phase modulator


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phase modulator

[′fāz ‚mäj·ə‚lād·ər]
(electronics)
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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

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

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
A phase modulator introduces a phase shift of 90 degrees over one of the arms to generate the Q component.
Caption: FIGURE 1: Configuration of optical frequency combs (CW-LD1, 2: continuous wave laser sources, IM: intensity modulator, PM: phase modulator, PS: phase shift, Amp: optical amplifier, and PCF: photonic crystal fiber).
The resulting response allows the grating to be used as phase modulator.
The simulated and measured phase noise depicted in Figure 13 of the fractional-N PLL, dominating the phase modulator system noise, is -120 and -104 dBc/Hz at 400-kHz offset frequency from the oscillating frequency of 1.8 GHz, respectively.
The phase modulators feature high optical power (100mW) along with a low Vpi.
We propose a novel prism phase modulator (PPM) to modulate the phase difference between p- and s-polarization lights and apply it in a SPR-PI sensor.
The optical carriers are multiplexed into a single phase modulator driven by a chirp-free wideband baseband pulse.
Wullert, "Programmable shaping of femtosecond optical pulses by use of 128-element liquid crystal phase modulator," IEEE J.
The content of the accumulator represents the residual phase error in the PLL and, by routing this signal to a D-to-A converter and applying the analog signal to a phase modulator within the PLL, the residual errors can, in principle, be eliminated, as shown in Figure 3.
The small package integrates a wavelength-tuneable laser, a transmitter phase modulator, and a coherent receiver.
[25.] Ou, H., et al., "Microwave-photonic frequency doubling utilising phase modulator and fibre Bragg grating," Electronics Letters, Vol.