Abstract
This paper presents a broadband 3–3.7 GHz class-J Doherty power amplifier exploiting second harmonic tuning in the output network. Furthermore, the output impedance inverter is eliminated and its effect is embedded in the main device’s output matching network, thus trading off among bandwidth, efficiency, and gain. The proposed amplifier adopts two 10 W packaged GaN transistors, and it achieves in measurement 60–74%, and 46–50% drain efficiency at saturation and 6 dB output back-off, respectively, with a saturated output power of 43–44.2 dBm and a small-signal gain of 10–13 dB. The proposed DPA exhibits a simulated adjacent channel power ratio less than −30 dBc at 36 dBm average output power, when a 16-QAM modulation with 5 MHz bandwidth is applied to the 3.5 GHz carrier.
Highlights
Due to the increasingly growing demand for wireless communication systems with high quality and high data rates, the radio frequency (RF) transceiver is being pushed to operate at higher frequencies and wider bandwidths, and with modulation schemes characterized by high Peak-to-Average Power Ratios (PAPRs)
A possible solution to mitigate this issue is to remove the λ/4 line acting as inverting network (IIN) and designing the output matching network (OMN) of the main device so as to perform the impedance inversion required by the Doherty load modulation [32]
Simulation Results The Doherty PA (DPA) performance is evaluated in simulation in the frequency range 3–3.7 GHz, under the following operating conditions: VGM = −2.95 V, VGA = −6 V, VDD = 28 V, with a quiescent drain current of 112 mA
Summary
Due to the increasingly growing demand for wireless communication systems with high quality and high data rates, the radio frequency (RF) transceiver is being pushed to operate at higher frequencies and wider bandwidths, and with modulation schemes characterized by high Peak-to-Average Power Ratios (PAPRs). The power amplifier (PA) strongly affects the performance of the transmitter [1,2,3], and it should operate as efficiently as possible over wide bandwidths, maintaining a sufficient level of linearity, which is especially challenging for 5G systems, based on Orthogonal Frequency Division Modulation (OFDM). In conventional PA architectures, the efficiency drops significantly when output power decreases with respect to its maximum value, where the efficiency is maximum This being a major drawback for non-constant envelope modulations, the efficiency enhancement in back-off has been addressed resorting to various techniques.
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