CN1292189A

CN1292189A - Method and circuit for demodulation

Info

Publication number: CN1292189A
Application number: CN 99803259
Authority: CN
Inventors: 福里迪·皮特森; 阿恩·米特高德; 海恩·E·皮德森
Original assignee: TSS TRAFFIC SUPERVISION SYSTEMS AS
Current assignee: TSS TRAFFIC SUPERVISION SYSTEMS AS
Priority date: 1998-02-23
Filing date: 1999-02-23
Publication date: 2001-04-18
Also published as: AU2412199A; DK24798A; WO1999043132A3; BR9908174A; EP1050141A2; CA2320699A1; JP2003527754A; WO1999043132A2

Abstract

The invention relates to a method for simultaneous AM demodulation of data which are transferred between a transponder and an interrogator in connection with metal detection. The carrier wave signal is amplitude modulated by the information signal and is fed to an input of a receiver where it is branched into two parts, so that the first part is fed to a severe limiter, while the second part is fed to a first input of a mixer whose second input receives the output signal from the severe limiter. The two signal parts are multiplied in the mixer. A DC signal used for metal detection and an AC signal used for determining a possible information signal occur on the output of the mixer. The AM signal is fed to the receiver from an antenna which contains an adjusted circuit, which receives a signal galvanically separated from a generator.

Description

The Method and circuits of demodulation

The method of the part signal that the present invention relates to amplitude modulation (AM) demodulation part data-signal simultaneously and form by metal interaction.

Especially, the present invention relates in WO 98/07052 for example, describe the monitoring system of type.The system that is used for identifying purpose is commonly called the RF-ID system.

For the purpose of monitoring, monitored object can be provided with TAG, if TAG and electromagnetic field near the time, its identification code that can obtain by the antenna of emission electromagnetic field responds.There are many such systems, for example, are used for monitor vehicle.

For the vehicle that will be identified, this vehicle must be provided with TAG.On the other hand, can not obtain not have the information of the vehicle of described TAG.

The purpose of this invention is to provide a kind of method of information that allows to discern the vehicle that for example is provided with TAG and obtain for example not have the vehicle of TAG.

Realize this purpose by implementing the method for claim 1.The standard according to the rules of the present invention is based on is used under the very little situation of the signal modulation degree of identifying purpose.The present invention also based on the metal part of the antenna by the emission electromagnetic signal by causing the received signal of a big relatively modulation degree of antenna record.The order of magnitude that is used for the signal modulation degree of identifying purpose is 10 ^-4, according to the present invention, the modulation degree that is used for metal detection is generally 10 ^-1

If monitor a crowded highway, not only can obtain to be provided with the identification of the vehicle of TAG, and can obtain the information of all other vehicles, if this is because the full-length of supposition vehicle for example can be measured average speed.Thereby, comprise that the other parts that the received signal of information appears in metal relatively slowly change, in a preferred embodiment, obtain described information based on the DC content of the correction pattern of the signal that receives.

Claim 3 limits the preferred details of the demodulation according to the present invention, and the details that claim 4 qualification is favourable is because current separation has reduced forming the regulating circuit influence on every side that part detects.

Best, adjuster is suitable for carrying out strict restriction, and it causes the phasing demodulation.

The present invention also comprises the circuit that is used for while AM restituted signal, and described signal comprises first with relatively little modulation index and the second portion with relative big modulation index.

Purpose according to circuit of the present invention is to improve the sensitivity of the signal processing that limits in claim 1-5.As described, it is very little to be used for the modulation degree of identification division signal.This means that TAG of the prior art must be relatively near the antenna that transmits and receives electromagnetic signal.Otherwise signal to noise ratio is with non-constant.

When circuit of the present invention comprised a blender, the very good signal to noise ratio of new-type blender circuit not only was used to identifying purpose, and is used to detect the appearance of metal.

Embodiment with reference to the accompanying drawings will describe the present invention in detail, wherein

Fig. 1 represents the basic structure of the receiver according to the present invention,

Fig. 2 represents an example of the signal that the receiver by Fig. 1 receives,

Fig. 3 represents to handle through first in the receiver of Fig. 1 the signal of back Fig. 2,

An output signal of Fig. 4 presentation graphs 1 receiver, and

Fig. 5 represents to use a basic structure of the inventive method.

In Fig. 1, label 1 expression is as the receiver of a transponder of the present invention or an interrogator part.This receiver has an input 4 of received signal, and this signal is two parts 5 and 5a along separate routes.Signal 5 is fed in the limiter 2 of restricting signal effectively, and signal 5a is fed on the first input end of blender 3.

In addition, blender 3 receives confined signal 6, and signal 7 and 8 appears on the output of blender 3, explains it in more detail in conjunction with following accompanying drawing.

Signal 4 among Fig. 1 can be the shape shown in Fig. 2.Signal 9 can be near the signal that (visible Fig. 5 and relevant explanation) is received when TAG and metal are not transponder or interrogator.Under the situation of metal part branch near interrogator, owing to absorb energy in the metal part, the amplitude of the signal that receives will drop to the curve shape shown in 11.In fact, described amplitude will descend with 10% rank, and for the sake of clarity it is exaggerated in Fig. 2.Typical frequency can be 125kHz, and this frequency is general for radio-frequency (RF) identification purpose (FR-ID).

When TAG enters the range of sensitivity of interrogator, TAG will launch identification signal, thereby with 10 ^-4Signal 9 among modulation index amplitude modulation Fig. 2 of the order of magnitude.Because the principle of the demodulation of identification signal is known altogether, therefore is not described in detail.On the other hand, the signal processing that below explanation is used for metal detection.

In Fig. 3, the signal 6 of the output of label 13 and 14 expression limiters 2.As seen in fig. 3, signal 9 has strictly been limited and has been occurred to be similar to square wave on output 6.Strictly restriction is favourable, and this is because it produces possible phase difference minimum between signal 6 and the 5a, multiplying signal 6 and 5a in blender subsequently.This has produced the signal shape 16 shown in Fig. 4.The mean value of signal 16 (DC) is as 17 indications.

If metal object is near interrogator, the signal 9 of Fig. 2 will drop to signal level 11 among Fig. 2 usually, be equally applicable to the DC value according to the explanation acquisition of Fig. 3 and 4.Occurring under the situation of metal, signal level descends 10% usually, and for example arrives the 5%DC reduction by regulating threshold value, because the identification signal of TAG only comprises the modulation degree of order of magnitude 10-4, so metal can fully be detected, and whether there is TAG irrelevant with metal object.

Fig. 5 represents the basic application of system of the present invention.Metal object is represented with label 31.This object is provided with and is suitable for the TAG 32 that communicates by letter with interrogator 20.

As can be seen, antenna comprises emitter/receiver coil 21 and capacitor 28, and it constitutes oscillating circuit.The signal of generator 22 is provided on the antenna by

transformer

24,25.

The receiver of label 1 presentation graphs 1, it receives the signal from

transformer

26,27.

Obtain by the power supply of oscillating circuit by control unit 35 and circuit 29 to antenna.

With reference now to the example among Fig. 5, comes the mode of operation of illustrative system.

When object 31 is near antenna 21, the part signal of responding to from the oscillating circuit of generator 22 will be absorbed by object 31, that is to say that receiver will receive more weak signal.This signal changes by the interaction with metal bump, referring to the above-mentioned explanation of Fig. 4.

In addition, if object has the TAG 32 that is suitable for signal is transmitted into antenna 20, this signal will be received in the antenna 21 as amplitude-modulated signal, referring to the above-mentioned explanation of Fig. 4.The information of this signal comprises the identification of vehicle, and the identification of described vehicle can be sent in the control unit 35 and further pass through center cell 36 selectively.

Thereby, owing to will detect near any objects of the appearance antenna 20, can provide a kind of very effective system by disclosed system, this system need not rely on can with the object of system communication.

Claims

1. be used for signal that demodulation receives so that the method for data-signal to be provided, the AC of the demodulation pattern of the signal that the part that described data-signal usefulness has relatively little modulation index receives partly represents, it is characterized in that producing simultaneously the signal that the expression metal occurs, described signal relies on the demodulation pattern of the second portion of the signal that receives, and the second portion of the described signal that receives has high relatively modulation index.

2. according to the method for claim 1, it is characterized in that coming the second portion of the signal that demodulate reception arrives by the DC content that obtains the signal correction pattern.

3. according to the method for claim 1 or 2, it is characterized in that

Amplitude-modulated signal is received on the input of receiver,

Amplitude-modulated signal is first and second portion along separate routes,

First is fed in the limiter, and

Second portion is fed on the first input end of blender, second input of blender receives an output of limiter.

4. according to the method for claim 2 or 3, it is characterized in that the input of receiver receives the received signal of separating from an adjusting antenna electricity.

5. according to any the described method among the claim 1-4, it is characterized in that the strict restriction of limiter execution.

6. be used for the circuit of signal that demodulation simultaneously comprises the second portion of first with relatively little modulation index and relative big modulation index, it is characterized in that described circuit comprises a blender, it has first output of representing first signal section and second output of representing the secondary signal part.