Compensation method for a nonlinear amplifier using the gain expansion phenomenon in a Doherty amplifier

This paper proposes a new predistortion method using the gain expansion phenomenon in a Doherty amplifier. In the proposed structure, the drive stage Doherty amplifier, which has a gain expansion characteristic, precedes the final stage Doherty amplifier. The gain expansion characteristic compensates for the gain compression of the final stage amplifier and the overall linearity is improved based on an increase in the total output P_{1 dB} compression point. Using a behavioral model, we simulated the effect of increasing the P_{1 dB} point to the adjacent channel power ratio (ACPR) of the CDMA2000 signal. The experimental results show that the overall output P_{1 dB} compression point is improved by 1.5 dB and the ACPR for the one-carrier CDMA2000 signal is improved by 8.5 dB. In addition, we tested a power amplifier with a four-carrier WCDMA signal to verify the validity of this configuration for wide-band applications.