An Adaptively Biased Class-C VCO With a Self-Turn-Off Auxiliary Class-B Pair for Fast and Robust Startup

In this letter, an adaptively biased class-C Voltage Controlled Oscillator (VCO) with a self-turn-off auxiliary class-B pair is presented for fast and robust startup in a 65-nm CMOS process. It consists of a main class-C core and an auxiliary class-B cross-coupled pair. The class-B auxiliary pair is used to solve the inherent startup problem of class-C VCOs. It works only during startup and turns itself off when the VCO reaches a steady state using an adaptive bias scheme. The dc current consumption of the VCO and bias circuit is 5 mA at 1.2 V
${\rm V}_{\rm DD}$
. Here, a good phase noise level of
$-132.41~{\rm dBc}/{\rm Hz}$
at a 1 MHz offset frequency from a 2.46-GHz carrier is shown, to yield a Figure-of-Merit (FOM) of 192.45.