DELTA MODULATION

The 'Delta modulation' (DM or Δ-modulation) is an analog-to-digital or digital-to-analog signal conversion. Its main features are:

★ the analog signal is approximated with a series of segments;

★ each segment of the approximated signal is compared to the original analog wave to determine the increase or decrease in relative amplitude,
★ the decision process for establishing the state of successive bits is determined by this comparison,

★ only the change of information is sent, that is only an increase or decrease of the signal amplitude from the previous sample is sent whereas a no-change condition causes the modulated signal to remain at the same 0 or 1 state of the previous sample.
To achieve high signal-to-noise ratio, delta modulator can use oversampling technique, that is the analog signal is sampled at a rate several time higher than Nyquist rate, and then a decimation filter which enhance the resolution lowering the output frequency.
Derived forms of delta modulation are continuously variable slope delta modulation, delta-sigma modulation, and differential modulation. The Differential Pulse Code Modulation is similar.

Contents

Principle

Bibliography

External links

Principle

Delta modulation is based in quantizing not the absolute value of the input analog waveform, but only the difference between the current and the previous step. Let's examine a system block diagram.
The modulator is made by a quantizer which converts the difference between the input signal and the average of the previous steps. In its simplest way, the quantizer can be realized with a comparator referenced to 0 (two levels quantizer), whose output is ''1'' or ''0'' if the input signal is positive or negative. The demodulator is made by an integrator (like the one in the feedback loop) which averages the steps, and its output is filtered with a low pass filter

Bibliography

★ Delta Modulation Systems, , R., Steele, Pentech Press, 1975,

External links

Delta Modulator