A Low Gain Variation LC-VCO With Mutual Inductive Tuning for K_VCO Linearity Compensation

A high-linearity LC-voltage-controlled oscillator (LC-VCO) with a mutual coupled inductive tuning technique is proposed to reduce VCO-gain (K_vco) variation induced by varactors in finite linear region. The oscillator is fabricated in a standard 180-nm CMOS process occupying 0.88 mm × 0.9 mm and consuming 3.6 mW from mixed 0.9/1.8 V supply voltage. With the variable effective inductance of the resonant tank, the proposed topology achieves a low gain variation of less than 6.1%, possessing a linear-tuning control voltage range from 0.5 to 1.8 V and operating from 3.40 to 4.04 GHz. The phase noise is measured to be −108.59 dBc/Hz at 1 MHz offset with a carrier frequency of 4.04 GHz, and the figure of merit (FoM) is −173.8 dBc/Hz.