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Abstract

Outdoor passive infra-red motion detector circuitry with circuit improvements that greatly reduce incidents of false activation. The motion detector includes one or more infra-red sensors and circuitry for amplifying and filtering the signal from the sensors. The amplification and filtering circuitry has a pass band for signals from the one or more sensors corresponding to a range of speeds of motion of a person moving in the field of view of the motion detector. The ability of the motion detector circuitry to filter out certain environmental sources of false activations is enhanced by providing the pass band with a very steep rolloff at the lower cutoff. In one embodiment the amplification and filtering circuitry is provided with three op amp stages, each stage being configured to contribute a nominal 6 db per octave rolloff to the lower cutoff. The amplification and filtering circuitry is also configured to provide the lower cutoff of the pass band with a fourth-order rolloff, which provides greatly enhanced protection against false activations from signals below the cutoff.

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First Claim