A Linearization Technique for Ring VCO Exploiting Bulk-Modulation

Abstract

This paper presents a power-efficient linearization technique based on bulk-modulation for the voltage-to-frequency conversion characteristic of the ring voltage-controlled oscillator (VCO), which can be easily adopted in VCO-based analog-to-digital converters (ADCs) to achieve high resolution. A bulk-control voltage generator is utilized to modulate the threshold voltages of the VCO input transistors. Combined with the conventional gate-control scheme, the nonlinearity of the VCO can be reduced effectively. A second-order sigma-delta ADC with proposed linearized VCO is implemented in 0.18μm CMOS technology to verify the effectiveness. Simulation results show the nonlinearity of the VCO drops from 10% to 2% and the total distortion can be reduced by 19dB through bulk-modulation compared with conventional VCO.