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Design of Electronic Devices & Circuits - MCQ from AMIE exams (Winter 2018)

 
Choose the correct answer for the following (10 x 2)
 
1. Compared to NMOS OP-AMP, most CMOS OP-AMPs have
(a) higher CMRR
(b) lower CMRR
(c) lower slew rate
(d) higher power dissipation
 
2. The operational transconductance amplifier is a single chip amplifier in which the transconductance is controlled by an externally connected
(a) resistance
(b) capacitor
(c) choke
(d) voltage

3. In a full-wave rectifier, independently of the filter used, the peak inverse voltage across each diode divided by the maximum transformer voltage measured from midpoint to either end equals to
(a) 0.25
(b) 0.50
(c) 10
(d) 2.0

4. For Butterworth & Chebyshev filters, the correct statement is:
(a) Butterworth response has a sharp cut-off
(b) Chebyshev response has a flat response in the pass band
(c) Butterworth response has ripples in the pass band
(d) Chebyshev response has ripples in the pass band

5. A zero crossing detector converts a sinusoid into a
(a) saw tooth wave
(b) triangular wave
(c) square wave
(d) staircase wave

6. In every practical oscillator, the loop gain is
(a) slightly larger than unity
(b) equal to unity
(c) less than unity
(d) infinite

7. Consider the following statements:
1. A Schmitt trigger circuit can be an emitter-coupled bi-stable circuit.
2. Schmitt trigger circuit exhibits hysteresis phenomenon.
3. The output of a Schmitt trigger will be triangular if the input is square wave.
Which of these statements are correct?
(a) 1, 2 and 3
(b) 1 and 2 only
(c) 2 and 3 only
(d) 1 and 3 only

8. A synchronous demodulator comprises
(a) choke, switch and high-pass filter
(b) capacitor, switch and low-pass filter
(c) capacitor, switch and band-pass filter
(d) resistance, switch and notch filter

9. The reduced state table of a sequential machine has nine rows. In order to implement the machine, the minimum number of flip-flops needed is equal to
(a) 10
(d) 9
(c) 5
(d) 4

10. The free-running frequency of a PLL is 100 kHz. The supply voltage is ±6V. The lock range is equal to
(a) 2.4 kHz
(b) 130 kHz
(c) 240 kHz
(d) 600 kHz

Answers

1. (b) CMOS amplifiers usually offer inferior offset drift, CMRR, and PSRR specifications.

2. (d) The operational transconductance amplifier (OTA) is an amplifier whose differential input voltage produces an output current. Thus, it is a voltage controlled current source (VCCS).

3. (d) In case of a center-tapped full-wave rectifier:
PIV = 2Vm

4. (d) Chebyshev Filter:
  • It is also called an equal rip­ple filter.It gives a sharper cut-off than the Butterworth filter in the passband.
  • It has a ripple response in the passband and a flat response in the stopband. it is also known as an equal-ripple response.Both Butterworth and Chebyshev filters exhibit large phase shifts near the cut-off frequency.
  • A drawback of the Chebyshev fil­ter is the appearance of gain maxima and minima below the cut-off frequency.
  • This gain ripple, ex­pressed in dB, is an adjustable parameter in filter design.
  • A Chebyshev filter is used where a very sharp roll-off is required. However, this is achieved at the expense of a gain ripple in the lower frequency passband.
5. (c)

6. (a)

7. (b)

8. (c)

9. (d) Number of rows ≤ 2n
n = number flip-flops
9 ≤ 24
n = 4

10. (b) 130 kHz; 
△fL = ±(7.8×fo)/V = 7.8 x 100/6 = 130

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