A 7.9-GHz Transformer-Feedback Quadrature Oscillator With a Noise-Shifting Coupling Network

A noise-shifting coupling network is proposed for nonlinear passively coupled quadrature voltage-controlled oscillators (QVCOs). Both detailed analysis and circuit implementation demonstrate that the noise contribution by the coupling network can be minimized by re-aligning the phases of the noise modulation function and the impulse sensitivity function with a reduced magnitude. In addition, the QVCO with the proposed coupling network also incorporates the transformer-feedback technique to improve its performance in terms of phase noise, quadrature phase error, and low supply voltage. Fabricated in a 65-nm CMOS process, the QVCO prototype operating at 7.9-GHz measures phase noise at 10-MHz offset frequency of -143 dBc/Hz and minimum quadrature phase error of 0.23° while consuming 27.2 mW with a 0.8-V supply voltage.