JP5245860B2 - Non-contact communication device and demodulator - Google Patents

Description

  The present invention relates to a contactless communication device that performs close proximity wireless communication with a contactless information medium such as a contactless IC card, a receiving device thereof, and the like.

  In recent years, contactless IC cards have been widely used in fields such as electronic money and electronic tickets. The non-contact IC card system is composed of a reader / writer and a non-contact IC card, and the non-contact IC card activates the built-in IC by a magnetic field radiated from the reader / writer. By modulating the amplitude of the radiated magnetic field, communication from the reader / writer to the non-contact IC card is realized, and communication from the non-contact IC card to the reader / writer is not performed with respect to the magnetic field radiated by the reader / writer. This is done by switching the load in the contact IC card and detecting this by the reader / writer (load modulation).

  Communication between the contactless IC card and the reader / writer becomes impossible even within the communicable distance range due to the positional relationship between the reader / writer and the contactless IC card and the relationship between the resonance frequencies of both antennas. It is known that a region (null point) occurs. In particular, a null point may occur when the card is in close contact with the antenna, but this is not desirable due to the usage characteristics of the non-contact IC card.

  In general, as a method for suppressing the null phenomenon, a method of controlling the output power and impedance of the transmission circuit on the reader / writer side when the occurrence of the null phenomenon is detected (determined as unreceivable) has been proposed. For example, this is done by switching the position where the null point is generated by switching the impedance of the transmission control unit. However, in this method, since control such as impedance switching is performed when it is determined that reception is impossible, if a null point occurs during the communication processing sequence, it is necessary to re-execute the communication processing sequence from the beginning. As a result, there is a problem that the communication processing performance deteriorates.

  For the above problem, for example, methods described in Patent Documents 1, 2, and 3 have been proposed as a method in which processing overhead (deterioration of communication processing performance) does not occur (due to detection of occurrence of a null phenomenon and impedance switching control). ing. When a non-contact IC card performs load modulation, even if amplitude modulation cannot be detected by the reader / writer, the phase is also modulated at the same time, so this is detected by the reader / writer. Therefore, it is intended to suppress the occurrence of the null point problem (to enable normal reception (demodulation) processing).

JP 2005-318385 A JP 2006-344228 A JP 2007-12076 A

  However, all of these proposals in Patent Documents 1 to 3 provide a phase modulation detection means separately from the conventional amplitude modulation demodulation means in order to detect the phase, and synthesize these output signals. However, there is a problem that the circuit scale and power consumption are increased because the demodulated output is to be obtained.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a non-contact type communication device, a receiving device, and the like that can perform normal communication by solving a null point problem with a relatively small circuit scale without lowering communication processing performance. It is.

  The contactless communication device of the present invention receives a load modulation signal from a contactless information medium, detects an envelope of the received signal and outputs an envelope, and an amplifier that amplifies the envelope detection output, In a non-contact type communication device having a comparator for inputting and binarizing the amplifier output, detecting whether or not the distance from the non-contact type information medium is equal to or less than a predetermined distance based on the envelope detection output And a position detection control means for controlling the hysteresis width of the comparator according to the detection result.

  For example, in the comparator, a switch is provided in series with a positive feedback resistor, and the position detection control unit performs ON control of the switch when a distance from the non-contact information medium is a predetermined distance or less. Make the hysteresis of the comparator work.

  The above non-contact type communication device cannot be correctly decoded because the input signal waveform to the comparator is greatly distorted when the distance between the antenna of the non-contact type communication device and the IC card is close, and the duty ratio of the comparator output is shifted. This solves the null point problem.

  For this purpose, the position detecting means is provided to control the hysteresis width of the comparator. For example, as described above, when the distance from the non-contact information medium is equal to or less than a predetermined distance, control is performed so that hysteresis of the comparator works. Even if the waveform of the input signal to the comparator is greatly distorted somewhere within the predetermined distance, the hysteresis of the comparator works, so that the duty ratio of the comparator output can be prevented from shifting and decoding can be performed correctly.

Further, for example, the gain of the amplifier is further controlled by the detection output of the position detection control means.
For example, the amplifier is provided with two negative feedback resistors in parallel and a second switch connected in series with one of the two resistors. When the distance from the contact-type information medium is equal to or less than a predetermined distance, the second switch is also turned on to lower the gain of the amplifier.

  Even if the waveform of the input signal to the comparator is very distorted and correct decoding may not be possible even if the hysteresis of the comparator works, reduce the amplitude of the input signal waveform by reducing the gain of the amplifier in the previous stage. Thus, the duty ratio of the comparator output can be prevented from shifting and decoding can be performed correctly.

  According to the non-contact type communication device, the receiving device, etc. of the present invention, in the non-contact IC card system, it is normal to suppress the occurrence of the null point problem with a relatively small circuit scale without reducing the communication processing performance. To be able to communicate.

1 is a configuration diagram of a non-contact IC card reader / writer according to Embodiment 1. FIG. It is an example of the input signal waveform to a detection circuit. It is an example of the output waveform (envelope detection output waveform) of a detection circuit. It is a figure which shows the antenna-IC card | curd distance characteristic of the direct current | flow component of an envelope detection output. It is a figure which shows the antenna-IC card distance characteristic of the amplitude of the AC component of an envelope detection output. It is a figure which shows an example of the AC component waveform of an envelope detection output. FIG. 6 is a configuration diagram of a non-contact IC card reader / writer according to a second embodiment.

Embodiments of the present invention will be described below with reference to the drawings.
Examples 1 and 2 will be described below.
FIG. 1 is a configuration diagram of a non-contact IC card reader / writer according to the first embodiment.

  The communication partner of the reader / writer is not limited to a card-type form such as a non-contact IC card, but may be, for example, a mobile phone with a built-in IC card function, a tag-type (IC tag), or a watch-type form. These are collectively referred to as non-contact information media. Further, the reader / writer is not limited to the non-contact IC card / reader / writer, and is collectively referred to as a non-contact communication apparatus. However, in the following description, a non-contact IC card and a non-contact IC card reader / writer are taken as an example. In some cases, the non-contact IC card is omitted and referred to as an IC card.

  The non-contact IC card reader / writer according to the first embodiment shown in FIG. 1 includes a control unit 1, a transmission circuit 2, an antenna 3, and a detection circuit 4, an amplifier 5, a comparator 6, a card position detection unit 7 and the like as a demodulation unit. Have. Among these configurations, the feature of the present example is mainly that the card position detection unit 7 is provided, the comparator 6 can operate as a so-called “hysteresis comparator”, and the output of the card position detection unit 7 By providing the switch SW1 that is turned on / off, the comparator 6 is switched between a mode that operates as a “hysteresis comparator” and a mode that does not.

Therefore, the configuration other than these may be substantially the same as the conventional configuration, and will be briefly described below.
The control unit 1 is a CPU / MPU or the like, and controls data transmission / reception processing with a non-contact IC card. That is, arbitrary transmission data is sent to the transmission circuit 2, and the transmission data is wirelessly transmitted to the IC card by the transmission circuit 2 and the antenna 3. In addition, response data (demodulated signal) obtained from the demodulator from the IC card is input, and predetermined data reception processing is executed.

The transmission circuit 2 modulates the magnetic field in accordance with the transmission data input from the control unit 1 and radiates it from the antenna 3 to wirelessly transmit the transmission data to the IC card.
The response from the non-contact IC card is a state in which a non-modulated magnetic field is output from the transmission circuit 2 and the load modulation by the non-contact IC card is detected by the detection circuit 4 (the envelope of the load modulation signal is detected). ) The envelope detection signal is amplified by the amplifier 5, binarized by the comparator 6 as a binarization circuit, and input to the control unit 1.

  The waveform of the magnetic field that is load-modulated by the non-contact IC card (input signal waveform to the detection circuit 4) is, for example, as shown in FIG. 2 is actually a waveform in which a non-modulated signal (for example, a carrier wave having a frequency of 13.56 MHz) from the transmission circuit 2 is load-modulated as shown in FIG. 15 of Patent Document 3, for example. In FIG. 2, the carrier wave is omitted.

The detection circuit 4 detects an envelope of the load-modulated magnetic field waveform. Therefore, the output waveform (envelope detection output waveform) of the detection circuit 4 for the example of FIG. 2 is as shown in FIG. As shown in FIG. 3, the output waveform of the detection circuit 4 is a waveform obtained by extracting the envelope of the signal shown in FIG. 2, consists of an AC component of the amplitude Vm shown, the DC component of the voltage V _H.

  The AC component (signal of amplitude Vm) of the envelope is amplified by the amplifier 5, converted into a binary value of “1” and “0” by the comparator 6, and decoded by the control unit 1. Response data from the IC card is reproduced.

Here, the distance characteristic between the reader / writer antenna and the IC card of the DC component Vdc (corresponding to _VH in FIG. 3) of the envelope detection output depends on the card (medium), for example, as shown in FIG.

  As shown in FIG. 4, when the IC card is close to the antenna 3, the voltage is high because the proximity of the IC card increases the degree of coupling of the reader / writer with the antenna 3, resulting in a transmission circuit. This is because it becomes inconsistent with the output impedance of 2.

  On the other hand, the antenna-IC card distance characteristic of the amplitude Vm (its absolute value | Vm |) of the AC component of the envelope detection output is, for example, as shown in FIG. An example of the AC component waveform of the envelope detection output at the null point is shown in FIG.

  When FIG. 5 is seen, at first glance, even when the IC card is close to the antenna, there is sufficient amplitude to be binarized by the comparator 6 and it appears that the control unit 1 can perform decoding. However, the envelope detection signal should originally have a waveform that is close to a rectangular wave, but when the IC card is close to the antenna 3, the waveform is greatly distorted as shown in FIG. The duty ratio of the output is shifted, and as a result, the decoder (control unit 1) may not be able to decode correctly.

  Conventionally, the cause of the “null point problem” is that the load modulation result does not appear in the amplitude of the load modulation signal (envelope detection signal), as described in Patent Document 1, for example, It is known that the amplitude Vm becomes almost 0 (zero) (a state in which the amplitude change cannot be detected), but other than this, the duty ratio of the comparator output is shifted due to the distorted waveform as described above. Incorrect decoding is also known as one of the causes of the “null point problem” (null phenomenon).

This technique solves the “null point problem” that occurs when the envelope detection signal has a distorted waveform.
Therefore, in the present configuration shown in FIG. 1, by providing the card position detection unit 7, the card position detection unit 7 detects that the IC card is approaching and controls the hysteresis width of the comparator 6. As a result, even when such a distorted waveform is input to the demodulator, the duty ratio of the comparator output is not shifted, and the controller 1 (decoder) can correctly decode the duty ratio.

Hereinafter, the configuration of FIG. 1 (particularly, the configuration related to the card position detection unit 7 and the comparator 6) will be described in more detail.
First, the amplifier 5 may have a general amplifier configuration using an operational amplifier M1 as illustrated. That is, as shown in the figure, the output of the detection circuit 4 is input to the negative terminal (inverting input terminal) of the operational amplifier M1 through the capacitor C and the resistor R3, and a negative feedback resistor R5 is provided. The reference voltage Vref1 is applied to the + (plus) terminal of the operational amplifier M1 through the resistor R4. With this configuration, the envelope detection signal is amplified with a predetermined amplification factor and output to the comparator 6.

  In the comparator 6, the output of the amplifier 5 is input to the negative terminal of the operational amplifier M 2 through the resistor 6. The reference voltage Vref1 is applied to the + terminal of the operational amplifier M2 via the resistor R1, and a positive feedback resistor R2 is provided. However, a switch SW1 (analog switch or the like) is provided in series with the resistor R2, and the hysteresis of the comparator 6 works when the switch SW1 is in the ON state (connected state), but the switch SW1 is in the OFF state ( In the open state), there is no hysteresis of the comparator 6.

  Here, for example, the threshold level of the comparator 6 becomes level A shown in FIG. 6 when there is no hysteresis, and in the state where hysteresis works, the level is shifted by ± Vh as shown (levels B and C shown in the figure) from this level A. Is set to be Strictly speaking, the level A itself is also composed of two levels. Since these two levels are almost the same value, they are treated as one level here.

  The ON / OFF of the switch SW1 is controlled by the output of the card position detector 7. In this example, when the output of the card position detection unit 7 is ‘1’ (Hi level), the switch SW <b> 1 is in an ON state, and when the output is ‘0’ (Low level), the switch SW <b> 1 is in an OFF state (open state).

  The card position detection unit 7 includes an LPF (low-pass filter) 8, a resistor R7, and an operational amplifier M3. An output (envelope detection output) of the detection circuit 4 is input to an LPF (low-pass filter) 8. The LPF 8 removes the AC component of the envelope detection output and outputs a DC component Vdc. The output of the LPF 8 is input to the + terminal of the operational amplifier M3 via the resistor R7. A predetermined reference voltage (threshold voltage) Vref2 is applied to the negative terminal of the operational amplifier M3. Thus, the output of the operational amplifier M3 is Hi when the input value (DC component value) at the + terminal is higher than the threshold voltage value Vref2, and is Low when the input value is low.

  Here, since the DC component Vdc of the envelope detection output has the characteristics as shown in FIG. 4 as described above, the threshold voltage Vref2 of the operational amplifier M3 is set to an appropriate value (for example, the distance shown in FIG. 4). It is possible to set the output of the operational amplifier M3 to the Hi level in a state where the IC card is closer than a certain distance.

  That is, as shown in FIG. 4, the value of the DC component Vdc of the envelope detection output increases as the distance between the IC card and the antenna 3 decreases. Therefore, when the threshold voltage Vref2 is set to a value corresponding to the distance P shown in FIG. 4, for example, an area having a shorter distance than the corresponding distance between the antenna 3 and the IC card (the distance P shown in the drawing) , The left side of P), the output of the operational amplifier M3 becomes Hi level. On the other hand, in the region where the distance is longer than P (the region on the right side of P in the figure), the output of the operational amplifier M3 is at the low level. The value of the threshold voltage Vref2 (that is, the distance P) may be determined as appropriate by a designer or the like.

  In this way, the card position detection unit 7 detects the DC component of the output of the detection circuit 4 and compares the DC component voltage with the threshold voltage Vref2 corresponding to a predetermined distance set in advance, thereby obtaining an equivalent value. In particular, it detects whether the position of the IC card is equal to or less than a predetermined distance P. Based on the detection result, the switch SW1 of the comparator 6 is ON / OFF controlled.

  As described above, by controlling the switch SW1 of the comparator 6 by the output of the card position detection unit 7, in a state where the IC card is separated from the predetermined distance P (the output of the card position detection unit 7 is low level), The switch SW1 is controlled to be OFF and is in an open state. Therefore, the comparator 6 is not in a hysteresis state. On the other hand, when the IC card is closer to the antenna than the predetermined distance P, the output of the card position detection unit 7 becomes Hi level, the switch SW1 is ON-controlled and short-circuited, and the hysteresis of the comparator 6 works (functions). It becomes like this.

  When the hysteresis of the comparator 6 works, the hysteresis width Vh of the comparator 6 is expressed by the following equation (1) from the values of the connected resistors R1 and R2 when the Hi level output voltage of the comparator 6 is Vouth.

  The designer or the like may appropriately determine the resistance values of the resistors R1 and R2 so that the hysteresis width Vh becomes a value that is considered appropriate in consideration of the equation (1). For example, by setting the waveform shown in FIG. 6 to have a hysteresis width Vh as shown in the figure, the hysteresis of the comparator 6 works, so that the duty ratio of the output waveform does not collapse, and the decoder (control unit) It becomes possible to correctly decode in 1).

  In addition, in the conventional method of detecting the null point and controlling the impedance as described above, processing overhead occurs. However, in the above method, the impedance is not changed by detecting the null point, but the IC card has a certain distance. Since the switch SW1 is simply switched when it is closer (before the null point is reached), no processing overhead occurs.

  The hysteresis width Vh of the comparator 6 is a value corresponding to the above equation (1) when the switch SW1 is ON-controlled, but is substantially controlled to the hysteresis width Vh≈0 when the switch SW1 is OFF-controlled. Will be. From this, it can be said that the hysteresis width of the comparator 6 is controlled by the output of the card position detector 7.

  Further, the hysteresis of the comparator 6 is not always in a state where the hysteresis is applied, as shown in FIG. 5, the amplitude Vm of the AC component of the envelope detection output (its absolute value |) as the distance between the IC card and the antenna 3 increases. This is because Vm |) becomes smaller (that is, the amplitude of the waveform shown in FIG. 6 becomes smaller). In other words, when the distance is increased to some extent, the peak of the amplitude of the waveform shown in FIG. 6 does not exceed the threshold values of the levels B and C. Therefore, the distance is more than a certain distance (region on the right side from the distance P in the drawing). In, the threshold value of the level A is applied instead of the threshold values of the levels B and C. The distance P may be determined appropriately by a designer or the like, considering such a matter, and the value of the threshold voltage Vref2 may be set accordingly.

  Further, as described above, the waveform distortion that causes the duty ratio of the comparator output to deviate occurs when the IC card is close to the antenna 3. Even if a threshold is used, decoding can be performed correctly without any problem.

  As described above, according to this method, in the non-contact IC card system, there is no overhead for the communication protocol, and it is possible to substantially suppress the null phenomenon (null point generation) with a relatively small circuit scale. Thus, normal communication can be performed anywhere as long as the distance between the IC card and the antenna 3 is within the communicable range.

In the above, Example 1 was demonstrated.
Example 2 will be described below.
In the second embodiment, not only the hysteresis width of the comparator 6 but also the gain of the amplifier 5 in the previous stage is controlled by the output of the card position detection unit 7 to further improve the effect of suppressing the null phenomenon (null point generation). be able to. This will be described below with reference to FIG.

  Here, in FIG. 7, components that are substantially the same as those shown in FIG. 1 are given the same reference numerals, and descriptions thereof are omitted. 7, the configuration of the second embodiment shown in FIG. 7 is different from the configuration of the first embodiment shown in FIG. 1 in that the amplifier 10 shown in the figure is provided instead of the amplifier 5 and the output of the card position detector 7 is It is also used for controlling the gain of the amplifier 10.

  In addition to the configuration of the amplifier 5, the amplifier 10 further includes a resistor R8 and a switch SW2 in parallel with the negative feedback resistor R5. In other words, two negative feedback resistors are provided in parallel and a switch SW2 connected in series to either one of these two resistors is provided. The output of the card position detector 7 is used not only for the control of the switch SW1 but also for the control of the switch SW2. That is, in the configuration of FIG. 7, the output of the card position detection unit 7 is not only the switch SW1 that controls the hysteresis width of the comparator 6, but also the control of the switch SW2 connected in series to the feedback resistor R8 of the amplifier 10 in the previous stage. Also used for.

Similarly to the switch SW1, the switch SW2 is ON (short-circuited) when the output of the card position detection unit 7 is Hi level, and is OFF (opened) when the output is Low.
Therefore, in a state where the IC card is separated from the predetermined distance P (the output of the card position detection unit 7 is Lo level), the switch SW2 is in an open state, and thus the gain of the amplifier 10 is R5 / R3. .

  On the other hand, when the IC card is closer to the antenna 3 than the predetermined distance P, the output of the card position detection unit 7 becomes Hi level, and the switch SW2 is short-circuited. Therefore, the gain G of the amplifier 10 at this time is expressed by the following equation (2).

  That is, in the state where the IC card is closer to the antenna 3 than the predetermined distance P, the gain of the amplifier 10 is lower than when the output of the card position detection unit 7 is at the low level (when far from the predetermined distance P). Therefore, the amplitude of the signal input to the comparator 6 is lowered.

  Here, in the state where the IC card is close to the antenna 3, as shown in FIG. 5, the amplitude of the AC component of the envelope detection output is sufficiently large, and there is no problem even if the gain of the amplifier 10 is reduced. In the configuration of 2, the following effects can be obtained by reducing the gain of the amplifier 10 in the short distance region.

That is, the configuration of the second embodiment is particularly effective when a distorted waveform that cannot be dealt with only by controlling the hysteresis width of the comparator 6 according to the first embodiment is input.
In other words, for example, when the waveform shown in FIG. 6 is further distorted and the portion other than the peak (for example, the portion of β shown in FIG. 6) exceeds the threshold value of level B or C, it is originally shown in FIG. Where the threshold value exceeding should be detected at the peak portion (for example, the portion indicated by α), there is a possibility that the threshold value is detected at the position of β (false detection). For this reason, even if the hysteresis of the comparator 6 is activated, the duty ratio of the comparator output is shifted, and as a result, there is a possibility that the decoder (control unit 1) cannot correctly decode.

On the other hand, in the second embodiment, by narrowing the amplitude of this waveform, portions other than the peak can be prevented from exceeding the threshold values of levels B and C.
As described above, in the second embodiment, in addition to the hysteresis width control of the first embodiment, the gain of the amplifier is also controlled, thereby further improving the effect of suppressing the null phenomenon (null point generation).

  As described above, according to the present invention, stable communication with no null point can be performed between a non-contact IC card and a reader / writer with a simple configuration.

DESCRIPTION OF SYMBOLS 1 Control part 2 Transmission circuit 3 Antenna 4 Detection circuit 5 Amplifier 6 Comparator 7 Card position detection part 8 LPF (low pass filter)
M1, M2, M3 Operational amplifier R1, R2, R3, R4, R5, R6, R7 Resistor SW1 switch C capacitor 10 Amplifier R8 Resistor SW2 switch

Claims (5)

An envelope detection circuit that receives a load modulation signal from a non-contact information medium and detects and outputs an envelope of the received signal, an amplifier that amplifies the envelope detection output, and binarization by inputting the amplifier output In a contactless communication device having a comparator to
Position detection control means for detecting whether the distance from the non-contact type information medium is a predetermined distance or less based on the envelope detection output, and controlling the hysteresis width of the comparator based on the detection result ,
In the comparator, a switch is provided in series with a positive feedback resistor,
The said position detection control means makes the hysteresis of the said comparator work by carrying out ON control of the said switch, when the distance with the said non-contact-type information medium is below a predetermined distance. The non-contact communication device according to 1. It said position by the detection output of the detection control unit, further, the non-contact type communication apparatus according to claim 1 Symbol placement and controls the gain of the amplifier. The amplifier is provided with two resistors for negative feedback in parallel and a second switch connected in series with one of the two resistors,
The position detection control means, said second switch when the distance between the noncontact information medium is a predetermined distance or less by controlling ON, claim 2, wherein lowering the gain of the amplifier The contactless communication device described. The position detection control means detects a direct current component of the envelope detection output, and compares the direct current component voltage with a predetermined threshold voltage that is set in advance so that the distance from the non-contact type information medium is predetermined. noncontact communication device according to any one of claims 1 to 3, characterized in that to detect whether a distance less. Demodulator having an envelope detection circuit for detecting and outputting an envelope of a load modulation signal by a non-contact type information medium, an amplifier for amplifying the envelope detection output, and a comparator for inputting the amplifier output and binarizing it The demodulator in a non-contact communication device having:
Position detection control means for detecting whether the distance from the non-contact type information medium is a predetermined distance or less based on the envelope detection output, and controlling the hysteresis width of the comparator based on the detection result ,
In the comparator, a switch is provided in series with a positive feedback resistor,
The said position detection control means makes the hysteresis of the said comparator work by carrying out ON control of the said switch, when the distance with the said non-contact-type information medium is below a predetermined distance. The demodulation unit of the non-contact communication device according to 1.