Terminology » RF Basics » Modulator vs. Demodulator: Understanding the Difference

Modulator vs. Demodulator: Understanding the Difference

modulation demodulation rf digital communication analog communication

This page explains the basics of modulators and demodulators and highlights the key differences between them. In telecommunications, modulation techniques are used to transmit information over long distances and to handle the high bit rate requirements of modern systems.

There are two main types of modulation:

  • Analog Modulation: Used when the baseband information to be transmitted is analog.
  • Digital Modulation: Used when the baseband information to be transmitted is digital (i.e., consisting of binary 1s and 0s).

Modulator

A modulator is a device that performs the function of modulation. An RF modulator is a modulator that operates on Radio Frequencies.

In essence, a modulator converts input information bits into a complex waveform. The parameters of the output waveform (e.g., amplitude, frequency, phase) are changed according to the modulating input signal, based on the modulation type.

Typical analog modulators include Amplitude Modulation (AM), Frequency Modulation (FM), and Phase Modulation (PM). Digital modulators include Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), Phase Shift Keying (PSK), 16QAM, 64QAM, and 256QAM.

Figure 1 illustrates a digital modulator and demodulator of the FSK type.

Modulator Demodulator

Figure 1: Modulator Demodulator Process

In FSK, the frequency of the carrier input is varied according to the modulating signal input. For a binary ‘1’, frequency f1 is output, while for a binary ‘0’, frequency f2 is output.

In AM or ASK, the amplitude of the carrier is changed according to the baseband modulating signal input. For PM and PSK, the phase of the carrier is changed according to the input.

Demodulator

A demodulator is a device that performs the function of demodulation. An RF demodulator is a demodulator that operates on Radio Frequencies.

The demodulator converts a received complex waveform back into baseband information (i.e., analog or digital).

The following table lists typical modulation techniques widely used in various RF, Microwave, and Wireless communication systems for diverse applications.

Modulation TechniqueDescription
BPSKBinary Phase Shift Keying, used for robust long-distance communication.
QPSKQuadrature Phase Shift Keying, used for a compromise between long distance and medium data rate requirement.
8-PSK8-level Phase Shift Keying.
QAMQuadrature Amplitude Modulation, utilizes both QPSK and PSK functionalities. Used to increase the data rate of the system.
MSK, GMSKMinimum Shift Keying and Gaussian Minimum Shift Keying, Used in GSM technology.
DPSKDifferential Phase Shift Keying.
OQPSKOffset QPSK.
SSB, VSBSSB stands for Single Sideband Modulation, VSB stands for Vestigial Sideband Modulation.
SSBSC, DSBSCSSBSC stands for Single Sideband Suppressed Carrier, DSBSC stands for Double Sideband Suppressed Carrier.