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A Low Phase Noise NMOS LC-VCO using New Degeneration Structure
Background/Objectives: It is necessary to reduce the contribution of a differential pair for a low phase noise LC-VCO because previous works are mainly focused on the LC tank and tail current source. Methods/Statistical Analysis: A new NMOS LC-VCO with an LC degenerated structure is proposed for linearizing a cross coupled differential pair. The NMOS LC-VCO with the proposed structure is designed using a 0.18 μm CMOS process and simulated by Spectre RF. Findings: The proposed structure is very useful for suppressing the flicker and thermal noise contribution of a cross coupled differential pair which forms a negative transconductance. Especially, the proposed structure overcomes the limitation the previous capacitive degeneration structure when it operates at higher oscillator frequency above 5 GHz. Application/Improvements: Its phase noise performance is improved about 3 dB compared with that of the conventional NMOS LC-VCO structure with no degeneration consuming the same bias current of 2mA from a 1.8 V supply.
CMOS, Degeneration, LC-VCO, LC Tank, Negative Impedance Transform, Phase Noise.
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