Improving the linearity of the AD8361 “Tru-Pwr” RF detector IC

The AD8361 is a wideband linear RMS radio-frequency (RF) detector IC widely used in the RF industry. This paper presents a method to extend the dynamic range of the detector to nearly 40 decibels, over a range from less than -30dBm to +8dBm with absolute accuracy typically +0.5/-1dB. In addition, most samples can be made to track to a very high degree over an even wider range. The increase in accuracy and tracking allows improved power calibration, real-time power regulation, and calculation of VSWR (voltage standing wave ratio) for the multimegawatt RF transmitters used to heat plasmas on NSTX at PPPL. The method presented here is simpler and lower cost than the dual-detector-amplifier technique presented by its manufacturer. Test results and distributions are presented for approximately 20 samples of a dual-detector module built by PPPL.