Experiences with non-intrusive sensors for RF built-in test

This paper discusses a new type of sensors to enable a built-in test in RF circuits. The proposed sensors provide DC or low-frequency measurements, thus they can reduce drastically the testing cost. Their key characteristic is that they are nonintrusive, e.g. they are not connected electrically to the RF circuit. Thus, the performances of the RF circuit are unaffected by the monitoring operation. The sensors function as process monitors and share the same environment with the RF circuit. The underlying principle is that the sensors and the RF circuit are subject to the same process variations, thus shifts in the performances of the RF circuit can be inferred implicitly by shifts in the outputs of the sensors. We present experimental results on fabricated samples that include an LNA with embedded sensors. The samples are collected from different sites of a wafer such that they exhibit process variations. We demonstrate that the performances of the RF circuit can be predicted with sufficient accuracy through the sensors by employing the alternate test paradigm.