Research On Equivalent Noise Model Of RF Transistor Used At Low Temperature And Low Voltage

Cryogenically cooled microwave low-noise amplifier(LNA)is a very importent part of some highly sensitive receivers.At present,the most advanced cyogenic LNAs employ indium-phosphide(In P)high-electron mobility transistor(HEMT)or silicon-germanated(Si Ge)heterojunction bipolar transistor(HBT).In recent years,there is a lack of research on the noise characteristics of Si Ge HBTs operating under ultra-low temperature and low bias voltage.However,in order to reduce design time,improve design efficiency and success rate,the noise modeling of Si Ge HBT under ultra-low temperature has important theoretical and practical value.This dissertation analyzes the theoretical DC characteristics,AC characteristics and small-signal properties of Si Ge HBT under ultra-low temperature and low bais voltage conditions,then compares them with other different temperature and bias voltage conditions to prove the feasibility of Si Ge HBT operating under ultra-low temperature and low bias voltage conditions.In this dissertation,a small signal equivalent circuit model for Si Ge HBTs operating under different temperatures and voltages is established by using parameter direct extraction method.By simplifying the analysis,a simplified small-signal equivalent circuit model suitable for Si Ge HBT operation in the amplified and saturated states is established.And by comparing the Y-parameters under different temperature and different bias voltage conditions,the accuracy of this small-signal equivalent circuit model is proved.Since the common shot noise model either does not describe the relationship between shot noise and frequency,or it is too complex to be applied under ultra-low temperature and low voltage conditions.So this dissertation has built a high-frequency noise model based on the simplified small-signal equivalent circuit model,and extracts the shot noise parameters.Based on several common shot noise models,a semi-empirical shot noise model was established using the mathematical fitting method.Finally,using this semi-empirical shot noise model,a practical four noise parameters model is established.It was found that each noise parameter of the Si Ge HBT has a certain relationship with the collector-emitter voltage.But,aslong as the Si Ge HBT is guaranteed to operate in the amplification region or the weak saturation region,the noise parameters of the Si Ge HBT will not be attenuated.