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

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)...

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Bibliographic Details
Published in:IEEE transactions on microwave theory and techniques 2001-12, Vol.49 (12), p.2472-2479
Main Authors: Iwamoto, M., Williams, A., Pin-Fan Chen, Metzger, A.G., Larson, L.E., Asbeck, P.M.
Format: Article
Language:English
Subjects:
Amplification
Amplifiers
Equations
Gain
Gallium arsenide
Heterojunction bipolar transistors
High power amplifiers
Impedance matching
Linearity
Mathematical analysis
Multiaccess communication
Noise levels
Power amplifiers
Power generation
Power measurement
Semiconductor devices
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Summary: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 P/sub 1dB/ of 27.5 dBm and 45% is measured at 9 dB backed off from P/sub 1dB/. Additionally, PAE of at least 39% is maintained for over an output power range of 12 dB backed off from P/sub 1dB/. This is an improvement over the classical Doherty amplifier, where high efficiency is typically obtained up to 5-6 dB backed off from P/sub 1dB/. Compared to a single transistor class-B amplifier with similar gain and P/sub 1dB/, the extended Doherty amplifier has PAE 2.6 /spl times/ higher at 10 dB back off and 3 /spl times/ higher at 20 dB back off from P/sub 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.
ISSN:0018-9480
1557-9670
DOI:10.1109/22.971638