A wide tuning range VCO design using multi-pass loop complementary current control with IMOS varactor for low power applications

Abstract

In this work a wide-bandwidth low-power voltage-controlled oscillator (VCO) design is presented using a new differential delay cell with complementary current control mechanism and inversion mode MOSFET (IMOS) varactor. The variations in output oscillation frequency of the VCO has been achieved by changing the capacitance of the delay cell with the usage of IMOS varactor containing two PMOS transistors connected in parallel. The proposed three-stage VCO has been designed with 1.8 V power supply in 180 nm CMOS technology. Capacitance of IMOS varactor has been varied by altering the source/drain voltage Vcontrol and back-gate voltage Vsb of IMOS. The variations in power supply voltage from 1 V to 2.4 V provides output frequency from 1.893 GHz to 7.926 GHz with power dissipation of 0.953 mW to 24.261 mW with IMOS varactor width of 5 µm. The results have been extended for the IMOS width of 10 µm, 15 µm and 20 µm. The tuning range of 122% has been achieved with the power supply tuning method. The variations in source/drain voltage of IMOS from 1 V to 2.4 V provides the output frequency from 6.373 GHz to 5.460 GHz with power dissipation of 9.62 mW. The tuning range of 15.7%, 22.3%, 44% and 40.6% has been obtained for IMOS with widths of 5 μm, 10 μm, 15 μm and 20 μm with the source/drain voltage Vcontrol variations. Further, frequency variation from 5.895 GHz to 6.406 GHz has been obtained with back-gate voltage Vsb tuning of IMOS varactor from 0 V to 2.4 V. The phase noise measured for the VCO is −90.67 dBc/Hz@1 MHz and the figure of merit (FoM) for the VCO is 172.86 dBc/Hz with supply voltage of 1.8 V. Proposed VCO circuit achieved a low power dissipation, wide tuning range, better phase noise and figure of merit (FoM).