Wat is Adaptive Delta Modulation plz give some links from where i can find out abt it in detail......thanxx?

Question

hELpp!!!!

Answer 1

In the quoted paragraphs below, note that the "reference" and the "approximation" are the same signal, obtained by integrating the DM output, just as the receiving end does.
From the reference : "Delta Modulation (DM) is an analog-to-digital conversion used for transmitting analog signals by simply transmitting the difference of an input signal to a reference signal. This difference, as determined by a comparator, is represented by a "0" or a "1", which in this implementation is 0 V and 3 V respectively. A 0 V comparator output indicates that the input signal is less than the approximated signal, whereas a 3 V output indicates that the input signal is greater than the approximated signal. The reference signal consists of the sum of all previous differences between these two voltage signals. However, a significant issue exists in using delta modulation for the encoding of analog signals. The DM is unable to track rapid changes in the amplitude of the input signal giving a distorted demodulated signal. Should an input signal vary rapidly over time, slope overload occurs. As the modulated signal is transmitted and recovered, it will demonstrate large amplitude variations from the input signal. A solution to this slope overload issue is an adaptive delta modulator (ADM). In this implementation of an ADM, slope overload is eliminated by using digital logic to adjust the step size of the integrator used to construct the reference voltage signal. By using previous values of the differences between the two voltage signals, the digital logic will increase or decrease the step size to provide more accurate tracking of the input voltage signal."
The trick is in the logic that changes the step size, without having to notify the receiving end of the change. Again from the ref.: "After experimenting with simulations of several different adaptive logic schemes we realized that the simplest logic scheme works the best. If the comparator value is different from the one immeadiately before it, it means our input signal and our approximation have crossed each other and we need to change the direction of the approximation. In order to minimize over-correction, we want to decrease the step size. Conversely, if our comparator value is the same as the one immeadiately before it, it means that our signals have not crossed and that we want to increase the approximation's step size so as to minimize slope overload. This can be implemented very easily; with a latch to save the previous value of the comparator output and an XNOR gate to check if the current and previous values are equal."