Delta modulation (continued)

Quantistion noise

In DM, quantized is the difference of and . If is used instead of the transmitter does not have to include the receiver structure to compute . However quantisation noise can accumulate from one Pixel to next.

The solid staircase is the result of DM when is used. The dotted staircase is the result when is used. The reconstructed signal can be significantly different from in this case, since the receiver does not have and therefore, uses in reconstructing . While error quantized at the transmitter is based on .

An important design parameter in DM is step size . Consider a signal reconstructed by DM shown in Fig (16 ). In the region where signal varies slowly, the reconstructed signal varies rapidly around the original signal. This is called granular noise .

A large results in large granular noise, so a small is desired.

When the signal or rapidly, it may take many pixels before can catch up with using a small . The reconstructed will appear blurred in such region. This is called slope overload distortion.

This is shown in figure (17)

.A small results in large degree of slope overload distortion.

Clearly reduction of granular noise and slope overload distortion have conflicting requirements. So is chosen through some compromise between the two requirements.