modulators

Modulators are devices or circuits that impose a modulating signal onto a carrier wave, producing a modulated carrier that can carry information. In communications, modulation enables the transmission of signals over a physical medium by shifting a carrier in amplitude, frequency, or phase, or by mapping data onto symbols. Modulation can be performed in analog form or in digital form, with schemes chosen to balance bandwidth, power efficiency, and robustness to noise. Most transmitters include a modulator as part of a chain that also contains a carrier generator and a demodulator at the receiver.

Common analog modulators include amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM). Digital modulators create symbols with schemes such as binary phase shift keying (BPSK), quadrature amplitude modulation (QAM), and various phase-shift keying formats (PSK); higher-order forms such as multi-level QAM are used for greater spectral efficiency. Pulse modulation methods, including pulse-width modulation (PWM) and pulse-position modulation (PPM), are widely used in control and some data-link applications.

Implementation can be analog, using mixers and varactors to vary the carrier, or digital, using software-defined radio techniques that generate the modulated waveform in software and convert it to radio frequency with digital-to-analog converters and RF upconverters. The choice of modulator affects bandwidth, power efficiency, and error performance. Key metrics include modulation index, symbol rate, and bit error rate, as well as spectral occupancy and adjacent-channel leakage.

Modulators are fundamental in radio and network systems, including broadcasting, cellular networks, satellite communications, and radar. They enable digital data transmission over analog channels and facilitate recovery of the original information through demodulation.