)       

Due to overheating, the series pass element of regulator may get damaged. To avoid this, thermal shutdown is provided, In this protection scheme, the junction temperature of the series pass element is sensed.

9. Name two applications of an isolation amplifier.  (Apr/May-2003) (Nov/Dec-2008)       

It is used in

(i)             Power sensors.

(ii)            Flow meter.

10. Define the line regulation of voltage regulator. (Apr/May 2004)

  Line regulation is defined as the ratio of the change in the output voltage to a change in the regulator input voltage. It is expressed in millivolts are a percentage of output voltage. Line regulation=∆V₀/∆V_in.

11. What is switched capacitor filter? (Nov/Dec-2006)    (May/Jun-2008,09)

A switched capacitor filter is a three terminal device, which consists of capacitors, periodic switches and operational amplifier whose open circuit voltages transfer characteristics represents filtering characteristics.

12. What do you mean by linear voltage regulators?  (Nov/Dec-2005)

  Series or linear regulator uses a power transistor connected in series between the unregulated dc input and the load and it conducts in the linear region .The output voltage is controlled by the continuous voltage drop taking place across the series pass transistor.

13. What is an opto-coupler IC? Give examples. (Nov/Dec-2005)

  Opto-coupler IC is a combined package of a photo-emitting device and a photo sensing device. Examples for opto-coupler circuit: LED and a photo diode, LED and photo transistor, LED and Darlington. Examples for opto-coupler IC: MCT 2F, MCT 2E.

14. Define voltage regulators and give the types? (Apr/May-2010)

  A voltage regulator is an electronic circuit that provides a stable dc voltage independent of the load current, temperature, and ac line voltage variations.

The classification of voltage regulators:

*Series / Linear regulators

*Switching regulators

15. List out the applications of 555 timer in as table mode. (Apr/May-2006)

a. missing pulse detector b. Linear ramp generator c. Frequency divider

d. Pulse width modulation.

16. What is an isolation amplifier? (Nov/Dec-2009)

  An isolation amplifier is an amplifier that offers electrical isolation between its input and output terminals.

17. What is wave generator? Mention its uses. 

  Waveform generators are the signal processing circuits that generates the signals in the form of sine, square, triangular and saw tooth waveforms etc. Generally these signals are used as clock pulses, signal carriers for signal transmitter, sweep signals for information display, audio signals for electronic music and speech synthesis, and test signals for automatic measurement and test.

18.What is Voltage to Frequency (V/F) converter? (Apr/May 2008)

  Voltage to Frequency converter is a circuit which produces pulse train of frequency is proportional to an analog input voltage. F₀=KV_in Where, K->Sensitivity constant, in hertz/volts.

19. Define the load regulation of the voltage regulator. (Apr/May 2011)

  Load regulation is defined as the ratio of change in the output voltage to a change in load current. It is also expressed in millivolts or a percentage of output voltage. Load regulation=∆V₀/∆I_o.

20. Whish is three different wave forms generated by ICL 8038? (Apr 2010)

The three different waveforms generated by ICL8038 are sinusoidal, triangular   and square.

21. Define the ripple rejection of voltage regulator. (Apr/May 2005)

  Ripple rejection is the ratio of the A.C ripple voltage on the output to the A.C ripple in the input voltage i.e., the ability of ripple rejection. It is usually expressed in decibels.

Ripple rejection= 20log₁₀ ∆V₀/∆V_in.

22 Define switched voltage regulators?

  Switching regulators are those which operate the power transistor as a high frequency on/off switch, so that the power transistor does not conduct current continuously. This gives improved efficiency over series regulators.

23. What are the advantages of adjustable voltage regulators over the fixed voltage regulators?

i)    Improved line and load regulation by a factor of 10 or more.

ii)   Because of the improved overload protection, greater load current can be drawn.

        iii)Improved reliability.

24. What is multi-vibrator? Classify.

  Multi-vibrator is a re-generative circuits that intended specially for timing applications. There are three types of multi-vibrators such as astable multi-vibrator, monostable multi-vibrator and bistable multi-vibrator.

25. List out the parameters related to the fixed voltage regulators?

1)     Line regulation 2.Load regulation 3.Ripple rejection 4.Output impedance 5.Maximum power dissipation 6.Rated output current.

26. Define duty cycle?    

It is defined as the ratio of on time to the total time of one cycle. D = W/ T

W – time for output is high = TON

T – total time of one cycle.

27. Define dropout voltage of a fixed voltage regulator?

It is the minimum voltage that must exist between input and output terminals. For most of regulators, it is 2 to 3 volts.

28. What is the frequency of oscillation of free running mode of 555 timer? (Nov/Dec-2004)

  F = 1.44/ (RA + 2 RB) C Hz

29. Write the main function of 555 Timer.

The 555 Timer is a highly stable device for generating accurate time delay or oscillation.

30. Mention the main applications of missing pulse detector monostable circuit.

The main applications of missing pulse detector monostable circuit are:

1. It is used to detect missing heart beat and

2. It is used for speed control and measurement.

31. Write the main function of voltage regulator.

The main function of voltage regulator is to provide a stable DC voltage for processing other electronic circuits.

32. List the limitations of IC-723 regulators.

The limitations of IC-723 regulators are:

1. No in-built thermal protection and

2. No short circuit current limits.

33. List the drawbacks of series regulators.

The draw backs of series regulators are:

1. The input step down transformer used is bulky and most expensive component.

2. Since it operates at low line frequency, large values of filter capacitors are required.

3. Efficiency is less and 4. More power is dissipated in the series pass transistor, which is always in the active region.

34. Mention the advantages of opto-couplers.

  *Better isolation between the two stages. *Impedance problem between the stages is eliminated. *Wide frequency response.*easily interfaced with digital circuit*Compact and light weight.*Problems such as noise, transients, contact bounce, are eliminated.

35. Why are series regulators called as linear regulators?

Since the transistors conduct in the active or linear region, these regulators are called as linear regulators.

36. Write the uses of voltage regulators.

Voltage regulators are commonly used for on-card regulation and laboratory type power switches. Switch type regulators are used as control circuits in pulse width modulation, Push Pull Bridge and series type switch mode supplies.

37. Where are switched capacitor filter used?

Switched capacitor filter are used in:

1. Low pass filter,

2. High pass filter,

3. Band pass filter and

4. Band reject filter.

38. What is frequency to voltage converters?

A converter which generates an output voltage that is linearly proportional to the input frequency waveform is frequency to voltage converter.

39. Where does the thermal noise occur? What is the cause?

Thermal noise occurs in all passive resistors including the stray series resistances of practical inductors and capacitors. Thermal noise is due to the random thermal motion of electrons.

40.What is a counter timer?

When a timer circuit is connected as an oscillator  and is used to drive a counter, it is then known as a counter timer.

41.Give the expression for the frequency of oscillations in an op-amp sine wave oscillator?

The expression for the frequency of oscillations in an op-amp sine wave oscillator is f=1/2πRC.

42.What are the limitations of linear voltage regulators?

(i) IT requires a bulky and expensive step-down transformer at the input.

(ii) low efficiency.

(iii) large values of capacitors are required to reduce the ripple.

43.What are the limitations of a 3 pin regulator?

(i) Fixed output voltage

(ii) No short –circuit protection.

44.What is the current fold back? Draw the characteristic curve?

Current fold back is the technique used to protect the IC regulator from the enormous current flow during short circuit or over load conditions.

45. List the advantages of using optic fibres.

The advantages of using optic fibres are:

1. Creator information capacity,

2. Immunity to cross talk,

3. Immunity to static interferences,

4. Environmental immunity, 5. Safety and 6. Security and longer lasting.

46.What are the basic configurations of switching regulators?

(i) step-down or buck  switching regulators

(ii) step-up or boost switching regulators

(iii) inverting type switching regulators.

47. Which are the package in which IC 555 is available?

Ic 555 is available in dual in line package and flat package

48. Write the expression for total time period of 555 timer in astable mode?

  T = 0.693 (RA + 2 RB) C seconds

49. Write the expression for pulse width of 555 timer in monostable mode?

Pulse width W = 1.1 RC seconds

R – resistor in ohms, C – capacitor in farads.

50. What are the operating modes of a 555 timer?

Monostable mode b.Astable mode.

PART B - (8 &16 MARKS)

1.     Draw & explain the functional block of LM 317 three terminal regulator.(12)         (Nov/Dec-2005)

2.     Explain the working of video & power amplifier.(8)

3.     Draw & explain the functional block of 723 regulator. (8)                                       (Nov/Dec-2010)

4.     Explain the working of isolation amplifier & opto coupler.

5.     Draw the internal block diagram of IC 555 timer & its pulse width expression.(16) (Apr/May 2011)

6.     Explain the working of step down switching regulator.(8)                                         (Nov/Dec-2007)

7.     Briefly explain the working principle of SMPS.(10)                                                   (Apr/May 2007)

8.     With functional block diagram explain the working principle of function generator 8038  IC .                        (Nov/Dec-2010)

9.     Explain the working of triangular wave generator with neat diagram.(8)

10.  Explain the working of saw tooth generator with neat diagram.(10)                        (Apr/May 2010)

11.  Explain RC phase shift oscillator with design procedure.(10)                                  (Nov/Dec-2006)

12.  Explain the working of bitable multivibrator.(6)        (Apr/May 2005)

13.  Explain the working of monostable multivibrator.(6)

14.  Explain the working of astable multivibrator.(6)