CN210514473U

CN210514473U - EAS detection system based on superheterodyne principle

Info

Publication number: CN210514473U
Application number: CN201920887850.6U
Authority: CN
Inventors: 尚浩; 姬翔宇; 靳春生
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-06-13
Filing date: 2019-06-13
Publication date: 2020-05-12
Anticipated expiration: 2029-06-13

Abstract

The utility model discloses an EAS detection system based on superheterodyne principle, including antenna, transmitting circuit, receiving channel circuit, signal generating circuit and CPU, the antenna is connected with the output of transmitting circuit, the antenna is connected with the input of receiving channel circuit; the output end of the signal generating circuit is respectively connected with the input end of the transmitting circuit and the input end of the receiving channel circuit and is used for providing a local oscillation signal source for the transmitting circuit and the receiving channel circuit; the input end of the signal generating circuit is further connected with the output end of the CPU, the output end of the receiving channel circuit is further connected with the input end of the CPU, and the CPU is further connected with a peripheral circuit. The detection distance and the detection sensitivity are improved, synchronous operation of a plurality of detectors can be realized, and interference of a plurality of detection devices during simultaneous operation can be effectively prevented.

Description

EAS detection system based on superheterodyne principle

Technical Field

The utility model belongs to anti-theft system design field, concretely relates to EAS detecting system based on superheterodyne principle.

Background

The open shopping mode is rapidly popularized and popularized in China, and meanwhile, the risk that the merchant is stolen is increased. Based on the situation, an Electronic Article Surveillance (EAS) system is designed, the EAS system is widely used in the global scope at present, the field relates to various industries such as department goods, supermarkets, books and the like, and the loss caused by theft is greatly reduced due to the appearance of the EAS system. Currently, EAS systems are classified into four categories according to their operating principles, namely: acousto-magnetic EAS, radio frequency EAS, microwave EAS and electromagnetic EAS. Radio frequency EAS system and acoustic magnetic EAS system adopt than many, but still have various problems, for example detection sensitivity is low, and the interference killing feature is poor, and the false alarm rate is high.

SUMMERY OF THE UTILITY MODEL

To the defect among the prior art, the utility model provides an EAS detecting system based on superheterodyne principle has improved detection distance and detectivity, can realize the synchronous operation of many detectors simultaneously, can prevent effectively that many check out test set simultaneous workings from being disturbed.

Therefore, the utility model discloses an EAS detection system based on superheterodyne principle, including antenna, transmitting circuit, receiving channel circuit, signal generating circuit and CPU, the antenna is connected with transmitting circuit's output, the antenna is connected with receiving channel circuit's input; the output end of the signal generating circuit is respectively connected with the input end of the transmitting circuit and the input end of the receiving channel circuit and is used for providing a local oscillation signal source for the transmitting circuit and the receiving channel circuit; the input end of the signal generating circuit is further connected with the output end of the CPU, the output end of the receiving channel circuit is further connected with the input end of the CPU, and the CPU is further connected with a peripheral circuit.

A primary amplifying circuit is connected between the signal generating circuit and the transmitting circuit, and a secondary amplifying circuit is arranged between the transmitting circuit and the antenna.

The transmitting circuit and the receiving channel circuit share the antenna, the antenna comprises two coils which are in an 8-shaped structure and divide signals into two channels, each channel is divided into two paths of signals, and the two paths of signals in each channel are a pair of mutually opposite signals.

The transmitting circuit comprises a signal conversion circuit, a four-way comparator and a power amplifier, wherein the input end of the signal conversion circuit is connected with the output end of the signal generating circuit, the output end of the signal conversion circuit is connected with the four-way comparator, the output end of the comparator is connected with the power amplifier, and the output end of the power amplifier is connected with the antenna.

The digital signal generator is designed by adopting two DDS integrated chips, and the sweep frequency bandwidth is set to be 7.7MHz-8.7 MHz; one of them is used as a transmission source of radio frequency signals, and the other is used as a local oscillation source of mixing signals.

The peripheral circuit comprises a synchronous sequential circuit used for realizing synchronous operation of a plurality of devices.

The modulation signal frequency of the signal transmitted by the transmitting circuit is 4 KHz.

The receiving channel circuit comprises a frequency mixing circuit, the output end of the frequency mixing circuit is connected with the CPU through a crystal filter, the bandwidth of the crystal filter is 30KHz, and the design of equally dividing the bandwidth is adopted to ensure that no detection blind area exists.

The input end of the mixing circuit adopts a transformer to provide input signals, and is isolated by a capacitor, so that image interference caused by external useless signals in series is prevented.

The signal conversion circuit is connected with the four-way comparator through a low-pass filter.

The utility model has the advantages that: on the basis of the existing EAS detector, the detection channel and the digital processing unit circuit in the hardware circuit are replaced and replaced on a large scale, and the superheterodyne principle is applied to the detection channel. The problems of low detection sensitivity, poor anti-interference capability, high false alarm rate and the like in the existing design are solved, meanwhile, the transmission and the reception are completed by time division multiplexing of the same coil, the influence of the detectors close to each other on the detection of the detectors after the detectors send signals can be effectively prevented, and the false alarm rate is reduced. And the volume of the equipment can be reduced, and the production cost is saved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the technical solutions in the prior art will be briefly described below. In the drawings, like elements or portions are generally identified by like reference numerals. In the drawings, elements or portions are not necessarily drawn to scale.

Fig. 1 is a block diagram of the system architecture of the present invention.

Fig. 2 is a schematic block diagram of the transmitting circuit of the present invention.

Fig. 3 is a schematic circuit diagram of a primary amplifying circuit according to the present invention.

Fig. 4 is a schematic circuit diagram of the mixer circuit of the present invention.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and therefore are only examples, and the protection scope of the present invention is not limited thereby.

It is to be noted that unless otherwise specified, technical or scientific terms used herein shall have the ordinary meaning as understood by those skilled in the art to which the present invention belongs.

As shown in fig. 1-4, the superheterodyne technology can convert the local oscillation frequency and the signal frequency into an intermediate frequency signal due to the inconsistency between the local oscillation frequency and the signal frequency, and the frequency of the electronic tag center frequency has a dispersion error of plus or minus 5%, so that the frequency sweeping signal in the scheme is 7.7-8.7KHz, the frequency of the adopted intermediate frequency signal is 455KHz, which can effectively suppress the image frequency interference, and meanwhile, the false triggering caused by local oscillation leakage can be effectively avoided by adopting a crystal filter of 450KHz-460 KHz. As shown in fig. 1: the EAS detection system based on the superheterodyne principle comprises an antenna, a transmitting circuit, a receiving channel circuit, a signal generating circuit and a CPU, wherein the antenna is connected with the output end of the transmitting circuit and the input end of the receiving channel circuit; the output end of the signal generating circuit is respectively connected with the input end of the transmitting circuit and the input end of the receiving channel circuit and is used for providing a local oscillation signal source for the transmitting circuit and the receiving channel circuit; the input end of the signal generating circuit is further connected with the output end of the CPU, the output end of the receiving channel circuit is further connected with the input end of the CPU, and the CPU is further connected with a peripheral circuit.

And a primary amplifying circuit is connected between the signal generating circuit and the transmitting circuit, and a secondary amplifying circuit is arranged between the transmitting circuit and the antenna and used for increasing the gain of the signal.

During detection, a sweep frequency signal needs to be transmitted outwards through equipment, the electronic tag in a detection space region is excited by the sweep frequency signal, and then whether the electronic tag exists in the space is identified and judged by receiving a resonance signal of the electronic tag. The antenna receiving is used as a gate for receiving and receiving the label signal and entering the detection channel through a high-speed electronic analog switch.

Specifically, two signals are divided into two channels of CH1 and CH2, each channel is divided into A, B signals, so that the two channels have four signals, the four signals are converted into square wave signals by using a comparator, the square wave signals are sent to a high-speed double-channel N-MOSFET driver, and the square wave signals are amplified by a power amplifier to provide larger energy for transmission. The signal conversion circuit uses a gate circuit as a hardware circuit, and selects a CPU to generate signals to work in a matched mode. The two channels work alternately and both comprise 32 frequency points, and the A, B two-path signals in each channel have the same characteristics except the reverse direction.

Specifically, need set up 32 scanning points and equally divide 1MHz bandwidth, every frequency point outwards launches 10us, two adjacent frequency point intervals 250us, therefore, the modulation signal frequency to the transmitted signal is 4KHz, and the circuit needs synchronizing signal, synchronizing signal is with 32 frequency points as a transmission cycle, synchronizing signal is 62.5Hz duty cycle and is 50% square wave, this synchronizing signal's emergence is acted on other slave units by a master unit, make many detectors can send and receive signals simultaneously, avoid many equipment work desynchronized, produce the interference.

And the signal conversion circuit is connected with the four-way comparator through a low-tube filter.

In the chip that adopts in this scheme, because its inner structure leads to the sweep frequency output signal to have high frequency component noise, consequently, adopt low pass filter to filter its output signal to restrain other signals and get into the amplifier, its realization method has the multiple, as shown in the figure, only exemplifies it in this scheme. The chip adopted in the scheme has a certain internal resistance value, the amplification gain can be changed only by adjusting the peripheral resistance value, the balance principle is considered, the same resistance value is connected in series between the input pin of the grounding end and the ground, and 5 times of signal amplification is realized.

In addition, in the power amplification circuit, the chip is provided with two channels, CH1-A and CH1-B passing through the signal conversion circuit are connected to the input end of the chip, the maximum amplitude of the driving output voltage is consistent with the power supply voltage of the chip, and the circuit uses direct current voltage as the power supply voltage of the chip to amplify the square wave output signal. The circuit schematic diagram of the primary amplifying circuit is shown.

The A, B two paths of signals are coupled to the next stage in a time-sharing mode through a transformer, and the signals are amplified again through a secondary amplification circuit.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the scope of the embodiments of the present invention, and are intended to be covered by the claims and the specification.

Claims

1. An EAS detection system based on the superheterodyne principle is characterized by comprising an antenna, a transmitting circuit, a receiving channel circuit, a signal generating circuit and a CPU, wherein the antenna is connected with the output end of the transmitting circuit and the input end of the receiving channel circuit; the output end of the signal generating circuit is respectively connected with the input end of the transmitting circuit and the input end of the receiving channel circuit and is used for providing a local oscillation signal source for the transmitting circuit and the receiving channel circuit; the input end of the signal generating circuit is further connected with the output end of the CPU, the output end of the receiving channel circuit is further connected with the input end of the CPU, and the CPU is further connected with a peripheral circuit.

2. An EAS detection system based on superheterodyne principle as claimed in claim 1, wherein a primary amplification circuit is connected between the signal generating circuit and the transmitting circuit, and a secondary amplification circuit is provided between the transmitting circuit and the antenna.

3. An EAS detection system based on superheterodyne principle as claimed in claim 1, wherein the antenna is shared by the transmitting circuit and the receiving channel circuit, and the antenna includes two coils, and presents an "8" word structure, and divides the signal into two channels, each of which is divided into two signals, and the two signals in each channel are a pair of reciprocal signals.

4. An EAS detection system based on the superheterodyne principle as claimed in claim 1, wherein the transmission circuit includes a signal conversion circuit, a four-way comparator and a power amplifier, an input terminal of the signal conversion circuit is connected to an output terminal of the signal generation circuit, an output terminal of the signal conversion circuit is connected to the four-way comparator, an output terminal of the comparator is connected to the power amplifier, and an output terminal of the power amplifier is connected to the antenna.

5. An EAS detection system based on the superheterodyne principle as recited in claim 4, wherein the signal generation circuit is designed with two DDS integrated chips, and the sweep bandwidth is set at 7.7MHz-8.7 MHz; one of them is used as a transmission source of radio frequency signals, and the other is used as a local oscillation source of mixing signals.

6. An EAS detection system based on the superheterodyne principle as claimed in claim 1, wherein the peripheral circuit includes a synchronous sequential circuit for enabling synchronous operation of a plurality of devices.

7. An EAS detection system based on the superheterodyne principle as claimed in claim 1, wherein the modulation signal frequency of the signal transmitted by the transmission circuit is 4 KHz.

8. An EAS detection system based on superheterodyne principle as claimed in claim 1, wherein the receiving channel circuit includes a mixer circuit, the output of the mixer circuit is connected to the CPU via a crystal filter, the bandwidth of the crystal filter is 30KHz, and the design of dividing the bandwidth equally is adopted to ensure that there is no detection blind area.

9. An EAS detection system according to claim 8 characterised in that the input of the mixer circuit is transformer fed and isolated by a capacitor to prevent external unwanted signals from entering the system and causing image interference.

10. An EAS detection system according to claim 4, characterised in that the signal conversion circuit is connected to the four-way comparator via a low barrel filter.