A Current-Mirror-Based GaAs-HBT RF Power Detector Suitable for Base Terminal Monitoring in an HBT Power Stage

Kazuya YAMAMOTO  Hitoshi KURUSU  Miyo MIYASHTA  Satoshi SUZUKI  Hiroaki SEKI  

IEICE TRANSACTIONS on Electronics   Vol.E98-C   No.12   pp.1150-1160
Publication Date: 2015/12/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E98.C.1150
Type of Manuscript: PAPER
Category: Microwaves, Millimeter-Waves
power detector,  current-mirror circuits,  heterojunction bipolar transistors (HBTs),  WiMAX,  MMIC,  

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This paper describes the circuit design and measurement results of a new GaAs-HBT RF power detector proposed for use in WiMAX and wireless LAN transmitter applications. The detector, which is based on a simple current-mirror topology, occupies a small die area. It is, therefore, not only easy to implement together with a GaAs-HBT power amplifier, but can also offer approximately logarithmic (linear-in-dB) characteristics. Because it can also be driven with small voltage amplitudes, it is suitable for base-terminal monitoring at an HBT power stage. When the detector is used as a base-terminal power monitor, an appropriate base resistance added to the detection HBT effectively suppresses frequency dispersion of the detected voltage characteristics. Measurements of a prototype detector incorporated into a single-stage HBT power amplifier fabricated on the same die are as follows. The detector is capable of delivering a detected voltage of 0.35-2.5 V with a slope of less than 0.17 V/dB over a 4-to-24-dBm output power range at 3.5 GHz while drawing a current of less than 1.8 mA from a 2.85-V supply. While satisfying a log conformance error of less than 1 dB over an amplifier output power range from 4 dBm to 24 dBm, it can also suppress the detected power dispersion within 0.18 dB at approximately 15 dBm of output power over a 3.1-3.9-GHz-wide frequency range. This dispersion value is approximately one-tenth that of a conventional collector-terminal-monitor-type diode detector.