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Abstract

A passive infrared detection and conversion circuit includes a pyrosensor, a current amplifier, a capacitor, and a signal processor circuit. The signal processor is operable to charge the capacitor to a first voltage level and to measure a capacitor discharge time, the time required for the capacitor to discharge from the first voltage level to a second voltage level. The signal processor is further operable to generate an electrical control signal responsive to a variation in the capacitor discharge time which corresponds to a significant motion event. When the pyrosensor is exposed to infrared motion, it generates a transient current, and the capacitor discharge time corresponds to the transient current. The signal processor circuit includes logic operable to compare the capacitor discharge time with a long-term average capacitor discharge time. The signal processor circuit generates the electrical control signal only when the capacitor discharge time deviates from the long-term average capacitor discharge time by exceeding a predetermined threshold margin and/or satisfying other timing and/or pulse sequence patterns. The logic of the signal processor circuit may be further operable to calculate and update the long-term average capacitor discharge time based on the capacitor discharge time such that the logic filters out unwanted background signals and component tolerance variations, thereby creating a dynamic threshold system for detecting significant motion.

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