Patent ID: 6677589
Filing Date: 2004-01-13
Classification: G01J,G08B

Abstract:
An object detecting device comprising:a pyroelectric sensor generating a sensing current in accordance with changes in the amount of infrared radiation incident on said sensor from an object; an I/V converter which converts said sensing current from said pyroelectric sensor into a corresponding voltage; a voltage amplifier which amplifies said voltage from the I/V converter into an amplified voltage; a detector including a level monitor which compares said amplified voltage with a predetermined detection threshold (TH2) to provide a detection signal when said amplified voltage satisfies a detection criterion with regard to said threshold, said detector responding to said detection signal for issuing a control output which is indicative of the detection of the object and is adapted to actuate an external device; whereinsaid voltage amplifier provides a restricted voltage output of low amplitude when receiving a limited source current and provides a rated voltage output of high amplitude when receiving a rated source current greater than said limited source current, said detector includes a threshold selector which has said detection threshold (TH2) and a preliminary threshold (TH1) lower than said detection threshold, and which is normally set to provide the preliminary threshold to said level monitor, said level monitor compares said restricted voltage output from said voltage amplifier with the preliminary threshold to provide a wake-up signal when the restricted voltage output satisfies a preliminary criteria with regard to said preliminary threshold; said threshold selector switches said preliminary threshold to said detection threshold in response to said wake-up signal; and said device further includes a mode selector which, in response to the wake-up signal, provides an operation mode for supplying said rated source current from a power source to said voltage amplifier such that said level monitor compares the rated voltage output with said detection threshold for detection of the object, and otherwise provides a standby mode for supplying said limited source current to said voltage amplifier from said power source.