Pulse coded modulation (PCM)
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Pulse coded modulation involves analogue data being transmitted as digital signals. The digital form is then transmitted over the transmission media. At the receiver the digital code converts back into an analogue form. Digital signals are generally less affected by noise and thus provide a more reliable method of transmitting data. Figure 10.1 shows an example digital signal with noise added to it. The comparator outputs a HIGH level (a ‘1’) if the signal voltage is greater than the threshold voltage, or it will output a LOW. If the noise voltage is less than half the threshold voltage then the noise will not affect the recovered signal. Even if the noise is greater than this threshold there are techniques which can reduce its effect. One method is to add extra bits to the data to either detect errors or even to correct the bits in error.
KeywordsTime Slot Quantization Level Quantization Noise Quantization Step Digital Code
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