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11. Intermodulation Distortion Analysis of Class-F and Inverse Class-F HBT Amplifiers.

Author

Ohta, Akira, Inoue, Akira, Goto, Seiki, Ueda, Kazuhiro, Ishikawa, Takahide, and Matsuda, Yoshio

Subjects
*CODE division multiple access, *BIPOLAR transistors, *POWER amplifiers, *TRANSISTORS, *SPREAD spectrum communications, *ELECTRONIC amplifiers
Abstract

The third-order intermodulation distortions (IM3s) of class-F and inverse class-F heterojunction bipolar transistor amplifiers were compared experimentally. It was revealed that the IM3 of inverse class F is lower than that of class F at high input power (Pin), although the better class for IM3 at low Pin changes from class F to inverse class F according to the increase of the quiescent current (Iq). The different IM3 behaviors are mainly caused by the different gain variations in both amplifiers. At a low Pin the gain of class F is larger than that of inverse class F. The larger gain in class F causes a gradual gain decrease and a steep gain rise at high and low Iq respectively. On the other hand, the gain of inverse class F is larger than that of class F at a high Pin. The larger gain in inverse class F causes a gradual gain decrease at all Iq values. These gradual gain decreases are one of main causes of a lower IM3. These phenomena can be explained by the output current (Iout) and voltage (Vout) waveforms, which differ according to the harmonic loads. The Iout and Vout positive half-sinusoidal waveforms, which consist of in-phase second harmonics, are effective for large-gain operations. The positive half-sinusoidal Iout waveform of the class-F amplifier prevents a gain decrease at a low Pin and high Iq and the similar Vout waveform in inverse class F prevents a gain decrease at a high Pin. [ABSTRACT FROM AUTHOR]

Published
2005
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