### GATE 1990 ECE Analog Circuits (Analog Electronics) - Video Solutions

1. For good stabilized biasing of the transistor of the CE amplifier of the figure shown, the condition is 2. Which of the following statements are correct for biasing transistor amplifier configurations?
a. CB amplifier has low input impedance and a low current gain
b. CC amplifier has low output impedance and a low current gain
c. CE amplifier has very poor voltage gain but has very high input impedance
d. The current gain of CB amplifier is higher than the current gain of CC amplifier

3. For the same a.c. voltage and load impedance, which of the following statements about rectifier are correct?
a. The average load current in a full wave rectifier is twice than in a half wave rectifier
b. The average load current in a full wave rectifier is n times that in a half wave rectifier
c. Half wave rectifier will have a bigger sized transformer compared to full wave rectifier
d. Half wave rectifier will have a small sized transformer compared to full wave rectifier

4. The operational amplifier has a very poor open loop gain of 45, otherwise is ideal. The gain of the amplifier is a. 5
b. 20
c. 4
d. 4.5

5. The CMRR of the differential amplifier shown is a. Infinity
b. Zero
c. 900
d. 1800

6. If the input to the circuit shown is a sine wave, the output will be a. Half wave rectified sine wave
b. Full wave rectified sine wave
c. Triangular wave
d. Square wave

7. Figure shows an RC phase shift oscillator. Solve the network to find the minimum value of hfe for the transistor for oscillations to be possible. Also determine the frequency of such oscillations. Take C = 0.01 µF and hie = 2 KΩ.

8. A pick up signal is power amplified using a complementary symmetry push pull amplifier and fed to a 5 Ω loud speaker as shown. The specifications of power transistors are as follows:
ICmax = Maximum collector current = 2 Amps and PCmax = Maximum power dissipation = 1 Watt.
Find the maximum power delivered to the loud speaker, if the maximum output voltage subject to OP-AMP voltage limitations is 15 volts.
If the transistors are mounted on a heat sink, so that PDmax changes to 3 Watts. What will be the new value of the maximum power delivered?
Answer: (i) 3.08 Watts, circuit gets breakdown (ii) 3.08 Watts, circuit gets breakdown