ABSTRACT
In transmit path, the amplified phase noise of the transmitter’s oscillator can desensitize a nearby receiver. Furthermore, as one of the most power hungry blocks in the transceiver, its power consumption limits the efficiency of the transceiver. If the impulse sensitivity function of a certain oscillation waveform is negligible for some amount of oscillation period, the circuit noise cannot be upconverted to phase noise during that time, which is beneficial in reducing the oscillator’s phase noise. Class-F oscillators realize such oscillation waveforms by giving rise to either third or second harmonic of oscillation voltage. Class-C oscillators improve phase noise for the same power consumption but only when the oscillation amplitude is low enough to keep the core transistors in saturation. Class-D oscillators offer a very low noise without requiring large supply voltages, but they are limited to low supply voltages due to reliability concerns.
