Phase-locked loop circuit used for inhibiting VCO (voltage-controlled oscillator) voltage ripple

Abstract

The invention discloses a phase-locked loop circuit used for inhibiting a VCO (voltage-controlled oscillator) voltage ripple, which comprises a frequency-phase detector, a charge pump, an automatic frequency band selector, a loop filter, a voltage-controlled oscillator, a frequency divider and a first transmission gate. In the invention, as the transmission gate is used as a mode-converting switch, the VCO control voltage ripple caused by traditional MOS (metal-oxide semiconductor) transistor in different working models converting in the phase-locked loop, the electric charge injection and the clock feed-through are reduced, thus, the purpose of inhibiting the VCO voltage ripple is achieved. Meanwhile, the transmission gate is embedded in the third order loop filter, thus, the converting of different working models of the phase-locked loop is realized, and an onstate resistor of the transmission gate is utilized as the resistor of the third order loop filter, the noise is effectively filtered, and the VCO voltage ripple caused by the noise is greatly reduced.

Description

technical field [0001] The invention belongs to the technical field of radio phase-locking, and in particular relates to a phase-locked loop circuit for suppressing VCO voltage ripple. Background technique [0002] Charge-pump phase-locked loop (CP-PLL) has the characteristics of high speed, low noise and high precision, and is widely used in various communication circuits, frequency synthesizers and clock recovery circuits. A conventional charge pump phase-locked loop such as figure 1 As shown, it includes the following modules: phase frequency detector (Phase Frequency Detector, PFD), charge pump (Charge-Pump, CP), loop filter (Loop Filter), voltage controlled oscillator (Voltage Controlled Oscillator , VCO) and frequency divider (Frequency Divider). Among them, the frequency and phase detector detects the phase difference between the reference signal and the feedback signal output by the frequency divider, and outputs a discrete voltage pulse signal. The charge pump con...

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Problems solved by technology

[0005] However, the phase-locked loop with the automatic frequency band selection function will generate charge injection and clock feedthrough when the switch is turned off and on, which will directly lead to fluctuations in the VCO control voltage.

In addition, due to the existence of the parasitic resistance of the MOS tube, the thermal noise generated by it also causes the fluctuation of the VCO control voltage

Therefore, there is a large voltage ripple in the control voltage of the VCO in the phase-locked loop with automatic frequency band selection function, which greatly deteriorates the phase noise of the phase-locked loop

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