Phase-locked loops

Phase-locked loops

Electronic circuits for locking an oscillator in phase with an arbitrary input signal. A phase-locked loop (PLL) is used in two fundamentally different ways: (1) as a demodulator, where it is employed to follow (and demodulate) frequency or phase modulation, and (2) to track a carrier or synchronizing signal which may vary in frequency with time. When operating as a demodulator, the PLL may be thought of as a matched filter operating as a coherent detector. When used to track a carrier, it may be thought of as a narrowband filter for removing noise from the signal and regenerating a clean replica of the signal. See Demodulator

The basic components of a phase-locked loop are shown in the illustration. The input signal is a sine or square wave of arbitrary frequency. The voltage-controlled oscillator (VCO) output signal is a sine or square wave of the same frequency as the input, but the phase angle between the two is arbitrary. The output of the phase detector consists of a direct-current (dc) term, and components of the input frequency and its harmonics. The low-pass filter removes all alternating-current (ac) components, leaving the dc component, the magnitude of which is a function of the phase angle between the VCO signal and the input signal. If the frequency of the input signal changes, a change in phase angle between these signals will produce a change in the dc control voltage in such a manner as to vary the frequency of the VCO to track the frequency of the input signal.

The most widespread use of phase-locked loops is undoubtedly in television receivers. Synchronization of the horizontal oscillator to the transmitted sync pulses is universally accomplished with a PLL. The color reference oscillator is often synchronized with a phase-locked loop. Phase-locked loops are also used as frequency demodulators. They have been applied to stereo decoders made on silicon monolithic integrated circuits. High-performance amplitude demodulators may be built using phase-lock techniques. See Amplitude-modulation detector

References in periodicals archive ?
Talbot, who develops radio-frequency and analog engineering products, explains the frequency acquisition assistance techniques necessary and/or available for phase-locked loops (PLL) at a mathematical level suitable to engineers and technicians--that is, an occasional and optional formula rather than pages and pages of dense equations.
The final chapter considers miscellaneous topics, including testing and debugging, sampled phase-locked loops, multiloop synthesizers, and the direct digital synthesizer.
The company's first product, PLL Noise Analyzer(TM), the industry's first noise analysis tool for phase-locked loops (PLLs), has already been adopted by semiconductor industry leaders.
The book begins with the basics of phase-locked loops, the building blocks of frequency synthesizers.
was able to meet the high-performance, low-noise, and low-power specifications for the phase-locked loops (PLLs) in their advanced memory chips by using the fast and accurate noise analysis and diagnostic capabilities provided by Berkeley Design's Precision Circuit Analysis(TM) technology.
The employed architecture is a blend of both digital phase-locked loops, with programmable ratio dividers for the step modules, and analog phase-lock loops for the summation modules.
Phase-locked loops provide a challenge for self-testing and fault isolation.
Faraday's analog and mixed-signal design teams are using Sandwork's tools to debug high-speed, high-precision, high-accuracy designs such as analog-digital converters (ADCs), phase-locked loops (PLLs), and network semiconductor intellectual property (SIP).
VIA's design teams are using Sandwork's tools to debug DVD decoder designs and PC-related project designs containing analog-digital converters (ADCs), phase-locked loops (PLLs), and other analog and mixed-signal devices.
The device integrates such components as three independent phase-locked loops (PLLs) with non-integer frequency multiplication capabilities, spread-spectrum generation, independent post dividers, and universal output buffers.
The company also announced its initial product, PLL Noise Analyzer(TM), the industry's first noise analysis tool for circuits containing phase-locked loops (PLLs) (see today's related press release).
a new analog/RF electronic design automation company, today announced its initial product, PLL Noise Analyzer(TM), the industry's first noise analysis tool for high-performance analog/RF integrated circuits containing phase-locked loops (PLLs).

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