JP3955832B2 - Reader / writer for modulation circuit and non-contact IC card - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a modulation circuit that inputs a carrier signal and a baseband signal and outputs a modulated signal subjected to ASK modulation to an antenna, and a reader / writer for a non-contact IC card.
[0002]
[Prior art]
Patent Document 1 discloses a transmission / reception circuit applicable to an IC card reader / writer. This transmission / reception circuit (non-contact type response unit) has an antenna that is electromagnetically coupled by a transmission signal from a communication partner, and an electric power receiving unit that converts an AC output generated from the antenna according to a transmission signal from the communication partner into electric power and stores it. A demodulating means for extracting write data and its write position designation information from a transmission signal from a communication partner using the stored power as operating power, a non-volatile storage means for recording the extracted write data, and a demodulating means. The control means for writing the write data to the address of the storage means specified by the extracted write position designation information, and the write data written to the storage means after the data writing is read, modulated and sent back from the antenna to the communication partner side Transmitting means.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-13295
[Problems to be solved by the invention]
FIG. 5 shows an electrical configuration of a reader / writer that performs a data transmission / reception operation with a non-contact IC card adopting the ISO 14443 TYPE-B method. The encoding circuit 2 of the reader / writer 1 generates a baseband signal Sb obtained by converting transmission data sent from the CPU 3 into an NRZ code, and receives a 13.56 MHz clock from the oscillation circuit 4 together with the carrier signal Sc. The signal is output to the modulation circuit 5. The baseband signal Sb is inverted by the inverter 6 before being input to the modulation circuit 5 to become a baseband signal Sb ′.
[0005]
The modulation circuit 5 employs, for example, a single tuning transmission method, and transmits a signal modulated by the 10% ASK modulation method to the IC card 8 via the antenna 7. The demodulating circuit 9 demodulates the signal received via the antenna 7, and the demodulated signal is input to the encoding circuit 2 via the decoding circuit 10. The encoding circuit 2 outputs the combined data to the CPU 3 as received data.
[0006]
FIG. 4 shows a specific configuration of the modulation circuit 5. When the level of the baseband signal Sb ′ changes, the current (baseband drawing current Ia) flowing from the buffer circuit 11 to the diode 12 and the variable resistor 13 changes, and accordingly, the base current Ib of the transistor 14 changes.
[0007]
FIG. 6 shows signal waveforms at various parts when transmitting from the reader / writer 1 to the IC card 8. When the baseband signal Sb is at a low level (the baseband signal Sb ′ is at a high level), the baseband pulling current Ia becomes 0, the base current Ib of the transistor 14 increases, and the amplitude of the collector current Ic and the collector voltage Vc and thus to the antenna 7. Output amplitude increases. On the other hand, when the baseband signal Sb ′ is at the high level (baseband signal Sb ′ is at the low level), the baseband pulling current Ia flows, the base current Ib of the transistor 14 decreases, and the output amplitude to the antenna 7 decreases. That is, ASK modulation and amplification are performed by the transistor 14.
[0008]
In this configuration, since the base current Ib of the transistor 14 is modulated, the power required for the modulation is small. However, it is easily affected by variations in parts, for example, variations in the current amplification factor of the transistor 14, and the modulation factor and output level must be adjusted by the variable resistors 13 and 15 for each reader / writer. Further, in the above configuration, design parameters for the amplification factor of the transistor 14, the filter circuit 17, and the matching of the antenna 7 are added, so that the design for obtaining the target modulation degree (range from 8% to 14%) becomes complicated. There is a problem that it is difficult to determine parameters and it is difficult to obtain a stable modulation degree.
[0009]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a modulation circuit and a non-contact IC card reader / writer capable of obtaining a stable modulation degree and obtaining a target modulation degree without adjustment. It is to provide.
[0010]
[Means for Solving the Problems]
According to the first aspect of the present invention, the buffer circuit that outputs the carrier signal has a predetermined current output capability sufficient to drive the antenna. The dump circuit itself feeds a current having a magnitude corresponding to the baseband signal out of the current output from the buffer circuit. As a result, the current supplied from the buffer circuit to the antenna changes according to the baseband signal, and ASK modulation is performed.
[0011]
In this means, a dump circuit is provided on the output side of the buffer circuit having a high power level, and the connection state is controlled to modulate the output signal to the antenna, so that a stable modulation degree can be obtained with little variation. In addition, the variation in the current output capability of the buffer circuit is smaller than the variation in the current amplification factor of the transistor alone, and the dump circuit can be accurately configured with a resistor or the like described later, so that the variation can be further reduced. This eliminates the need to adjust the modulation level or output level for each product. This means is particularly suitable for low-power applications such as a non-contact IC card reader / writer described later.
[0012]
According to the means described in claim 2, since the first and second carrier signals based on the carrier signal are generated and the respective carrier signals are modulated, the output signal to the antenna is the same as in the conventional modulation circuit. The amplitude can be increased.
[0013]
According to the means described in claim 3, since the dump circuit is constituted by a series circuit of a resistor and a switch circuit that opens and closes according to the baseband signal, the modulation degree can be determined by setting the resistance value accurately. The variation of the can be further reduced. For example, a semiconductor switching element is used for the switch circuit.
[0014]
According to the means described in claim 4, since the buffer circuit is configured as a CMOSIC, the variation in the current output capability of the buffer circuit for each product is small, and the variation in the modulation degree can be further reduced. In the case of the means described in claim 2, if the buffer circuits in the same IC package are used as the first and second buffer circuits, the stability with respect to the temperature change can be increased.
[0015]
According to the means described in claim 5, a reader / writer for a non-contact IC card which has a stable modulation degree and does not require a modulation degree adjustment process at the time of manufacture can be obtained.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 2 is a functional block diagram showing the configuration of a reader / writer for a non-contact IC card that performs data transmission / reception operations with the non-contact IC card. In FIG. 2, the same parts as those in FIG. 5 showing the conventional configuration are denoted by the same reference numerals, and the description thereof is omitted. The non-contact IC card reader / writer 21 (hereinafter simply referred to as the reader / writer 21) communicates with the proximity non-contact IC card 8 (hereinafter simply referred to as the IC card 8) defined by the ISO 14443 standard. Is what you do. The proximity type non-contact IC card 8 includes TYPE-A and TYPE-B depending on the data modulation method.
[0017]
When transmitting from the reader / writer 21 to the IC card 8, the TYPE-A system uses the combination of 0% and 100% of the amplitude of the carrier signal (fc = 13.56 MHz) to represent 100% of data “0” and “1”. An ASK (Amplitude Shift Keying) modulation method is employed. On the other hand, the TYPE-B system employs a 10% ASK modulation system that represents data “0” and “1” by combining the amplitude of the carrier signal (fc = 13.56 MHz) with 90% and 100%. In the above standard, the modulation degree in the TYPE-B system needs to be in the range of 8% to 14%. In the present embodiment, the TYPE-B method will be described as an example, but the same applies to the TYPE-A method.
[0018]
FIG. 1 shows an electrical configuration of a modulation circuit 22 which is a characteristic part of the present invention. The carrier signal Sc output from the encoding circuit 2 is directly input to the buffer circuit 23 (corresponding to the first buffer circuit) and output as the inverted first carrier signal Sc1. The carrier signal Sc is input to the buffer circuit 25 (corresponding to the second buffer circuit) via the inverter 24 (corresponding to the signal generation circuit) and output as the second carrier signal Sc2. . The inverted buffer circuits 23 and 25 are configured as CMOSICs in one package so that the current output capability characteristics and the temperature characteristics are equal to each other.
[0019]
The output terminal of the buffer circuit 23 is connected to one terminal (corresponding to the first terminal) of the antenna 7 via the filter circuit 26 and the coupling circuit 27, and the output terminal of the buffer circuit 25 is coupled to the filter circuit 28. It is connected to the other terminal (corresponding to the second terminal) of the antenna 7 through the ring circuit 29. The intermediate terminal of the antenna 7 is connected to the ground.
[0020]
A dump circuit 32 (corresponding to a first dump circuit) composed of a series circuit of a resistor 30 and an analog switch 31 is connected between the output terminal of the filter circuit 26 and the ground. And a ground are connected to a dump circuit 35 (corresponding to a second dump circuit) composed of a series circuit of a resistor 33 and an analog switch 34. The analog switches 31 and 34 (corresponding to a switch circuit) are turned on when the baseband signal Sb ′ is at a high level (data “0”), and are turned off when the baseband signal Sb ′ is at a low level (data “1”). It comes to become.
[0021]
Next, the operation and effect of this embodiment will be described with reference to FIG. FIG. 3 shows signal waveforms at various parts when data is transmitted from the reader / writer 21 to the TYPE-B IC card 8. Each waveform is as follows.
(A) Carrier signal Sc1 output from the buffer circuit 23
(B) Carrier signal Sc2 output from the buffer circuit 25
(C) Baseband signal Sb ′
(D) Current Id1 flowing through the dump circuit 32
(E) Current Id2 flowing through the dump circuit 35
(F) Current Ie1 flowing through the antenna 7
(G) Current Ie2 flowing through the antenna 7
(H) Output of antenna 7
During the period when the baseband signal Sb 'is at the low level, the analog switches 31 and 34 are turned off, and the output currents of the buffer circuits 23 and 25 are all currents Ie1 and Ie2 flowing through the antenna 7. As a result, the output amplitude of the antenna 7 becomes large and corresponds to 100% amplitude in 10% ASK modulation. On the other hand, during the period when the baseband signal Sb ′ is at the high level, the analog switches 31 and 34 are turned on, and a part of the output current of the buffer circuits 23 and 25 flows through the dump circuits 32 and 35, and therefore flows to the antenna 7. The currents Ie1 and Ie2 are reduced by the currents Id1 and Id2. As a result, the output amplitude of the antenna 7 is reduced, corresponding to 90% amplitude in 10% ASK modulation.
[0023]
Thus, the modulation circuit 22 realizes 10% ASK modulation by controlling the power consumption of the dump circuits 32 and 35. Since the dump circuits 32 and 35 are provided in a portion where the power level between the output terminals of the buffer circuits 23 and 25 and the antenna 7 is high, variations can be reduced and stable compared to the case where minute power is controlled. There is an advantage that it is easy to obtain the modulation degree.
[0024]
Here, the buffer circuits 23 and 25 are configured as CMOSICs. In general, CMOSIC has a smaller product variation in current output capability than the current amplification factor of the transistor 14 used in the conventional configuration (see FIG. 4). In addition, with respect to the resistors 30 and 33 constituting the dump circuits 32 and 35, the product variation can be easily reduced by selecting the used parts. For this reason, even if the resistors 30 and 33 are constituted by fixed resistors, the currents Ie1 and Ie2 that flow through the antenna 7 when the analog switches 31 and 34 are turned off and the currents Ie1 and Ie2 that flow through the antenna 7 when the analog switches 31 and 34 are turned on are The ratio is almost constant regardless of the product, and once this ratio is set to an appropriate value at the design stage, the modulation degree of the ASK modulation signal output from the antenna 7 for each product is changed from the standard value of 8% to 14%. It is possible to fit within the range. Further, even when there is a design change related to the filter circuits 26 and 28 and the antenna 7, the design change can be made relatively easily.
[0025]
Furthermore, the variation in the current output capability of the buffer circuits 23 and 25 and the variation in the resistance values of the resistors 30 and 33 are smaller than the variation in the current amplification factor of the transistor 14 with respect to the temperature change. Further, since the buffer circuits 23 and 25 are formed in the same package of the CMOS IC, a stable modulation degree can be obtained without causing an imbalance between the output currents of the buffer circuits 23 and 25.
[0026]
The modulation circuit 22 includes two buffer circuits 23 and 25, and drives the antenna 7 with carrier signals Sc1 and Sc2 having opposite phases. Therefore, as described above, an amplifier circuit composed of a transistor having a large characteristic variation between elements. The amplitude of the output signal to the antenna 7 can be increased without using.
[0027]
The present invention is not limited to the embodiments described above and shown in the drawings, and can be modified or expanded as follows, for example.
Only one set of the buffer circuit, the filter circuit, the coupling circuit, and the dump circuit may be provided.
The present invention can be applied to a modulation circuit that performs ASK modulation regardless of the modulation degree.
The modulation circuit 22 described above is not limited to the application to the non-contact IC card reader / writer 21.
[Brief description of the drawings]
FIG. 1 is an electrical configuration diagram of a modulation circuit showing an embodiment of the present invention. FIG. 2 is an electrical configuration diagram of a reader / writer for a non-contact IC card. FIG. 3 is a signal waveform of each part when transmitted to an IC card. FIG. 4 is a diagram equivalent to FIG. 1 showing the prior art. FIG. 5 is a diagram equivalent to FIG. 2. FIG.
7 is an antenna, 8 is a contactless IC card, 21 is a reader / writer for a contactless IC card, 22 is a modulation circuit, 23 is a buffer circuit (first buffer circuit), 24 is an inverter (signal generation circuit), and 25 is a buffer. Circuit (second buffer circuit), 30 and 33 are resistors, 31 and 34 are analog switches (switch circuits), 32 is a dump circuit (first dump circuit), and 35 is a dump circuit (second dump circuit). is there.

Claims (5)

In a modulation circuit for inputting a carrier signal and a baseband signal and outputting a modulated signal subjected to ASK modulation to an antenna,
A buffer circuit having a predetermined current output capability provided between an input terminal of the carrier signal and a terminal of the antenna;
A modulation circuit comprising: a dump circuit that is provided on an output terminal side of the buffer circuit and feeds an output current of the buffer circuit according to the baseband signal. A signal generation circuit for generating first and second carrier signals having opposite phases based on the carrier signal;
The buffer circuit includes first and second buffer circuits connected between an output terminal for the first and second carrier signals of the signal generation circuit and the first and second terminals of the antenna, respectively. Configured,
2. The dump circuit is composed of first and second dump circuits respectively connected between first and second terminals of the antenna and an intermediate terminal of the antenna. The modulation circuit described. The modulation circuit according to claim 1, wherein the dump circuit includes a series circuit of a resistor and a switch circuit that opens and closes in response to the baseband signal. 4. The modulation circuit according to claim 1, wherein the buffer circuit is configured as a CMOSIC. A reader / writer for a non-contact IC card, comprising the modulation circuit according to claim 1 and performing data transmission / reception operation with a non-contact IC card.

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