Clock selection circuit and synthesizer

Abstract

A clock selection circuit and synthesizer that is capable of selecting an optimum clock signal from among a plurality of clock signals in a short time. A reference-clock counter counts clock pulses in an inputted reference clock signal (REF). A clock counter counts clock pulses in one of the plurality of clock signals which is selected by a selection unit and frequency-divided by a frequency divider. An instruction-signal output unit outputs a plurality of comparison-instruction signals during an interval in which a difference occurs between the counts of two of the plurality of clock signalshaving the closest frequencies. A comparison unit compares the count of the reference-clock counter and the count of the clock counter. The selection unit selects a clock signal by a binary search according to the result of the comparison.

Description

technical field [0001] The present invention relates to a clock selection circuit and a synthesizer (synthesizer), in particular to a clock selection circuit that selects a clock whose frequency after frequency division is the same as that of a reference clock REF from a plurality of clocks with different frequencies, and a clock selection circuit from multiple A synthesizer that selects a clock whose divided frequency is the same as that of the reference clock from the clocks output from two voltage-controlled oscillators. Background technique [0002] In the development process of high functionality and high integration of electronic integrated circuits, the functions required for a chip turn to a higher direction. In a synthesizer that supplies clocks required for various circuit operations at the necessary frequency, it is still necessary to simultaneously satisfy various requirements such as widening the frequency band provided, narrowing the frequency interval, and imp...

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Problems solved by technology

Therefore, the selected VCO deviates greatly from the target VCO, and even if the count value differs immediately, it cannot be compared, and there is a problem that it takes time to select the optimal VCO for no reason.

[0045] And, as in Figure 17 As explained in , when the characteristics of the VCOs are not equal intervals, the comparison time between the VCOs with the smallest frequency interval must be set

Therefore, the selected VCO deviates greatly from the target VCO, and even if the count value differs immediately, it cannot be compared, and there is a problem that it takes time to select the optimal VCO for no reason.

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