phase modulator

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phase modulator

[′fāz ‚mäj·ə‚lād·ər]
An electronic circuit that causes the phase angle of a modulated wave to vary (with respect to an unmodulated carrier) in accordance with a modulating signal.

Phase modulator

An electronic circuit that causes the phase angle of the modulated wave to vary (with respect to the unmodulated carrier) in accordance with the modulating signal. Since frequency is the rate of change of phase, a phase modulator will produce the characteristics of frequency modulation (FM) if the frequency characteristics of the modulating signal are so altered that the modulating voltage is inversely proportional to frequency. Commercial FM transmitters normally employ a phase modulator because a crystal-controlled oscillator can then be used to meet the strict carrier-frequency control requirements of the Federal Communications Commission. The chief disadvantage of phase modulators is that they generally produce insufficient frequency-deviation ratios, or modulation index, for satisfactory noise suppression. Frequency multiplication can be used, however, to increase the modulation index to the desired value, since the frequency deviation is multiplied along with the carrier frequency. See Phase-modulation detector

Many types of phase modulators have been devised. A simple modulator is shown in the illustration. In this circuit the modulating voltage changes the capacitance of the varactor diode. The phase shift depends upon the relative magnitudes of the capacitive reactance of the varactor diode and the load resistance R. Therefore the phase shift varies with the modulating voltage and phase modulation (PM) is accomplished. However, the phase shift is not linearly related to the modulating voltage if the PM exceeds a few degrees, because the phase shift is not linearly related to the capacitance and the capacitance of the varactor diode is not linearly related to the modulating voltage. See Varactor

References in periodicals archive ?
LS), an optical splitter, an Optical Combiner (OC), two Mach-Zehnder Modulators (MZMs) and a Phase Modulator (PM) (see Figure 1).
DWDM laser sources, DWDM multiplexers and de-multiplexers, MCFBG, circulators and phase modulators are all available in the whole C or L band range.
Microwave-photonic frequency doubling utilising phase modulator and fibre Bragg grating," Electronics Letters, Vol.
Garver, "360 [degrees] Varactor Linear Phase Modulator," IEEE Transactions on Microwave Theory and Techniques, Vol.
The device of Figure 9 is a very accurate amplitude and phase modulator.
It is evident that the MMIC linear QPSK modulator's performance had to be better than that of the four MIC phase modulators over the entire band.
These include intensity modulators that convert to an optical-intensity signal and phase modulators that convert to light-phase signals.
Electro-optic devices -- including semiconductor lasers, amplitude and phase modulators and photodetectors -- are the building blocks of microwave photonics networks.
There are intensity modulators for converting input electrical signals to optical intensity signals and phase modulators for converting them to optical phase signals.
In addition, capabilities for the full electrical and optical characterization of optoelectronic devices, including active and passive waveguides, diode lasers and laser arrays, amplitude and phase modulators, photodiodes, photodiode arrays and optical logic elements, are available.