A Linearized Tuning Varactor for Voltage Controlled Oscillator

Abstract

A linearized tuning varactor for the voltage controlled oscillator (VCO) is proposed in this paper. The capacitance-voltage (C-V) curve is linearized by combining an accumulation MOSFET (AMOS) and PMOS in parallel to form the varactor. Two ring voltage controlled oscillators (ring VCOs) are fabricated and measured with a standard 65-nm CMOS process. They are both identical except for the varactor. The first VCO uses the proposed varactor, and the second one is tuned by a conventional AMOS-only varactor for reference. The ring VCO with the proposed varactor operates from 500.5 to 807.6 MHz, and the VCO gain (K_VCO) varies from 183 to 284 MHz/V. Comparing the reference VCO with the AMOS-only varactor, the measured K_VCO variability is reduced by 82%. The phase noise is between -89 dBc/Hz and -92 dBc/Hz at 1 MHz offset while dissipating 0.8 mA from a 1.2-V supply.