Exact offset voltage cancellation of sensitive IRFPA microbolometers by a novel feedback readout circuit

Abstract

A new feedback readout circuit of microbolometers for sensing radiant power is proposed in this paper. Due to excellent thermal characteristics of microstructure on infrared application recently, the readout circuits of the microsensors would not concern the responsivity only, but should also take offset voltage cancellation, digitalization, and signal-to-noise ratio under considerations. Although Wheatstone bridge readout circuit has been widely used in resistive thermal sensor readout for several decades, its nonlinear output voltage acting as the offset voltage still perplex us, as well as its digitalization and signal-to-noise ratio could be unsatisfied for microbolometer applications. Hence, we present the feedback readout which could optimize the key factors simultaneously and increase the responsivity without any layout modification of the bridge structure on Infrared Focal Plane Array (IRFPA) microbolometer chip. The results revealed that the balanced parameter, frequency, equal to 0.5 would be the best condition for these requirements instead of the balanced parameter equal to unity by intuition traditionally. Compared to traditional Wheatstone bridge readout circuit, the feedback readout circuit would improve the responsivity of 2.86 times, immunize the offset voltage exactly, obtain a very large OVRR, and reduce the noise of the readout circuit of 5.6 dB. These significantly important results will improve significantly the performance of the readout circuit, and speed up the commercialization of infrared focal plane array of microbolometers.