Phase noise optimization of CMOS VCO with double-harmonic-tuned LC tank

A double-harmonic-tuned LC tank (DHT tank) is proposed for significant phase-noise suppression in CMOS voltage-controlled oscillator (VCO). The DHT tank presents open at the fundamental and third harmonic and short at the second harmonic, which ensures square-like output waveform to significantly suppress the flicker-noise up-conversion and the noise around 2f_o. This fundamental open and the second-harmonic short effect are valid for the entire tuning range such that low phase noise can be obtained over the entire tuning range. The measured phase noise is -137.5 dBc/Hz at 1 MHz offset from 2.53 GHz, demonstrating excellent phase noise suppression by the DHT tank. A very good figure-of-merit of -197.5 dBc/Hz is achieved.