0749cDelta Modulation

8/12/2019 0749cDelta Modulation

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ASET

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B.Tech., Semester V

Course: Digital Communication

Faculty: Kumar Vaibhav, Assistant Professor, Department of

Electronics & Communication, ASET, Amity University Rajasthan


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Delta

Modulation2


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ASETBlock Diagram

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Fig. 1.


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4Fig. 2. The response of a delta modulator to a baseband signal m(t).


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and there is a consequent downwards jumps in

() by amount S and so on.

Note that at start-up, there may be a brief

interval when () may be a poor

approximation to the baseband signal m(t).

This feature is illustrated in fig. 3.

Hence we note an initial large discrepancybetween m(t) and () and the stepwise

approach of () to m(t).

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Fig.3. Illustrating the start-up response in delta

modulation and the hunting of () about m(t). 7


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We note further that even when ()

hascaught up to m(t), and even though m(t)

remains unvarying, () hunts, swinging up or

down, above and below m(t).

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ASETAdvantages of DM

Since, the delta modulation transmits only onebit for one sample, therefore the signaling

transmission channel bandwidth is quite small

for delta modulation compared. The transmitter and receiver implementation is

very much simple for delta modulation

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ASETDrawbacks of DM

Slope overload distortion Granular or idle noise

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ASETSlope Overload Distortion This distortion arises because of large dynamic

range of the input signal.

As can be observed from figure 4, the rate of

rise of input signal x(t) is so high that the

staircase signal cannot approximate it.

The step size '' becomes too small for

staircase signal u(t) to follow the step segment

of x(t).

Hence, there is a large error between the

staircase approximated signal and the original

input signal x(t). 11


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This error or noise is known as slope overloaddistortion.

To reduce this error, the step size must be

increased when slope of signal x(t) is high. Since step size of delta modulator remains

fixed, its maximum or minimum slopes occur

along straight lines. Therefore, this modulator is also known as

Linear Delta Modulator.

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ASETGranular or Idle Noise

Granular or Idle noise occurs when the step

size is too large compared to small the input

signal.

This means that for very small variations in the

input signal, the signal is changed by large

amount () because of large step size.

Figure 4 shows that when the input signal is

almost flat, the staircase signal u(t) keeps onoscillating by around the signal.

The error between the input and approximated

signal is called granular noise. 14


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The solution to this problem is to make stepsize small.

Therefore, a large step size is required to

accommodate wide dynamic range of theinput signal (to reduce slope overload

distortion) and small steps are to reduce

granular noise. Adaptive delta modulation is the modification

to these errors.

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THANK YOU

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0749cDelta Modulation