ANALOG-TO-DIGITAL CONVERSION

We know that a digital signal is superior to an analog signal. The tendency today is to change an analog signal to digital data. In this section we describe two techniques, pulse code modulation and delta modulation.

Topics discussed in this section:

• Pulse Code Modulation (PCM)
• Delta Modulation (DM)

Components of PCM encoder

Three different sampling methods for PCM

Note

According to the Nyquist theorem, the

sampling rate must be

at least 2 times the highest frequency

contained in the signal.

Nyquist sampling rate for low-pass and band-pass signals

Quantization and encoding of a sampled signal

Example: What is the SNRdB in the example of Figure above?

Solution

We can use the formula to find the quantization. We have eight levels and 3 bits per sample, so

SNRdB = 6.02(3) + 1.76 = 19.82 dB

Increasing the number of levels increases the SNR.

Components of a PCM decoder

The process of delta modulation

Delta modulation components

Delta demodulation components