JPS61239116A - Output pulse automatic shaping circuit for magnetism detecting circuit - Google Patents

Abstract

PURPOSE:To obtain automatically an optimum threshold level by detecting the maximum value and the minimum value of an output signal from a magnetism detecting element. CONSTITUTION:An output of an operational amplifier 12 is connected to a connecting point of a resistor R1 and a capacitor C1 through a diode D1, and in the same way, an output of an operational amplifier 13 is connected to a connecting point of a resistor R2 and a capacitor C2 through a diode D2. These circuits detect the maximum value B and the minimum value A of an output signal from a magnetism detecting element 11, respectively, and are held by the connecting point. The connecting point of the resistors R1, R2 is connected to a non-inversion terminal of an operational amplifier 14, and its output is connected to an inversion terminal of a comparator 15. Therefore, by the resistors R1, R2, a center voltage C of the maximum value and the minimum value is obtained as a threshold level, and outputted through the amplifier 14. Next, the center voltage C and an output D of the detecting element 11 are compared, and a shaped pulse E is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magnetic detection circuit, and more particularly to an automatic output pulse shaping circuit of a magnetic detection circuit.

(Prior Art) A magnetic detection circuit is used, for example, as a tachometer of the motor in combination with a gear-shaped magnet element attached to the rotating shaft of the motor. Conventionally, in the above-mentioned magnetic detection circuit with a built-in magnetic detection element, when pulse shaping is performed,
The threshold level was finely adjusted using a variable resistor by installing a reference voltage resistor in parallel with the magnetoresistive element. That is, as shown in FIG. 3, the reference R
A resistor 22 was connected, and the threshold voltage level was obtained by this reference resistor 22, but its fine adjustment was performed by a variable resistor 23. Note that the output from the magnetic detection element and the obtained threshold level are the same as the comparator 2.
4, and the shaped pulses were output.

(Problems with the Prior Art) However, in the conventional magnetic detection circuit, as shown in FIG. 4, the potential at the neutral point drifts depending on the direction of rotation, and as shown in FIGS. 5 and 6, Since the resistance value of the magnetic detection element changes due to temperature change, the potential at the neutral point also drifts.

Furthermore, as shown in Fig. 7, the resistance value does not change depending on the frequency of the rotation signal taken out, so the potential at the neutral point does not drift, but as shown in Fig. 8, the resistance value does not change depending on the frequency of the rotation signal taken out. There was a drawback that the potential at the neutral point would drift due to changes in the magnetic detection element.Furthermore, the output of the magnetic detection element fluctuates due to aging, etc., so it was necessary to readjust the threshold level using a variable resistor to match the fluctuation. there were.

(Object of the Invention) An object of the present invention is to provide an output pulse automatic shaping circuit for a magnetic detection circuit that can automatically adjust a threshold level without requiring readjustment of the threshold level.

(Combined invention) The present invention includes a magnetic detection element that detects magnetism and outputs an electrical signal, a circuit that receives the electrical signal of the magnetic detection element, detects and holds the maximum value of the electrical signal, a circuit that receives the electric signal of the magnetic detection element, detects and holds the minimum value of the electric signal; a circuit that obtains a center voltage as a threshold level from the maximum value and the minimum value; An automatic output pulse shaping circuit for a magnetic detection circuit is provided, comprising: a comparison circuit that compares a signal and the center voltage to generate a shaped pulse.

As described above, according to the present invention, since the threshold level is determined from the maximum and minimum values of the output signal from the magnetic sensing element, it is not affected by changes in the rotational direction of the magnetic sensing element, temperature changes, and aging. The optimal threshold level is automatically obtained.

(Example) wIJ1 is a schematic diagram showing the output pulse automatic shaping circuit of the magnetic detection circuit of the present invention, and FIG. 2 is a time chart showing the waveform at each point.

Referring to FIG. 1, the output of the magnetic detection element 11 is connected to the non-inverting terminal of a comparator 15 composed of an operational amplifier, and the output of the magnetic detection element 11 is
2 and 13 non-inverting terminals. The output of the operational amplifier 12 is connected to the connection point of the resistor R1 and the capacitor C1 via the diode D1.
Similarly, the output of the operational amplifier 13 is connected via a diode D2 to a connection point between a resistor R2 and a capacitor C2. The operational amplifier 12, diode-FDI and capacitor CI, and the operational amplifier 13, diode D2 and capacitor C2 are the maximum value B and minimum value A of the output signal from the magnetic detection element, respectively.
It consists of a circuit that detects and holds the Therefore, the maximum value B and the minimum value A are obtained and held at the aforementioned connection point. The connection point between the resistors R1 and R2 is connected to the non-inverting terminal of the operational amplifier 14, and the output thereof is connected to the inverting terminal of the comparator 15 mentioned above. Therefore, the center voltages of the maximum and minimum values are obtained as threshold levels by the resistors R1 and R2, and are outputted via the operational amplifier 14. That is,
A center voltage C will be obtained. The center voltage C as a threshold level and the output of the magnetic detection element are compared in a comparator 15, and a shaped pulse E is output.

Referring to Figure 2, the maximum value B of the output of the magnetic detection element
and the minimum value A are obtained via operational amplifiers 12 and 13. A center voltage C between the maximum value B and the minimum value A is obtained via the resistors R1 and R2 and the operational amplifier 14. The output of the magnetic detection element is compared with the center voltage C by a comparator 15, and a shaped pulse E is obtained.

(Effects of the Invention) As explained above, in the automatic output pulse shaping circuit of the magnetic detection circuit of the present invention, the threshold level is determined from the maximum and minimum values of the output signal from the magnetic detection element. Unaffected by changes in rotation direction, temperature changes, and aging.

The optimal threshold level is automatically obtained and does not require readjustment.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the output pulse automatic shaping circuit of the magnetic detection circuit of the present invention, FIG. 2 is a time chart showing waveforms at each point in FIG. 1, and FIG. 3 is a circuit diagram of 5 conventional techniques. 4 to 8 are characteristic diagrams for explaining the drawbacks of the conventional magnetic detection circuit. 11... Magnetic detection element, 12, 13.14... Operational amplifier, 15... Comparator, DI, D2.
...Diode, C1, C2...Capacitor, R1゜R2...Resistor.

Claims (1)

[Claims] a magnetic detection element that detects magnetism and outputs an electrical signal; a circuit that receives the electrical signal of the magnetic detection element and detects and holds the maximum value of the electrical signal; and a circuit that receives the electrical signal of the magnetic detection element; a circuit that detects and holds the minimum value of the electrical signal;
It is characterized by comprising a circuit that obtains a center voltage as a threshold level from the maximum value and minimum value, and a comparison circuit that compares the electric signal of the magnetic detection element and the center voltage to generate a shaped pulse. Output pulse automatic shaping circuit of magnetic detection circuit.