Bias Circuit Design for Microw...

Bias Circuit Design for Microwave AmplifiersBias Circuit Design for Microwave Amplifiers
ECE145A/218A UCSB/ECE S. Long We need to provide a stable bias condition for our device in any amplifier application. Bipolar transistors: Must force the DC (average) value of VCE and IC to desired values and keep them constant using feedback techniques. Never fix VBE: IC = ISE e VBE/VT . IC varies exponentially with temperature. Never fix IB: IC = b IB b varies tremendously from device to device and increases with temperature as well (0.7%/degree C). Field Effect Transistors: Force VDS and ID to desired values and keep them constant. The main weakness of microwave FETs is the variation in threshold voltage, VT, and the transconductance gm from device to device and with temperature. In some cases, bias stabilization may be accomplished with pass