JP2975861B2 - Signal receiving circuit of burglar alarm device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving circuit for a self-sounding tag device in which a tag (a drip tag), which is a theft alarm device used for preventing theft such as shoplifting, emits an alarm sound by itself.

[0002]

2. Description of the Related Art In recent years, in order to prevent shoplifting or theft of merchandise in stores and the like, a self-sounding tag device for preventing theft has been often attached to the merchandise. In this type of anti-theft device, for example, a gate device (antenna device) as a transmitting side that emits an electromagnetic wave using an electromagnetic induction coupling method is installed at an entrance of a store, and a product with a tag device as a receiving side is attached to the product. When passing through the gate device, the electromagnetic wave is detected and the tag device emits an alarm sound.

The tag device includes, for example, a wire, a pin,
It is attached to the product via an adhesive tape or the like, and is placed at the sales floor together with the product. And if the customer takes the product out of the store without completing the accounting process, the tag device will pass through the gate device attached to the product,
The tag device detects an electromagnetic wave of a specific frequency from the gate device and generates an alarm sound. Also, when the customer forcibly removes the tag device from the product, the tag device detects that the wire has been removed, and also generates an alarm sound.

[0004] On the other hand, in the case of normal shopping, the clerk removes the tag device from the product at the time of checkout, so that the alarm does not sound even if the customer passes the gate device with the product. In this case, there is an antenna device that emits an electromagnetic wave of a specific frequency at the checkout place so as not to generate an alarm sound even if the wire is removed from the tag device. It does not emit.

[0005]

However, since the tag device uses a battery as a power source, the current consumption must be extremely small in a standby state in which an alarm sound is not emitted. In addition, since replacing the battery of the tag device requires a lot of trouble and cost, this is a very important problem when the tag device is attached to many products.

[0006]

According to the present invention, there is provided a battery power source, an antenna, a signal amplifying means for amplifying a signal received by the antenna, and a signal amplifying means for amplifying a signal received by the antenna. A signal shaping means for waveform shaping and envelope detection of the signal, wherein the signal receiving circuit of a burglar alarm device for receiving or receiving an external signal by the antenna means and generating or stopping an alarm sound; It is an object of the present invention to provide a signal receiving circuit of a theft alarm device in which a DC bias voltage of an amplifying transistor is set to a cutoff voltage or less.

Further, according to the present invention, a battery power source, antenna means, signal amplifying means for amplifying a signal received by the antenna means, and waveform shaping means for waveform shaping and envelope detection of the signal amplified by the signal amplifying means In a signal receiving circuit of a burglar alarm device that receives an external signal with the antenna means and generates or stops an alarm sound, a DC bias voltage of an amplifying transistor in the signal amplifying means is cut off voltage. It is another object of the present invention to provide a signal receiving circuit of a burglar alarm device having the following features and an increased amplification factor.

[0008]

With the configuration described above, the collector current of the amplifying transistor of the signal amplifying means does not flow when the signal is on standby.

Also, with the above configuration, the collector current of the amplifying transistor of the signal amplifying means does not flow at the time of signal standby, and the signal amplifying means operates like a comparator whose threshold value is a cutoff voltage.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a receiving circuit of the tag device of the present invention. The reception antenna 1 receives an alarm activation signal or an alarm stop signal from a transmission device (not shown) such as a gate device, and the subsequent signal amplification unit 3 amplifies the input signal.
The input protection unit 2 between the receiving antenna 1 and the signal amplification unit 3 is a protection circuit for the signal amplification unit 3 against an excessive reception signal. The input signal amplified by the signal amplifying unit 3 is subjected to waveform shaping and envelope detection by the next-stage waveform shaping unit 4, and is output as a digital signal. Reference numeral 5 denotes a power supply composed of a battery.

Usually, in an amplifier circuit using a transistor, an appropriate DC bias voltage is applied to the base of the transistor because the active region of the transistor is used. In the circuit of FIG. 1, a DC bias voltage equal to or higher than the cutoff voltage (0.6 V) determined by the resistors R1 and R2 is applied to the transistor Q1 (silicon transistor) of the signal amplifying unit 3, and a sufficient base is applied to the transistor Q1. A stable collector bias is obtained by flowing a bias current.

[0013] However, in the tag device, current flows even during reception standby, so that the current consumption of the battery increases. In order to reduce the current consumption, it is necessary to prevent the transistor Q1 of the signal amplifier 3 from operating (the collector current does not flow) during the signal reception standby. By the way, in the collector current (Ic) -base-emitter voltage (Vbe) characteristics of a general transistor, the base-emitter voltage (Vbe) sharply increases from around 0.6V. Therefore, the transistor Q determined by the resistors R1 and R2
By setting the DC bias voltage of No. 1 to 0.6 V or less, the collector current Ic can hardly flow even during signal reception standby.

In the signal amplifying section 3, a resistor R
By increasing the amplification factor determined by e and the resistance Rc, the signal amplification unit 3 operates like a comparator having a threshold of about 0.6 V. In this case, the reception sensitivity is:

[0015]

(Equation 1)

## EQU1 ##

[0017]

As described above in detail, according to the present invention, a battery power source, antenna means, signal amplifying means for amplifying a signal received by the antenna means, and a signal amplified by the signal amplifying means are provided. A signal shaping means for performing waveform shaping and envelope detection, wherein a signal from an external signal is received by the antenna means and an alarm sound is generated or stopped, and the signal receiving circuit of the theft alarm device is used for amplification in the signal amplifying means. Since the DC bias voltage of the transistor is set to be equal to or lower than the cutoff voltage, the collector current of the amplifying transistor in the signal amplifying means does not flow during reception standby (that is, the amplifying transistor does not operate), and the current consumption is greatly reduced. This can contribute to prolonging the life of the battery. Therefore, it is extremely useful for a burglar alarm device powered by a battery.

Further, according to the present invention, a battery power supply, antenna means, signal amplifying means for amplifying a signal received by the antenna means, and waveform shaping and envelope detection of the signal amplified by the signal amplifying means. A signal receiving circuit of a burglar alarm device that receives a signal from the outside by the antenna unit and generates or stops an alarm sound, wherein a DC bias voltage of an amplifying transistor in the signal amplifying unit is provided. Since the gain is increased below the cut-off voltage and the amplification factor is increased, the current consumption during standby for reception is greatly reduced, which contributes to prolonging the life of the battery and improving the reception sensitivity. Therefore, it is extremely useful for a burglar alarm device powered by a battery.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram illustrating a configuration of a signal receiving circuit of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Receiving antenna (antenna means) 2 Input protection part 3 Signal amplification part (signal amplification means) 4 Waveform shaping part (waveform shaping means) 5 Battery

Claims (2)

(57) [Claims] 1. A battery power supply, antenna means, signal amplifying means for amplifying a signal received by the antenna means, and waveform shaping means for waveform shaping and envelope detection of the signal amplified by the signal amplifying means. In a signal receiving circuit of a burglar alarm device that receives an external signal by the antenna means and generates or stops an alarm sound, a DC bias voltage of an amplifying transistor in the signal amplifying means is set to a cutoff voltage or less. A signal receiving circuit for a burglar alarm device. 2. A battery power supply, antenna means, signal amplifying means for amplifying a signal received by the antenna means, and waveform shaping means for waveform shaping and envelope detection of the signal amplified by the signal amplifying means. In a signal receiving circuit of a burglar alarm device for receiving an external signal by the antenna means and generating or stopping an alarm sound, a DC bias voltage of an amplifying transistor in the signal amplifying means is set to a cutoff voltage or less. A signal receiving circuit for a burglar alarm device, wherein the amplification factor is increased.