A 3.2-V operation single-chip dual-band AlGaAs/GaAs HBT MMIC power amplifier with active feedback circuit technique

This paper describes the design and experimental results for a 3.2-V operation single-chip AlGaAs/GaAs heterojunction bipolar transistor (HBT) monolithic microwave integrated circuit (IMMIC) power amplifier for GSM900 and DCS1800 dual-band applications. The following two new circuit techniques are proposed for implementing the power amplifier. One is an on-chip HBT bias switch which in turn switches the amplifier between 900 and 1800 MHz. The proposed switch configuration allows the switch using a high turn-on voltage of 1.3 V of AlGaAs/GaAs HBT´s to operate with a 3-V low supply voltage, because the switch circuitry needs no stacked configuration. The other is an active feedback circuit (AFB) to prevent permanent failure of HBT´s in the output power stage even under severe conditions of oversupply voltage and strongly mismatching load. Experimental results revealed that the proposed feedback circuit, which works as a voltage limiter, can protect the output stage HBT´s from an excessive collector voltage swing even when the amplifier is operated under a condition of a 5-V oversupply voltage and a 10:1 voltage standing-wave ratio (VSWR) mismatching load. Under a normal condition of 3.2 V and a 50-/spl Omega/ matching load, the IC is capable of delivering an output power of 34.5 dBm and a power-added efficiency (PaE) of 52% in a GSM900 mode, and a 32-dBm output power and a 32% PAE in a DCS1800 mode.