A high linearity amplifier using an optimized transconductance process

High linearity, high gain and wide frequency bandwidth are key parameters for amplifiers used for broadband systems where distortion levels define the architecture of the network. Amplifiers with high output third order intercept points require a flat transconductance curve versus the gate voltage. The surface states between the GaAs and the nitride passivation layer and the material etching in the ungated area reduce the flatness of the transconductance curve. High gate leakage current of the devices can also degrade the transconductance. However the transconductance needs to remain constant in the operating range of the gate bias to achieve low third order intermodulation distortion. In this investigation an amplifier was designed and manufactured to validate the optimization of the process to obtain flat transconductance curves. The amplifier third order intercept point improved 7 dB typically when using the optimized process. The amplifier exhibited 20 dB of gain, 4.5 dB noise figure, and +45 dBm output third order intercept point across 50 MHz to 1000 MHz.