Article surveillance security system with self-alarm
First Claim
1. 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 ±
- 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 MΩ
, an operating current of said differential amplifier is set to 3 μ
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.
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Accused Products
Abstract
An article surveillance security system with self-alarm operates at 6 through 10 MHz as a central frequency, receives a swept low level radio wave within ±5 through 15% from the central frequency, and sounds the alarm. It includes a tuning circuit (1) tuning to the central frequency, and a differential amplifier (2) for amplifying and detecting the output of the tuning circuit. The load resistance (R1) of the differential amplifier is set to 3 through 5 MΩ, and the operating current of the differential amplifier is set to 3 μA or less. The base-emitter of the amplification/detection transistor (Tr1) of the differential amplifier are connected to the base-emitter of another diode-connected transistor (Tr2) to stabilize a bias drift by temperature. Thus, a receiving circuit of an article surveillance security system with self-alarm (tag) is realized with ability having a power supply of approximately four-year durability, stably operating with a very low level radio wave at 8.2 MHz, and suppressing external noise, especially a malfunction at a frequency band of a mobile telephone.
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Citations
11 Claims
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1. 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 ±
- 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 MΩ
, an operating current of said differential amplifier is set to 3 μ
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. - View Dependent Claims (2, 3, 4)
- 5 through 15% from the central frequency, and sounding an alarm, comprising;
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5. 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 ±
- 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 the output of the tuning circuit, wherein;
an inductance having low impedance at 6 through 10 MHz, and high impedance at 1 GHz or more is inserted in series with a signal path before said differential amplifier having a high load resistance for amplifying and detecting the output of said tuning circuit supplied through the inductance. - View Dependent Claims (6, 7, 8, 9, 10, 11)
- 5 through 15% from the central frequency, and sounding an alarm, comprising;
Specification