## Nonlinear Waveshaping Interview Questions and Answers:

1. What is meant by nonlinear waveshaping?

Ans. When any wave is applied at the input of a nonlinear device (such as a diode or transistor), the shape of the output wave varies nonlinearly with input wave. This process is called the nonlinear waveshaping.

2. What is clipping?

Ans. Clipping is the process of clipping or removing a part of the input waveform.

3. What is meant by a clipping circuit?

Ans. A waveshaping circuit which controls the shape of the output waveform by removing or clipping a portion of the input wave is known as the clipping circuit.

4. What is the difference between a positive clipper and negative clipper?

Ans. The positive clipper removes the positive half cycles of the input waveform while the negative clipper removes the negative half cycles of the input waveform.

5. What is the drawback of having a diode as a series element in a clipper?

Ans. The use of the diode as a series element has a drawback that when the diode is in ‘off’ condition, there should be no trans­mission of input signal to the output. But in case of high-fre­quency signals, transmission occurs through diode capacitance which is undesirable.

6. What is the drawback of having a diode as a shunt element in a clipper?

Ans. The use of the diode as a shunt element has a drawback that when the diode is in the ‘off’ condition, transmission of input signal should take place to output. But in case of high-frequency input signals, diode capacitance affects the circuit operation adversely and the signal gets attenuated (i.e., it passes through diode capacitance to ground).

7. Write advantage of using parallel clipper over series clipper.

Ans. Parallel clipper arrangement provides piecewise linear and continuous input-output voltage curve. This circuit is used for converting sinusoidal waveform to square wave.

8. “Clipping circuit is to suppress amplitude variations in the input signal voltage”. Is this statement correct and why?

Ans. This statement is correct, because sometimes due to noise or other sources input signal may contain variations, which are undesirable and are below certain limits. Such variations can be removed by using clipping circuits.

9. “Clipping circuit is to remove a certain portion of input signal above or below a certain level”. Is this statement correct and why?

Ans. Yes, the given statement is correct because clipping is a process of removing a portion of the input signal.

10. Describe the operation of non-saturating transistor clipper.

Ans. The transistor has two pronounced norilinearities — one occurs when the transistor passes from cutin region to the active region and the second occurs when it passes from active region to the saturation region. If any input signal makes excursion which takes the transistor across the boundary between cutin region and active region, or across the boundary between the active region and saturation region, a portion of the input signal waveform will be clipped off.

11. Define a limiter?

Ans. Limiter is also called a clipper. It is useful for signal shaping and also used for protecting circuits that receive the signal.

12. What are amplitude selectors?

Ans. Amplitude selectors are also called clipping circuits. These circuits are used to select for transmission that part of an arbitrary waveform which lies above or below some particular reference voltage level.

13. What is an emitter coupled clipper?

Ans. The emitter coupled clipper is a two-level clipper. It is an emitter coupled differential amplifier.

14. What are clipper circuits? Mention their applications.

Ans. A waveshaping circuit which controls the shape of the output waveform by removing or clipping a portion of the input wave is known as the clipping circuit.

Clipping circuits are used to select for transmission that part of an arbitrary waveform which lies above or below some particular reference voltage level. A clipping circuit may be used to convert a sinewave into a square wave.

15. What are slicers?

Ans. A waveshaping circuit which controls the shape of the output waveform by removing or slicing a portion of the input wave is known as the slicer.

16. What is meant by a comparator?

Ans. A circuit used to mark the instant when an arbitrary waveform attains some particular reference level is called a comparator.

17. How does comparator differ from clipper?

Ans. The only difference between the comparator and clipper is that, in a clipping circuit part of the signal is required to be reproduced without any distortion whereas in a comparator circuit we have no interest in reproducing any part of the signal waveform.

18. What do you mean by non-regenerative comparator? Give an example.

Ans. Comparator is used to compare two signals, but when the output of comparator destroys input signals, then it is known as non-regenerative comparator. Clipping circuit is an example of such circuit, wherein the input voltage is compared w.r.t. some reference point. But in the output some portion of the input signal is lost.

19. What do you mean by regenerative comparator? Give an example.

Ans. Regenerative comparator is a fast operating voltage level detector and makes use of positive feedback.

Blocking oscillators, Schmitt trigger circuits are the examples of regenerative comparators in which a positive feedback is employed to have an infinite forward gain (unity loop gain). The Schmitt trigger comparator generates a step input whereas the blocking oscillator comparator generates a pulse output waveform. Operational amplifiers and tunnel diodes may also be used as comparators.

20. What is meant by a clamping circuit?

Ans. A circuit that places either the positive or negative peak of a signal at a desired level is known as a clamping circuit. It simply adds or subtracts a dc component to the input signal and, therefore, it is also called a dc restorer.

21. What is the difference between a positive clamping circuit and a negative clamping circuit?

Ans. A positive damper pushes the signal on the positive side or upward while a negative damper pushes the signal on the negative side or downward.

22. A damper circuit sometimes uses a dc battery in addition to a diode, a capacitor and a resistor, why?

Ans. A damper circuit uses sometimes a dc battery in addition to a diode, a capacitor and a resistor to cause an additional shift.

23. How does a damper circuit affect the peak-to-peak and rms values of a waveform?

Ans. No change.

24. How does a damper circuit affect the peak and average values of the waveform?

Ans. The peak and average values of a waveform are changed by a damper circuit.

25. Differentiate between clippers and dampers.

Ans. The clipper removes some portion of an input signal where as damper places either the positive or negative peak of the signal at a desired level.

26. What is the difference between the output from a clipping circuit and a clamping circuit?

Ans. The output of a clipping circuit appears as if a portion of the input signal were clipped off but a damper circuit simply clamps (lifts up or down) the input to a different dc level.

27. List two uses of clamping circuits.

Ans. Clamping circuits are often employed in television receivers as dc restorers. Clamping circuits are also used in storage counter analog frequency meter, capacitance meter, divider and staircase waveform generator.

28. What is meant by a practical clamping circuit?

Ans. A practical clamping circuit is one in which source and diode forward resistances are not negligible and capacitor C is not arbitrarily large.

29. State clamping circuit theorem.

Ans. Under steady-state conditions, for any input waveform, the shape of the output waveform of a clamping circuit is fixed and also the area in the forward direction and the area in the reverse direction are related.

According to clamping circuit theorem, under steady-state conditions, the ratio of area in forward direction Af to that of reverse direction Ar of output voltage is equal to the ratio of diode forward resistance Rf to resistance R connected across diode.

30. What is peak-to-peak detector and where is it used?

Ans. Peak-to-peak detector is a combination of a dc damper and a peak detector, the output of a peak detector is a dc voltage of magnitude 2VP where VP is the peak value of the input ac signal. It is used in measurement of nonsinusoidal signals.

31. What are sweep generators? List their applications.

Ans. Most of the CRO applications involve measurement or display of a quantity which varies with respect to time. This requires that the CRT spot moves across the screen with a constant velocity. For this a voltage which varies linearly with time has to be applied to one set of deflection plates. This voltage is used to sweep the electron beam across the screen, so it is called a sweep voltage. Because of its shape, it is also sometimes called a sawtooth or ramp voltage. The circuits which develop these linearly varying voltages are called time-base generators or sweep circuits.

Other applications of time base circuits are in Radar and Television indicators, computer monitors, automatic control systems, A/D converters, in precise time measurements and in time modulation.

32. List applications of voltage and current sweep generators.

Ans. Voltage sweep generators generate a voltage linearly varying with time and are used where electrostatic deflection is used, such as in CRO.

Current sweep generators generate a current varying linearly with time and this current is used to flow through inductors or deflection coils. Current time-base generators are used where electromagnetic deflection is used, such as in RADARS, TVs etc.

33. What is a linear time-base generator?

Ans. A linear time-base generator is one that provides an output waveform, a portion of which exhibits a linear variation of voltage or current with time.

34. Why sweep voltage should be a small fraction of the aiming potential or supply voltage?

Ans. Sweep voltage should be a small fraction of the aiming potential so as to achieve good linearity in output waveform.

35. Which amplifier is used to generate Miller sweep?

Ans. Amplifier with -∞ gain is used in a Miller sweep circuit.

36. Which amplifier is used in Miller bootstrap time-base generator?

Ans. Emitter follower (amplifier with unity gain) is used in Miller bootstrap time-base generator.

37. Why electrostatic deflection is not used in Radars and TV indicators?

Ans. If electrostatic deflection is used in Radars and TV indicators inconveniently large deflection voltages would be required.

38. Which type of time-base generator is used in electromagnetic deflection system?

Ans. Current time-base generators are used in electromagnetic deflection systems.

39. Which type of time-base generator is used in electrostatic deflection systems?

Ans. Voltage time-base generators are used in electrostatic deflection systems.

40. How does a signal generator differ from an ordinary oscillator?

Ans. The signal generator, like an ordinary oscillator, is a source of sinusoidal signals but it is also capable of modulating its sinusoidal output signal with other signals. This is the main difference between the signal generator and an ordinary oscillator.

41.Why use of regulated power supply is essential for signal generators?

Ans. Frequency of output voltage from a signal generator changes with the change in supply voltage so use of regulated power supply is essential.

42. Why are buffer amplifiers used in signal generators?

Ans. Buffer amplifiers are used in the signal generators for isolating the oscillator circuit from the output circuit so that any change in the circuit connected to the output does not affect the frequency and amplitude of the oscillator output.

43. Why are temperature compensating devices used in signal generators?

Ans. In signal generators, oscillator output frequency varies with the variation in temperature, so temperature compensating devices are used.

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