IC Waveform Generators Interview Questions and Answers:

1. What is an oscillator?

Ans. Oscillator may be defined as a circuit which generates an ac output signal of very high frequency without requiring any externally applied input signal or it may be defined as an electronic source of alternating current (or voltage) having sinusoidal or non-sinusoidal (square, sawtooth or pulse) waveshape. It can also be defined as a circuit that converts dc energy into very high-frequency ac energy.

2. What are the conditions which are to be satisfied for the successful operation of phase-shift oscillator?

Ans. The phase-shift oscillator will generate sinusoidal waveform only if the gain is ≥ 29 and total phase-shift of the circuit is 360°.

3. What is the maximum frequency range of Wien bridge oscillators?

Ans. 1 MHz.

4. Why are crystal oscillators used in communication transmitters and receivers?

Ans. Crystal oscillators are used in communication transmitters and receivers because of their greater frequency stability.

5. Why is quadrature oscillator called by this name ?

Ans. Because quadrature oscillator generates two signals (sine and cosine) that are in and out of phase by 90°, it is called quadrature oscillator.

6. How does a twin-T oscillator differ from a Wien bridge oscillator?

Ans. In the Wien bridge oscillator, a bandpass filter is used in the positive feedback path, but in twin-T oscillator, a notch filter is placed in the negative feedback path.

7. Why twin-T oscillator is not a popular circuit like Wien bridge oscillator?

Ans. Twin-T oscillator is not popular like Wien bridge oscillator because it operates well only at one frequency i.e. it cannot be easily adjusted over a large frequency range as the Wien bridge oscillator can.

8. Why is square-wave generator also called the astable multivibrator?

Ans. Square-wave generator is also called the free-running or astable multivibrator because it has two quasi stable states.

9. Give the frequency range of square-wave generator.

Ans. 10 Hz to 10 kHz.

10. Write an application of astable multivibrator.

Ans. Astable multivibrator or free running multivibrator has no stable state i.e., it keeps oscillating between high and low states. Its applications include (i) free-running ramp generator and (ii) square-wave generator.

11. Write an application of monostable multivibrator.

Ans. A monostable multivibrator (MMV) has one stable state and one quasi stable state. The circuit remains in its stable state till an external triggering pulse causes a transition to the quasi stable state. The circuit comes back to its stable state after a time period T. Thus it generates a single output pulse in response to an input pulse and is referred to as a one-shot or single shot.

The applications of MMV include (i) frequency divider; (ii) pulse stretcher.

12. What is difference between a triangular wave and a sawtooth wave?

Ans. The difference between a triangular wave and a sawtooth wave is that in a triangular wave the rise time is always equal to its fall time while the sawtooth waveform has different rise time and fall time.

13. Why LM311 is used in place of an op-amp in audio-range triangular wave generators ?

Ans. This is because LM311 is much faster than a comparatively priced op-amp.

14. What is a VCO ? Give two applications that require VCO.

Ans. The oscillator whose output frequency is controlled by varying the magnitude of the input voltage is called a voltage-controlled oscillator (VCO). Applications requiring VCO are frequency modulation (FM) and frequency shift keying (FSK).

15. What is function generator ?

Ans. A function generator is a signal source that has the capability of producing different types of waveforms as its output signal. The most common output waveforms are sine waves, triangular waves, square waves and sawtooth waves. The frequencies a such waveforms may be adjusted from a fraction of a hertz to several hundred kHz.