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Concept
Frequency synthesizer
Summary
A frequency synthesizer is an electronic circuit that generates a range of frequencies from a single reference frequency. Frequency synthesizers are used in many modern devices such as radio receivers, televisions, mobile telephones, radiotelephones, walkie-talkies, CB radios, cable television converter boxes, satellite receivers, and GPS systems. A frequency synthesizer may use the techniques of frequency multiplication, frequency division, direct digital synthesis, frequency mixing, and phase-locked loops to generate its frequencies. The stability and accuracy of the frequency synthesizer's output are related to the stability and accuracy of its reference frequency input. Consequently, synthesizers use stable and accurate reference frequencies, such as those provided by a crystal oscillator.
Three types of synthesizer can be distinguished. The first and second type are routinely found as stand-alone architecture: direct analog synthesis (also called a mix-filter-divide architecture as found in the 1960s HP 5100A) and the more modern direct digital synthesizer (DDS) (table-look-up). The third type are routinely used as communication system IC building-blocks: indirect digital (PLL) synthesizers including integer-N and fractional-N. The recently emerged TAF-DPS is also a direct approach. It directly constructs the waveform of each pulse in the clock pulse train.
It is in some ways similar to a DDS, but it has architectural differences. One of its big advantages is to allow a much finer resolution than other types of synthesizers with a given reference frequency.
Recently, a technique named Time-Average-Frequency Direct Period Synthesis (TAF-DPS) emerges as a new member to the frequency synthesizer family. It focuses on frequency generation for clock signal driving integrated circuit. Different from all other techniques, it uses a novel concept of Time-Average-Frequency. Its aim is to address the two long-lasting problems in the field of on-chip clock signal generation: arbitrary-frequency-generation and instantaneous-frequency-switching.
Official source
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