Abstract: The method for testing a passive infrared sensor, the sensor comprising a housing in which an infrared sensor element with two terminal pins and a circuitry connected to the terminal pins of the infrared sensor element are arranged, the method comprises the steps of repeatedly generating and applying individual known electric charges to one of the terminal pins (26, 28) with a predetermined frequency per time unit and measuring the voltage between the two terminal pins (26, 28), and indicating failure of the passive infrared sensor (10) if the voltage differs from a desired voltage by more than a predetermined value.

Abstract: A multiplier circuit for obtaining the product of two input signals has a modulator for modulating a first input signal to produce an intermediate pulse train whose pulse density is dependent on the amplitude of the first input signal. A combiner derives from the second input signal and the intermediate pulse train a composite signal whose average value is equal to the product of the first and second input signals.