A Quasi-Balanced Power Amplifier With Feedforward Linearization

In this letter, a feedforward (FFW) linearized power amplifier (FFW PA) composed of quasi-balanced PA (QBPA) and cancellation stages is proposed by suppressing the third-order intermodulation (IM3) tones. The QBPA stage is used for extracting the IM3 tones and the FFW technique is used for suppressing IM3 tones in the cancellation stage. Compared to the conventional FFW amplifier, the proposed FFW PA does not require a phase shifter and attenuator in the QBPA stage and does not need to employ a high-gain auxiliary amplifier in the cancellation stage. The measured output-referred 1-dB gain compression point of the proposed FFW PA is +30.8 dBm at 3.5 GHz, which is 3.8 dB higher than the single PA used in the FFW PA. In two-tone measurement at 7.8-dB back-off output power (+20 dBm/tone), the IMD3 level of the FFW PA is −54.6 dBc, which is lower by 14 dB compared to that of the conventional balanced PA. In the LTE evaluation with a 64 quadrature amplitude modulation signal in 20-MHz bandwidth and +23-dBm transmitting power, the measured output spectra of the proposed FFW PA exhibit an adjacent channel leakage ratio of −48.7 dB, which is a 6.6-dB improvement over the conventional balanced PA.