A low supply voltage and wide-tuned CMOS Colpitts VCO

Abstract

This paper presents a g_m-boosted differential Colpitts VCO with a switched capacitor tuning scheme which achieves low phase noise and a wide tuning range at a low supply voltage. In the proposed VCO, a voltage boosting circuit increases a turn-on resistance of the switching transistor for the capacitor array by generating higher gate bias voltage. As a result, the proposed VCO can achieve a wide frequency tuning range at a low supply voltage. The proposed VCO is implemented with 0.18-µm CMOS technology and oscillates from 3.60 to 4.14 GHz. Measurement results indicate a phase noise of −123.65 dBc/Hz at 1-MHz offset at 3.63 GHz, while dissipating 2.53 mA from the 0.7-V supply.