JPH01140277A - Non-contact id card identifying device - Google Patents

Abstract

PURPOSE:To prevent a malfunction due to an impulsive noise by attenuating the level of an inputted signal for a constant period at the time of detecting a signal exceeding a preset reference level. CONSTITUTION:A digital data signal transmitted from an ID card is received by an antenna 1. The output of a demodulating part 6 is supplied to a BPF 8 and an impulse detector 21. The reference voltage VB of the comparator CO of the detector 21 is set slightly higher than a noise level having no carrier input and an original signal level. Accordingly, only the impulse exceeding the reference voltage VB turns on the comparator CO to output an impulsive signal. A timer part 22 shapes the detected output to the pulse signal of a constant time to transmit to a level control part 23 disposed between the BPF 8 and a detecting circuit 9. In such a way, even when there is the output of the BPF 8 due to the impulsive noise, the output of the detecting circuit 9 is deteriorated to prevent the malfunction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field 1] The present invention relates to a contactless ID card identification device that transmits a digital data signal using a high frequency carrier wave.

[Background Art 1] This type of ID card identification device is installed on a gatepost B as shown in FIG.
The output signal from the rftA is used to open and close the gate. Therefore, I.D.D.
The card has a built-in transmitting device for transmitting digital data, and the ID card identification device jlA has a built-in reception discriminator that receives a digital data signal superimposed on a carrier wave and outputs the signal.

FIG. 11 shows a conventional example of a reception discriminator used in a device for contactless transmission of digital data signals.

In this device, a carrier wave is pulse-modulated at a first frequency f2 for digital data "1", and a so-called subcarrier FSK is pulse-modulated at a second frequency f2 for digital data "0". Transmission is carried out using a modulation method.The receiving identification device is generally of the superheterogeneous gain method, and FIG. 11 shows one of the single superheterogeneous gain method.

In FIGS. 11 and 12, fpJl, which corresponds to digital data (FIG. 12(a)), is sent from the ID card.
A carrier wave (fpJl2 diagram (b)) modulated at the second frequency Ltrz is received by the antenna 1, the received signal from the antenna 1 is amplified by the high frequency amplification section 2, and the high frequency amplified output and the carrier wave frequency of the received signal are and the output of a local oscillator 4 which generates a signal with a frequency separated by an intermediate frequency from the oscillator 4 in a mixer 3 to convert it into an intermediate frequency (FIG. 12(C)). Further, the output of the mixer 3 is amplified by an intermediate frequency amplifying section 5, and the filtered output is sent to a demodulating section 6 to which an AGC circuit 7 adds an AGCfi function.
AM demodulation is performed at the 1st. “1” at the second frequency f,, f2
″.

Obtain a so-called FSK signal indicating 0''(#S12 figure (d))
.

This demodulated output is passed through a band pass filter (hereinafter referred to as BPF) 8 at 8 which extracts the respective frequencies f, , f2.
b. Each of the BPFs 8a and 8b is generally composed of a tank circuit or an active filter.

And the BPF8m, 8b output (Fig. 12(e)) is
After being detected by the detection circuit 9 at 9 b (Fig. 12 (
f)), low pass filter (hereinafter referred to as LPF) 10m
.

10) After integrating the waveform with + and removing ripples (#
S12 (g)), the comparator 11a * 11b compares with the reference voltage and reproduces the original digital data signal (12th
Figure (11)). Note that each circuit 8 to 11 after the demodulation section 6 constitutes a tone detection section.

If such a receiver identification device is installed inside or outside a building,
Depending on the environment, it may be affected by electromagnetic noise generated from automobiles, machine tools, other electronic devices, etc. Generally, these noises are often impulsive noises, and their pulse width is, for example, 200 to 300 μs or less, which is extremely short compared to the time width of transmitted data (for example, several ms).

Interference due to such impulsive noise causes reception identification Hf.
The phenomenon when added to i'i is shown in the 1:1 S13 diagram.

At the output of the intermediate amplifier 5, impulse noise (Fig. 13(b)
)), the waveform becomes a waveform on which surge-like noise is superimposed, as shown in FIG. When this signal is input to the receiver 1i11 section 6, the pulse width of the surge generation portion is extremely short as described above, and the AGC of the AGC circuit 7 whose time constant is set in accordance with the normal modulation signal does not follow it, so The result is a demodulated waveform that includes impulses higher than the signal level ((d) in the same figure). Furthermore, such a signal is BP
When you reach F8, you will experience the following symptoms: In other words, B
t'I"8 is generally shown in the same figure (e
), it generates ringing at the modulation frequency, i.e., f2, which persists for a time that depends on the passband width of BPF8. Shideori (same figure (
f) (g)), if it exceeds the reference voltage of the comparator 11, an erroneous data pulse will be generated ((11) in the figure).

Here, if the setting of the reference voltage of the comparator 11 is lowered, the original signal can be received with high sensitivity, but this will make it easier to generate the above-mentioned erroneous data pulses, and if the setting of the reference voltage is increased, erroneous data pulses will occur. However, a contradictory problem arises in that the reception sensitivity of the terminal's signal decreases.

Furthermore, when the level of the carrier wave to be received is extremely high, the moment the carrier wave rises as shown in Fig. 13(c),
A C and C may not be able to follow up, resulting in an impulse-like demodulated waveform as shown in (d) of the same figure, and erroneous data pulses may be generated as described above ((e) to (h) of the same figure).
).

[Objective of the Invention 1] The present invention has been provided in view of the above-mentioned points, and provides a contactless ID card identification device that aims to reduce malfunctions caused by impulsive noise without reducing sensitivity. It is something to do.

[Disclosure of the Invention 1 (Structure) The present invention consists of a combination of signals that are pulse-modulated at different frequencies corresponding to digital data "1" and "()" after transmitting an unmodulated carrier wave for a certain period of time. A device for receiving a data signal, which performs AM demodulation on the data signal, decomposes it into two frequency components corresponding to "1" and 0" of digital data, and extracts the original digital data from the level of the decomposed signal. In a contactless ID card identification device having a tone detector for reproducing, the demodulated signal has a noise level that is higher than either the noise level when there is no carrier wave or the signal level demodulated from a carrier wave modified at a different frequency. A high preset reference level is provided in the tone detection section, and the tone detection section is provided with attenuation means that attenuates the level of the input signal for a certain period of time when a signal exceeding the reference level is detected, When a signal exceeding a preset reference level, which is higher than either the noise level without a carrier wave or the demodulated signal level of a carrier wave modulated at a different frequency, is detected from the demodulated signal, the attenuation means The present invention is characterized in that the level of the input signal is attenuated for a certain period of time, and in particular, the level of the signal is reduced by 1! for a certain period of time to prevent malfunctions due to impulsive noise.

(Example 1) Hereinafter, an example of the present invention will be described with reference to the drawings. In this embodiment, impulsive noise is detected from the demodulated output, and the signal level at any part after the BPF is reduced or eliminated for a certain period of time to suppress the generation of erroneous data pulses.

The first leap shows the overall block diagram, which includes a conventional configuration including an impulse detection section 21, a timer section 22, and a level control section 23.
a and 23b are added, and the other configurations are the same as the conventional one, so only the gist will be explained. The output of the converter 14 section 6 is connected to the BPF 8 as well as the impulse detector 21.
is also connected. FIG. 2 shows a specific circuit of the impulse detection section 21. As shown in FIG. Here, since the impulse waveform is higher than the noise level or the main signal level when there is no carrier wave input, the reference level of the comparator CO, that is, the base i
I! Impulses can be detected by setting the voltage VB to be slightly higher than the noise level and the signal level when no carrier wave is input. In other words, as shown in Fig. 3, the input signal swings around the reference voltage ■^, and since the reference voltage vB is higher than the noise level or the main signal level when there is no carrier wave input, this reference voltage VB Only impulses that exceed the threshold turn on the comparator CO, and output an impulse-like signal as shown in FIG. 3(b).

Next, the timer part 22 uses a monostable multi-pie break or the like to output the impulse detection output for a certain period of time (see Figure 5).
)) into the pulse output. The output of the timer section 22 is input to a level control section 23 provided between the BPF 8 and the detection circuit 9, and this level control section 23 has, for example,
When the input is at H level, it operates to reduce or eliminate the level of the signal passing through it. FIG. 4 shows a concrete circuit of the level control fi23, with a transistor T, a resistor R
, ~R, etc. In addition, the transistor Tr
In addition to +, a diode, FET1 analog switch, etc. may be used.Here, when the control input is at L level, the ratio of the signal output to the signal input is expressed by the following equation.

Issou J"bi Garshi □ Signal input R, +R2 In other words, when there is no control input, a predetermined signal is output. Furthermore, when the control input is at H level when impulse noise is detected, the level decreases as shown by the following equation.

Issa No. IL2m---Private dUb Signal power R1+(R2//R3) Therefore, R3=
When it is 0, the transistor Trl is on and the signal output is L.
level.

Detection circuit 9 and LPF connected after level control section 23
The IO1 comparator 11 and the like operate in the same manner as conventional ones. Here, when impulsive noise is input, an impulsive signal is output from the demodulator 6 (FIG. 5(d)), and the impulse detector 21 (Figure 5(e))
, the timer part outputs 22 outputs as shown in FIG. 5(f) using the impulse output. The level control section a 23 is driven by the output of this timer section 22, and even if there is a BPF8 output due to impulse noise as shown in FIG. 5(g), the detection output will be as shown in FIG. 5(h). , lower the detection output level. Further, control may be performed so that the level disappears here. Therefore, since the LPFIO output is lower than the reference voltage of the comparator 11, an erroneous data pulse is not generated (or is made less likely to occur) as shown in FIG. 5(j). Incidentally, the impulse detection section 21 and the timer ff1s2
2, the level control unit 23, and the like constitute liquid reduction means that reduces the signal level for a certain period of time when impulsive noise is input.

In the above description, the level control unit 23
Although the explanation has been made on the assumption that the detection circuit 9 is located between the detection circuit 9 and the detection circuit 9, it goes without saying that the same operation can be performed even if the detection circuit 9 and the detection circuit 9 are located after the LPFIO.

Next, the time tm for changing the signal level will be explained. In general, when a bandpass filter is subjected to an impulse force, ringing occurs in the bandpass filter's passing frequency after a certain response time, as shown in FIG. This duration and delay time depend on the bandwidth, cutoff characteristics, etc. of the BPF. Therefore, if the BPF is fixed, it is uniquely determined.

Therefore, after detecting impulsive noise, the sum of this delay time + ringing duration is set as tl, and this time t1
By lowering the signal level for a longer period of time, the impulse response of the BPF can be ignored. That is, let tl< be -.

On the other hand, if we consider the case where the carrier wave level is large and an impulse-like thing appears in the demodulated waveform at the beginning of the idle period t^ (Fig. 5(e) and (d)), the signal level is lowered (
If the period of time - is made shorter than the idle period rlflt^, the level control section 23 is controlled by the output of the timer part 22 in the same way as described above when impulsive noise is input, and the detection output ( By lowering the level in FIG. 5(h)), it is possible to correctly reproduce the first data after the idle period L without reducing the sensitivity. Therefore,
Set Lm<Lx. Note that the idle period t is
It is set longer than the time tACC required for the demodulated output to stabilize after the operation of the AGC circuit 7 stabilizes from the start of the non-modulated carrier wave. Therefore, it is set as EAcc<tA.

(Embodiment 2) In Embodiment 2, impulsive noise is detected from the demodulated output and the reference voltage of the comparator is increased for a certain period of time to suppress the generation of erroneous data pulses. 7th
The figure shows a block diagram thereof, and includes the same impulse detection section 21 and timer section 22 as in the previous embodiment, and a reference voltage generation section 24.
is added. The output from the timer section 22 is input to a reference voltage generating section 24, and a specific circuit of this reference voltage generating section 24 is shown in FIG. The reference voltage generating section 24 is composed of a transistor Tr2, resistors R1 to R7, etc.
When the level is high, the normal reference voltage VRI is generated and the input is high.
At the level, the resistor R7 operates to generate a reference voltage VR2 higher than the reference voltage VRI. Note that a diode, FE'r, is used instead of the transistor Tr2.
, an analog switch, etc. may also be used.

FIG. 9 shows an operation waveform diagram, and when impulsive noise is detected (FIG. 9(d)) as in the previous embodiment, the output of BPF8 generated by the impulsive noise (FIG. 9(f)) is detected. It is input to circuit 9 and detected ((g) in the same figure), and further L
It is input to the comparator 11 via PFIO, but since a pulse of attenuation is generated for a certain period from the timer part 22 (9th
(e)), by increasing the reference voltage of Lm reference voltage generation ff1s24 from VRI to ■2□ for a certain period of time by this pulse, no signal is output from the comparator 11, and therefore,
No erroneous data pulse occurs (#IJ9 figure (i)). The time tm for changing the reference voltage is the sum of the delay time of the BPF 8 + the ringing duration when impulsive noise is input, 1. as in the previous embodiment. Set it longer and BP
I am trying to ignore the impulse response of F8 (tl
＜〇）. In addition, the impulse detection section 21 and the timer section 22
The first reference voltage generating section 24 and the like constitute an attenuation means.

In addition, even if the carrier wave level is large and an impulse-like thing appears in the demodulated waveform at the beginning of the idle period t^, the time to raise the reference voltage is set to −1 during the idle period.
By making it shorter, it is possible to correctly reproduce the data from the beginning after the idle period without reducing the sensitivity (tact^) as in the previous embodiment.Furthermore, as in the above, the idle period tA is A from the start of the unmodulated carrier wave.
It is set longer than the time tACC required for the demodulated output to become stable after the operation of the GC circuit 7 stabilizes. Therefore,
It is set as tAcc<tA.

[Effect of the invention 1 As described above, the present invention transmits an unmodulated carrier wave for a certain period of time, and then pulse-modulates the signals at different frequencies corresponding to the dinotal data '1' and 1'0'. A device for receiving a data signal consisting of a In a contactless ID card identification VC device having a tone detection section for reproducing data, it is determined from the demodulated signal that the noise level when there is no carrier wave and the signal level when a carrier wave modulated at a different frequency is demodulated. A high preset reference level is provided in the tone detection section, and when a signal exceeding the reference level is detected, the tone detection section is provided with attenuation means that attenuates the level of the input signal for a certain period of time. , when a signal exceeding a preset reference level, which is higher than either the noise level when there is no carrier wave or the signal level demodulated from a carrier wave modulated at a different frequency, is detected from the demodulated signal, the attenuation means By attenuating the level of the input signal for a certain period of time, in particular, by causing the level of the signal to collapse for a certain period of time, it is possible to prevent malfunctions due to impulsive noise without reducing sensitivity. It is.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a specific circuit diagram of the impulse detecting section of the above, Fig. 3 is an explanatory diagram of the operation of the impulse detecting section of the above, and Fig. 4 is a level control diagram of the same as above. 5 is an explanatory diagram of the same operation as above, FIG. 6 is an explanatory diagram of the operation in the impulse response of the BPF as above, FIG. 7 is a block diagram of another embodiment of the same as above, and #S8 is the same as above. 9 is a diagram explaining the operation of the same as above, FIG. 10 is a diagram showing the state of use of the same as above, FIG. 11 is a block diagram of the conventional example, and FIG. 12 is the operation of the same as above. The explanatory diagram, FIG. 13, is an explanatory diagram of the operation when there is impulsive noise as described above. 7 is an AGC circuit, and 8 is a band pass filter. Agent Patent Attorney Ishi 1) Ai Shichi

Claims (1)

[Claims] (1) A device that receives a data signal consisting of a combination of pulse-modulated signals at different frequencies corresponding to digital data "1" and "0" after transmitting an unmodulated carrier wave for a certain period of time, The above data signal is A
A non-contact ID card identification device having a tone detection unit that performs M demodulation, decomposes digital data into two frequency components corresponding to “1” and “0”, and reproduces the original digital data from the level of the decomposed signal. A preset reference level higher than both the noise level when there is no carrier wave and the signal level obtained by demodulating a carrier wave modulated at a different frequency is provided in the tone detecting section from the demodulated signal, and the tone detection unit detects the reference level. A non-contact ID characterized in that the tone detection section is provided with attenuation means that attenuates the level of the input signal for a certain period of time when a signal exceeding the level is detected.
Card identification device. (2) In the tone detection section, a bandpass filter is used to decompose the signal into two frequency components, and a fixed period of time during which the level of the signal after the bandpass filter is attenuated is defined as tm, and an unmodulated carrier wave is sent out before the digital data. The time required for the operation of the AGC circuit to stabilize and the demodulated output to stabilize from the start of reception of the unmodulated carrier wave is defined as the AGC rise time t_A_G_C, and the response to the impulse input of the above bandpass filter is defined as the idle time t_A. The sum of the delay time and ringing duration at t_1 is the impulse response time t_1, and these tm
, t_A, t_A_G_C, t_1, tA_G_C<
Claim 1, characterized in that the relationship is set to t_A t_1<tm<t_A.
The contactless ID card identification device described in Section 1. (3) The contactless ID according to claim 2, characterized in that the reference voltage of the comparator that outputs the original digital data is increased by tm for a certain period of time as the signal level attenuation means.
Card identification device.