High-Efficiency Harmonic-Peaking Class-EF Power Amplifiers With Enhanced Maximum Operating Frequency

Abstract

The recently introduced Class-EF power amplifier (PA) has a peak switch voltage lower than that of Class-E PA. However, the value of the transistor output capacitance at high frequencies is typically larger than the required Class-EF optimum shunt capacitance. Consequently, soft-switching operation that minimizes power dissipation during OFF-to-ON transition cannot be achieved at high frequencies. Two new Class-EF PA variants with transmission-line load networks, namely, third-harmonic-peaking (THP) and fifth-harmonicpeaking (FHP) Class-EF PAs are proposed in this paper. These permit operation at higher frequencies at no expense to other PA figures of merit. Analytical expressions are derived in order to obtain circuit component values which satisfy the required Class-EF impedances at fundamental frequency, all even harmonics, and the first few odd harmonics as well as simultaneously providing impedance matching to a 50 Ω load. Furthermore, a novel open-circuit and shorted stub arrangement which has substantial practical benefits is proposed to replace the normal quarter-wave line connected at the transistor's drain. Using GaN HEMTs, two PA prototypes were built. Measured peak drain efficiency of 91% and output power of 39.5 dBm were obtained at 2.22 GHz for the THP Class-EF PA. The FHP Class-EF PA delivered output power of 41.9 dBm with 85% drain efficiency at 1.52 GHz.

A High-Efficiency GaN Doherty Power Amplifier With Blended Class-EF Mode and Load-Pull Technique

“…To find the electrical lengths and characteristic impedances of the idealized transmission lines TL1-TL8 shown in Fig. 3, we have followed the same circuit design methodology for the FHP Class-EF PA reported in [11].…”

“…However, when operated at high frequency to deliver high output power, the theoretical value of the capacitance shunting the ideal switch in the Class-EF topology is typically lower than the actual transistor's equivalent output capacitance. To address this problem, the so-called Fifth-Harmonic-Peaking (FHP) Class-EF PA was proposed in [11]. This new PA variant specifically satisfies the Class-EF load-impedance requirements at fundamental frequency (f0), all even harmonics, and the first two odd harmonics, i.e.…”

Analysis of the second harmonic effect on power amplifier intermodulation products

“…The third-harmonic-peaking Class-EF PA reported in [9] is now investigated for its IM3 behavior. Implemented using a GaN HEMT transistor from Cree (CGH40010F), this PA operates at 2.22 GHz and delivers 40-dBm output power.…”

A broadband microwave GaN HEMTs class EF₃ power amplifier with π-type network

“…The mixed mode class EF [5] or E/F [6] operation provides a tradeoff between the simplicity of class E and benefits of class F or inverse class F. Class E/F achieve zero voltage and zero voltage derivative switching conditions when even harmonics are open circuits and odd harmonics are short circuits. In contrast, class EF achieve zero voltage and zero voltage derivative switching conditions when even harmonics are short circuits and odd harmonics are open circuits.…”