JPH0363785B2 - - Google Patents

Description

[Detailed Description of the Invention] <<Industrial Application Field>> The present invention relates to a magnetic pattern reading device used, for example, in a device that reads a magnetic pattern printed with magnetic ink on a banknote and determines the authenticity of the banknote. In particular, it relates to improvements using magnetoresistive heads.

<<Prior Art>> FIG. 1A shows a schematic structure of a general magnetoresistive head. This magnetoresistive head 1 has two magnetoresistive elements 2, 2 and a permanent magnet 3 for generating a bias magnetic field built into its core. Figure B shows an example of an object 4 to be read, such as a banknote.
A pattern 5 is printed on this using magnetic ink. When the pattern 5 of the object to be read 4 is scanned by the magnetoresistive head 1 in the direction of arrow a, the magnetoresistive head 1 produces an output with a waveform as shown in FIG. As shown in the figure, the output of the magnetoresistive head 1 has a differential waveform, and extremely sharp pulse outputs are generated at random intervals depending on the presence or absence of magnetic ink in the pattern 5 of the object to be read.
Note that in the waveform diagram of C, a small-level pulse indicated by the symbol N is a noise component.

Conventionally, apparatuses have been known in which the output of the above-mentioned magnetoresistive head is processed by a processing circuit such as a microcomputer (called a CPU), and the magnetic pattern of the pattern 5 is read and recognized. In conventional magnetic pattern reading devices of this type,
Sampling the output of magnetoresistive head 1
The following two methods are well known as circuit methods for reading data into the CPU.

Here, in the first method, as shown in FIG. 2C, the output of the magnetoresistive head 1 is directly A/D converted by an A/D conversion circuit 8 via an amplifier circuit 6.
The sampling pulse is read into the CPU 9, and the CPU 9 supplies the sampling pulse to the A/D conversion circuit 8.

In the second method, as shown in FIG. 2A, after the output of the magnetoresistive head 1 is amplified by an amplifier 6,
The signal is smoothed by a smoothing circuit 7 consisting of a diode, a resistor, a capacitor, etc., the smoothed output is converted into a digital signal by an A/D conversion circuit 8, and the digital output is read into the CPU 9.

<<Problem to be Solved by the Invention>> However, in the conventional device as described above, in the first method, the output of the magnetoresistive head 1 is a sharp pulse-like output as shown in FIG. 1C. Therefore, if the timing of A/D conversion deviates even slightly from the sharp pulse output that should be read, the converted data will differ greatly from the actual pulse peak value, and the accuracy of the data will deteriorate significantly. There were flaws. In addition, in order to read the sharp pulse output shown in Figure 1C, the sampling period must be extremely short.
Therefore, a high-speed A/D conversion circuit 8 is required, and the reading load on the CPU 9 also increases.

On the other hand, FIG. 2B shows the relationship between the input of the smoothing circuit 7 (output of the magnetoresistive head 1) and its smoothed output in the second method. While the pulse width is very small, the smoothed output has a waveform with an expanded time width, so in the second method, slight errors in the timing of A/D conversion do not pose a problem.
However, since the pulse width of the output of the magnetoresistive head 1 is extremely small, the level of its smoothed output does not rise sufficiently, and in the second method, the degree of discrimination between the noise component and the signal component, that is, the signal-to-noise ratio, deteriorates. There were flaws.

This invention was made in view of the above-mentioned problems in the prior art, and its purpose is to reliably sample the peak value of the sharp pulse output of the magnetoresistive head, and to obtain accurate data with a good signal-to-noise ratio. An object of the present invention is to provide a magnetic pattern reading device that can read magnetic patterns.

<Means for Solving the Problems> In order to achieve the above object, the present invention provides a magnetoresistive head that scans an object to be read, an amplifier circuit that amplifies the output of the magnetoresistive head, and an amplifier circuit that amplifies the output of the magnetoresistive head. A peak hold circuit that peak-holds the output, an A/D conversion circuit that converts the analog output of this peak hold circuit into a digital signal, a pulse generation circuit that generates a read pulse that defines the read timing, and a A data processing circuit that reads the output of the A/D conversion circuit and performs magnetic pattern recognition processing every time a read pulse is generated; and means that resets the peak hold circuit in synchronization with the read pulse from the pulse generation circuit. It is characterized by being composed of.

"Example" Hereinafter, this invention will be explained based on the drawings.

FIG. 3 shows the configuration of a magnetic pattern reading device according to an embodiment of the present invention, and FIG. 4 is a waveform chart showing its operation.

In this reading device, the output of the magnetoresistive head 1 is passed through an amplifier circuit 6 to a peak hold circuit 10.
is input. The output b of the peak hold circuit 10 is input to the A/D conversion circuit 8 and converted into a digital signal at the timing described below, and the digital output is read into the CPU 9.

A/D conversion operation of the A/D conversion circuit 8 and
The digital signal reading process by the CPU9 is as follows:
This is done in synchronization with the read pulse c from the pulse generating circuit 11. In addition, the peak hold circuit 10
is reset by the CPU 9 immediately after reading the digital signal. As shown in FIG. 4, the pulse generation circuit 11 outputs a read pulse c with a constant period that defines the read timing, and this read pulse c is applied as a conversion timing pulse to the A/D conversion circuit 8. , is applied to the CPU 9 as an interrupt signal.

The A/D conversion circuit 8 receives the read pulse c and converts the analog output b of the peak hold circuit 10 into a digital signal. When the CPU 9 finishes reading the digital signal, it supplies a reset signal d to the peak hold circuit 10 to reset it. Therefore, the peak hold circuit 10 then operates to hold the peak value of the signal a given from the amplifier circuit 6.

The above operation will be explained in more detail with reference to the waveform diagram of FIG. 4. At the rising edge of the read pulse c, t1, the A/D conversion circuit 8 performs the A/D conversion operation. That is, at time t1, the analog data of the A1 portion of the signal b is converted into digital data, as shown in FIG.

Further, in the CPU 9, an interrupt process is activated at the falling edge of the read pulse C, t2, and reads the digital data sent from the A/D conversion circuit 8. At the same time, the CPU 9 sends a reset signal d to reset the peak hold circuit 10.
Output. In this case, the pulse width w of the reset signal d is sufficiently shorter than the period F of the read pulse c, and the output b of the peak hold circuit 10 is initialized by the reset signal d. The peak hold circuit 10 then holds the amplifier circuit 6 until the next reset signal d is input.
An operation is performed to peak-hold the output a of.

The above operations are repeated in synchronization with the read pulse c from the pulse generation circuit 11, and the CPU
9 executes magnetic pattern recognition processing according to the digital data read in sequence, and performs, for example, determining the authenticity of banknotes.

Note that in the above embodiment, the peak hold circuit 1
Although the reset to 0 is performed by the CPU 9, it may be configured to be reset by another circuit as long as it can be synchronized with the digital data reading process by the CPU 9.

<<Effects of the Invention>> As explained above, in this invention, the peak value of the output of the magnetoresistive head during the sampling period of each period of the read pulse can be reliably read into the data processing circuit, and the peak value of the output of the magnetoresistive head can be reliably read into the data processing circuit. This has the effect of making it possible to read magnetic patterns with extremely high reliability.

[Brief explanation of drawings]

Figures A, B, and C show the configuration of a magnetoresistive head;
Diagrams showing an example of an object to be read and the output waveform when it is read with a magnetoresistive head,
2A, B, and C are diagrams showing a configuration example of a conventional reading device and its operating waveforms, FIG. 3 is a block diagram showing the configuration of a magnetic pattern reading device according to an embodiment of the present invention, and FIG. 4 3 is a diagram showing operation waveforms of each part in FIG. 3. FIG. 1... Magnetoresistive head, 2... Magnetoresistive element,
3...Permanent magnet, 4...Permanent magnet, 5...Pattern by magnetic ink, 6...Amplification circuit, 8...A/D
Conversion circuit, 9...CPU (data processing circuit), 10
...Peak hold circuit, 11...Pulse generation circuit.

Claims (1)

[Claims] 1 A magnetoresistive head that scans the object to be read, an amplifier circuit that amplifies the output of this magnetoresistive head, a peak hold circuit that peak-holds the output of the amplifier circuit, and converts the analog output of this peak hold circuit into a digital signal. Convert A/
A D conversion circuit, a pulse generation circuit that outputs a read pulse that defines read timing, and each time a read pulse is generated from this pulse generation circuit, the output of the A/D conversion circuit is read and magnetic pattern recognition processing is performed. A magnetic pattern reading device comprising a data processing circuit and means for resetting the peak hold circuit in synchronization with a read pulse from the pulse generating circuit.