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

Abstract

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 equal‐but‐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.

Keywords

• Amplifiers
• Mobile radio systems