PCM MCQs

Practice PCM MCQs with four options, answers and explanations for focused Electronics & Telecommunication Engineering revision.

Question 1

Communication SystemsPCM

For a uniform quantizer with full-scale input range of 8 V and 256 equal levels, the quantization step size is?

A0.03125 V
B0.0625 V
C0.125 V
D0.25 V

Show AnswerHide Answer Report an error

Correct Answer: A. 0.03125 V

Explanation: Step size Delta = range/L = 8/256 = 0.03125 V.

Reference: Standard communication systems: pcm

Question 2

Communication SystemsPCM

For an ideal uniform quantizer, the magnitude of quantization error is normally bounded by approximately?

ADelta/4
BDelta/2
CDelta
D2Delta

Show AnswerHide Answer Report an error

Correct Answer: B. Delta/2

Explanation: With rounding to the nearest level, the quantization error lies approximately between -Delta/2 and +Delta/2.

Reference: Standard communication systems: pcm

Question 3

Communication SystemsPCM

Companding in PCM telephony is mainly used to?

AImprove effective quantization performance for low-level signals
BEliminate sampling completely
CIncrease antenna height
DSuppress every binary zero

Show AnswerHide Answer Report an error

Correct Answer: A. Improve effective quantization performance for low-level signals

Explanation: Nonuniform quantization implemented through companding gives finer effective resolution to weaker signals and improves their quantization SNR.

Reference: Standard communication systems: pcm

Question 4

Communication SystemsPCM

Which pair represents commonly known companding laws used in digital telephony?

AA-law and mu-law
BOhm-law and Faraday-law
CKirchhoff-law and Coulomb-law
DShannon-law and Carson-law

Show AnswerHide Answer Report an error

Correct Answer: A. A-law and mu-law

Explanation: A-law and mu-law are logarithmic companding characteristics used in PCM telephony systems.

Reference: Standard communication systems: pcm

Question 5

Communication SystemsPCM

PCM stands for?

APulse Code Modulation
BPhase Carrier Multiplication
CPulse Current Mixing
DPeriodic Code Measurement

Show AnswerHide Answer Report an error

Correct Answer: A. Pulse Code Modulation

Explanation: PCM means Pulse Code Modulation, in which sampled amplitudes are quantized and represented by binary code words.

Reference: Standard communication systems: pcm

Question 6

Communication SystemsPCM

The main operations in a basic PCM transmitter are?

ASampling, quantization and encoding
BRectification, regulation and inversion
CMixing, filtering and mechanical switching only
DDemodulation, decoding and amplification only

Show AnswerHide Answer Report an error

Correct Answer: A. Sampling, quantization and encoding

Explanation: A basic PCM transmitter samples the analog signal, quantizes each sample and encodes the quantized value into a binary word.

Reference: Standard communication systems: pcm

Question 7

Communication SystemsPCM

If a PCM system uses 8 bits per sample, the number of available quantization levels is?

A8
B16
C128
D256

Show AnswerHide Answer Report an error

Correct Answer: D. 256

Explanation: For n bits, the number of binary quantization levels is L=2^n. For n=8, L=256.

Reference: Standard communication systems: pcm

Question 8

Communication SystemsPCM

A PCM system samples at 8 kHz and uses 8 bits per sample. Ignoring framing and overhead, its bit rate is?

A8 kbps
B16 kbps
C64 kbps
D128 kbps

Show AnswerHide Answer Report an error

Correct Answer: C. 64 kbps

Explanation: Bit rate = sampling rate × bits/sample = 8000×8 = 64000 bit/s = 64 kbps.

Reference: Standard communication systems: pcm

Question 9

Communication SystemsPCM

A PCM system uses 256 uniform quantization levels. How many bits are required per sample?

Show AnswerHide Answer Report an error

Correct Answer: C. 8

Explanation: Since 256=2^8, eight bits are required to identify each quantization level.

Reference: Standard communication systems: pcm