Varactor circuit with low phase noise

Abstract

The invention relates to the technical field of varactor circuits, and discloses a low-phase noise varactor circuit, which comprises two capacitors and two resistors, the two capacitors and the two resistors are connected in series, the two resistors are positioned between the two capacitors, a plurality of first variable capacitors are connected in parallel between the two resistors, and a plurality of second variable capacitors are connected in parallel between the two resistors. The two common end nodes are located between the capacitor and the resistor, a plurality of second variable capacitors are connected to the two common end nodes in parallel, and the first variable capacitor and the second variable capacitors are the same in gain but opposite in polarity. According to the invention, the first variable capacitor and the second variable capacitor with the same gain and opposite polarity are selected and connected to the resistor in the same way, so that the phase noise generated by the thermal noise of the resistor through the first variable capacitor at a certain moment can be exactly counteracted by the phase noise generated by the second variable capacitor; and the resistance can select a larger value to improve the quality factor Q value.

Description

technical field [0001] The invention relates to the technical field of varactor circuits, in particular to a varactor circuit with low phase noise. Background technique [0002] With the rapid development of integrated circuits, the system has higher and higher requirements for the clock circuit, and the voltage-controlled oscillator (VCO), as a very important module in the clock circuit, has been paid more and more attention. In scenarios where high-speed and low-noise requirements are required, LC-VCO has an irreplaceable position. Among them, variable capacitors have a significant impact on the noise and other performance of VCOs. The C-V curve of variable capacitors is greatly affected by the process. In order to be more flexible in use, And from the perspective of reliability, reducing the nonlinearity of the variable capacitor, reducing Kvdd, etc., the C-V curve is usually shifted by changing the voltage value of the bias voltage Vbias, so that the Kv of the VCO (the r...

AI Technical Summary

Problems solved by technology

[0005] Aiming at the deficiencies of the prior art, the present invention provides a varactor circuit with low phase noise, which solves the problem that the larger resistance value of the current varactor circuit will contribute noise, but the smaller resistance value will affect the performance of the VCO. The problem that the noise cannot be reduced while increasing the resistance value

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