Starting circuit for phase locked loop and phase locked loop

Abstract

The invention relates to a starting circuit for phase locked loop and a phase locked loop; the phase locked loop comprises a loop filter and a voltage-controlled oscillator, wherein the loop filter comprises a first resistor unit, a first capacitor unit and a second capacitor unit; an input end of the voltage-controlled oscillator is coupled to an output end of the loop filter and is suitable forgenerating a clock signal according to an output signal of the loop filter; the starting circuit comprises a frequency detection circuit and a control circuit, wherein the frequency detection circuitis suitable for detecting frequency of the clock signal; the control circuit is suitable for controlling the first resistor unit to be shorted when the frequency of the clock signal is smaller than atarget frequency of the phase locked loop and relieving the control of the first resistor unit when the frequency of the clock signal is larger than or equal to the target frequency of the phase locked loop. According to the scheme, the phase locked loop can be quickly locked through the starting circuit.

Description

technical field [0001] The invention relates to the field of electronic circuit design, in particular to a start-up circuit for a phase-locked loop and a phase-locked loop. Background technique [0002] Phase Locked Loop (PLL) is a typical feedback control circuit, which uses an externally input reference frequency signal to control the frequency and phase of the oscillating signal inside the loop, so as to automatically track the frequency of the output signal to the frequency of the input signal. Charge pump phase-locked loops are widely used in electronic circuits, such as figure 1 As shown, the phase-locked loop 100 may include a phase frequency detector (Phase Frequency Detector, PFD) 10, a charge pump (Charge Pump, CP) 20, a loop filter (generally a low-pass filter (Low-pass filter), which are serially connected in series. Pass Filter (LPF)) 30, Voltage Controlled Oscillator (VCO) 40 and Divider (Divider) 50, and form a loop; wherein, the output end of the VCO 40 serv...

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Problems solved by technology

However, in fact, the startup circuit 60 will be affected by process, voltage, temperature (Process, Voltage and Temperature, PVT) fluctuations

Specifically, the resistors R1 and R2 are generally precision resistors, and the voltage applied to them, the ambient temperature and the process accuracy will all affect the resistance of the resistors R1 and R2, thereby affecting the control voltage, so that The actual output signal frequency of the voltage-controlled oscillator 40 that should output the target frequency f1 has a certain error, and this error may be relatively large, which will seriously hinder the rapid stability of the phase-locked loop.

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