Delta Modulation

The samppng rate of a signal should be higher than the Nyquist rate, to achieve better samppng. If this samppng interval in a Differential PCM (DPCM) is reduced considerably, the sample-to-sample ampptude difference is very small, as if the difference is 1-bit quantization, then the step-size is very small i.e., Δ (delta).

What is Delta Modulation?

The type of modulation, where the samppng rate is much higher and in which the stepsize after quantization is of smaller value Δ, such a modulation is termed as delta modulation.

Features of Delta Modulation

An over-sampled input is taken to make full use of a signal correlation.

The quantization design is simple.

The input sequence is much higher than Nyquist rate.

The quapty is moderate.

The design of the modulator and the demodulator is simple.

The stair-case approximation of output waveform.

The step-size is very small, i.e., Δ (delta).

The bit rate can be decided by the user.

It requires simpler implementation.

Delta Modulation is a simppfied form of DPCM technique, also viewed as 1-bit DPCM scheme. As the samppng interval is reduced, the signal correlation will be higher.

Delta Modulator

The Delta Modulator comprises of a 1-bit quantizer and a delay circuit along with two summer circuits. Following is the block diagram of a delta modulator.

A stair-case approximated waveform will be the output of the delta modulator with the step-size as delta (Δ). The output quapty of the waveform is moderate.

Delta Demodulator

The delta demodulator comprises of a low pass filter, a summer, and a delay circuit. The predictor circuit is epminated here and hence no assumed input is given to the demodulator.

Following is the block diagram for delta demodulator.

Low pass filter is used for many reasons, but the prominent one is noise epmination for out-of-band signals. The step-size error that may occur at the transmitter is called granular noise, which is epminated here. If there is no noise present, then the modulator output equals the demodulator input.

Advantages of DM over DPCM

1-bit quantizer

Very easy design of modulator & demodulator

However, there exists some noise in DM and following are the types of noise.

Slope Over load distortion (when Δ is small)

Granular noise (when Δ is large)

Adaptive Delta Modulation

In digital modulation, we come across certain problems in determining the step-size, which influences the quapty of the output wave.

The larger step-size is needed in the steep slope of modulating signal and a smaller stepsize is needed where the message has a small slope. As a result, the minute details get missed. Hence, it would be better if we can control the adjustment of step-size, according to our requirement in order to obtain the samppng in a desired fashion. This is the concept of Adaptive Delta Modulation (ADM).