JPH0528328A - Recording medium writer/reader - Google Patents

Abstract

PURPOSE:To reduce power consumption of a drive circuit and to reduce the scale of a power source circuit operating the drive circuit. CONSTITUTION:In the device, a drive circuit 6 has a small output impedance. A current detection means composed of a magnetic connection element 8, a detection coil 9 and a resistance 19 detects the current flowing through the coil 7, and its voltage drop is small and approximately constant with respect to the fluctuation of the current flowing through the coil 7. At the time of reading data from an IC card 2, an MOS switch 16 is turned on/off in accordance with the data and the load of the drive circuit 6 is changed accordingly. The drive circuit 6, however, drives the coil 7 at constant voltage and the voltage applied to the coil 7 is kept approximately constant even when the current flowing through the coil 7 is fluctuated by the change of the load. Thus, the input voltage of a rectification smoothening circuit 12 and the input voltage of a regulator 13 are also kept approximately constant and therefore, the amplitude of the output high frequency voltage of the drive circuit 6 can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording medium writing / reading device for writing / reading data to / from a recording medium such as a non-contact type IC card.

[0002]

2. Description of the Related Art A conventional IC card has an electric contact, and by bringing this electric contact into contact with an electric contact of a recording medium writing / reading device (hereinafter referred to as a reader / writer),
Although it is of a contact type that is connected to a reader / writer, as disclosed in, for example, Japanese Patent Laid-Open No. 62-186392, a coil is used instead of an electrical contact, and the reader / writer and the coil magnetically connect the coil. There has been proposed a non-contact type IC card that is connected in a non-contact manner.

Since this non-contact type IC card will be described below, the term "IC card" simply means a non-contact type IC card.
In Japanese Patent Laid-Open No. 186392, an IC card is provided with a coil of a metal loop and an electronic switch means for shortening and releasing the terminals of this coil, while the reader / writer has a transmitting coil and a receiving coil. Are coaxially provided at a predetermined interval, and by inserting the coil of the IC card between the transmitting coil and the receiving coil of the reader / writer, these are magnetically coupled and the reader / writer and the IC card are connected. It When reading data from an IC card, a high frequency signal of a sine wave or a rectangular wave is supplied from an oscillation circuit to an oscillation coil.
The electronic switch means is turned on and off according to "1" and "0" bits of data. As a result, the amplitude of the high-frequency signal induced in the receiving coil is changed by the magnetic flux generated from the transmitting coil by the high-frequency signal, and the high-frequency signal is amplified, rectified, and amplitude-detected, so that the reader / writer can read the IC card from the IC card. Data is read.

By the way, in an IC card, a power supply voltage is required to drive a built-in microcomputer, an external memory and the like. For contact type IC cards,
An electric contact dedicated to power supply was provided, and a DC power supply voltage was supplied from the reader / writer via this electric contact. However, in an IC card (non-contact type), a high frequency signal is transmitted from the reader / writer via a coil. The high-frequency signal sent is processed by a rectifying and smoothing circuit and a regulator to obtain a predetermined power supply voltage.

When data is transmitted from the reader / writer to the IC card, the drive circuit drives the coil with a high frequency signal amplitude-modulated, frequency-modulated or phase-modulated by the data, and the reader / writer reads the data from the IC card. As described above, in the reader / writer, the drive circuit drives the coil with a high-frequency signal having a constant amplitude,
The data is read by detecting the amplitude fluctuation of the high frequency current flowing in this coil caused by turning on and off the electronic switch means in the IC card.

[0006]

However, in the conventional reader / writer, a general drive circuit using a conventional linear amplifier or the like is used as the drive circuit, and therefore the drive circuit of the drive circuit is not used. There is a problem that power consumption becomes excessive. On the other hand, as a means for detecting the high frequency current of the coil, there is used a means for detecting the current by converting the current into a voltage from a voltage drop corresponding to the magnitude of the high frequency current by a resistor having a large resistance value.
When reading data from the C card, the amplitude of the high frequency voltage supplied to the coil fluctuates depending on whether the electronic switch means of the IC card is on or off.

In the IC card, a predetermined power supply voltage is required even when reading data from the IC card of the reader / writer, so the power supply voltage is obtained from the high frequency voltage supplied from the reader / writer as described above. When the amplitude of the high frequency voltage fluctuates by turning on and off the electronic switch means according to the transmission data, if the amplitude is large, the IC card cannot obtain a predetermined power supply voltage.
Since a stable power supply voltage cannot be obtained, it is necessary to obtain a predetermined power supply voltage even at the lowest amplitude of the high frequency voltage. That is, it is necessary to sufficiently increase the amplitude of the high frequency voltage to be driven, which causes extra power consumption.

On the other hand, if the above-mentioned amplitude is small, there is a problem that the S / N of data detection becomes insufficient and reliable data detection cannot be performed. Therefore, conventionally, in the drive circuit in the reader / writer, it is necessary to output a high-frequency voltage having a sufficiently large amplitude to compensate for a large voltage drop in the drive circuit and the current detection means. The power supply voltage required to drive it had to be high enough. As a result, there is a problem in that the power consumption of the reader / writer becomes large, and the power supply circuit becomes large so that the reader / writer becomes large in size.

An object of the present invention is to provide a recording medium writing / reading device which can solve such problems, reduce the power consumption, and realize the downsizing.

[0010]

In order to achieve the above object, the present invention uses a voltage source drive type circuit having a small output impedance as a coil drive circuit, and has a sufficiently small voltage drop as a coil current detecting means. I shall.

[0011]

When the data on the recording medium is read, a high frequency voltage having a constant amplitude is applied to the coil from the drive circuit, and the magnitude of the current flowing through the coil changes according to the data from the recording medium. Since the output impedance of the drive circuit is low, the drive circuit drives the coil as a voltage source. Further, since the voltage drop in the coil current detecting means is sufficiently small regardless of the coil current, the high frequency voltage applied to the coil has a constant amplitude even if the magnitude of the coil current changes.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a recording medium writing / reading device according to the present invention together with an IC card as a recording medium. Reference numeral 1 is a recording medium writing / reading device (reader). Writer), 2 is I
C card, 3 host, 4 signal processing circuit, 5 modulation circuit, 6 drive circuit, 7 coil, 8 magnetic coupling element, 9 detection coil, 10 comparator, 11 coil, 12 rectifying and smoothing Circuit, 13 is a regulator, 14 is a receiving circuit, 15 is a load resistor, 16 is a MOS switch, 1
Reference numeral 7 is a signal processing circuit, 18 is a memory, and 19 is a resistor.

In the figure, when writing data to the IC card 2, the data to be written is output from the host 3 or the like and supplied to the reader / writer 1. In the reader / writer 1, this data is processed by the signal processing circuit 4 and supplied to the modulation circuit 5 to modulate a high frequency signal having a constant amplitude by amplitude modulation, frequency modulation or phase modulation. The high frequency signal modulated with this data is supplied to the coil 7 via the drive circuit 6.

The IC card 2 is mounted on the reader / writer 1, whereby the coil 7 and the coil 11 of the IC card 2 are magnetically coupled. Therefore, the high frequency signal modulated with the data is transmitted from the reader / writer 1 to the IC card 2 by the coils 7 and 11.

2 (a) shows the data input to the modulation circuit 5, and assuming that the modulation circuit 5 performs amplitude modulation, the coils 7 and 11 cause the reader / writer 1 to I.
The high frequency signal transmitted to the C card 2 has a waveform shown in FIG.

In the IC card 2, the high frequency signal output from the coil 11 is, on the one hand, the rectifying and smoothing circuit 12
After being rectified and smoothed by, it is supplied to the regulator 13 to form a predetermined power supply voltage, and on the other hand, it is supplied to the receiving circuit 14 and demodulated into data. The demodulated data is processed by the signal processing circuit 17 and written in the memory 18.

Although a series circuit of a load resistor 15 and a MOS switch 16 is connected between the output terminal of the rectifying / smoothing circuit 12 and the ground line, this MOS switch 16 is turned off when writing data. is doing.

Here, the drive circuit 6 has a sufficiently small output impedance. In addition, a current detecting means including a magnetic coupling element 8, a detection coil 9 and a resistor 19 for detecting a current (coil current) flowing through the coil 7 is provided in series with the coil 7. The magnetic coupling element 8 is, for example, an annular magnetic core, and an electric wire passing through the center hole of the magnetic core serves as a primary coil and is connected to the coil 7. Detection coil 9
Is wound around the magnetic core N times (where N is an integer of 1 or more), and a resistor 19 for converting the detection current of the detection coil 9 into a voltage is connected between both terminals of the detection coil 9 so-called current. Configure a transformer.

When the data in the memory 18 of the IC card 2 is read from the reader / writer 1, the modulation circuit 5 outputs a non-modulated high frequency signal having a constant amplitude, passes through the drive circuit 6, and further the coils 7 and 11 by the IC card. Send to 2. In the IC card 2, the high frequency signal from the coil 11 is rectified and smoothed by the rectifying and smoothing circuit 12 and supplied to the regulator 13 to form a power supply voltage, as in the case of writing data.

On the other hand, the data read from the memory 18 is processed by the signal processing circuit 17 and then supplied to the MOS switch 16. FIG. 3B shows the data supplied to the MOS switch 16. Here, the MOS switch 16 is turned on by "1" of this data,
When it is "0", it is turned off.

Therefore, when the MOS switch 16 is turned on, the load resistor 15 is added, so that the load seen from both terminals of the coil 7 on the coil side and the load of the drive circuit 6 increase, and the load flows to the coil 7. High frequency current increases. When the MOS switch 16 is turned off, the high frequency current flowing through the coil 7 decreases. FIG. 3A shows the waveform of the high frequency current of the coil 7 with respect to the data shown in FIG. This high frequency current is detected by the detection coil 9,
After being converted to a high frequency voltage by the resistor 19, the comparator 1
At 0, envelope detection and waveform shaping are performed and data is extracted. After this data is processed by the signal processing circuit 4,
It is sent to the host 3 or the like.

In reading such data, the drive circuit 6 has a low output impedance, and the current detection means including the magnetic coupling element 8, the detection coil 9 and the resistor 19 has a sufficiently small input impedance and a voltage drop thereof. Since it is sufficiently small regardless of the current, the coil 7 is turned on and off by turning the MOS switch 16 on and off as described above.
The amplitude of the high frequency voltage applied to the coil 7 is kept substantially constant even if the magnitude of the current flowing through the coil changes. Therefore, the high frequency voltage induced in the coil 11 also has a substantially constant amplitude, regardless of whether the MOS switch 16 is on or off.
The high frequency voltage input to the rectifier circuit 12 has a substantially constant amplitude, and the rectified voltage input to the regulator 13 also has a substantially constant amplitude.

Therefore, the amplitude of the high-frequency voltage output from the drive circuit 6 can be set to a substantially minimum amplitude required to obtain a predetermined power supply voltage by the regulator 13, and the above power supply circuit in the IC card can be used. In addition to reducing the extra power consumption of the drive circuit, conventionally, the amplitude of the high frequency voltage output from the drive circuit must be increased by the amount by which the output impedance of the drive circuit or the voltage drop of the current detection means causes a decrease in the high frequency voltage. The power supply voltage for operating the drive circuit 6 can be lowered, and the power consumption can be reduced. Further, the power supply circuit can be downsized.

FIG. 4 is a block diagram showing a specific example of the modulation circuit 5 and the drive circuit 6 in FIG. 1, in which 20 is an oscillator, 21 is a data output circuit, 22 is a selection switch circuit,
Reference numeral 23 is a power supply circuit, and parts corresponding to those in FIG.

In FIG. 4, the selection switch circuit 22 has the functions of the modulation circuit 5 and the drive circuit 6 as the amplitude modulation circuit in FIG. The oscillator 20 outputs a high-frequency pulse signal as a carrier and supplies it to the selection switch circuit 22. The selection switch circuit 22 receives + V and −V power supply voltages from the power supply circuit 23, selects + V, for example, + V during the carrier “H” (high level) from the oscillator 20, and selects “L” (low level) for the carrier. ) Period-V
To output.

The power supply circuit 23 is controlled by the data from the data output circuit 21 in the signal processing circuit 4 (FIG. 1),
When the data is “1”, the positive / negative power supply voltage ± V of the selection switch circuit 22 is set to ± V1, and when the data is “0”, ± V2.
And Here, assuming that | V1 |> | V2 |, the selection switch circuit 22 outputs the data shown in FIG.
The high frequency signal of (b) is obtained and supplied to the coil 7.

FIG. 5 shows the selection switch circuit 22 shown in FIG.
24a and 24b are MOS switches, which are circuit diagrams showing a driver composed of a complementary switch as a specific example of FIG.

In the figure, the drains of the P-channel MOS switch 24a and the N-channel MOS switch 24b are connected to each other and connected to the coil 7 of FIG. A power supply voltage of + V is applied to the source of the MOS switch 24a, and a power supply voltage of -V is applied to the source of the MOS switch 24b. Is supplied. When this carrier is "H", MOS
When the switch 24a is turned on and the voltage of + V is supplied to the coil 7 and the carrier is "L", the MOS switch 24
b is turned on and a voltage of -V is supplied to the coil 7.

When reading data from the IC card 2 (FIG. 1), the power supply voltage of the selection switch circuit 22 is + V.
It is fixed to either 1, -V1 or + V2, -V2.

According to such a selection switch circuit, the amplitude of the high frequency signal is twice the power supply voltage (that is, 2 V), and a power supply voltage sufficiently higher than the amplitude of the high frequency signal is required as in the conventional drive circuit. Compared with the above, the power supply voltage can be set to a necessary minimum value, and the power supply circuit of the drive circuit can be downsized. Further, since the high frequency signal can be formed into a rectangular wave, the rectifying and smoothing circuit 12 in the IC card 2
The rectifying / smoothing efficiency of (FIG. 1) is increased.

FIG. 6 is a circuit diagram showing a specific example of the power supply circuit 23 in FIG. In the figure, data from the data output circuit 21 (FIG. 4) is supplied to the MOS transistors 26 and 27 via the previous value drive circuit 25. The drain of the MOS transistor 26 is the MOS switch 2
The drain of the MOS transistor 27 is M
The gates of the OS switches 29 are respectively connected. Then, the source of the MOS switch 28 is + V1
-V1 is applied to the sources of the switches 29, respectively.
The drain of the MOS switch 28 and the cathode of the diode 30 correspond to the drain of the MOS switch 29 and the diode 3
The anodes of 1 are connected to each other, + V2 is connected to the anode of the diode 30, and -V2 is connected to the cathode of the diode 31. However, here, | V1 |> | V2
|

Therefore, assuming that data "1" is input to the drive circuit 25, the MOS transistor 2
The MOS switches 28 and 29 are both turned on by the outputs of 6 and 27. As a result, + V1 is supplied to the selection switch circuit 22 as the power supply voltage + V via the MOS switch.
(FIG. 4), -V1 is applied to the selection switch circuit 22 as the power supply voltage -V via the MOS switch 29. At this time, the diodes 30 and 31 are reverse-biased and are in the off state. In addition, the drive circuit 25
When "0" of data is input to, the MOS switches 28 and 29 are both turned off, and + V2 is supplied as the power supply voltage + V via the diode 30, and -V2 is supplied as the power supply voltage -V via the diode 31. It is applied to the selection switch circuit 2.

FIG. 7 is a circuit diagram showing another specific example of the power supply circuit 23 in FIG. In the figure, + V1 is applied to the collector of the NPN type transistor 32, and −V1 is applied to the collector of the PNP type transistor 33, and the emitter voltage of the transistor 32 is + V.
Assuming that the emitter voltage of the transistor 33 is -V, they are respectively shown in FIG.
Is applied to the selection switch circuit 22. The data of the data output circuit 21 (FIG. 4) is the Zener diodes 34, 3
5 to the bases of the transistors 32 and 33.

When the data "1" is supplied, the base voltages of the transistors 32 and 33 are high, and the emitter voltages thereof are + V1 and -V1, respectively. In contrast,
When the data is "0", the base voltages of the transistors 32 and 33 are low, and therefore the emitter voltages thereof are + V2 and -V2.

FIG. 8 is a block diagram showing another concrete example of the modulation circuit 5 and the drive circuit 6 in FIG.
2b is a selection switch circuit, 36 and 37 are inverters, 3
Reference numerals 8a and 38b are AND gates, and the portions corresponding to FIG.

In the figure, the selection switch circuit 22a,
22b is similar to the selection switch circuit 22 in FIG. 4, and has the configuration shown in FIG. 5, for example, but the power supply voltage of the selection switch circuit 22a is + V1, -V1.
The power supply voltage of the selection switch circuit 22b is fixed to + V2 and -V2, respectively.

On the other hand, the data output from the data output circuit 21 is inverted by the inverter 36, supplied to the AND gate 38b, further inverted by the inverter 37, and supplied to the AND gate 38a. The AND gates 38a and 38b are supplied with the carrier output from the oscillation circuit 20.

Therefore, data "1" is now output from the data output circuit 21, and at this time the AND gate 38a.
When is turned on, carriers are supplied to the selection switch circuit 22a through the AND gate 38a. At this time, the AND gate 38b is off. Therefore, 2 is applied to the coil 7 from the selection switch circuit 22a. A high frequency signal of amplitude V1 is supplied. When data "0" is output from the data output circuit 21, the AND gate 38a is turned off and the AND gate 38b is turned on, contrary to the above.
2 to the coil 7 from the selection switch circuit 22b. A high frequency signal having an amplitude of + V2 is supplied.

When reading data from the IC card 2 (FIG. 1), either one of the AND gates 38a and 38b may be held in the ON state. As described above, also in this specific example, the same effect as that of the specific example shown in FIG. 4 can be obtained.

In the specific example shown in FIG. 8, the selection switch circuits 22a and 22b have the configuration shown in FIG. 5, but another configuration is shown in FIG. However, the same reference numerals are given to the portions corresponding to FIG.

In the figure, when the AND gate 38a is turned on and the carrier from the oscillation circuit 20 (FIG. 4) passes through the AND gate 38a, this carrier is MOS-transmitted via the pulse transformer 39a in the selection switch circuit 22a. The switches 40a and 41a are supplied to alternately turn them on and off at the carrier cycle. The source of the MOS switch 40a is + V1 and the MOS switch 41 is
-V1 is applied to the source of each a, and the drains thereof are connected to the coil 7 through the diodes 42a and 43a, respectively. Therefore, the MOS switch 4
By alternately turning on and off 0a and 41a, a high frequency signal having an amplitude of 2 · V1 is supplied to the coil 7.

The AND gate 38b is turned on, and the oscillation circuit 2
When a carrier from 0 (FIG. 4) passes through the AND gate 38b, this carrier is transferred to the selection switch circuit 22.
In b, it is supplied to the MOS switches 40b and 41b via the pulse transformer 39b, and alternately turns them on and off at the carrier cycle. + V2 is applied to the source of the MOS switch 40b and -V2 is applied to the source of the MOS switch 41b, and the drains of these are connected to the coil 7 via diodes 42b and 43b, respectively. Therefore, when the MOS switches 40b and 41b are alternately turned on and off, the amplitude of the coil 7 becomes 2
-V2 high frequency signal will be supplied.

FIG. 10 is a circuit diagram showing still another specific example of the modulation circuit 5 and the drive circuit 6 in FIG.
80a and 380b are AND gates, 381a and 381b
Is an inverter, 382a and 382b are NAND gates, 3
Reference numerals 83a, 383b, and 44 are inverters having a front-end drive function, and the same reference numerals are given to the portions corresponding to the above drawings.

In the figure, when data "1" is output from the data output circuit 21, the AND gate 380a and the NAND gate 382a are turned on, and the AND gate 380b.
And the NAND gate 382b are turned off. The "H" (high level) of the carrier from the oscillator 20 passes through the AND gate 380a, is inverted by the inverter 381a, and is supplied to the selection switch circuit 22a.
Turn on a. The “L” (low level) of this carrier is inverted by the inverter 44 and the NAND gate 382.
After passing through a, it is inverted by the inverter 383a and supplied to the selection switch circuit 22a to turn on the MOS switch 41a.

Therefore, when the data "1" is output from the data output circuit 21, the selection switch circuit 22a is selected.
The MOS switches 40a and 41a in FIG.
It turns on and off alternately by the carrier from the coil 7
A high frequency signal having an amplitude of 2 · V1 is supplied to.

Similarly, when data "0" is output from the data output circuit 21, the AND gate 380.
b, the NAND gate 382b is turned on, so that the "H" of the carrier from the oscillator 20 is AND gate 380b,
It is supplied to the selection switch circuit 22b via the inverter 381b to turn on the MOS switch 41b, and "L" of this carrier is supplied to the selection switch circuit 22b via the NAND gate 382b and the inverter 383b.
The MOS switch 41b is turned on.

Therefore, when the data "0" is output from the data output circuit 21, the selection switch circuit 22b.
The MOS switches 40b and 41b in FIG.
It turns on and off alternately by the carrier from the coil 7
A high frequency signal having an amplitude of 2 · V2 is supplied to.

In FIG. 1, the means for detecting the current flowing through the coil 7 is not limited to the above means as long as the voltage drop is sufficiently small with respect to the fluctuation of the current. For example, as shown in FIG. 11, two diodes 45 and 46 connected in parallel with opposite polarities are connected between one terminal of the coil 7 and a ground terminal, and the diodes 45 and 46 and the coil 7 are connected to each other. The coil current may be supplied to the comparator 10 from the connection point. Since the voltage drop between both terminals of these diodes 45 and 46 is sufficiently small and constant as compared with the amplitude of the high frequency voltage output from the drive circuit 6 (FIG. 1), the high frequency voltage applied to the coil 7 is constant. ..

[0050]

As described above, according to the present invention,
When reading data, the power supply voltage of the drive circuit that drives the coil can be lowered, power consumption can be significantly reduced, and the power supply circuit can be downsized.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a recording medium writing / reading device according to the present invention.

FIG. 2 is a waveform diagram showing write data in FIG. 1 and a high frequency signal modulated by the data.

FIG. 3 is a waveform diagram showing read data and detected current in FIG.

FIG. 4 is a configuration diagram showing a specific example of a modulation circuit and a drive circuit in FIG.

5 is a circuit diagram showing a specific example of a selection switch circuit in FIG.

6 is a circuit diagram showing a specific example of the power supply circuit in FIG.

FIG. 7 is a circuit diagram showing another specific example of the power supply circuit in FIG.

8 is a configuration diagram showing another specific example of the modulation circuit and the drive circuit in FIG.

9 is a circuit diagram showing a circuit configuration example of the specific example shown in FIG.

10 is a circuit diagram showing still another specific example of the modulation circuit and the drive circuit in FIG.

FIG. 11 is a circuit diagram showing another specific example of the coil current detecting means in FIG.

[Explanation of symbols]

 1 Recording Medium Writing / Reading Device 2 IC Card 5 Modulation Circuit 6 Drive Circuit 7 Coil 8 Magnetic Coupling Element 9 Detection Coil 11 Coil 12 Rectifying and Smoothing Circuit 13 Regulator 15 Load Resistor 16 MOS Switch 19 Resistor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Takeuchi 1-26-5 Toranomon, Minato-ku, Tokyo, NTT DATA Communications Co., Ltd. (72) Inventor Shunne Iranaki Toranomon, Minato-ku, Tokyo 1-26-5 NTT DATA Communications Co., Ltd.

Claims (1)

Claim: What is claimed is: 1. A recording medium is magnetically coupled to a recording medium by a coil. When reading data from the recording medium, a high-frequency signal having a constant amplitude is supplied from a drive circuit, and the amplitude changes in accordance with the data. In the recording medium writing / reading device in which the high frequency current of the coil is detected by the current detecting means, the drive circuit is a low output impedance circuit, and the voltage drop in the current detecting means is A recording medium writing / reading device characterized by being substantially constant and sufficiently small with respect to changes in high-frequency current.