This paper discusses the design of a wideband class AB-C Doherty power amplifier suitable for 5G applications. Theoretical analysis of the output matching network is presented, focusing on the impact of the non-ideally infinite output impedance of the auxiliary amplifier in back off, due to the device’s parasitic elements. By properly accounting for this effect, the designed output matching network was able to follow the desired impedance trajectories across the 2.8 GHz to 3.6 GHz range (fractional bandwidth = 25%), with a good trade-off between efficiency and bandwidth. The Doherty power amplifier was designed with two 10 W packaged GaN HEMTs. The measurement results showed that it provided 43 dBm to 44.2 dBm saturated output power and 8 dB to 13.5 dB linear power gain over the entire band. The achieved drain efficiency was between 62% and 76.5% at saturation and between 44% and 56% at 6 dB of output power back-off.
Summary
This paper proposes an inductorless fully differential transimpedance amplifier (TIA) with a single‐ended photo current to offer high bandwidth for applications of beyond 10 Gb/s optical communications. The presented TIA provides a much lower input impedance by modifying the cross‐coupled regulated cascode (CC‐RGC) configuration. The introduced method is able to enhance the bandwidth in the presence of wide range of input photodiode capacitance from small to large values, with a negligible increase in the peaking of frequency response. The proposed circuit is designed and simulated using the TSMC 130‐nm CMOS technology to validate the proposed technique. The post‐layout simulation results show that the TIA delivers a transimpedance gain of 46.5 dB
normalΩ, a bandwidth of 8.8 GHz, and an input‐referred current noise of 33 pA/√Hz. The circuit occupies an active area of 0.004 mm2 and consumes 9.8 mW from a 1.3 V supply. Furthermore, the robustness of the proposed TIA is verified by means of the Monte Carlo simulations.
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