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Delta Modulation Questions and Answers

1.

Slope overload distortion in delta modulation can be reduced by :

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: D

Slope overload is reduced by increasing the step size.

A delta modulator can change its staircase approximation by only one step \(\Delta\) per sample, so the steepest slope it can follow is \(\Delta f_{s}\). Slope overload occurs when the signal changes faster than that:

\[ \left| \frac{dm(t)}{dt} \right|_{max} \gt \Delta f_{s} \]

Raising \(\Delta\) (or the sampling rate) lets the staircase keep up. Decreasing the sample rate or the step size makes the overload worse; a smaller step reduces granular noise instead, which is why adaptive delta modulation varies the step. 'Differential gain' is not the controlling quantity.

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2.

Delta modulation is a special case of DPCM in which only the polarity of the .................. signal is encoded as output.

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: C

Only the polarity of the difference signal is encoded.

In DPCM the transmitter quantises and codes the difference between each sample and a prediction of it. Delta modulation is the simplest case: it uses a one-bit quantiser, so it sends only the sign of the difference between the input and its staircase approximation. A 1 means the signal is above the approximation, which steps up; a 0 means it is below, which steps down.

The receiver integrates the bits to rebuild the signal, but integration and summation are operations on the decoded bits, not what is encoded, and differentiation is not used.

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