Match List-I with List-II :List-IList-II(a) Active filters(i) Hysteris(b) Multivibrators(ii) dc output(c) Schmitt trigger(iii) Pulse/Pulse train(d) Voltage regulator(iv) R-C network with OP-Amp.

The correct matching is a-iv, b-iii, c-i, d-ii.(a) Active filters are built from R-C networks with an op-amp (iv).(b) Multivibrators produce a pulse or pulse train (iii).(c) A Schmitt trigger is a comparator with positive feedback, which gives it hysteresis, printed 'Hysteris' (i).(d) A voltage regulator provides a steady dc output (ii).The other codes put hysteresis or the dc output against the wrong circuit.

Waveform Generators Questions and Answers

Q: For converting a triangular wave to a wave shape close to a sinusoidal wave which circuit would be used ?

The key gives a clipper.A triangular wave can be shaped into a near-sinusoid with a diode shaping network, which is a clipper with several break points. As the triangle rises, successive diodes conduct and progressively reduce the slope of the output, so the straight sides are bent into curves and the sharp peaks are rounded off, approximating a sine wave. Function generators use this method.A clamper only shifts the DC level of a waveform without changing its shape. A rectifier removes one polarity. An integrator turns a triangle into a series of parabolic segments, which is still not a sine wave and does not round the peaks in the required way.

Q: Following circuits can be used as voltage to frequency converter :

An astable multivibrator can be used as a voltage-to-frequency converter.An astable circuit switches back and forth continuously as a timing capacitor charges and discharges between two thresholds. If the charging current, or the threshold, is set by a control voltage, the time per cycle changes with that voltage, so the output frequency becomes a function of the input voltage. This is how a 555 timer with its control pin driven, or a VCO such as the 566, works as a V/F converter.A crystal oscillator is designed for a fixed, very stable frequency and resists being pulled. A Schmitt trigger converts a level into a clean switching edge but does not oscillate by itself, and a CE amplifier amplifies; neither produces a frequency proportional to voltage.

Q: Which of the following ICs is the standard IC used for V to F conversion ?

The IC used for V to F conversion among these is the 566.The LM566 (NE566) is a voltage-controlled oscillator: the frequency of its square and triangular outputs is set by an external RC and varies linearly with a control voltage. A voltage-controlled oscillator is in effect a voltage-to-frequency converter, and the 566 is the standard textbook example.The 741 is a general-purpose operational amplifier. The 7400 is a TTL quad two-input NAND gate. The 723 is an adjustable voltage regulator. None of them converts a voltage to a frequency.

Match List-I with List-II :

List-I	List-II
(a) Active filters	(i) Hysteris
(b) Multivibrators	(ii) dc output
(c) Schmitt trigger	(iii) Pulse/Pulse train
(d) Voltage regulator	(iv) R-C network with OP-Amp.

A.a-i, b-ii, c-iii, d-iv
B.a-iv, b-iii, c-i, d-ii
C.a-iv, b-iii, c-ii, d-i
D.a-iii, b-ii, c-i, d-iv

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: B

The correct matching is a-iv, b-iii, c-i, d-ii.

(a) Active filters are built from R-C networks with an op-amp (iv).
(b) Multivibrators produce a pulse or pulse train (iii).
(c) A Schmitt trigger is a comparator with positive feedback, which gives it hysteresis, printed 'Hysteris' (i).
(d) A voltage regulator provides a steady dc output (ii).

The other codes put hysteresis or the dc output against the wrong circuit.

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For converting a triangular wave to a wave shape close to a sinusoidal wave which circuit would be used ?

A.Clamper
B.Rectifier
C.Clipper
D.Integrator

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: C

The key gives a clipper.

A triangular wave can be shaped into a near-sinusoid with a diode shaping network, which is a clipper with several break points. As the triangle rises, successive diodes conduct and progressively reduce the slope of the output, so the straight sides are bent into curves and the sharp peaks are rounded off, approximating a sine wave. Function generators use this method.

A clamper only shifts the DC level of a waveform without changing its shape. A rectifier removes one polarity. An integrator turns a triangle into a series of parabolic segments, which is still not a sine wave and does not round the peaks in the required way.

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Following circuits can be used as voltage to frequency converter :

A.Astable multivibrator
B.Crystal oscillator
C.Schmitt trigger
D.CE amplifier

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: A

An astable multivibrator can be used as a voltage-to-frequency converter.

An astable circuit switches back and forth continuously as a timing capacitor charges and discharges between two thresholds. If the charging current, or the threshold, is set by a control voltage, the time per cycle changes with that voltage, so the output frequency becomes a function of the input voltage. This is how a 555 timer with its control pin driven, or a VCO such as the 566, works as a V/F converter.

A crystal oscillator is designed for a fixed, very stable frequency and resists being pulled. A Schmitt trigger converts a level into a clean switching edge but does not oscillate by itself, and a CE amplifier amplifies; neither produces a frequency proportional to voltage.

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Which of the following ICs is the standard IC used for V to F conversion ?

A.741
B.7400
C.566
D.723

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: C

The IC used for V to F conversion among these is the 566.

The LM566 (NE566) is a voltage-controlled oscillator: the frequency of its square and triangular outputs is set by an external RC and varies linearly with a control voltage. A voltage-controlled oscillator is in effect a voltage-to-frequency converter, and the 566 is the standard textbook example.

The 741 is a general-purpose operational amplifier. The 7400 is a TTL quad two-input NAND gate. The 723 is an adjustable voltage regulator. None of them converts a voltage to a frequency.

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Match List – I with List – II.

List – I	List – II
a. Monostable multivibrator	1. No-stable state
b. Astable multivibrator	2. One-stable state
c. Free-running multivibrator	3. Two-stable state
d. Bistable multivibrator	4. Alternate high and low output

Codes : a b c d

A.2 3 1 4
B.3 2 4 1
C.1 3 4 2
D.2 1 4 3

Exam Year(s)

UGC NET - 2012,

Answer: D

A monostable multivibrator has one stable state, so a matches 2. An astable multivibrator has no stable state, since it keeps switching, so b matches 1. A free-running multivibrator is another name for the astable one, and it gives an output that alternates between high and low, so c matches 4. A bistable multivibrator has two stable states, so d matches 3. The code is therefore 2 1 4 3. The codes 2 3 1 4 and 3 2 4 1 swap the first pairs, and 1 3 4 2 gives the monostable the astable's no-stable-state. The answer is 2 1 4 3.

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A relaxation oscillator is one which

A.oscillates continuously
B.has two stable states
C.relax indefinitely
D.produces non-sinusoidal output

Exam Year(s)

UGC NET - 2012,

Answer: D

A relaxation oscillator is one that produces a non-sinusoidal output, such as a square, triangular or sawtooth wave, by the repeated charging and discharging of a capacitor between two thresholds, so option D is the keyed answer. The multivibrator and the Schmitt-trigger based oscillator are the usual examples. Sinusoidal oscillators produce continuous sine waves. The statements that it relaxes indefinitely or has two stable states describe neither the circuit nor its output.

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List - I	List - II
(a) Monostable multivibrator	(i) Quasi stable state
(b) Astable multivibrator	(ii) One stable state
(c) Schmitt trigger	(iii) Two stable state
(d) Bistable multivibrator	(iv) No stable state

Codes :
(a) (b) (c) (d)

A.(i) (ii) (iv) (iii)
B.(ii) (iv) (i) (iii)
C.(iii) (i) (ii) (iv)
D.(iv) (i) (ii) (iii)

Exam Year(s)

UGC NET - 2012,

Answer: B

The keyed code B is (ii) (iv) (i) (iii). The monostable multivibrator has one stable state (ii) and returns to it after a timed pulse, the astable multivibrator has no stable state (iv) and switches back and forth between two quasi-stable states, and the bistable multivibrator has two stable states (iii). The Schmitt trigger is left with the quasi stable state (i) in the list. The monostable and the astable are easily swapped, and the codes that swap them, options A and D, are wrong, while option C pairs the monostable with two stable states.

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