Postmatching Doherty Power Amplifier With Extended Back-Off Range Based on Self-Generated Harmonic Injection

In this paper, an asymmetric drain biased postmatching Doherty power amplifier (DPA) using harmonic injection is proposed for further back-off extension. The injected harmonic components are generated by the two active devices. Aided by the proposed harmonic injection network, drain waveform amplitude modulation for both devices can be achieved at saturation, which results in enhanced saturated power for both carrier and peaking devices, while carrier back-off power remains unchanged. As a consequence, the back-off region is extended. Moreover, the power utilization factor of the asymmetric drain biased DPA is also improved. A DPA for wideband code-division multiple access systems was designed and fabricated based on commercially available gallium nitride HEMT (Cree CGH 40010F) devices to validate the proposed technique. Measured results of the proposed DPA demonstrated that operation at 10-dB back off is possible between 1.6 and 1.9 GHz, with efficiency better than 46%.