Charge pump circuit used for reducing current mismatch at extra-low voltage in phase-locked loop

Abstract

The invention discloses a charge pump circuit used for reducing current mismatch at an extra-low voltage in a phase-locked loop. The charge pump comprises a gate current mirror, a pull-up circuit, a pull-down circuit and an operational amplifier, wherein the gate current mirror consists of a first p-metal oxide semiconductor (PMOS) device, a second PMOS device and a first n-metal oxide semiconductor (NMOS) device; the pull-up circuit consists of a third PMOS device, a fourth PMOS device, a first switch and a second switch; the pull-down circuit consists of a second NMOS device, a third NMOS device, a third switch and a fourth switch; the fourth PMOS device realizes the functions of both a pull-up current tube and a pull-up switching tube; and the third NMOS device realizes the functions of both a pull-down current tube and a pull-down switching tube, so that the charge pump circuit realizes the parallel connection of the switching tubes and the current tubes and is suitable to work in an environment of low power supply voltage. A feedback loop formed by the operation amplifier increases the output impedance and reduces the mismatch of charging and discharging current.

Description

technical field [0001] The invention relates to the technical field of integrated circuits, in particular to a charge pump circuit for reducing current mismatch under extremely low voltage operation in a phase-locked loop. Background technique [0002] The charge pump phase-locked loop (CP-PLL) has the characteristics of high speed and low noise, so it has become the most common phase-locked loop circuit today, and is widely used in various communication circuits, frequency synthesizers and clock recovery circuits. The charge pump circuit plays a very important role in the CP-PLL. Its main function is to integrate the pulse reflecting the phase difference between the output signal and the input signal, and output the result of the integration in the form of voltage variation, and then use this output The voltage controls the frequency of the VCO. [0003] With the development of microelectronics technology in the direction of nanometer size, integrated circuit design is req...

AI Technical Summary

Problems solved by technology

In addition, the charge pump with this structure, because the switch tube and the output of the charge pump are directly connected, the charge sharing effect is particularly obvious, and the current tube has experienced a process from linearity to saturation, which may easily cause charge and discharge current mismatch.

[0006] When the MOS switch tube is placed at the source, although the switch tube is not directly connected to the output, it is less affected by the charge injection effect, and the current tube always works in the saturation region, which can eliminate the charge sharing effect, but the switch tube is also connected to the current tube In series, there is also the problem of insufficient power supply voltage drive capability

[0007] When the MOS switch tube is placed on the gate, the switch tube and the current tube are connected in parallel, but the output impedance of the charge pump with this structure is small, and it is easily affected by the output voltage, which makes the charge and discharge current mismatch and increases the CP-PLL output. Reference spurs on the spectrum

[0008] Therefore, the traditional charge pump circuit has a serious problem of current mismatch in the working environment of extremely low power supply voltage.

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