A low phase noise quadrature ring oscillator using 0.5µm GaN-on-Si HEMT

A quadrature ring oscillator designed for wireless communications has been and implemented in 0.5 μm GaN-on-Si HEMT technology. Based on the large-signal GaN HEMT and the transmission line models on silicon substrate, the oscillation frequency and output power can be predicted accurately in the simulation. The operating frequency of the two-stage ring oscillator is close to 5.76 GHz. By using a spiral inductor to be a resonated load in the differential pair, the measured output power of 9.9 dBm can be achieved for each output port without using buffer amplifiers at a 10-V dc supply. The oscillator has an output phase noise of -116 dBc/Hz at 1-MHz offset frequency. A 2^nd-order subharmonic injection technique was used to further improve the phase noise performance. The improved phase noise is -131 dBc/Hz at 1-MHz offset under injection locking status.