The Analysis of Power and Linearity Characteristics of SiGe HBTs at Low Temperatures

This work investigates the temperature dependence, from 300K to 77K, of the output power, PAE, and linearity for SiGe HBTs with and without SIC. The NADC pi/4DQPSK signal is used to analyze the linearity of SiGe HBTs. For device without SIC, the heterojunction barrier effect becomes more propound, which seriously reduces the current gain and cutoff frequency at cryogenic temperatures. The output power, PAE and linearity at 2.4 GHz decrease conspicuously with decreasing operation temperatures. This barrier effect can be negligible in SiGe HBT with SIC and thus the device achieves better power and linearity performance at cryogenic temperatures