JP2694371B2 - Magnetic recording medium reading circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium reading circuit used for reading data from a magnetic recording medium such as a prepaid card. Circuit for obtaining a correct read waveform.

(Prior Art) Recently, prepaid cards using magnetic cards have been introduced in various fields, and there is the following demand as a reading circuit for reading data from these magnetic cards.

That is, the reproducing frequency used in the reading circuit of the magnetic card is relatively low at 0.2 to 25 Kz, but the corresponding frequency width is large, so that it is necessary to increase the frequency bandwidth. Also,
Compared to other magnetic readers, magnetic card readers have many instability factors in the contact state between the magnetic head and the magnetic stripe, and due to the handling of the magnetic card itself, demagnetization and destruction of recorded data easily occur. Therefore, it is necessary to have a wide gain bandwidth so as to cope with such output fluctuation.

A conventional reading circuit for a magnetic card that meets the above requirements is shown in FIG. This circuit is composed of a magnetic head 1, resistors 11, 12, 13, and 14, an amplifier 10 including an operational amplifier 15, a capacitor 21, resistors 22 and 23, a capacitor 24, and a diode 2.
5, 26, differential amplifier 20 consisting of operational amplifier 27, resistors 31, 3
A Schmitt circuit 30 composed of 2, 33 and an operational amplifier 34 is provided. The operation of this circuit will be described with reference to the waveform chart shown in FIG. The magnetic head 1 reads data from a magnetic card (not shown) and amplifies the read waveform with an amplifier 10. The output waveform of the amplifier 10, that is, the waveform of point a is shown in FIG. The output of the amplifier 10 is the differential amplifier 20.
The output of the capacitor 21, that is, the waveform at the point b, is differentiated through the capacitor 21 of FIG. The output of the capacitor 21 is supplied to the operational amplifier 27 via the resistor 22.
Applied to the inverting input of. The operational amplifier 27 includes a resistor 23, a capacitor 24, and diodes 25 and 26 connected in opposite polarities.
Is connected to the feedback circuit, and the output of the capacitor 21 is amplified and clamped so that the waveform at the point c becomes a waveform as shown in FIG. 8 (c). The waveform signal shown in FIG. 8 (c) output from the differential amplifier 20 is the Schmitt circuit 30.
Is added to The Schmitt circuit 30 compares this waveform signal with two threshold levels + Vth and -Vth, and outputs a waveform-shaped waveform signal as shown in FIG.

(Problems to be Solved by the Invention) By the way, it is assumed that noise is superimposed on the output of the magnetic head 1 and a waveform as shown by a dotted line in FIG. In this case, if the noise level is relatively low as indicated by the dotted line n1, this effect is n1 in FIG. 8 (b).
2. As shown by n13 in FIG. 8 (c), it enters between the two threshold levels + Vth and −Vth of the Schmitt circuit 30 and does not appear in the output waveform as shown in FIG. 8 (d). , If the noise level is relatively high as indicated by the dotted line n2, this effect is n22 in FIG. 8 (b) and n23 in FIG. 8 (c).
And exceeds the two threshold levels + Vth and -Vth of the Schmitt circuit 30, the influence appears in the output waveform as shown in FIG. 8 (d). That is, small level noise can be removed by the Schmitt circuit 30, but large level noise cannot be removed by the Schmitt circuit 30,
In this case, a read error will occur.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a reading circuit of a magnetic recording medium which eliminates the above-mentioned drawbacks of the conventional circuit and can obtain a stable reading waveform against noise, waveform distortion, etc. without causing a reading error. And

(Means for Solving the Problems) In order to achieve the above object, a reading circuit of a magnetic recording medium of the present invention detects a peak value of a signal read from the magnetic recording medium and outputs a reference voltage corresponding to the peak value. A peak circuit, an inverting circuit that inverts a signal read from the magnetic recording medium, a first comparison circuit that compares a reference voltage output from the peak circuit with an output signal of the inverting circuit, and the peak circuit. A second comparing the reference voltage output from the magnetic recording medium with a signal read from the magnetic recording medium;
Binarization for forming a binary data signal corresponding to the signal read from the magnetic recording medium, which is set and reset corresponding to the outputs of the first comparison circuit and the second comparison circuit. And a circuit.

Here, the peak circuit includes a capacitor to which the output of the inverting circuit is added via a diode and which is charged by the output of the inverting circuit, a resistor circuit which discharges the capacitor with a predetermined time constant, and the resistor circuit. And means for generating a voltage signal corresponding to the charging voltage of the capacitor.

Further, the read circuit from the magnetic recording medium of the present invention detects the positive peak value and the negative peak value of the signal read from the magnetic recording medium, and the first circuit corresponds to the positive peak value and the negative peak value, respectively. And a peak circuit that outputs a second reference voltage, an inverting circuit that inverts the signal read from the magnetic recording medium, and a first reference voltage output from the peak circuit and an output signal of the inverting circuit. And a second comparison circuit for comparing the second reference voltage output from the peak circuit with the output signal of the inverting circuit, the first comparison circuit and the second comparison circuit.
And a binarization circuit that forms a binary data signal corresponding to the signal read from the magnetic recording medium, which is set and reset according to the output of the comparison circuit.

Here, the peak circuit includes a first capacitor to which a signal read from the magnetic recording medium is applied via a first diode and which is charged by a positive peak of the signal read from the magnetic recording medium, and A first discharge circuit that discharges the first capacitor with a predetermined time constant when a positive peak occurs in the inverting circuit; and a signal read from the magnetic recording medium is applied via a second diode,
A second capacitor charged by the negative peak of the signal read from the magnetic signal medium, and a second discharge circuit for discharging the second capacitor with a predetermined time constant when the negative peak of the inverting circuit occurs. And can be configured.

(Operation) The peak value of the signal read from the magnetic recording medium is detected by the peak circuit, and the signal read from the magnetic recording medium is binarized based on the reference voltage corresponding to this peak value. As a result, even if there is noise or disturbance in the waveform, only the signal component can be reliably binarized, and a stable read waveform that is not affected by noise or the disturbance in the waveform can be obtained.

(Embodiment) An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows an embodiment of a read circuit for a magnetic recording medium according to the present invention. Note that, in FIG. 1, parts having the same configurations as those of the conventional circuit shown in FIG. 7 are denoted by the same reference numerals as those in FIG. 7 for convenience of explanation.

In FIG. 1, the magnetic signal read by the magnetic head 1 is amplified by the amplifier 10 and input to the inverting circuit 40.

The inverting circuit 40 is composed of an operational amplifier OP1 in which an input resistor R1 is connected to the inverting input, and a feedback resistor R2 is connected between the output and the inverting input, and the magnetic signal input via the input resistor R1 is inverted. Output. The output of this inverting circuit 40 is applied to the peak circuit 50.

The peak circuit 50 has a diode D1 whose anode is connected to the output of the operational amplifier OP1, a capacitor C1 which is connected to the cathode of this diode D1 and whose other end is grounded, and resistors R3 and R4 which are connected in parallel to this capacitor C1. It consists of a series circuit, charging the condenser C1 by the peak value of the output of the operational amplifier OP1, discharging it through the series circuit of the resistors R3, R4, and from the connection point of the resistors R3, R4 of the operational amplifier OP1. A voltage signal corresponding to the output peak value is output as a reference signal. This reference signal is applied as a comparison reference voltage to the comparators COM1 and COM2 of the comparator circuit 60.

The outputs of the operational amplifier OP1 and the amplifier 10 are added to the comparators COM1 and COM2 of the comparator circuit 60, respectively. Comparator of comparator circuit 60
COM1 and COM2 are the output of operational amplifier OP1 and amplifier 1
Each output of 0 is compared with the reference voltage output from the peak circuit. The output of the comparator COM1 is applied to the set input S of the flip-flop 70, and the output of the comparator COM2 is applied to the reset input R of the flip-flop 70.

The flip-flop 70 is set and reset by this, and the waveform-shaped target output signal is obtained from its output Q.

The operation of this embodiment will be further described with reference to the waveform chart shown in FIG. Assuming that the output of the amplifier 10 shown in FIG. 1, that is, the signal waveform at the point a is the waveform shown by the solid line in FIG. 2 (a), the output of the inverting circuit 40 shown in FIG. The signal waveform of is the waveform shown by the dotted line in FIG.

The capacitor C1 in FIG. 1 is charged by the peak value of the output of the inverting circuit 40, and the time constant C1 (determined by the resistance value of the series circuit of the resistors R3 and R4 and the capacitance value of the capacitor C1 until the next peak value comes It is discharged at R3 + R4). Since the voltage of this capacitor C1 is divided by resistors R3 and R4, the peak circuit
The output waveform of 50, that is, the waveform of the point a3 becomes the waveform shown by the alternate long and short dash line in FIG.

The comparator COM1 of the comparator circuit 60 compares the output of the inverting circuit 40 indicated by the dotted line a2 in FIG. 2A with the output of the peak circuit 50 indicated by the alternate long and short dash line a3 in FIG. It outputs a high level signal while the output of 40 is larger than the output of the peak circuit 50. Therefore, the output waveform of the comparator COM1, that is, the waveform at the point b is the second
As shown in FIG.

Further, the comparator COM2 of the comparator circuit 60 is the second
The output of the amplifier 10 shown by the solid line a1 in FIG. 2A is compared with the output of the peak circuit 50 shown by the alternate long and short dash line a3 in FIG. 2A, and the output of the amplifier 10 is larger than the output of the peak circuit 50. Outputs a high level signal. Therefore, the output waveform of the comparator COM2, that is, the waveform at the point c is as shown in FIG. 2 (c).

The output waveform of the comparator COM1 shown in FIG. 2 (b) is applied to the set input S of the flip-flop 70, and the output waveform of the comparator COM2 shown in FIG. 2 (c) is applied to the reset input R of the flip-flop 70. Therefore, the output Q of the flip-flop 70 outputs a signal waveform as shown in FIG.

Here, even if the output of the amplifier 10 contains noise or waveform disturbance as indicated by waveform portions n1 and n2 in FIG. 2 (a), this noise or waveform disturbance is the flip-flop 70 which is the target waveform signal. Output Q does not appear.

By the way, in the embodiment shown in FIG. 1, when the cycle of the magnetic signal input from the magnetic head becomes long, the peak circuit 50
The reference voltage output from the peak circuit 50 decreases due to the discharge of the capacitor C1 of the comparator C1. Therefore, the noise of the portion indicated by point A in FIG.
Responds, and the noise in the portion indicated by point A cannot be removed. To solve this, the peak circuit
The discharge time constant of 50 can be increased by increasing C1 (R3 + R4), but when the discharge time constant of peak circuit 50 is increased by increasing C1 (R3 + R4), the output of peak circuit 50 is the peak of the magnetic signal input from the magnetic head. When the peak value of the magnetic signal input from the magnetic head fluctuates greatly as shown by the point B in FIG. 4, the comparator circuit 60 stops responding to the peak value of the magnetic signal.
Therefore, a read error occurs.

FIG. 5 shows another embodiment of the present invention in which the above points are improved. In this embodiment, the positive peak value and the negative peak value of the signal read from the magnetic card are detected, and the positive peak value and the negative peak value are respectively corresponded to, and the next negative peak value and the positive peak value are detected. The peak circuit 500 that outputs the first and second reference voltages holding the value up to is provided, and the peak circuit 500 is provided by the comparator circuit 600.
The first reference voltage output from 500 is compared with the output signal of the inverting circuit that inverts the signal read from the magnetic card, and the second reference voltage output from the peak circuit 500 and the output signal of the inverting circuit are compared. And the target waveform signal is obtained based on the output of the comparator circuit 600.

In FIG. 5, the signal waveform output from the amplifier 10,
That is, if the waveform at the point a1 is the waveform a1 shown by the solid line in FIG. 6 (a), the output waveform of the inverting circuit 40, that is, the point a2.
Waveform becomes a waveform a2 as shown by the dotted line in FIG. 6 (a).

The output of the amplifier 10 is added to the capacitor C2 via the resistor R5 and the diode D2 of the peak circuit 500, and is also added to the capacitor C3 via the resistor 8 and the diode D3.
The other ends of the capacitors C2 and C3 are respectively grounded, a series circuit of a resistor R6 and a transistor TR1 is connected in parallel to the capacitor C2, and a series circuit of a resistor R9 and a transistor TR2 is connected in parallel to the capacitor C3. The outputs of capacitors C2 and C3 are applied to comparators COM5 and COM6, respectively, and the inverting circuit is connected to the other inputs of comparators COM5 and COM6.
The outputs of 40 are applied respectively, and the outputs of comparators COM1 and COM4 are applied to the bases of transistors TR1 and TR2 via resistors R7 and R10, respectively.

Therefore, the capacitor C2 is first charged when the positive peak occurs from the amplifier 10. Transistor here
Since TR1 is off, this charge is retained. Amplifier 10
Causes a negative peak, and in response thereto causes a positive peak from the inverting circuit 40, the output of the comparator COM3 becomes high level. This turns on transistor TR1 and discharges capacitor C2 via resistor R6. Then, the positive peak of the inverting circuit 40 rises, and the comparator CO
When the output of M3 becomes low level, the transistor TR1 is turned off, and the output of the capacitor C2 is held in this state.
As a result, the output of the capacitor C2, that is, the signal waveform at the point a3 becomes the waveform a3 shown by the alternate long and short dash line in FIG. 6 (a). The tree waveform a3 is applied to the comparator COM5 of the comparator circuit 600 as the first reference voltage.

Also, the capacitor C3 is first charged when the amplifier 10 has a negative peak. Here, since the transistor TR2 is off, this charge is maintained. When a positive peak is generated from the amplifier 10 and a negative peak is generated from the inverting circuit 40 in response to the positive peak, the output of the comparator COM4 becomes high level. This turns on the transistor TR2, and the capacitor C3 is discharged via the resistor R9. Then, when the negative peak of the inverting circuit 40 rises and the output of the comparator COM4 becomes low level, the transistor TR2 is turned off and the output of the capacitor C3 is held in this state. As a result, the output of the capacitor C3, that is, the signal waveform at the point a4 becomes the waveform a4 shown by the alternate long and short dash line in FIG. 6 (a). This waveform a4 is used as the second reference voltage by the comparator circuit 600.
Added to the comparator COM6.

The comparator COM5 of the comparator circuit 600 outputs the output of the inverting circuit 40 indicated by the dotted line a2 in FIG. 6 (a) and the first reference voltage (waveform a3) indicated by the alternate long and short dash line in FIG. 6 (a).
When the output of the inverting circuit 40 is larger than the first reference voltage, a high level signal is output. Therefore, the output waveform of the comparator COM5, that is, the waveform at the point b is as shown in FIG. 6 (b).

Further, the comparator COM6 of the comparator circuit 600 is the output of the inverting circuit 40 indicated by the dotted line a2 in FIG.
The second reference voltage (waveform a shown by the dashed line in FIG.
4) is compared, and when the output of the inverting circuit 40 is smaller than the second reference voltage, a high level signal is output. Therefore, the output waveform of the comparator COM6, that is, the waveform at the point c is as shown in FIG. 6 (c).

The output waveform of the comparator COM5 shown in FIG. 6 (b) is applied to the set input S of the flip-flop 70, and the output waveform of the comparator COM6 shown in FIG. 6 (c) is applied to the reset input R of the flip-flop 70. Therefore, a signal waveform as shown in FIG. 6 (d) is output from the output Q of the flip-flop 70.

Here, even if the output of the amplifier 10 contains noise or waveform disturbance as shown by waveform portions n1 and n2 in FIG. 6 (a), this noise or waveform disturbance is the flip-flop 70 which is the target waveform signal. Output Q does not appear.

(Effect of the Invention) As described above, according to the read circuit of the magnetic recording medium of the present invention, even if the signal from the magnetic head has noise or waveform disturbance, a stable and correct signal waveform is obtained. be able to.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a magnetic recording medium reading circuit according to the present invention, and FIG. 2 is a signal waveform diagram for explaining the operation of the embodiment shown in FIG. 1, FIG. 3, and FIG. Is a signal waveform diagram for explaining the inconvenient operation of the embodiment shown in FIG. 1, FIG. 5 is a circuit diagram showing another embodiment of the read circuit of the magnetic recording medium of the present invention, and FIG. 6 is shown in FIG. FIG. 7 is a signal waveform diagram for explaining the operation of the embodiment shown in FIG. 7, FIG. 7 is a circuit diagram showing a reading circuit of a conventional magnetic recording medium, and FIG. 8 is a signal waveform diagram for explaining the operation of the circuit shown in FIG. is there. 1 ... magnetic head, 10 ... amplifier, 20 ... differential amplifier,
30 …… Schmidt circuit, 40 …… Inversion circuit, 50,500 ……
Peak circuit, 60, 600 ... Comparator circuit, 70 ... Flip-flop.

Claims (4)

(57) [Claims] 1. A peak circuit for detecting a peak value of a signal read from a magnetic recording medium and outputting a reference voltage corresponding to the peak value; an inverting circuit for inverting the signal read from the magnetic recording medium; A first comparing circuit for comparing a reference voltage output from the peak circuit with an output signal of the inverting circuit; and a second comparing circuit for comparing the reference voltage output from the peak circuit with a signal read from the magnetic recording medium. And a comparator circuit which is set and reset corresponding to the outputs of the first comparator circuit and the second comparator circuit to form a binary data signal corresponding to the signal read from the magnetic recording medium.
And a reading circuit for the magnetic recording medium, which comprises a digitizing circuit. 2. The peak circuit includes a capacitor to which the output of the inverting circuit is applied via a diode and which is charged by the output of the inverting circuit, and a resistor circuit which discharges the capacitor with a predetermined time constant. A read circuit for a magnetic recording medium according to claim 1, further comprising: a voltage signal divided by a resistance circuit to generate a voltage signal corresponding to a charging voltage of the capacitor. 3. A positive peak value and a negative peak value of a signal read from a magnetic recording medium are detected, and first and second peak values corresponding to the positive peak value and the negative peak value, respectively.
A peak circuit for outputting the reference voltage of the above, a inverting circuit for inverting the signal read from the magnetic recording medium, and a first circuit for comparing the first reference voltage output from the peak circuit with the output signal of the inverting circuit. Comparing circuit, a second comparing circuit for comparing the second reference voltage output from the peak circuit with the output signal of the inverting circuit, and outputs of the first comparing circuit and the second comparing circuit. 2 is set and reset corresponding to, and forms a binary data signal corresponding to the signal read from the magnetic recording medium.
And a reading circuit for the magnetic recording medium, which comprises a digitizing circuit. 4. The peak circuit includes a first capacitor to which a signal read from the magnetic recording medium is applied via a first diode and which is charged by a positive peak of the signal read from the magnetic recording medium. A first discharge circuit that discharges the first capacitor with a predetermined time constant when a positive peak occurs in the inverting circuit; and a signal read from the magnetic recording medium is applied via a second diode, A second capacitor charged by the negative peak of the signal read from the magnetic recording medium; and a second discharge circuit for discharging the second capacitor with a predetermined time constant when the negative peak of the inverting circuit occurs. The read circuit for a magnetic recording medium according to claim 1, further comprising: