A true differential pyroelectric IR detector with improved D*

Abstract

Pyroelectric infrared detectors are used in many commercial and industrial applications. These by nature are “single ended” and thus any electronic perturbation from an external or internal source such as AC pickup or from a nearby RF or other sources of noise can be coupled onto the detector’s output signal. This is in contrast to other IR detectors such as thermopiles, thermistor bolometers and others which are much lower impedance and don’t require these impedance converters are often used in the differential mode. In practice each electrode forming the capacitor is directly connected to an impedance converting amplifier. While exposed to a changing IR signal the capacitor produces current which flows out of one electrode and must be balanced by an equal but opposite current from the other electrode. When these two signals are connected to separate impedance converters the outputs are the same but of opposite sense. When these are connected to a differential amplifier the output is doubled while all the common mode artifact is canceled out. (Patent Pending) The noise in this configuration is primarily from the impedance converters. However as this noise is random it only RMS’s, thus it is only increased by a factor of 1.41 thus the D* of a detector connected will be increased by this factor This connection will work with any pyroelectric material with current or voltage mode impedance conversion and configurations such as parallel or series with and without temperature fluctuation compensation and of course with standard single elements.