A temperature stabilized RF detector with extended dynamic range

Abstract

The purpose of this paper is to document some of the finer points which became apparent during the development of an RF powermeter. The powermeter, intended for use in a hostile thermal environment, was an integral part of an automated test set used to evaluate mobile telephone units. The initial task was to develop circuitry that produced a DC output voltage which was simply related to the RF input power. The circuit performance was further specified to accommodate a wide dynamic range of inputs and to remain reasonably accurate despite wide temperature variations. The development was begun by employing DC current biasing to improve the detector's sensitivity to low level input signals. Next a subtractive technique was utilized to provide improved temperature stability. An additive technique was devised to extend the range of linear operation. Only by employing all of these methods was the resultant circuit able to meet its requirements. In the sections which follow, the current biased envelope detector with the proposed improvements is discussed, a circuit is introduced, and experimental results which confirm the validity of the suggested techniques are presented.