A low power VCO design using composite load for delay cell with IMOS varactor for wider tuning range

摘要

In this paper, a new low-power voltage-controlled oscillator (VCO) design is presented using inductive composite load for the delay cell and inversion mode MOSFET (IMOS) varactor using 180nm CMOS technology. The output oscillation frequency of the VCO has been changed by varying the capacitance of the delay cell with the usage of IMOS varactor comprising two PMOS transistors connected in parallel. Variation in source/drain voltage (V_(ct)) and back-gate voltage (V_(sb)) of IMOS changes the capacitance of IMOS resulting in variations in output oscillation frequency of VCO. Power supply voltage (V_(dd)) variations from 1V to 2. 4V gives output oscillation frequency from 0. 972 GHz to 4. 231 GHz and consumes power from 0. 002mW to 0.919mW with IMOS varactor width of 2um. The results have been drawn out for the IMOS width of 5μm, 8μm and 12μm. The source/drain voltage (V_(ct)) variation of IMOS from 1V to 2.4V show the output oscillation frequency from 2. 648 GHz to 3. 253 GHz and achieves power consumption of 0.279mW. Results have been further extended for IMOS with widths of 2μm, 5μm, 8μm and 12μm and a tuning range of 21% has been obtained for source/drain voltage (V_(ct)) variations. Further, the back-gate voltage (V_(sb)) tuning of IMOS varactor from 1V to 2. 4V shows frequency variations from 3. 114 GHz to 3. 282 GHz. The VCO shows a phase noise of-107. 77dBc/Hz@1MHz offset from centre frequency and the figure of merit (FoM) for the VCO is -168. 94dBc/Hz with supply voltage of 1. 8V. Proposed VCO tunes the output frequency with IMOS varactor loading without changing the overall power dissipation of circuit. Proposed VCO circuit achieved a low power dissipation, wide tuning range, better phase noise and figure of merit (FoM).