A charge pump applied to a frequency synthesizer

Abstract

The invention discloses a charge pump applied to a frequency synthesizer. The charge pump comprises a charge-discharge current branch and an output impedance multiplication circuit. The charging and discharging current branch is composed of a unit negative feedback loop and a current source, wherein the unit negative feedback loop is composed of a complementary CMOS switch and a rail-to-rail inputand output amplifier, and the charging and discharging current branch is used for charging and discharging an output node and eliminating a clock feed-through effect and a charge sharing effect. Theoutput impedance multiplication circuit is composed of a folding type cascode structure and is used for improving the output impedance of the charge pump. The output impedance multiplication circuit comprises a reference current source, first, second, third, fourth, fifth, seventh, eighth, tenth, eleventh and sixteenth NMOS tubes, and first, second, third, fourth, sixth, seventh, ninth, tenth andfifteenth PMOS tubes. The invention is suitable for the drain terminal switch charge pump with good matching characteristic under low voltage, improves the matching degree of charging and dischargingcurrent, improves the phase noise of the frequency synthesizer, and improves the output impedance of the charge pump.

Description

technical field [0001] The invention relates to a charge pump applied to a frequency synthesizer, belonging to the technical field of phase-locked loops. Background technique [0002] A frequency synthesizer is a technology that uses the principle of feedback control to achieve frequency and phase synchronization. It generally has five components, a frequency detector, a charge pump, a loop filter, a voltage-controlled oscillator, and a frequency divider. As an important part of the frequency synthesizer, the pump is a hot topic in the research of analog integrated circuits. figure 2 The performance of the conventional charge pump shown is affected by non-ideal factors such as current mismatch, charge sharing, and clock feedthrough, where the current mismatch of the charge pump will cause spurs in the output of the frequency synthesizer, thereby constraining the frequency synthesizer. Therefore, designing a charge pump with high linearity and reducing the mismatch between t...

AI Technical Summary

Problems solved by technology

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, provide a charge pump applied to a frequency synthesizer, and solve the problem that the output voltage of the charge pump varies greatly When the charging and discharging current changes too much, the current does not match and the linearity of the charge pump is reduced, which leads to the problem of poor spurious performance of the frequency synthesizer.

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