A Low Phase Noise Quadrature VCO Using Symmetrical Tail Current-Shaping Technique

This letter presents a new symmetrical tail current-shaping technique to improve the phase noise of a quadrature voltage-controlled oscillator (QVCO). This proposed QVCO consists of two first-harmonic injection-locked oscillators (ILOs) and the outputs are injected back to the gates of the QVCO's tail transistors in order to shape the tail currents. A switching current path is provided between the two tail current sources in order to eliminate the asymmetric phenomenon of the tail currents. The measured phase noise can be improved by 4 dB using this technique. This CMOS LC-tank QVCO has been implemented using the TSMC 0.18 μm mixed-signal/RF CMOS 1P6M technology and the die area is 0.7 × 1.1 mm
²
. The total power consumption is 11.2 mW at the supply voltage of 1.4 V. The measured phase noise at 1 MHz offset is -119.3 dBc/Hz at the oscillation frequency of 5.28 GHz. The figure of merit (FOM) of the proposed QVCO is -183 dBc/Hz.