Low-phase-noise LC VCO based on improved tail current source structure

Abstract

The present invention relates to a low-phase-noise LC VCO (a voltage controlled oscillator based on inductance-capacitance resonance) based on an improved tail current source structure, wherein the tail current source is in series with a P-MOSFET M6 working in a linearity area and a P-MOSFET M8 working in a saturation area, wherein the grids of the P-MOSFET M6 and the P-MOSFET M8 are connected with each other; a current mirror is composed of four P-MOSFETs in such a manner that two P-MOSFETs M5 and M6 which are connected in series are arranged parallelly with two P-MOSFETs M7 and M8 that are connected in series; the current is biased to the VCO through the current mirror. Because the P-MOSFET M6 working in the linearity area has a low drain-source voltage, introducing the M6 has little influence on the largest amplitude of VCO output signal. Moreover, introducing the M6 can increase the equivalent resistance looked from the drain terminal (i.e. point A) of the M8 so as to decrease theloss of a resonant cavity and make the LC VCO realize a lower phase noise.

Description

technical field [0001] The present invention relates to a low phase noise LC VCO (voltage controlled oscillator based on inductance-capacitance resonance) circuit structure, in particular to an improved tail current source structure based on improved tail current source circuit structure to improve phase noise performance Low Phase Noise LC VCO. Background technique [0002] LC VCO is an important module of the frequency synthesizer in the communication system, and its phase noise, power consumption, area and other performances have an important impact on the communication system. Phase noise affects communication quality. Various communication systems such as GSM, CDMA, ZigBee, 802.11, GPS, UWB, etc. have strict regulations on phase noise, while power consumption and area play a decisive role in the cost of mobile communication terminals. Therefore, under the premise of not increasing power consumption and area, improving the phase noise performance of LCVCO has become a c...

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Problems solved by technology

[0003] Generally, the phase noise performance of LC VCO can be improved by increasing the power consumption or increasing the inductor Q, but both methods will increase the cost of the communication system

In response to this problem, Emad Hegazi and Asad.A.Abidi wrote in A Filtering Technique to Lower LC Oscillator Phase Noise in 2001 [1] A noise filtering technology is proposed in , which can improve the phase noise performance of LC VCO without increasing power consumption, but it needs to introduce additional inductors and capacitors to filter the second harmonic component of the tail current source, so This method significantly increases the chip area; in 2004, C.C.Boon et al. proposed in the document RF CMOSLow-Phase-Noise LC Oscillator Through Memory Reduction TailTransistor to change the tail current source of the LC VCO from a fixed bias to a complementary switch control. The method can reduce the 1 / f noise of the tail current source without increasing the chip area, but because the tail current source is biased in the switching state, the tail current cannot be kept constant and the current size varies greatly with the process, and the non-constant The tail current will introduce amplitude noise, which will be converted into phase noise through the AM-FM modulation of the varactor, and the process deviation has a great impact on the performance of the structure

In 2005, Thierry Lagutere et al proposed to remove the tail current source of LC VCO in the literature Method to design low noise differential CMOS VCOs without tail current source. This method can get better phase noise performance without increasing the chip area, but Since there is no tail current source, the performance of this structure varies greatly with the process, and the power supply suppression performance and stability are poor

In various existing low phase noise LC VCO structures, the improvement of phase noise performance comes at the expense of increased area, performance stability or reduced voltage rejection performance

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