Phase Shift Techniques for Improving Varactor-Less QVCO Based on Rotated-Phase-Tuning

This brief proposes and verifies a new phase shifter applied in the rotated phase tuning (RPT) technique in Ka-band. The flexible phase shift in the RPT technique is significant for avoiding the phase ambiguity issue of oscillating mode and improve the phase noise and tuning range. The proposed common-source-common-gate (CSCG) transistor is simple and can provide a wide range of phase shift for different frequencies. A QVCO without varactor is designed by using a CSCG to replace the common-source (CS) as the negative resistance unit as well as the phase shifter. The negative impedance, tuning range, phase noise and quadrature accuracy of CS and CSCG QVCO are compared and numerically verified using a simulation model. Finally, we further fabricate the CSCG QVCO in a 65-nm CMOS process to verify the accuracy of the simulation model.