Patent ID: 6339377
Filing Date: 2002-01-15
Classification: G08B

Abstract:
An article surveillance security system with self-alarm operating at from 6 through 10 MHz as a central frequency, receiving a low level radio wave swept within Â±5 through 15% from the central frequency, and sounding an alarm, comprising: a tuning circuit tuning to the central frequency; and a differential amplifier amplifying and detecting an output of the tuning circuit, wherein: a load resistance of said differential amplifier is set to 3 through 5 M&OHgr;, an operating current of said differential amplifier is set to 3 &mgr;A or less; and a base-emitter of an amplification/detection transistor (Tr1) of said differential amplifier are connected to a base-emitter of another diode-connected transistor (Tr2) of said differential amplifier to stabilize a bias drift by temperature.