Abstract
Since Nathan Sokal's invention of the class-E power amplifier (PA), the vast majority of class-E results have been reported at kilohertz and millihertz frequencies, but the concept is increasingly applied in the ultrahigh-frequency (UHF) [1]-[13], microwave [14]-[20], and even millimeter-wave range [21]. The goal of this article is to briefly review some interesting concepts concerning high-frequency class-E PAs and related circuits. (The article on page 26 of this issue, A History of Switching-Mode Class-E Techniques by Andrei Grebennikov and Frederick H. Raab, provides a historical overview of class-E amplifier development.)
Highlights
The final results measured on all four power amplifier (PA), including performance over supply voltage, are shown in Fig.8, demonstrating over 45 W and over 80% efficiency in all cases, with the GaN HEMT amplifiers showing best overall performance in the UHF range (2008)
A two-stage 150-nm GaN on SiC PA is demonstrated with the output stage designed using ideal class-E equations as a starting point, with a power over 10 W, Gsat>20 dB and peak PAE>60% [19] where the efficiency remains above 50% at 10 dB back-off
In [40], single-ended and differential matching networks are investigated to obtain a 1.7-2.2 GHz operational bandwidth of a class-E PA implemented in 90nm CMOS operating in sub-optimal mode with efficiency over 42% and power above 25 dBm
Summary
Since Nathan Sokal’s invention of the class-E power amplifier (PA), the vast majority of class-E results have been reported at kHz and MHz frequencies, but the concept is increasingly applied in the UHF [1,2,3,4,5,6,7,8,9,10,11,12,13], microwave, e.g. [14,15,16,17,18,19,20], and even in the millimeter-wave range, e.g. [21]. Assuming a high-Q output circuit and ideal bias choke, the current and voltage waveforms across the transistor can be derived, and the Fourier expansion used to find the theoretical impedance at the fundamental frequency: ZZEE = 0.28/(ωωCCOOOOOO)eejj49°. This expression obtained from idealized circuit assumptions is the impedance at the virtual drain (current source) of the transistor, and if this impedance is presented to a device, it will operate in class-E mode, at frequencies governed by Eqs. The theory behind Eq (2) assumes that all higher harmonics are open-circuited At lower frequencies, this condition, along with a high-Q output circuit and a nearly ideal choke, can be implemented with lumped elements. With an 85% efficiency peak at 50 Ω loading condition, the measured efficiency was still as high as 70% at 10 dB of power backoff
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