JPH0415430B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a demodulation method for a receiver.
In particular, it is used in a receiving section of an interrogator of a mobile object identification device that transmits and receives data over a relatively short distance between a transmitting/receiving device serving as an interrogator and a transponder mainly attached to a mobile object.

<Background> In recent years, small-sized devices mainly attached to moving objects,
A simple mobile object identification device that transmits and receives data between a transponder, which is a lightweight and simple wireless terminal, and an interrogator, which has a transmitting and receiving function, has been in the spotlight. These applications include product management in factories,
Alternatively, gate control or room entry/exit control by having people carry transponders can be considered.

For example, when using this for production control in a factory, a transponder is attached to each part, with individual data such as part code numbers, processing procedures, transport routes, etc. on the production line input into the memory section in advance. Meanwhile, interrogators are installed at major points on the production line. The interrogator emits radio waves to the transponders installed on each part flowing on the production line, reads the internal data as mentioned above,
It outputs control signals that control the flow of the line and controls the production line according to each part. If such a mobile object identification device is used, it becomes possible to form a highly flexible production line, and its application range spans a wide range of fields.

<Prior Art> FIG. 6 shows an example of a conventional mobile object identification device.
1 shows the structure of an interrogator, and 2 shows the structure of a responder. The interrogator 1 includes an oscillator 104, a distributor 103, a circulator 102, a transmitting/receiving antenna 101, a mixer 106, and a signal processing circuit 107 for demodulating an identification signal. On the other hand, the transponder 2 is composed of a transmitting/receiving antenna 201, a modulator 202, and a signal processing circuit 203 storing an identification signal.

Frequency generated by oscillator 104 inside interrogator 1
The unmodulated wave of f ₀ is sent to the distributor 103 and the curculator 1
02 from the transceiver antenna 101 to the transponder 2
radiated towards. On the transponder 2 side, the transmitting/receiving antenna 201 receives this unmodulated wave, and the modulator 20
After being amplitude-modulated with the identification signal by the transmitter/receiver antenna 201, it is re-radiated from the transmitter/receiver antenna 201. On the interrogator 1 side, the re-radiated radio wave from the transponder 2 is received by the transmitting/receiving antenna 101, and the received signal is guided to the mixer 106 through the circulator 102.
Oscillator 1 of f ₀ taken out through distributor 103
04 is subjected to homodyne detection using a local oscillation signal that is part of the output. Furthermore, the detected signal is demodulated in the signal processing circuit 107, and the transponder 2 is identified.

However, in such a device, if the distance between the interrogator 1 and the transponder 2 changes, the phase of the received signal of the interrogator 1 changes, and the phase of the received signal and the f ₀ oscillator 104 used as the local oscillation signal change. A shift occurs between the phase of the As a result, the amplitude of the output of the homodyne detection also changes periodically in response to the phase shift, and the amplitude eventually becomes 0 at a certain distance, resulting in a phenomenon in which the identification signal cannot be demodulated correctly.

To prevent this phenomenon, it is possible to automatically control the phase of the local oscillation signal, or to use a synchronous detection method that performs carrier regeneration in synchronization with the received wave, but this increases the complexity of the circuit and increases the size. The drawbacks are that the size and cost are also high.

<Objective> It is an object of the present invention to improve these problems and to make it possible to always demodulate an identification signal with a small and simple circuit configuration.

<Example> FIG. 1 shows a configuration diagram of an embodiment of the present invention.

1 is an interrogator, and 2 is a responder. The interrogator 1 includes a transmitting/receiving antenna 101, a circulator 102, a distributor 103, an oscillator 104, a filter 105, a mixer 106, and a signal processing circuit 107. On the other hand, the transponder 2 includes a transmitting/receiving antenna 201,
It consists of a modulator 202 and a signal processing circuit 203 that stores an identification signal.

Now, the unmodulated wave of f ₀ generated by the oscillator 104 is divided into two parts by the distributor 103, one of which passes through the circulator 102 and is radiated from the transmitting/receiving antenna 101 to the transponder 2, and the other is sent to the mixer as a local oscillation source for homodyne detection. Sent to 106 to work. In the transponder 2, the identification signal written in the internal storage element is digitally frequency modulated (FSK) in the signal processing circuit 203, and this signal is used to generate an unmodulated wave from the interrogator received by the transmitting/receiving antenna 201. is amplitude-modulated by a modulator 202 composed of a shot sea barrier diode or the like, and is re-radiated from the transmitting/receiving antenna 201 to the interrogator 1.

The signal received by the transmitting/receiving antenna 101 of the interrogator 1 passes through the circulator 102, and after creating a level difference between the upper and lower sidebands depending on the frequency characteristics of the filter 105, the signal is transmitted to the oscillator 104 locally by the mixer 106. The oscillation source is homodyne detected,
A signal processing circuit 107 demodulates the identification signal.

By the way, when performing homodyne detection like this, if the received signal is a double sideband (DSB) signal in which the upper and lower sidebands are approximately equal in amplitude as shown in Figure 2, the relative relationship between interrogator 1 and transponder 2 will be Due to the phase difference Δφ between the phase φ _i of the input signal to the mixer 106 and the phase φ _l of the local oscillation signal due to a change in distance, Δφ=|φ _i −φ _l |
The output of the mixer, that is, the amplitude of the demodulated signal fluctuates with a period of cosΔφ, and in particular, the relative distance between interrogator 1 and transponder 2 is Δφ=(2n+1)/2π(n=0,1,2...) −. When it satisfies cosΔφ=0, the demodulated signal disappears.

However, in this embodiment, the received signal is filtered by a filter 105 to have a level difference between the upper and lower sidebands, and is converted into a vestigial sideband (VSB) signal and a single sideband (VSB) signal as shown in FIGS. 3 and 4. SSB) signal, etc., to prevent the demodulated signal from disappearing. That is, the general formula of the demodulated signal when homodyne detection is performed is expressed by the following formula, A/2 cos (φ _i - φ _l ) + B/2 cos {ωst + (φ _i - φ _l )} + C/2 cos {-ω st + (φ _i −φ _l )}− (A: carrier amplitude, B: upper sideband amplitude, C:
Amplitude of lower sideband, ωs: angular frequency of modulated signal) If it is a DSB signal, B=C, so the formula becomes A/2 cos (φ _i − φ _l ) + B cos ωst ・cos (φ _i − _{φ l} ) − , as described above. When the following equation is satisfied, Bcosωst·cos(φ _i −φ _l )=0 and the demodulated signal disappears. However, in the case of a signal such as VSB or SSB, since B≠C, the demodulated signal will not disappear in the equation even if the value of Δφ changes. The same is true for filter outputs such as those shown as other signals in FIG.

Therefore, as shown in the present invention, the filter 105
By converting the received signal into a signal with a level difference between the upper and lower sidebands and performing homodyne detection, the identification signal can be correctly demodulated even if the relative distance between the interrogator 1 and the transponder 2 changes.

<Effects of the Invention> As explained above, by using the filter as shown in the present invention, an effect equivalent to that of a synchronous detection circuit can be obtained with a simple circuit configuration, and a small and high-performance mobile object identification device can be realized at a low cost. It can also be constructed at low cost, and its benefits are great.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure shows the spectrum of the DSB signal, Figure 3 shows the spectrum of the VSB signal, and Figure 4 shows the spectrum of the VSB signal.
FIG. 5 is a diagram showing the spectrum of the SSB signal, FIG. 5 is a diagram showing the spectrum of other signals, and FIG. 6 is a configuration diagram showing a conventional mobile object identification device. In the figure, 1...interrogator, 2...responder, 101,
201... Transmitting/receiving antenna, 102... Circulator, 103... Distributor, 104... Oscillator,
105... Filter, 106... Mixer, 107
...Signal processing circuit, 202...Modulator, 203...
...Signal processing circuit.

Claims (1)

[Claims] 1. A mobile object identification device configured such that an unmodulated wave emitted from an oscillator inside an interrogator is received by a transponder, amplitude-modulated by an identification signal inside the transponder, and sent back to the interrogator. , a signal in which a level difference is created between the upper and lower sidebands of the received signal by a filter inside the interrogator is mixed with the output of the oscillator, and the mixed output is demodulated by a demodulation circuit. mobile object identification device.