A high isolation enhancement mode GaAs PHEMT buffer amplifier

The design and implementation of a high isolation buffer amplifier is described. The IC uses a 2-gain stage topology with variable maximum output power up to 22 dBm, this being determined by the use of an external bias resistor. It has better than 40 dB of input-output port isolation and operates from 0.5 GHz to 6 GHz. The IC is fabricated on Agilent Technologies´ proprietary enhancement-mode GaAs PHEMTs (pseudomorphic high-electron-mobility transistors) process. The enhancement-mode characteristic enables operation with a single supply voltage with high linearity and low noise. With a single 5 V supply, typical gain is 21dB with 40 mA quiescent current consumption. Total die size is 500 μm × 700 μm. The IC is packaged in an 8-lead low-profile 2 mm × 2 mm plastic package and features input and output matched ports to 50 ohms impedance. Input and output impedance matching can be further optimized for different frequency bands by the use of a single input inductor and a load inductor at the power supply. Typical uses of the part are for isolating VCO (voltage controlled oscillator) outputs and mixer local oscillator inputs as well as a buffer amplifier for driving passive mixers.