Digital Communications Questions and Answers – Receiver Synchronization

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This set of Digital Communications Multiple Choice Questions & Answers (MCQs) focuses on “Receiver synchronization”.

1. Phase locked loops consists of
a) Phase detectors
b) Loop filter
c) Voltage controlled oscillator
d) All of the mentioned

Explanation: Phase locked loops have three basic components – phase detector, loop filter and voltage controlled oscillator. It measures the phase difference between the incoming signal and local replica.

2. In VCO the output frequency is a linear function of its input
a) Frequency
b) Voltage
c) Time period
d) None of the mentioned

Explanation: A VCO is an oscillator whose output frequency is a linear function of its input voltage over some range of input and output.

3. PLL designs have
a) First order loop
b) Second order loop
c) Higher order loop
d) None of the mentioned

Explanation: Most of the PLL designs have second order loop as they can be made unconditionally stable.

4. A cycle slip occurs when the magnitude of the original phase error exceeds

Explanation: A cyclic slip occurs when the magnitude of the original phase error exceeds 2π radians.

5. When phase noise and phase jitter is doubled, the phase variance increases by
a) Two times
b) Four times
c) 0.5 times
d) 8 times

Explanation: In PLL, when the phase jitter and phase noise increases by 2, the phase variance increases by 4 than that of the original signal.

6. Acquisition is a ______ operation.
a) Linear
b) Non linear
c) Linear & Non linear
d) None of the mentioned

Explanation: Acquisition is accomplished by external signal or circuits or sometimes it might be unaided (self acquisition). This acquisition process is an inherently non linear operation.

7. To avoid the loop to be driven to lock, the sweep rate should be
a) Smaller
b) Larger
c) It does not depend on it
d) None of the mentioned

Explanation: The sweep rate must not be too large, or the loop will be driven through the lock point so fast that it will fail to acquire.

8. Which method is more accurate?
a) Closed loop synchronizer
b) Open loop synchronizer
c) Closed & Open loop synchronizer
d) None of the mentioned

Explanation: Closed loop synchronizers are more accurate, but they are much more complex and costly.

9. What is the function of the edge detector?
a) Differentiation
b) Rectification
c) Differentiation & Rectification
d) None of the mentioned

Explanation: The main operation of the edge detector is differentiation and rectification by the use of square law detector.

10. Continuous phase modulation has
a) More bandwidth efficiency
b) More smoothness
c) More bandwidth efficiency & smoothness
d) None of the mentioned

Explanation: Continuous phase modulation is an important signalling technique because of their bandwidth efficiency. Bandwidth efficiency is obtained by increasing the smoothness of the signal.

11. CPM has
a) Narrower bandwidth
b) Wider bandwidth
c) More bandwidth requirement
d) None of the mentioned

Explanation: The increase in smoothness in the signals concentrate the signal energy in a narrower bandwidth, reducing the amount of bandwidth required.

12. The number of filters in CPM receiver structure is
a) LM
b) ML
c) M/L
d) None of the mentioned

Explanation: The number of filters in CPM receiver structure is given by ML.

Sanfoundry Global Education & Learning Series – Digital Communications.