ABSTRACT
Pulse code modulation (PCM) is analog-to-digital conversion of a special type where the information contained in the instantaneous samples of an analog signal is represented by digital words in a serial bit stream. The PCM signal is generated by carrying out three basic operations: sampling, quantizing, and encoding. The PCM signal is obtained from the quantized pulse-amplitude modulated signal by encoding each quantized sample value into a digital word. The output of the ramp generator is continuously compared to the sample value; when the value of the ramp becomes equal to the sample value, the binary value of the counter is read. This count is taken to be the PCM word. The switches are controlled by digital logic. After the process converges, the value of the switch settings is read out as the PCM word. The high or low level of the comparator outputs determines the binary PCM word with the aid of some digital logic.
