JPS587949B2 - Shingo Kenshiyutsu Sochi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal detection device suitable for a system that utilizes the frequency sweep response characteristics of a resonant circuit.

In general, a transmitting device sends a frequency sweep signal to a responding device including a plurality of resonant circuits each having a different resonance frequency, and a receiving device processes the frequency swept response wave from the responding device. As a system for identifying information specific to an object, an identification system as shown in FIG. 1 is known.

In this system, a signal from a sweep signal generator 1 is amplified by a power amplifier 2, and an interrogation radio wave is emitted from a transmitting/receiving antenna 3 toward a response device.

The response device 4 is attached to, for example, a part of an object traveling at high speed, and receives the interrogation radio wave with a response antenna 5.

The antenna 5 has a plurality of resonant circuits 71, 72, . . . , 7n connected in parallel via a capacitor 6.

Each of the resonant circuits 71, 72, . . . , 7n can be composed of a piezoelectric element such as a ceramic or crystal, a lumped constant circuit made of L, R, and C, or an active element containing these.

Therefore, when the frequency of the interrogation signal reaches the resonant frequency, if the resonant element is a series resonant circuit, the impedance of the resonant circuit decreases and a large current flows through the response antenna 5. 72...7
Radio waves are reflected in correspondence to n.

The reflected radio wave is guided to the transmitting/receiving antenna 3, and only the signal in the required band is extracted by the band wave filter 8 to obtain a signal as shown in FIG. 2a.

Note that FIG. 2a shows a case where there are two response signals on the lower frequency side and a noise signal on the higher frequency side.

Furthermore, the radio wave reflection from the above-mentioned response antenna 5 to the transmitting/receiving antenna 3 can be regarded as a change in impedance or phase when looking at the response device 4 from the transmitting/receiving antenna 3. π/
By shifting the phase by 2 radians, using this as a reference phase, and comparing the signals of the transmitting and receiving antenna 3 with a phase detector 10, the phase change can be detected.

The phase detector 10 is preferably a product-type detector proportional to the amplitude and phase difference between the input signal and the reference signal, such as a ring modulator, from the viewpoint of detection sensitivity, but a phase detector such as a ratio detector is preferable. can also be used.

The output signal of the phase detector 10 is then converted into a binary signal by a level detector 11 such as a Schmitt circuit.

The object having the response device 4 is then identified by processing the binary signal.

However, the frequency swept wave response of a resonant circuit with an extremely high quality (sharpness) Q using ceramic or crystal, for example, is due to the frequency-amplitude characteristics (static characteristics) of the resonant circuit and the discharge of energy stored in the resonant circuit. , a ringing component whose amplitude decreases exponentially with time occurs at the resonant frequency of the resonant circuit.

Therefore, the output signal of the phase detector 10 is a response in which the ringing component and the static characteristics of the resonant circuit are compressed in the sweep direction.
That is, a beat signal is generated which has a component with quasi-static characteristics, and whose frequency gradually increases with time and whose amplitude decreases exponentially with time, as shown in FIG. 2b.

Therefore, the signal from the level detector 11 at the next stage of the phase detector 100 may form an erroneous signal as shown in FIG. 2C due to the beat signal. There is a risk of erroneous identification.

The above-mentioned malfunction is common to systems that utilize the frequency swept wave response of a resonant circuit, and also occurs in systems that use a linear detector or a square law detector in place of the phase detector 10, for example.

Further, when an impulsive noise signal is often induced in the transmitting/receiving antenna 3, and the distance between the transmitting/receiving antenna 3 and the response device 4 is large and the response signal is weak, the amplitude of this response signal and the noise signal The amplitude may be almost the same.

Since there is no significant difference in the detection characteristics of the phase detector 10 for these two signals, the detection output includes a noise component as well as a response component.

Since this noise component is also converted into a binary signal by the level detector 11 in the same way as the response component, a noise pulse is generated in addition to the response pulse, resulting in an error in signal processing.

It is known that this impulsive noise signal can be removed as described below with reference to FIGS. 3 to 5.

That is, by effectively utilizing the characteristics of the beat signal obtained by detecting a high-speed sweep frequency response signal of a resonant circuit with an extremely high sharpness (Q) using ceramic or crystal, it is possible to eliminate noise. It performs separation.

The pulse train obtained by binarizing this beat signal is
The generation interval changes at a predetermined rate, whereas the pulse train obtained by binarizing the noise component detected from the impulsive noise signal has a random generation interval and no characteristic.

For example, for a ceramic resonant circuit, the number of pulses corresponding to the response component is, for example, 4 to 5 in a period of about 1 to 1.5 ms, and the generation interval changes in accordance with the temporal change in the frequency of the sweep wave. However, the number of pulses corresponding to the impulsive noise component is 1 to 2, and their generation intervals are random.

Therefore, in order to detect the frequency and swept wave response of the resonant circuit, the detection output (see FIG. 4a) of the detector 21 for detecting the output signal of the resonant circuit is led to the bandpass wave generator 22.

This P-wave device 22 has a passband center frequency set near the frequency of a predetermined number of waves, for example, the fourth wave, among the beat signals included in the input response signal, and is set to have a frequency characteristic as shown in FIG. 5, for example. ing.

Therefore, the wave filter 22 attenuates as much as possible the relatively high frequency noise components contained in the detected output, and passes the beat component of the response component contained in the detected output.

In this case, the waves on the lower frequency side than the fourth wave have larger amplitudes, so they are attenuated a little to the same amplitude as the fourth wave, and the waves on the higher frequency side are greatly attenuated, as shown in Figure 4b. A P wave output b like this is obtained.

This wave output is amplified by an amplifier 23 and then converted into a binary signal by a pulse generator 24, such as a Schmitt circuit, to obtain a pulse output C as shown in FIG. 4C.

This pulse output C is supplied to a noise pulse removal circuit 25, and impulsive noise pulses are removed.

That is, in the noise pulse removal circuit 25, the input pulse c is supplied to one input terminal of an AND gate 26, and the clock pulse from the clock Hals generator 27 is supplied to the other input terminal of the AND gate 26.

This clock pulse generator 27 has a cycle narrower than the width of the pulse C4 obtained by extracting a predetermined number of waves, for example, the fourth wave, from the beat signal contained in the detected wave output and converting it into a binary signal. For example, a high speed clock pulse d as shown in FIG. 4d is generated.

An AND output e as shown in FIG.

The number of stages of this shift register 28 is at least the pulse train C1, C2, C3, C4, which is obtained by extracting the response component contained in the detection output and then converting it into a binary.
This is the number obtained by dividing the time interval Cn (C1 to C4 in this example) by the period of the clock pulse d.

Since the clock pulse d is supplied to the shift register 28 as a shift pulse, the AND output e is introduced into the shift register 28 and shifted.

On the other hand, the generation intervals of the pulse trains C1 to C4 are formed by a resonant circuit with an extremely high quality Q.

Although it changes in response to the temporal change in the frequency of the swept wave for a response device (not shown), since the sweep speed of the swept wave is kept constant, the generation intervals of the pulse trains C1 to C4 are at a predetermined rate. It has characteristics that change with.

Therefore, for the AND output e of the pulse train C1 to C4 and the clock pulse d, the number corresponding to the width of each pulse of the pulse train C1 to C4 is determined in advance in accordance with the change in the generation interval of each pulse of the pulse train. Occurs at intervals.

and a shift register 28 to which the AND output e is guided.
Among the outputs from each stage, the tap outputs taken out from, for example, different predetermined numbers of stages at intervals corresponding to the generation interval known in advance as described above are led to OR games 29, 30, 31, and 32, respectively. ing.

Therefore, if a state in which pulses are stored in the shift register 28 at predetermined intervals occurs, the OR gates 29, 30, 31, and 32 will output an OR output f as shown in FIG. 4f, g, h, and i. ,g+h,i are generated.

These OR outputs f to i are logically multiplied by an AND gate 33, and an AND output j is obtained from the AND gate 33 as shown in FIG. 4J.

That is, as described above, the noise pulse removal circuit 25 determines whether the generation interval of each pulse of the output pulse train of the pulse generation circuit 24 changes at a predetermined rate, and determines a pulse train having regular interval changes. When this happens, one pulse output (AND output j) is generated assuming that there is a response component, and a pulse train in which the change in generation interval is not normal is removed as a noise pulse.

As described above, according to the signal detection device, out of the detected output of the detector 21, the frequency side lower than the frequency of the predetermined wave of the beat signal included in the response component is passed, and the beat signal and noise on the higher frequency side are passed. After removing the signal, the passing signal is converted into a binary signal.

Then, a response signal and an impulsive noise signal are determined by determining whether the generation interval of this binary pulse train changes at a predetermined rate, and one output signal is detected for each response signal. I am getting Kapals.

Thus, accurate signal processing can be performed for each response, improving the reliability of the identification or detection system.

However, according to the signal detection device, the OR gates 29, 3
It is not necessary that the pulse widths of the OR outputs f, g, and h of 0 and 31 are larger than the pulse width of the OR output i of the OR gate 32;
, 30. If a pulse corresponding to the pulse width of the OR output i is present as the output of the AND gate 31, an AND output j appears at the AND gate 33.

This means that the frequency sweep period for the transponder (e.g. 1 to 1.5
This means that in a noisy environment in which a period of time (ms) includes several narrow pulses, there is a high probability that an erroneous output signal will appear in the AND circuit 33 even though the intervals at which the noise pulses are generated are random.

In order to improve this drawback, the OR gates 29 to 32 may be omitted and all of these inputs may be guided to the AND gate 33 to perform pulse width verification.

However, the pulse width and pulse interval of the pulse trains C1 to C4 fluctuate due to the phase shift and level fluctuation of the entire system, and in consideration of the permissible value of this fluctuation, it is necessary to provide a margin for the pulse width verification.

In this case, the response judgment output pulse j becomes considerably narrower than the pulse width of the actual response signal, and there is also a high probability that an erroneous output signal will be formed in the above-mentioned noisy environment.

The present invention has been made to eliminate the above-mentioned drawbacks, and is designed to more reliably separate a response signal and a noise signal in a received signal in an identification system or detection system that utilizes the frequency sweep response of a resonant circuit. The purpose of the present invention is to provide a signal detection device capable of extracting only the signal.

That is, the present invention is characterized by detecting the frequency of the beat signal output from the P-wave device, generating an output when it corresponds to a previously known frequency, and determining the output generation interval pattern. .

An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 6, the detector 21, band-pass amplifier 22, and amplifier 23 are the same as those shown in FIG. 3, so their explanations will be omitted.

The output beat signal of the amplifier 23 (see FIG. 7a) is led to a frequency measuring circuit 61 for detecting frequency components, where the frequency of each beat signal is measured.

This frequency measurement can be calculated by pulsing each signal at the zero crossing point and measuring the pulse width.

This measurement output is led to a frequency determination circuit 62, which determines to which of the plurality of beat frequencies that should originally be obtained the measurement result corresponds.

Then, according to the determination result, an output pulse is generated at one of the plurality of output terminals.

The plurality of output terminals are respectively connected to pulse generation circuits 631 to 63n for generating output pulses (frequency-corresponding pulse signals) having mutually different pulse widths at the time of pulse input.

Therefore, output pulses having different pulse widths are sequentially generated as shown in FIG. 7 b1 to bn according to the frequency determination result.

On the other hand, the output beat signal of the amplifier 23 is guided to the first and second pulsing circuits 64 and 65, respectively. The signals are respectively converted into pulses by pulsing circuits 64 and 65.

The respective outputs of the first and second pulsing circuits 64 and 650 (see FIGS. 7c and d) are respectively guided to first and second delay circuits 66 and 67, each of which is comprised of, for example, a shift register.

Each output pulse (the seventh
C1, C2..., d1, d2...) are respectively delayed by predetermined times T1 to Tn so that the timings match the output pulses of the pulse generation circuits 631 to 63n, respectively. Derived from each output terminal corresponding to the delay time.

Each of the delayed outputs and the outputs of the corresponding pulse generating circuits 631-63n are led to a first matching circuit, that is, AND gates 681-68n, and are ANDed.

Therefore, corresponding pulse outputs as shown in FIG. 7 e1 to en are obtained from the AND gates 68 and 68n,
These pulse trains correspond to the signal time sequence of the beat signal.

In order to determine the pattern of this pulse train, the output pulses of the AND gates 681-68n are respectively guided to third delay circuits 691-69n, each of which is comprised of, for example, a shift register.

Each delay time of the third delay circuits 691 to 69n is determined in advance so that the timing of each output pulse coincides with each other.

The respective outputs of the third delay circuits 691 to 69n are guided to a second matching circuit 70 consisting of, for example, an AND gate, where a match is made, and a response judgment output pulse (see FIG. 7f)
is obtained.

That is, according to the signal detection device as described above, the wave detector 22
After measuring the frequency of the output beat signal and performing frequency judgment to derive the signal component, at the same time measuring the level of the output beat signal and deriving the signal component, and taking the logical product of these derived outputs, The response is determined by determining the signal generation pattern.

Therefore, the response signal and noise signal in the received signal can be separated more reliably and only the response signal can be extracted.

[Brief explanation of drawings]

Fig. 1 is a configuration explanatory diagram showing an identification system having a conventional signal detection device, Fig. 2 a to e are waveform diagrams shown to explain the operation of Fig. 1, and Fig. 3 shows a conventional signal detection device. 4A to 4J are waveform diagrams shown to explain the operation of FIG. 3, FIG. 5 is a diagram showing the characteristics of the bandpass wave generator shown in FIG. FIGS. 7a to 7f are waveform diagrams shown to explain the operation of FIG. 6, which is a configuration explanatory diagram showing one embodiment of the signal detection device according to the invention. 21... Wave detector, 22... Wave wave detector, 61... Frequency measurement circuit, 62... Frequency determination circuit, 631-63n... Pulse generation circuit, 69, - 69n... Delay circuit, 70...
matching circuit.

Claims (1)

[Claims] 1. A detector that detects the output of the resonant circuit in order to detect the frequency swept wave response of the resonant circuit and derives an output signal whose frequency changes toward higher frequencies with the passage of time; a first pulse signal that generates a pulse signal that continues for a period of time that is greater than or equal to a positive level of or less than or equal to a predetermined negative level;
a second pulsing circuit; and first and second pulsing circuits that delay the pulse signals outputted from the first and second pulsing circuits by a predetermined time period when the level of the detector output signal is on the positive side or the negative side, respectively. The delay circuit detects the frequency from the time when the detector output signal is on the positive side or the negative side, and when this frequency is determined to be the frequency of the response signal that should originally be obtained, the pulse width is determined as the determination result. a pulse generation circuit that derives correspondingly different frequency-compatible pulse signals; and a plurality of pulse generation circuits that match the frequency-compatible pulse signals output from the pulse generation circuit with the corresponding output pulse signals of the first and second delay circuits. The first matching circuit and the matching circuit output to which a frequency corresponding pulse signal corresponding to the low frequency component of the detector output signal is added are the matching circuit output to which a frequency corresponding pulse signal corresponding to the high frequency component is added. A signal detection device comprising: a third delay circuit that delays each of the outputs of the first matching circuit so as to have a more uniform delay time; and a second matching circuit that matches the outputs of the third delay circuit. .