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# Telephone channels and PCM analysis

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The analog to digital converter (ADC) used in a telephone system outputs 8 bit words. The digital words are transmitted as a serial stream to form a PCM voice signal. The analog voice signal voltage always lies between -1.0 V and + 1.0 V.

a. Assuming that ADC is linear, what is the step size between quantization levels?

b. The PCM signal is converted back to an analog waveform. What is the quantization signal to noise ratio (SNR)?

https://brainmass.com/engineering/power-engineering/telephone-channels-pcm-analysis-345016

#### Solution Preview

(a) Start by considering the Analog signal range (VR) which is easily seen to be

Analog Range VR = Max V - Min V = 1 - (-1) = 2V.

Now consider the word size required for the PCM words.

If there are L = 8 bits per word then we can say that this gives rise to 2^8 possible binary digit
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#### Solution Summary

Using data of a PCM telephone link and some ADC parameters in the question a solution is shown that determines the quantisation spacing (level spacing) and the Quantisation SNR for the system.

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