Patent ID: 9698799
Date: 2017-07-04
CPC Classifications: H03L

Claim:
1. A phase locked loop frequency calibration circuit, comprising a timer, a counter, a control module, a frequency divider and a voltage controlled oscillator; an output of the voltage controlled oscillator is connected with a first input of the frequency divider, an output of the frequency divider is connected with a first input of the counter, a second input of the frequency divider, a first input of the timer, and a second input of the counter are respectively connected with a first output of the control module, a third input of the counter is connected with an output of the timer, an output of the counter is connected with a first input of the control module, a reference clock signal is sent to a second input of the timer and a second input of the control module, respectively, a number of clocks used by the frequency divider to perform frequency division on an output clock signal of the voltage controlled oscillator is sent to a third input of the control module, an output capacitor array control word of a second output of the control module is sent to an input of the voltage controlled oscillator; the control module is configured to: clear the timer, the counter and the frequency divider, respectively, and control the counter to count an output clock signal of the frequency divider within a preset time, wherein the preset time is duration required for the timer to change from zero to overflow; obtain a count value A resulting from the counter counting the output clock signal of the frequency divider within the preset time; calculate output frequency of the voltage controlled oscillator according to the count value A, and compare the output frequency with an expected frequency; and if an absolute value of a difference between the output frequency and the expected frequency is greater than or equal to a preset difference value, then adjust a number of switched capacitors of the voltage controlled oscillator, so as to adjust the output frequency of the voltage controlled oscillator.