Effects of Output Low Impedance Termination to Linearity of GaAs HBT Power Amplifier

Improving linearity over a broad band is a major goal in RF design. This paper demonstrates that adding a low impedance termination at the envelope frequency (2 – 1) to the output of a gallium Arsenide (GaAs) Heterojunction Bipolar Transistor (HBT) distributed amplifier (DA) improves the third order output intercept point (OIP3) over a bandwidth of 2.5 GHz to 3 GHz by 1.6 to 3.4 dB. The low impedance termination is easily implemented using an external series inductor-capacitor network (LC trap) to the Monolithic Microwave Integrated Circuit (MMIC) DA. The addition of the trap causes no reduction to the in-band gain, return loss, and P1dB.