- Delta modulation provides a staircase approximation of the input sampled signal where only one bit per sample is transmitted.
- This one bit is sent by comparing the present sample value with the previous sample value and the result whether the amplitude is to be increased or decreased is transmitted.
- If the step is reduced, 0 is transmitted and if the step is increased then 1 is transmitted.
- Delta modulation has a disadvantage of the presence of slope overload distortion and granular noise.
- Slope overload distortion arises due to large dynamic range of the input signal which results in large error between the original input signal and the staircase approximated signal. When the slope of the signal is high, the step size must be increased to reduce slope overload distortion.
- Granular noise arises when the step size is too large compared to the small variations in the input signal.
- To overcome these quantization errors due to slope overload and granular noise, the step size is made adaptive to the variations in the input signal i.e. the step size is not fixed and can be increased or decreased depending on the variations of the input signal.
- Step size is determined by the previous and the present input samples.
- If the input is varied slowly then the step size is decreased. These is then applied to the accumulator where staircase waveform is built at the transmitter end and at the receiver low pass filter passes out staircase waveform to reconstruct the original signal.
- Reduction in the slope overload distortion and granular noise in Adaptive delta modulation induces improved signal to noise ratio as compared to the Delta modulation.
- Since the step size is variable, the dynamic range of Adaptive delta modulation is wider than Delta modulation.
- Bandwidth utilization is better in Adaptive delta modulation as compared to Delta modulation.
- Thus Adaptive delta modulation superior to Delta modulation.
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