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19. What is analog-to-digital conversion of signals?
A discrete-time signal is defined by specifying its value only at discrete
times, called sampling instants. When the sampled values are quantised and
encoded, a digital signal is obtained. A digital signal is obtained from the
analog signal by using an analog-to-digital converter. This entire process is
referred to as the conversion of signals from analog to digital form.
20. What are the properties of ROC for z-Transform?
Properties of the ROC for the z-Transform :
1. X(z) converges uniformly if and only if the ROC of the z-transform X(z) of
the sequence includes the unit circle. The ROC of X(z) consists of a ring in
the z-plane centered about the origin. That is, the ROC of the z-transform of
x(n) has values of z for which x(n) r-n is absolutely summable.
2. The ROC does not contain any poles.
3. When x(n) is of finite duration then the ROC is the entire z-plane, except
possibly z=0 and/or z=infinity.
4. If x(n) is a right sided sequence, the ROC will not include infinity.
5. If x(n) is a left sided sequence, the ROC will not include z=0. However if
x(n)=0 for all n>0, the ROC will include z=0.
6. If x(n) is two sided and if the circle |z| = r0 is in the ROC, then the ROC
will consist of a ring in the z-plane that includes the circle |z|=r0.
7. If X(z) is rational, then the ROC extends to infinity, i.e. the ROC is
bounded by poles.
8. If x(n) is causal, then the ROC includes z=infinity.
9. If x(n) is anti- causal, trhen the ROC includes z=0.
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