Low-power Gm-boosted complementary Colpitts LC-VCO/QVCO

Abstract

In this work, a new differential topology of Colpitts VCO with an enhanced transconductance is presented. The proposed circuit is consisted of an NMOS and a PMOS differential Colpitts cores configured as complementary, and also an LC resonator. The VCO is designed to oscillate at 5 GHz which consumes 1.11 VA from 1.4 V supply voltage. In addition, a modified version of the proposed VCO is designed for lower power applications. This circuit employs new positive feedbacks to enhance the VCO’s transconductance and reduce the supply voltage. The modified VCO operates with 1.1 V power supply while dissipating 1 mW. To investigate the performance of the proposed circuits, the transconductance of them are theoretically analyzed. Also, two new quadrature VCOs (QVCOs) are presented which are realized by two identical latter proposed Colpitts VCOs. A linear analysis is presented to confirm that the first oscillator can generate outputs with 90° phase differences. The proposed circuits are designed in 0.18-μm RF-CMOS technology. Finally, prototype circuits of the proposed VCOs are fabricated to validate the theoretical results. The measurement results are summarized to demonstrate the main features of the proposed oscillators.