Residual and oscillator phase noise in GaAs metamorphic HEMTs

Residual phase noise measurements have been carried out on GaAs metamorphic high electron mobility transistors, mHEMT in order to explain phase noise results from mHEMT based VCOs. Noise is measured for several biases and input powers. The measurements show that the residual phase noise is increasing with increasing drain source voltages even in saturation, possibly due to the triggering of impact ionization mechanisms. This increase in noise will act deleterious on the phase noise performance of a VCO that have the drain bias increased in order to achieve higher power in the tank and thus reduce the phase noise. The reduction in phase noise due to higher power in the tank is shown to be counteracted by the increase in residual phase noise from the mHEMTs for higher drain source voltages.