Piezoelectric transducer signal processing circuit

#The present invention relates generally to piezoelectric transducer systems.

#Piezoelectric sensor systems are used in a wide variety of applications. As but one non-limiting example, some security systems detect movement in a monitored space using passive infrared (PIR) motion sensors, which detect changes in far infrared radiation (8-14 micron wavelength) due to temperature differences between an object (e.g. a human) and its background environment. Upon detection, motion sensors generally transmit an indication to a host system, which may in turn activate an intrusion “alarm”, change room lighting, open a door, or perform some other function. Such sensors advantageously are simple and relatively inexpensive.

#The detectors of a PIR sensor can include pyroelectric detectors that measure changes in far infrared radiation. Such detectors operate by the “piezoelectric effect”, which causes electrical charge migration in the presence of mechanical strain. Pyroelectric detectors take the form of a capacitor—two electrically conductive plates separated by a dielectric. The dielectric can be a piezoelectric ceramic. When far infrared radiation causes a temperature change (and thus some mechanical strain) in the ceramic, electrical charge migrates from one plate to the other. If no external circuit (or a very high impedance circuit) is connected to the detector (“voltage output mode”), then a voltage that can be measured appears as the “capacitor” charges. If an external circuit of relatively low impedance is connected between the plates (“current output mode”), then a current flows.

#The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which:

#FIG. 1 is a block diagram of a motion sensing system architecture using a piezoelectric transducer detector system;

#FIG. 2 is a schematic diagram of a first embodiment of a piezoelectric transducer transconductance circuit;

#Certain embodiments as disclosed herein provide for piezoelectric transducer signal processing circuits. For example, one circuit described herein has an input line and a piezoelectric transducer in the input line, an amplifier receiving signals on the input line and generating an output based on the transducer signal, and at least one feedback element through which the output is sent back to the input line.

#After reading this description it will become apparent to one skilled in the art how to implement the invention in various alternative embodiments and alternative applications. However, although various embodiments of the present invention will be described herein, it is understood that these embodiments are presented by way of example only, and not limitation. As such, this detailed description of various alternative embodiments should not be construed to limit the scope or breadth of the present invention as set forth in the appended claims.

#Referring initially to FIG. 1, an exemplary non-limiting embodiment of a detection system is shown, generally designated 10, for detecting a moving object 12, such as a human. The system 10 includes an optics system 14 that can include appropriate mirrors, lenses, and other components known in the art for focussing images of the object 12 onto a passive infrared (PIR) detector system 16. In response to the moving object 12, the PIR detector system 16 generates a signal that can be filtered, amplified, and digitized by a signal processing circuit 18, with a processing system 20 (such as, e.g., a computer or application specific integrated circuit) receiving the signal and determining whether to activate an audible or visual alarm 21 or other output device such as an activation system for a door, etc.