GATE 1994 ECE Analog Circuits (Analog Electronics) - Video Solutions

1. A Ramp voltage v(t) = 100t volts is applied to a RC differentiating circuit with R = 5 kΩ and C = 4 µF. The maximum output voltage is ______
a. 0.2 volts
b. 2.0 volts
c. 10.0 volts
d. 50.0 volts
Answer: B
Solution :

2. A class-A transformer coupled transistor power amplifier is required to deliver a power output of 10 watts. The maximum power rating of the transistor should not be less than ______
a. 5 watts
b. 10 watts
c. 20 watts
d. 40 watts
Answer: C
Solution :

3. In order to reduce the harmonic distortion in an amplifier, its dynamic range has to be _________
Answer : Dynamic Range expressed in decibels (dB), is the ratio of the highest signal level a circuit, component, or system can handle, to the lowest signal level it can handle. Several parameters can be used to define the highest-level signal, such as the 1-dB compression point as well as the TOi point.
The lowest level signal level is limited by output noise, while the highest level signal is limited most often by distortion.
The 1-dB compression point for an amplifier, for example, is where the linearity of the component begins to degrade. Under linear conditions, a 1-dB rise in input power will result in a 1-dB increase in output power. When the increase at the output is 1-dB less than the increase at the input, it is said to be the amplifier's 1-dB compression point.
High Dynamic Range Amplifiers have low noise figures, low gain, low distortion and high 1 dB compression points. This combination of performance characteristics provides the greatest range between the minimum detectable signal and the signal level that will start to compress the amplifier. So in order to reduce the harmonic distortion in an amplifier, its dynamic range has to be compressed to 1-dB compression point.

4. A common emitter transistor amplifier has a collector current of 1.0 mA when its base current is 25 µA at room temperature. Its input resistance is approximately equal to _______
Solution :

5. A pulse having a rise time of 40 nsec is displayed on a CRO of 12 MHz bandwidth. The rise time of the pulse as observed on the CRO would be approximately equal to ____________
Answer: 49.5 nSec
Solution :

6. For the 2N338 transistor, the manufacturer specifies Pmax = 100 mW at 25oC, free air temperature and the maximum junction temperature Tjmax = 125oC. Its thermal resistance is ________
Answer:1000 oC/W
Solution :

7. The frequency compensation is used in operational amplifiers is to increase its ___________
Answer: Stability
Solution :

8. Match the following:
a) Hartley 1) Low frequency oscillator
b) Wein-bridge 2) High frequency oscillator
c) Crystal 3) stable frequency oscillator
4) Relaxation frequency oscillator
5) Negative resistance oscillator
Answer: a-2, b-1, c-3
Solution :

9. Assuming that the amplifier shown in the figure below is a voltage controlled voltage source.
Show that the voltage transfer function of the network is given by


10. Calculate the frequency at which zero transmission is obtained from the Wien-bridge shown below.

Answer: f = 1/2πRC

11. Find the output voltage of the following circuit shown below, assuming ideal operational amplifier behavior.

Answer: 4 Volts

12. In the MOSFET amplifier shown in the figure below, the transistor has µ = 50, rd = 10 kΩ, Cgs = 5 pF, Cgd = 1 pF and Cds = 2 pF.

Draw a small signal equivalent circuit for the amplifier for mid band calculate its mid band voltage gain.
Answer: -7.04

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