JPS606130B2 - Amplitude modulated wave detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention amplifies the amplitude of an amplitude modulated wave from a modulated carrier wave obtained by modulating, for example, an AC bias current of a magnetic head with an amplitude modulated wave of a minute amplitude by a magnetic pattern on a banknote. This invention relates to a method for detecting amplitude modulated waves.

Traditionally, in addition to banknote authentication devices themselves, with the recent spread of automatic transaction devices such as currency exchange machines and automatic teller machines, devices with banknote identification functions have come into widespread use. There is a need for a method to determine the authenticity of banknotes.

Banknotes are identified by detecting various information such as printed figures, dimensions, watermarks, thickness, and magnetic strength and distribution contained in ink. Among these methods, magnetic detection methods have recently attracted attention. When the magnetic head used as a sensor in such a device having a banknote discrimination function is used as an AC bias type, the current flowing through the magnetic head undergoes amplitude modulation corresponding to the magnetic pattern on the banknote, but the degree of modulation is, for example, 1/1.
Very small, 1 to 1/1 pi. If the amplitude modulated wave does not have a certain amplitude, it will be difficult to demodulate it circuit-wise, so it is necessary to increase the degree of modulation. For this reason, conventionally, a differential magnetic head 1 is used as shown in FIG. In the method of increasing the modulation degree when using this differential magnetic head 1, first, the primary coil 2o of the transformer 2 is connected to the differential magnetic head 1, and the secondary coil 2o is connected to the differential magnetic head 1.
, , 22 are provided in series between the output terminals AB so that the respective induced voltages cancel each other out. The neutral point between the secondary coils 2, 22 is connected between A and B for the volume 5 through a capacitor C, and for the volume 6 through a resistor R to each variable voltage division point. .

First, adjust the volume so that the output between output terminals A and B is zero volts when no modulation is performed, and after achieving balance, when modulation is applied, the output frequency component of the magnetic head will be different from when no modulation is performed. The inductance of the magnetic head and the impedance of the capacitor change, causing imbalance. For this reason, a voltage will appear between AB to the extent that the balance is disrupted, and the degree of modulation will increase. However, in this case, the problem is that a special differential magnetic head is used as the magnetic head. SUMMARY OF THE INVENTION An object of the present invention is to provide an amplitude modulated wave detection method that amplifies the amplitude of an amplitude modulated wave from a magnetic head and detects the amplitude modulated wave without using a special magnetic head. In order to achieve the above object, the amplitude modulated wave detection method of the present invention detects an amplitude modulated wave from a modulated carrier wave modulated with an amplitude modulated wave of minute amplitude by amplifying its amplitude. An amplifier is provided to amplify the difference between the reference voltage and the modulated carrier wave, the absolute value of which is larger than the peak point of the half-wave of The amplification degree of the amplifier is set so that the voltage reaches the saturation voltage of the amplifier, and a detected signal of an amplitude modulated wave whose amplitude is amplified is obtained from a portion of the amplified signal that does not reach the saturation voltage.

Examples of the present invention will be described in detail below.

FIG. 2 is an explanatory diagram showing the configuration of an embodiment of the present invention.

In the same figure, the input waveform is a carrier wave modulated by a small amplitude amplitude modulation wave due to the magnetic pattern on the banknote, and it is input from the input end to the E terminal of the operational amplifier organ, and a negative voltage (Ichijo) is applied to the Y terminal. A reference voltage is supplied through a voltage adjustment volume electric board that is divided into two parts.A series of two or three diodes connected in series is installed in parallel with the voltage adjustment volume electric board to stably output a minute voltage. By adjusting the voltage adjustment volume controller 2 as appropriate, the operational amplification organ'
The input voltage is adjusted. FIG. 3 is an explanatory diagram of the operation of the embodiment shown in FIG.

Figure a shows the relationship between the input voltage, which is a carrier wave modulated with a minute modulation degree sent from the magnetic head, and reference voltage B, which is set to a voltage value lower than the negative peak value of input voltage A. It shows. As seen in the figure, the time L when the input voltage A reaches a negative peak value; t3, 9 t7,
..., the difference between input voltage A and reference voltage B is small "when input voltage A reaches a positive peak value" t2, t4
? Also, the difference between input voltage A and reference voltage B is large. Now, if reference voltage B is considered as a reference voltage, the voltage difference between input voltage A and reference voltage B is always a positive voltage, as is clear from Figure 3a, and this pen voltage is It is applied as an input voltage and is inverted and amplified.

FIG. 3b shows the output voltage of the operational amplifier 11. Since the differential voltage as described above is inverted and amplified, the output voltage is always a negative voltage. At that time, "Time et al, t3, et?,...
Since the input differential voltage is small in , by adjusting the voltage adjustment potentiometer 2, it is possible to set the operational amplifier 11 to a range in which it does not reach saturation. Therefore, near the negative peak value of the input voltage A, Amplification is performed according to the voltage difference from reference voltage B. On the other hand, at times t2, t4,
In ..., the input voltage difference is large, so it reaches the negative saturation voltage of operational amplifier 1. In other words, the area near the positive peak point of input voltage A reaches the saturation voltage, and the area near the negative peak point Even in this way, the circuit shown in FIG. 2 amplifies only the vicinity of the negative peak point every half wave, and the amplitude of the t-amplitude modulated wave is amplified.

Furthermore, as can be seen from the waveform in FIG. 3b, only one half wave is amplified and the other half wave is saturated, so a detected signal is obtained and amplification and detection can be performed all at once. The portion to be saturated can be adjusted as appropriate using the voltage adjustment knob 2. The first matrix diagram is an explanatory diagram of an application example of the present invention. This circuit is an example of a banknote authenticity determination circuit that detects changes in the density of magnetism of a magnetic pattern on a banknote. In the same figure, in order to use the AC bias method, AC bias is applied by the head bias oscillator Maitomi of the magnetic head 2. The amplification and detection of the output of the magnetic head 2 is performed by the operational amplifier Seiko of the present invention and the voltage adjustment volume. 23
This is done by a combination of This detection output waveform is demodulated into a low frequency signal with noise suppressed by the integration circuit umbrella.
This is differentiated through a differential circuit 8, and the output 27 amplified by the amplifier 2 becomes a waveform that can accurately determine the degree of shading of the banknote.Therefore, this is pulsed and a logic circuit automatically detects the true value of the banknote. As explained above, according to the present invention, by using an ordinary magnetic head and an operational amplifier without using a special magnetic head, it is possible to perform amplitude modulation of minute amplitude from a modulated carrier wave. It is possible to detect waves by amplifying their amplitude, and it is possible to obtain signals that are easy to demodulate.

In addition, since a single operational amplifier performs amplification and detection at the same time and does not require a special circuit for detection, the advantage of simple construction and low cost can be emphasized.

Further, it is clear in principle that the present invention can be applied not only to signals obtained from a magnetic head but also to general signals modulated by an amplitude modulated wave of L minute amplitude.

[Brief explanation of the drawing]

Fig. 2 is an explanatory diagram of the conventional example, Fig. 2 is an explanatory diagram showing the configuration of the embodiment of the present invention, Fig. 3 is an explanatory diagram of the operation of the embodiment of Fig. 2, and Fig. 4 is an application example of the present invention. In the figure, 10 is an input terminal, 11 is an operational amplifier, I2 is a voltage adjustment volume, and 13
indicates a diode string, and 14 indicates an output device. Figure 2 Figure 3 Figure 3 Sphere diagram Suto

Claims (1)

[Claims] 1. In order to amplify and detect the amplitude modulated wave from the modulated carrier wave modulated with the amplitude modulated wave of minute amplitude, a reference voltage with an absolute value larger than the peak point of the half wave of the modulated carrier wave and the modulated carrier wave are used. and setting the amplification degree of the amplifier so that the amplified signal of the difference with a portion other than the vicinity of the peak point of the half wave on the side closer to the reference voltage reaches the saturation voltage of the amplifier, An amplitude modulated wave detection method characterized by obtaining a detected signal of an amplitude modulated wave whose amplitude is amplified from a portion of the amplified signal that does not reach a saturation voltage.