Class-C Harmonic CMOS VCOs, With a General Result on Phase Noise

350 mV, 0.5 mW, 5 GHz, 130 nm CMOS Class-C VCO Design Using Open Loop Analysis

“…This can be obtained for example by setting the gate voltage of MOS transistors below a threshold voltage so the only force periodically switching the transistors "on" and "off", comes from the sinusoidal signal generated by the oscillator itself. Thus, while biased in class-C, active devices in the oscillator core stay "on" for shorter time during each period than during start-up [1][2][3][4][5][6].…”

A 0.5V 0.5mW switching current source oscillator

“…For the similar P DC (400-600 µW), only the transformer-feedback VCO [4] shows better FoM but with a much larger area, lower TR and extremely high frequency pushing. Class-C VCO [5] also shows better FoM but at a much higher P DC . Furthermore, it needs additional complex biasing circuits (such as opamp) for proper operation, which can potentially limit its minimum V DD and thus P DC .…”

Very low noise current- shaped optimally coupled CMOS LC quadrature VCO

“…These capacitive dividers also decrease voltage swing at the gate of the transistors and hence allow them to remain in saturation for higher oscillation amplitude. This in turn reduces the phase noise, because entering into the deep triode region deteriorates ISF of the switch transistors and reduces DC to RF conversion factor of the current waveforms [3]. In the proposed circuit, transistors are in saturation for the oscillation amplitude smaller than:…”

“…Indeed, in the proposed circuit, switch transistors operate in class-C mode. The class-C oscillator displays approximately 4 dB phase noise improvement compared to the conventional cross-coupled LC oscillators [3]. To reap the benefits of spike-like current waveforms, coupling circuit is also designed to work in the class-C mode (note to coupling current in Fig.…”