21. For the circuit shown below find the output voltage
A. Vo (+) = +10 v
B. Vo (+) = +12v
C. Vo (+) = +7v
D. None of the mentioned
Answer: B
The voltage at the terminal
V1 = (Vp -Vd1) /2
V1 = (12-0.7) /2 = 5.65 v (Vd1= voltage drop across diode=0.7)
Similarly, the voltage at the negative terminal
V2 = (Vo -Vd3 ) /2 = (Vo – 0.7) /2
Since Vid ≅ 0v , ∴ V1 = V2
Vo = (5.65 *2 ) + 0.7 = 12v.
22. What is the alternate method to measure the values of non-sinusoidal waveform other than ac voltmeter?
A. Clipper
B. Clamper
C. Peak detector
D. Comparator
Answer: C
A conventional ac voltmeter is designed to measure the RMS value of the pure sine wave whereas, the peak value of the non-sinusoidal waveforms can be a peak detector.
23. State the condition needed to be satisfied by the peak detector for proper operation of the circuit.
A. CRd ≤ T/10 and CRL ≥ 10T
B. CRd ≤ 10T and CRL ≥ T/10
C. CRd ≥ T/10 and CRL ≤ 10T
D. CRd ≥ 10T and CRL ≤ T/10
Answer: A
For proper operation of the circuit, the charging and discharging time constant must satisfy the following: CRd ≤ T/10 and CRL ≥ to 10T.
24. The resistor in the peak detector is used to
A. To maintain proper operation
B. Protect op-amp from damage
C. To get shaped non-sinusoidal waveform
D. None of the mentioned
Answer: B
The resistor is used to protect the op-amp against the excessive discharge current, especially when the power supply is switched off.
25. How the recovery time of the op-amp is reduced?
A. Diode is connected at the output of the amplifier
B. Load resistor
C. Forward biased diode resistor
D. Discharge capacitor
Answer: A
The diode-connected at the output of op-amp conducts during the negative half cycle of input voltage. Hence, prevent the op-amp from going into negative saturation. This in turn helps to reduce the recovery time of the op-amp.
26. How to detect the negative peaks of input signals in the peak detector given below?
A. Reversing D1 diode
B. Reversing D1 and D2 diodes
C. Reversing D2 diode
D. Charging the positions of D1 and D2
Answer: B
The negative peaks of the input signal Vin can be detected by reversing diodes D1 and D2.
27. In the sample and hold circuit, the period during which the voltage across the capacitor is equal to the input voltage
A. Sample period
B. Hold period
C. Delay period
D. Charging period
Answer: A
The time periods of the sample and hold control voltage during which the voltage across the capacitor is equal to the input voltage are called the sample period.
28. During which period the op-amp’s output of sample and hold circuits is processed?
A. Delay period
B. Sample and hold period
C. Sample period
D. Hold period
Answer: D
The hold period is the period during which the voltage across the capacitor is constant and the output of the op-amp is processed or observed during hold periods.
29. Which IC is mostly preferred for a sample and hold circuits?
A. µ771
B. IC741
C. LF398
D. µ351
Answer: C
LF398 has a significant reduction in size and improved performance and requires only an external storage capacitor.
30. Sample and hold circuits are used in
A. Analog to Digital modulation
B. Digital to analog modulation
C. Pulse position modulation
D. All of the mentioned
Answer: D
Sample and hold circuits are used in
Analog to Digital modulation
Digital to analog modulation
Pulse position modulation
All types of modulation involve taking samples of an input signal and hold on to its last sampled value until the input is sampled.
