Electric circuit and method for restraining fractional stray of fractional phase locking loops

Abstract

The invention provides an electric circuit for restraining fractional stray of fractional phase locking loops. The electric circuit for restraining the fractional stray of the fractional phase locking loops comprises at least two levels of the fractional phase locking loops, wherein the front level fractional phase locking loop is connected with the back level fractional phase locking loop through a frequency divider, an output signal of the front level fractional phase locking loop is used as a reference input signal of the back level fractional phase locking loop after frequency division is performed on the output signal of the front level fractional phase locking loop by the frequency divider, and the front level fractional phase locking loop and the back level fractional phase locking loop are of the same structure. The method for restraining the fractional stray of the fractional phase locking loops includes the steps that fractional frequency division is performed by the frequency divider on an output signal of a voltage controlled oscillator, phase discrimination operation is performed by a phase discriminator on the input signal after the frequency division and the reference input signal, an output signal of the phase discriminator is sent into a loop filter, and the loop filter generates voltage controlled voltage of the voltage controlled oscillator. The electric circuit and the method for restraining the fractional stray of the fractional phase locking loops can directly change fractional stray frequency, are not influenced by nonlinear circuits of the phase discriminator, the frequency divider and the like in a circuit, and have good stray restraining effects. Additionally, the fractional stray frequency of the fractional phase locking loops is shifted out of the bandwidth of the fractional phase locking loops and filtered out by the loop filter, and therefore the purpose of restraining the fractional stray is achieved.

Description

Technical field [0001] The present invention relates to the technical field of testing, in particular to a circuit for suppressing fractional phase-locked loop fractional spurs, and also relates to a method for suppressing fractional phase-locked loop fractional spurs. Background technique [0002] Fractional phase-locked loops are widely used in various frequency synthesizers because of their high frequency resolution and wide output frequency band. Although the output signal frequency of the fractional phase-locked loop is N.F decimal multiples of the reference signal frequency, the instantaneous frequency division ratio of the frequency divider in the fractional phase-locked loop is not a decimal but an integer. The frequency division ratio of the frequency divider is constantly changing, but the average frequency division ratio over many cycles is a decimal. Taking the 100.1 frequency division ratio as an example, it needs 9 times of 100 frequency division and 1 time of 101 ...

AI Technical Summary

Problems solved by technology

[0003] The present invention proposes a circuit and method for suppressing fractional spurs of a fractional phase-locked loop, which solves the problem of relatively large fractional spurs in the output signal of a fractional phase-locked loop in the prior art

Images