Adaptive delta modulation
- 1. Adaptive Delta Modulation Unit -2 Presented by Mrs. M.P.Sasirekha
- 2. Reasons to use Adaptive Delta Modulation • In order to overcome the quantization errors due to slope overload and granular noise, the step size (Δ) is made adaptive to variations in the input signal x(t). • Particularly in the step segment of the signal x(t), the step size is increased. And the step is decreased when the input is varying slowly. • This method is known as Adaptive Delta Modulation (ADM). • The adaptive delta modulators can take continuous changes in step size or discrete changes in step size.
- 3. Transmitter
- 4. Transmitter • The logic for step size control is added in the diagram. • The step size increases or decreases according to a specified rule depending on one bit quantizer output. • For an example, if one bit quantizer output is high (i.e., 1), then step size may be doubled for next sample. • If one bit quantizer output is low, then step size may be reduced by one step. • Fig.2 shows the staircase waveforms of adaptive delta modulator and sequence of bits to be transmitted.
- 5. Transmitter
- 6. Receiver
- 7. Receiver • The receiver has two portions. The first portion produces the step size from each incoming bit. Exactly the same process is followed as that in transmitter. • The previous input and present input decide the step size. • It is then applied to the second portion i.e., an accumulator which builds up staircase waveform. • The low pass filter then smoothens out the staircase waveform to reconstruct the original signal.
- 8. Advantages of Adaptive Delta Modulation • Adaptive delta modulation has certain advantages over delta modulation as under : 1.The signal to noise ratio of ADM is better than that of DM because of the reduction in slope overload distortion and idle noise. 2.Because of the variable step size , the dynamic range of ADM is wider than DM. 3.Utilization of bandwidth is better in ADM than DM.
- 10. Thank you