Analysis of high frequency noise of AlGaAs GaAs HBT

Abstract

Hawkins noise model is modified fur HBT application. The non-ideal ideality factor of HBT is included in both dynamic resistance and noise figure equations. Emitter resistance is also included. The extraction method of noise resistance R-n is developed. Based on the method, a simple analytic equation of R-n is derived and experimentally verified. The effects of noise sources on minimum noise figure are analyzed. The dominant noise sources are the shot noises of emitter and collector currents. Generally, when the minimum noise figure is measured at various current levels, there exists an current level at which the slope of minimum noise figure curve is zero. The zero slope current level coincides with the current level at which the noise contribution of the emitter and collector shot noises including the cancellation by correlation of two sources is minimum. Parasitic resistance degrades output noise through the shot noise amplification with a minor effect of the thermal noise of itself.