PCM Quiz: Pulse Code Modulation Fundamentals

Study Notes

Pulse Code Modulation (PCM)

A digital encoding modulation technique that converts an analog signal into a digital signal via sampling.
PCM signal consists of a group of pulses that represent the inputted analog data.

History of PCM

Invented by Alec H. Reeves in 1937 while working for AT&T.

Advantages of PCM

Most preferred method in tele-communications for digitizing voice and digital data.
Offers ease of digitizing voice and digital data with high-speed signal transmission through metallic and optic-fiber cables.

Limitations of Other Modulation Techniques

PPM and PWM have bandwidth limitations due to resolution requirements in transmitting 16-bits and beyond.
PAM is susceptible to noise, affecting the recovered signal.

PCM Transmitter and Receiver

Function of a sampling circuit in a PCM transmitter is to periodically sample the continually changing analog input voltage and convert those samples to a series of constant amplitude pulses.
Sampling circuit allows for accurate conversion of voltage to a binary code by the ADC.

Sampling Techniques

Natural Sampling
- Retains natural shape of sample pulses during the sample interval.
- Makes it difficult for an ADC to convert the sample to a PCM code.
- Alters the frequency spectrum of the sampled output.
Flat-top Sampling
- Most common method used for sampling voice signals in PCM systems.
- Accomplished in a sample-and-hold circuit.
- Introduces less aperture distortion than natural sampling.
- Can operate with a slower analog-to-digital converter.

Sample-and-Hold Circuit

Periodically samples the continually changing analog input voltage and converts those samples to a series of constant-amplitude PAM voltage-levels.

Description

Learn about the basics of Pulse Code Modulation, a digital encoding technique used to convert analog signals into digital signals. This quiz covers the concept of PCM, its history, and its applications in tele-communications.