JPS6111807Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a card reader that uses high frequency to read information on a card that records information with or without multiple metal pieces, and in particular, one high-frequency transmitting coil facing each other with a gap in between. This invention relates to a card reader equipped with multiple sets of one receiving coil.

Conventionally, this type of card reader generally has a configuration as shown in FIG. 1, and its operation is as follows. When a high frequency signal is supplied from the high frequency oscillator ₁ to the plurality of transmitting coils _L1 , each of the receiving coils _L2 is electromagnetically coupled to the opposing transmitting coil L1. A large detection signal and a small detection signal are generated in the receiving coil L ₂ when there is no magnetic flux absorber such as the metal piece 3 and when there is a magnetic flux absorber, respectively. These detection signals representing information recorded on the card 2 are each amplified by a high frequency amplifier 4, then detected by a detection circuit 5, and applied to a switch circuit 6, where they are converted into a binary level depending on the magnitude. .

FIG. 2 shows a specific example of the circuit configuration of the detection circuit 5 and the switch circuit 6. The detection signal amplified by the high frequency amplifier is sent to the detection circuit consisting of the diode D ₁ , capacitor C ₁ and resistor R ₁ . 5 and produces a DC output at resistor _R1 . This detection output is transmitted to the transistor in the switch circuit 6.
The transistor Q ₁ is made conductive or non-conductive depending on the magnitude of the detected output, which is applied to the base of Q ₁ and changes depending on whether there is a metal piece inside the card or not. The collector of transistor Q ₁ is resistor R ₂
It is connected to the power supply through the terminal 7, which is led out from the collector, and a binary level of ground level "0" and power supply level "1" is outputted according to the magnitude or magnitude of the detected output at this time. .

In this conventional method, the standard for converting the magnitude of the detection output into binary values is determined by the voltage Vbe between the base and emitter of transistor _Q1 .
Vbe, that is, the operating level of the switch circuit 6 is
It fluctuates greatly depending on temperature changes. Furthermore, if the power supply voltage or temperature changes, the output of the high-frequency oscillator 1, the amplification factor of the high-frequency amplifier 4, the efficiency of the detection circuit 5, etc. will change, resulting in fluctuations in the detected output. Furthermore, since these detection outputs and the operating level of the switch circuit 6 vary independently, conventional card readers are prone to read malfunctions, and their installation locations and power supply conditions are restricted.

The present invention aims to improve these conventional drawbacks and provide a card reader that can perform correct reading operations even in places with rapid temperature changes or in environments with unstable power supply voltage. Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 3 and 4. Note that parts common to FIGS. 1 and 2 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

As shown in the block diagram of FIG. 3, the card reader according to the present invention is provided with a voltage comparator 8 having a switching function in place of the switch circuit 6 of the conventional card reader. The detection output of the detection circuit 5 is determined based on a detection output proportional to the excitation voltage (hereinafter referred to as a reference voltage). Reference numeral 9 in FIG. 3 is a potentiometer for reading out the proportional component of the transmitting coil excitation voltage. is adjusted so that there is. Reference numerals 10 and 11 denote a high-frequency amplifier and a detection circuit having the same configuration as the high-frequency amplifier 4 and the detection circuit 5, respectively, and the output thereof, that is, the reference voltage, is input to the voltage comparator 8 together with the detection output of the detection circuit 5. .

The voltage comparator 8 having a switching function includes, for example, transistors Q ₂ and Q ₃ as shown in FIG.
, current source I, and load resistor _R4 are connected differentially,
Further, this output is configured to drive a switch circuit consisting of a resistor _R3 and a transistor _Q4 . And diode D ₂ and resistor R ₅ , transistor
The reference voltage output from the detection circuit 11 consisting of C ₂ is applied to the base of the transistor Q ₃ , and the detection output of the detection circuit 5 is applied to the base of the transistor Q ₂ . Now, when the detection output voltage of the detection circuit 5 is higher than the reference voltage, the transistors Q ₃ and Q ₄ are conductive, and a ground level "0" is generated at the output terminal 12 derived from the collector of the transistor Q ₄ . On the other hand, when the detected output voltage of the detection circuit 5 is lower than the reference voltage, the transistors Q ₃ and Q ₄ become non-conductive, and a power level "1" is generated at the output terminal 12.

As described above, in the card reader according to the present invention, the proportional component of the excitation voltage of the transmitting coil is extracted as the reference voltage for determining the magnitude of the detection output, which changes depending on whether there is a metal piece built into the card. This is obtained by passing the signal through a high frequency amplifier and detection circuit equivalent to those for the detection signal. Therefore, even if the output of the high-frequency oscillator 1, the amplification factors of the high-frequency amplifiers 4 and 10, and the efficiency of the detection circuits 5 and 11 change due to fluctuations in the power supply voltage and temperature, the detected output voltage of the detection circuit 5 Since the reference voltage follows fluctuations in the reference voltage, it is possible to extremely effectively prevent reading errors caused by environmental conditions as in the conventional case.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional card reader.
Fig. 2 is a block diagram of the detection circuit and switch circuit in the same card reader, Fig. 3 is a block diagram showing an embodiment of the card reader according to the present invention, and Fig. 4 is a block diagram of the detection circuit and voltage comparator in the same card reader. FIG. 1...High frequency oscillator, 2...Card, 3...Metal piece, 5, 11...Detection circuit, 8...Voltage comparator, _L1 ...Transmission coil, _L2 ...Reception coil.

Claims (1)

[Scope of utility model registration request] In a card reader that is equipped with a plurality of sets of one high-frequency transmitting coil and one receiving coil facing each other across a gap, and reads information from a card inserted into the gap and having information based on the presence or absence of a metal piece, each receiving coil The first detection output obtained by detecting the detection signal of A card reader characterized in that the magnitude of the first detection output is converted into a binary level output.