Amplifiers in the final stages of wireless transmitters boost the power level of the up-converted signals, but the ultimate power level is not same for all transmitters. One specific amplifier can be used as a driver in a cellular base station or as last stage in applications like a pico-cell. However, the amplifier has to meet the stringent linearity requirement imposed by these different standards. In this paper, we present a highly linear single stage two watt power amplifier in GaAs HBT process. The amplifier can be externally matched at the input and output, thus provides flexibility to optimize it across a specific frequency band of interest between 400 MHz and 2700 MHz. The design includes a novel approach of utilizing the nonlinear base-collector and base-emitter diode capacitances of a transistor biased in the saturation region to improve the linearity of the amplifier. The transistor provides a nonlinear feedback path between the output and input of the amplifier and thus minimizes the third order intermodulation distortion (IM3) component.

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This paper presents a novel circuit to minimize the third order intermodulation distortion component and thus improves the linearity of power amplifiers. The circuit utilizes the nonlinear base-collector and base-emitter diode capacitances of a transistor biased in the saturation region to provide a nonlinear feedback path between the output and input of the amplifier. This concept was implemented in the design of a two watt power amplifier in InGaP/GaAs heterojunction bipolar transistor process. The design demonstrated 51 dBm of output third order intercept point at 17 dBm/tone output power level at 2140 MHz in the WCDMA band. The output P1dB was measured to be about 32 dBm. The amplifier is externally matched, thus provides flexibility to optimize the amplifier across a specific frequency band of interest between 400 MHz and 2700 MHz.

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