Source-injection serial coupled CMOS LC quadrature VCO

A novel source-injection serial-coupled (SISC) topology for designing LC quadrature voltage-controlled-oscillator (QVCO) is proposed. The proposed topology uses the advantages of the cascode-coupling QVCO and source-injection parallel-coupled (SIPC) QVCO topologies and provides a good phase noise performance with good quadrature phase accuracy. A 1.8GHz, 1.8v designed QVCO based on this topology shows a phase noise of -136dBc/Hz at 1MHz offset frequency thereby showing 5dB and 7.3dB lower phase noise than the SIPC and the cascode-coupling topologies respectively. This result is obtained from the simulation based on 0.18u CMOS technology and on-chip spiral inductor with Q of 8.