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The CORRECT choice is (a) Effect occurred during switching of transistor after every half cycle

To explain I would say: Transistor takes 0.7V to turn on when during the end of half CYCLES, the input gets below 0.7V and it is not POSSIBLE to reproduce these signals. This is CALLED as Cross over DISTORTION.

The correct answer is (a) Expensive

The explanation is: SINCE class B amplifier USES a BALANCED centre-tapped transformer in its DESIGN, making it expensive to construct.

The CORRECT answer is (d) 50% to 70%

EXPLANATION: Class B amplifiers are more efficient compare to the class A amplifier because of good protection against noise EFFECTS.

Correct OPTION is (b) Cut off

Explanation: Class B amplifier are DESIGNED by fixing the Q point in cut off region of the transfer CHARACTERISTIC.

Right option is (a) True

The best explanation: Bode plots show the frequency response of a SYSTEM. There are two Bode plots ONE for GAIN (or MAGNITUDE) and one for phase.

 The Nyquist plot combines gain and phase into one plot in the complex plane. It is drawn by plotting the complex gain g(iω) for all frequencies ω. That is, the plot is a curve in the plane parameterized by ω.

Right option is (b) False

To elaborate: The OSCILLATOR is a device which gives an AC OUTPUT without any input. Oscillator needs an input signal for start. But once the CAPACITOR is charged then, Oscillator can effectively start WORK without an input signal.

The correct choice is (c) 180

Explanation: For CLASS B push-pull amplifier, the conduction angle is 180 degree that is it AMPLIFIES only one half CYCLE of the input in one time PERIOD.

The correct ANSWER is (b) False

Explanation: When INPUT PROVIDED to the class B AMPLIFIER is zero, no output will be ACHIEVED, because it is excellent against noise.

Correct answer is (d) Higher input IMPEDANCE & Better stabilized voltage gain

To elaborate: The APPLIED negative feedback can improve its performance (gain stability, linearity, frequency response, step response) and REDUCES SENSITIVITY to parameter variations due to MANUFACTURING or environment. Because of these advantages, many amplifiers and control systems use negative feedback.

Correct choice is (C) positive feedback greater than 1

The best explanation: In oscillators using positive feedback it is important that amplitude of the OSCILLATOR output REMAINS stable. Therefore the closed loop gain must be 1 (UNITY). In other words, the gain within the loop; PROVIDED by the amplifier, should exactly match the losses (caused by the feedback circuit) within the loop.

The CORRECT CHOICE is (d) Barkhausen law

Easiest explanation: For an oscillator circuit, it has to obey the Barkhausen criteria, OTHERWISE the output f the oscillator will tend to zero as the time advances.

The correct CHOICE is (a) No current flows through the transistor

The best EXPLANATION: When the transistor is in a QUIESCENT state, no input is applied ACROSS the base TERMINAL of the transistor and hence no current flows through the transistor.

The CORRECT ANSWER is (B) 1

Easy EXPLANATION: For self-oscillating circuits, the LOOP gain Aβ must be equal to 1, otherwise there will be the effect of noise.

The CORRECT answer is (d) Because of binary switch

The EXPLANATION: A class D amplifier or SWITCHING amplifier is an electronic amplifier where all power devices are OPERATED as binary switches.

Right choice is (a) minimum

Explanation: The slope of the crystals impedance suggests that as the frequency increases ACROSS its TERMINALS. At a particular frequency, the interaction between the SERIES capacitor and the inductor creates a series RESONANCE CIRCUIT reducing the crystals impedance to a minimum and equal to Resistance.

Correct option is (a) 10

Best explanation: For an oscillator, the OUTPUT voltage is the PRODUCT of loop GAIN and input voltage, hence output will be twice the input, that is 5*2 =10V.

Correct ANSWER is (c) 0

To explain: The CONDUCTION angle of class D amplifier is 0 because of its switching ability, it TURNS on and off non linearly.

Correct answer is (b) Converts dc to ac

For explanation: Oscillator circuits are the ONE which USES dc power supply and converts it to alternating sinusoidal signals.

Correct choice is (d) band-stop

Best explanation: TWIN T-oscillator is an RC oscillator consists of Twin T-network and an op-amp. Twin-T is actually a combination of low pass and HIGH pass filter combined parallel response provides a band-stop filter with a CENTER frequency EQUAL to

fr=1/2πRC

This is resonant frequency, Oscillations can occur only at this frequency as the filter provides significant negative feedback at frequencies below or above the resonant frequency which is not GOOD for oscillation.

The correct CHOICE is (d) 1/3

Explanation: The response curve for the lead-lag circuit indicates that the OUTPUT VOLTAGE peaks at a frequency called the RESONANT frequency, fr. At this point, the ATTENUATION (Vout/Vin) of the circuit is 1/3.

Vout/Vin = 1/3

The lead-lag circuit in the Wien-bridge oscillator has a resonant frequency fr, at which the phase shift through the circuit is and the attenuation is 1/3.

Right choice is (a) True

To EXPLAIN I WOULD say: For an oscillator circuit, the phase of LOOP gain MUST be equal to zero or integral MULTIPLE of 2nπ.

Correct answer is (a) 1

The explanation is: The AVERAGE VALUE of SATURATION factor is equal to loop gain of the PARTICULAR circuit, USUALLY it will be nearly equal to 1.

Correct option is (a) Output is completely DEPENDENT on the LOWER FREQUENCY spectrum

To elaborate: Output is completely dependent on the lower frequency spectrum of the output signal and hence to PROPERLY obtain lower frequency components, filters are required.

The correct ANSWER is (a) fundamental

For EXPLANATION I would say: The PHYSICAL size of the quartz CRYSTAL affects the final or fundamental frequency of OSCILLATIONS. The fundamental frequency is generally called the crystals “characteristic frequency”. The crystals characteristic or characteristic frequency is inversely proportional to its physical thickness between the two metalized surfaces.

The correct choice is (b) a VOLTAGE-controlled oscillator

The BEST I can explain: A Voltage controlled oscillator is an oscillator with an OUTPUT SIGNAL whose output can be varied over a range, which is controlled by the INPUT DC voltage. It is an oscillator whose output frequency is directly related to the voltage at its input.

The oscillation frequency varies from few hertz to hundreds of GHz.

Correct ANSWER is (c) 29

Easy EXPLANATION: Since the resistor-capacitor combination in the RC Oscillator circuit also acts as an attenuator producing an attenuation of -1/29th ( Vo/Vi = β ) per STAGE, the GAIN of the amplifier must be sufficient to overcome the circuit losses.

Therefore, in our three stage RC network above the amplifier gain must be greater than 29.

The CORRECT OPTION is (b) False

Best explanation: An OSCILLATOR circuit does not require an input VOLTAGE, an oscillator can be designed without giving an input signal.

The correct ANSWER is (d) It operates on lesser frequently

The best explanation: class D amplifier work by GENERATING a SQUARE wave of which the low FREQUENCY portions of the spectrum is essentially the WANTED output signal.

Right answer is (a) Aβ = 1

The BEST explanation: Barkhausen CRITERIA states that loop GAIN of the closed loop circuit MUST be equal to one in order to repeat the generation.

Correct ANSWER is (d) By SHIFTING the Q POINT above cut off

To elaborate: By using two more voltage sources and thus by shifting the Q point SLIGHTLY above the cut off, we can remove noise over distortion.

Right ANSWER is (a) 100%

The BEST explanation: Theoretically the efficiency of the class D power amplifier is 100% because of its SWITCHING ABILITY.

Right OPTION is (c) COMPLEMENTARY symmetry

To explain I would say: To avoid transformer usage in CLASS B amplifier, pair of TRANSISTOR is connected together in complemented manner.

Right answer is (C) Low power dissipation

The best I can explain: SINCE power dissipation in MOSFET is less, this results in smaller heat SINKS and thus the cost of the AMPLIFIER will be reduced.

Correct option is (c) Pulse generator

The explanation: The OUTPUT STAGES of class D AMPLIFIER are used as pulse generator, because of its SWITCHING ABILITY.