Harmonic Feedback Circuit Effects on Intermodulation Products and Adjacent Channel Leakage Power in HBT Power Amplifier for 1. 95 GHz Wide-Band CDMA Cellular Phones

Kazukiyo JOSHIN  Yasuhiro NAKASHA  Taisuke IWAI  Takumi MIYASHITA  Shiro OHARA  

IEICE TRANSACTIONS on Electronics   Vol.E82-C   No.5   pp.725-729
Publication Date: 1999/05/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Low Distortion Technology for Microwave Devices and Circuits)
heterojunction bipolar transistor,  intermodulation,  harmonics,  W-CDMA,  

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Second harmonic signal feedback technique is applied to an HBT power amplifier for Wide-band CDMA (W-CDMA) mobile communication system to improve its linearity and efficiency. This paper describes the feedback effect of the 2nd harmonic signal from the output of the amplifier to the input on the 3rd order intermodulation distortion (IMD) products and Adjacent Channel leakage Power (ACP) of the power amplifier. The feedback amplifier, using an InGaP/GaAs HBT with 48 fingers of 3 20 µ m emitter, exhibits a 10 dB reduction in the level of the 3rd order IMD products. In addition, an ACP improvement of 7 dB for the QPSK modulation signal with a chip rate of 4.096 Mcps at 1.95 GHz was realized. As a result, the amplifier achieves a power-added efficiency of 41.5%, gain of 15.3 dB, and ACP of 43.0 dBc at a 5 MHz offset frequency and output power of 27.5 dBm. At the output power of 28 dBm, the power-added efficiency increases to 43.3% with an ACP of 40.8 dBc.