Injection-locked CMOS active transformer voltage-controlled oscillators

This paper presents injection-locked CMOS active transformer voltage-controlled oscillators. The tunable coupling ratio, large and tunable self and mutual inductances, high and tunable quality factors, and a small silicon area consumption of CMOS active transformers allow the oscillators to have a large frequency tuning range with low silicon consumption. The injection-locking mechanism ensures that the phase noise of the oscillators is comparable to that of corresponding LC tank oscillators. The proposed oscillators can be used to construct frequency dividers of high-frequency frequency synthesizers where the oscillators are typically LC-tanks based. One active transformer VCO, three injection-locked active transformer VCOs, and one LC-tank VCO that oscillate at the same frequency have been designed in TSMC-0.18 mum 1.8 V CMOS technology and analyzed using SpectreRF from Cadence Design Systems with BSIM3v3 device models. Simulation results show that the phase noise of active transformer VCO without injection-locking is approximately -92 dBc/Hz at 1 MHz frequency offset. The phase noise of injection-locked active transformer VCOs is approximately -119 dBc/Hz while that of passive LC tank oscillator is -121 dBc/Hz at 1 MHz frequency offset.