# Pulse Code Modulation (PCM) MCQ

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## Pulse Code Modulation (PCM) MCQ

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### Multiple-Choice Questions

Q.1. In PCM, the quantization noise depends on

• sampling rate
• number of quantization levels
• signal power
• none of the above

Q.2. Which of the following modulation is digital in nature

• PAM
• PPM
• DM
• none of the above

• PCM
• DPCM
• DM
• none of the above

Q.4. In PCM, if the number of quantization levels is increased from 4 to 64, then the bandwidth requirement will approximately be

• 3 times
• 4 times
• 8 times
• 16 times

Q.5. Quantization noise occurs in

• PAM
• PWM
• DM
• none of the above

Q.6. Companding is used in PCM to

• reduce bandwidth
• reduce power
• increase S/N ratio
• get almost uniform S/N ratio

Answer: get almost uniform S/N ratio

Q.7. Pulse stuffing is used in

• synchronous TDM
• asynchronous TDM
• any TDM
• none of the above

Q.8. The main advantage of PCM is

• less bandwidth
• less power
• better performance in presence of noise
• possibility of multiplexing

Answer: better performance in presence of noise

Q.9. The main disadvantage of PCM is

• large bandwidth
• large power
• complex circuitry
• quantization noise

Q.10. The main advantage of DM over PCM is

• less bandwidth
• less power
• better S/N ratio
• simple circuitry

Q.11. In a DM system, the granular noise occurs when modulating signal

• increases rapidly
• decreases rapidly
• changes within the step size
• has high frequency component

Answer: changes within the step size

Q.12. Pick the odd man out

• URZ
• BRZ
• Manchester code
• differential code

Q.13. The number of bits per sample in a PCM system is increased from 8 to 16. The bandwidth of the system will increase

• 8 times
• 2 times
• 1/2 times
• 28 times

Q.14. The standard data rate of a PCM voice channel is

• 8 kbps
• 8 bps
• 16 bps
• 64 kbps

Q.15. The signal-to-quantization noise ratio for a sinusoidal signal quantized using 10 bit PCM is:

• 62 dB
• 10 dB
• 60 dB
• 32 dB

Q.16. The output SNR in a DM system for a 1 kHz sinusoid sampled at 32 kHz without slope overload and followed by a 4 kHz post-reconstruction filter is given as

• 30.6 dB
• 8 dB
• 24.9 dB
• 20 dB

Q.17. The line code that has zero d.c. component for pulse transmission of random binary data is

• UP-NRZ
• UP-RZ
• BPRZ-AMI
• BPNRZ

Q.18. The number of bits per sample in a PCM system with sinusoidal input is increased from n to n +1. The improvement in signal to quantization noise ratio will be

• 3 dB
• 6 dB
• 2n dB
• n dB

Q.19. The word length of a 64 quantization level PCM for S = 2 is

• 3
• 4
• 5
• 6

Q.20. The word length of a 64 quantization level PCM for S = 4 is

• 3
• 4
• 5
• 6

Q.21. In a PCM system, the number of quantization levels is 32 and the maximum signal frequency is 4 kHz. The bit transmission rate is

• 8 kbps
• 16 kbps
• 32 kbps
• 40 kbps

Q.22. For a PCM system with 256 quantization levels, the sampling frequency is 10 kHz. The BW is

• 20 kHz
• 40 kHz
• 80 kHz
• 10 kHz

Q.23. The bandwidth required for transmission of high quality speech is

• 10 kHz
• 15 kHz
• 4 kHz

Q.24. Consider the following statements comparing delta modulation with PCM systems: DM requires

1. a lower sampling rate
2. a higher sampling rate
3. a large bandwidth
4. simpler hardware

Which of these statements are correct?

• 1, 2 and 4
• 1, 2 and 3
• 1, 3 and 4
• 2, 3 and 4

Q.25. The ramp signal m(t) = at is applied to a delta modulator with sampling period Ts, and step size δ. Slope overload distortion would occur if

• δ< a
• δ> a
• δ < aTs
• δ> aTs

Q.26. In asynchronous TDM, for n signal sources, each frame contains m slots, where m is usually

• less than n
• 2n
• n
• greater than 2n

Q.27. A sinusoidal signal with peak-to-peak amplitude of 1.536 V is quantized in 128 levels using a mid-rise uniform quantizer. The quantization noise power is

• 0.768 V
• 48 x 10-6 V2
• 12 x 10-6 V2
• 3.072 V

Q.28. In a PCM system, if the code-word length is increased from 6 to 8 bits, the signal-to-quantization noise ratio improves by the factor

• 8/6
• 12
• 16
• 8

Q.29. In the output of a DM speech encoder, the consecutive pulses are of opposite polarity during time interval t1 < t < t2. This indicates that during this internal

• the input to the modulator is essentially constant
• the modulator is going through slope overload
• the accumulator is in saturation
• the speech signal is being sampled at the Nyquist rate

Answer: the input to the modulator is essentially constant

Q.30. The minimum step-size required for a delta-modulator operating at 32 K samples/second to track the signal [u(t) being the unit step function]

$x(t)=125t[u_{t}-u_{t-1}]+(250-125t)[u_{t-1}-u_{t-2}]$

so that slope-overload is avoided, would be

• $2^{-10}$
• $2^{-8}$
• $2^{-6}$
• $2^{-4}$

Answer: $2^{-8}$

Q.31. In delta modulation, the slope overload distortion can be reduced by

• decreasing the step size
• decreasing the granular noise
• decreasing the sampling rate
• increasing the step size

Q.32. Which is the most important sub-system for recovering and reconstructing signals in a TDM system?

• Envelope detector followed by a low pass filter
• Synchronization circuit for proper timing
• Bandpass filters to segregate channels
• Coherent detector to ensure frequency and phase correction

Answer: Coherent detector to ensure frequency and phase correction

Q.33. Which one of the following is correct?

In a TDM system, each signal is allotted in a frame a unique and fixed

• frequency slot
• time slot
• amplitude slot
• phase slot