A CMOS Back-Gate Coupling LC Quadrature VCO with Switched Self-Biasing Tail Transistor Technique

Abstract

In this paper, a novel complementary differential QVCO using back-gate coupling and switched self-biasing techniques is presented. Since the back-gates of the PMOS switching transistors are used as coupling terminals to achieve the quadrature outputs, the proposed circuit has the advantages of no additional noise source and power dissipation in the coupling process. By switched self-biasing the tail transistors in a complementary manner, the QVCO's own oscillation output waveforms are injected back into the gates of the tail transistors as biasing voltages to improve the phase noise. Together with the forward back-gate biasing technique which is used to the NMOS switching transistors, the proposed QVCO can be operated at reduced supply voltage and power dissipation while maintaining remarkable circuit performances in terms of low phase noise and wide tuning range. The simulation results show that the phase noise is $$-$$-123.2 dBc/Hz at 1 MHz offset frequency from the carrier frequency of 2.35 GHz, while it consumes only 3.3 mW under a 1.2 V supply voltage. The free-running frequency of the QVCO is tunable from 2.13 to 2.87 GHz as the tuning voltage is varied from 0.0 to 1.2 V. The corresponding figure of merit of the QVCO is $$-$$-185.5 dBc/Hz.