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An extended Doherty amplifier with high efficiency over a wide power range

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6 Author(s)
Iwamoto, M. ; Dept. of Electr. & Comput. Eng., California Univ., San Diego, La Jolla, CA, USA ; Williams, A. ; Pin-Fan Chen ; Metzger, A.G.
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An extension of the Doherty amplifier, which maintains high efficiency over a wide range of output power (>6 dB), is presented in this paper. This extended Doherty amplifier is demonstrated experimentally with InGaP/GaAs heterojunction bipolar transistors at 950 MHz. Power-added efficiency (PAE) of 46% is measured at P1dB of 27.5 dBm and 45% is measured at 9 dB backed off from P1dB. Additionally, PAE of at least 39% is maintained for over an output power range of 12 dB backed off from P1dB. This is an improvement over the classical Doherty amplifier, where high efficiency is typically obtained up to 5-6 dB backed off from P1dB. Compared to a single transistor class-B amplifier with similar gain and P1dB, the extended Doherty amplifier has PAE 2.6 × higher at 10 dB back off and 3 × higher at 20 dB back off from P 1dB. Under different bias and output matching conditions, the amplifier was also evaluated with CDMA signals. At the highest measured power of 25 dBm, the extended Doherty amplifier achieves a PAE of 45% with an adjacent channel power ratio of -42 dBc. Generalized design equations are also derived and the consequences of finite device output impedance on amplifier gain and linearity are explored

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Microwave Theory and Techniques, IEEE Transactions on  (Volume:49 ,  Issue: 12 )