JP2992728B2 - Contactless communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method in which a voltage is induced in a transmission / reception coil on a child side by bringing the child side close to an electromagnetic field generated by the parent side, and an operation power supply is generated on the child side by the induced voltage. Amplitude shift keying (AS)
The present invention relates to a non-contact communication system for transmitting data from a child side to a parent side by performing K modulation.

[0002]

2. Description of the Related Art Conventionally, as a non-contact communication system of this type, a reader (parent side) and an IC card (child side) are used, and an identification code written on an IC card is brought close to the reader. There is known an identification system that reads an ID and checks the identification code to unlock the door. In this identification system, when the IC card approaches the electromagnetic field generated by the transmission / reception coil of the reader, a voltage is induced in the transmission / reception coil of the IC card, and the induced voltage generates an operating power supply for the IC card. The IC card obtains the operating power and sets the carrier signal of the frequency fc (400 kHz) to a predetermined bit timing number ( ²⁵ bit timing = 64 bit timing) as one bit, and the amplitude of the carrier signal in one bit is determined. FSK modulation (frequency displacement modulation) is performed on both sides while applying ASK modulation (see FIG. 5A), and data at the “0” level is converted to a frequency f1 (12.5 k
Hz), and the data of the “1” level is converted to the frequency f2 (25 k
(Hz), the identification code assigned to itself (child-side identification code) is returned. The reader detects a transmission signal from the IC card (see FIG. 5B), and transmits the carrier signal having the frequency fc to the frequencies f1 and f1 through the band-pass filter.
The data signal of No. 2 is separated and taken out, FSK demodulated and the identification code is read, collated with the identification code (parent-side identification code) assigned to itself, and the door is unlocked when they match.

[0003]

However, in such a conventional identification system, since both sides of the amplitude of the carrier signal are FSK-modulated while adding ASK modulation in the IC card, the transmission sent from the IC card is performed. The frequency components of the signal are as shown in FIG. That is, the data signal is fc-f1, fc- with respect to the frequency fc of the carrier signal.
Appearing as f2, fc + f1, fc + f2, the frequency component band of the carrier signal and the frequency component band of the data signal are close to each other. For this reason, conventionally, the band of the frequency component of the data signal is separated from the carrier signal by detecting the transmission signal from the IC card on the reader side (see FIG. 7). There was a disadvantage that it was necessary. In the reader, the reception signal (IC) is compared with the transmission signal (transmission signal from the reader).
Since the transmitted signal from the card is extremely weak, the received signal is easily affected by distortion of the transmitted signal and the like, and there is a problem that the S / N ratio is easily deteriorated.

The present invention has been made to solve such a problem, and an object of the present invention is to eliminate the need for a detector on the parent side and to separate a frequency band between a transmission signal and a reception signal. Accordingly, it is an object of the present invention to provide a non-contact communication system capable of improving the S / N ratio.

[0005]

In order to achieve the above object, the present invention provides a wireless communication system as described above, wherein the amplitude shift keying is applied to only one side of the amplitude of the carrier signal. The data is transmitted from the side to the parent side.

[0006]

Therefore, according to the present invention, the frequency component of the data signal appears in a band separated from the carrier signal in the transmission signal sent from the slave side.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments.

FIG. 2 is a block diagram of an identification system showing one embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a reader arranged on the door side, and reference numeral 2 denotes an IC card which can be brought close to the reader 1.

The reader 1 includes a CPU 1-1, a communication control device 1-2, an ASK modulator 1-3, a driver 1-4, a transmission / reception coil 1-5, a band-pass filter 1-6, and FSK.
A demodulator 1-7 is provided. In this reader 1, C
PU1-1 is a communication control device 1-2, an ASK modulator 1-
3. The transmission / reception coil 1-5 is driven via the driver 1-4 to generate a predetermined electromagnetic field (400 kHz) and to transmit transmission data superimposed on the electromagnetic field.

The IC card 2 includes a transmission / reception coil 2-1, a rectifier 2-2, a shunt regulator 2-3, a low-pass filter 2-4, a control logic 2-5, and an EEPROM.
OM2-6, FSK modulator 2-7 and driver 2-8
It has. In this IC card 2, EEPRO
The identification code (child-side identification code) assigned to the IC card 2 is written in M2-6.

Next, the characteristic operation of the identification system configured as described above will be described with the function of each unit.

When the IC card 2 approaches the reader 1 and enters the electromagnetic field created by the transmitting / receiving coil 1-5 of the reader 1, the IC card 2
A voltage is induced in the transmitting / receiving coil 2-1 of the card 2. A current is generated by the induced voltage, and this current is generated by the rectifier 2.
The current is rectified by -2, supplied to the shunt regulator 2-3 to generate an operation power supply, and supplied to the control logic 2-5.

When the control logic 2-5 receives power from the regulator 2-3, the EEPROM 2-6 receives the power from the regulator 2-3.
Read the child side identification code written in
The signal is FSK-modulated by the K modulator 2-7, and is returned to the reader 1 from the transmission / reception coil 2-1 via the driver 2-8.

The reader 1 receives the transmission signal from the IC card 2 by the transmission / reception coil 1-5, and transmits the band pass filter 1-6, the FSK demodulator 1-7, and the communication control device 1-2.
Then, the received transmission signal (child-side identification code) is compared with the parent-side identification code assigned to itself, and if they match, the door is unlocked.

FIG. 1 is a time chart showing the FSK modulation status of "1" level data and "0" level data in the IC card 2. In this embodiment, the carrier signal f
The 64-bit timing of c (400 kHz) is one bit, and only one side of the amplitude of the carrier signal in one bit is AS
FSK modulation is performed while adding K modulation (see FIG. 1 (c)).
The “0” level data is transmitted at a frequency f1 (12.5 kHz) and the “1” level data is transmitted at a frequency f2 (25 kHz) from the IC card 2 to the reader 1.

FIG. 3 is a diagram showing frequency components of a transmission signal from the IC card 2. In the present embodiment, FSK modulation is performed while applying ASK modulation to only one side of the amplitude of the carrier signal.
Although the data signal slightly appears as 2, the data signal appears as f1 and f2 in a band separated from the carrier signal. Accordingly, in the present embodiment, the detector is not required on the reader 1 side, and the transmission signal from the IC card 2 is directly supplied to the band pass filter 1-6, and the band pass filter is applied as shown by the broken line in the drawing. The data signals of the frequencies f1 and f2 and the carrier signal of the frequency fc can be separated. Further, in the present embodiment, the frequency band of the transmission signal (400 kHz) and the frequency band of the reception signal are separated in the reader 1, so that the S / N ratio is improved.

FIG. 4 shows the FSK modulator 2- in the IC card 2.
7, the FET2 is conventionally provided as shown by the broken line in the figure, and the FET2 and the FET1 are driven (symmetric drive). In the present embodiment, only the FET1 is driven (asymmetric drive). Thus, a transmission signal as shown in FIG. 1C can be created.

[0018]

As is apparent from the above description, according to the present invention, data is transmitted from the child side to the parent side by applying amplitude shift keying to only one side of the amplitude of the carrier signal. Therefore, the frequency component of the data signal appears in a band distant from the carrier signal in the transmission signal sent from the child side, and the detector can be unnecessary on the parent side. Further, on the parent side, the frequency band of the transmission signal and the reception signal can be separated to improve the S / N ratio.

[Brief description of the drawings]

FIG. 1 is a time chart showing an FSK modulation state of data transmitted by an IC card in the identification system shown in FIG. 2;

FIG. 2 is a configuration diagram of an identification system showing one embodiment of the present invention;

FIG. 3 is a diagram showing frequency components of a transmission signal from an IC card in the identification system.

FIG. 4 shows an FS using an IC card in the identification system.
FIG. 3 is a diagram illustrating a main part of a K modulator.

FIG. 5 is a time chart showing an FSK modulation state of transmission data in an IC card in a conventional identification system.

FIG. 6 is a diagram showing frequency components of a transmission signal from an IC card in a conventional identification system.

FIG. 7 is a diagram showing frequency components of a received signal after detection by a reader in a conventional identification system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reader 1-5 Transmission / reception coil 1-6 Band pass filter 1-7 FSK demodulator 2 IC card 2-1 Transmission / reception coil 2-2 Rectifier 2-3 Shunt regulator 2-7 FSK modulator 2-8 Driver

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) H04B 5/00 G06K 17/00 G06K 19/26 H04B 7/26 H04L 27/32

Claims (1)

(57) [Claims] A voltage is induced in a transmission / reception coil on the child side by bringing the child side closer to an electromagnetic field created by the parent side, an operating power supply is generated on the child side by the induced voltage, and a carrier signal of a predetermined frequency is amplified. A non-contact communication system for transmitting data from a child side to a parent side by performing shift key modulation, wherein only one side of the amplitude of the carrier signal is amplitude shift keyed.