A bias circuit for the thermal stability of GaAs HBT power amplifier

Abstract

This letter proposes a current bias circuit that improves the thermal stability of the 5G power amplifier (PA) in the GaAs HBT process. A diode and resistor scheme combined with a diode-connected HBTs scheme are employed to generate temperature-related voltages of which the temperature coefficients (TC) are inversely proportional to the sizes of devices. Those multi-TC voltages are able to compensate for the equalbut-opposite TC of HBTs in the current mirrors so as to generate different zero-to-absolute-temperature (ZTAT) currents at the same time. The experimental results show that the TC of the proposed bias circuit has 4% error for a 5.5 V supply from -5 to 95°C. Compared with the traditional bias circuit, the variation of output power of the proposed bias circuit is reduced from 11% to 8% and the variation of PAE is reduced from 7% to 5%. The proposed bias circuit, which has no requirement for matching, can perform effective temperature compensation for PAs in the single-transistor GaAs HBT process.