JPH0685452B2 - Hall voltage processing device - Google Patents

Description

Description: [Industrial application] The present invention is used, for example, to configure a rotation angle detection device for a rotating body, and a hall voltage processing circuit that amplifies and outputs a minute voltage signal from a hall element. Regarding

[Background Art] For example, a rotation angle detection device for an automobile engine includes a rotating body having a plurality of magnetic poles that are rotated coaxially with the engine, and in a state of being close to a magnetic pole surface of the rotating body, By fixedly setting the Hall element, and detecting the proximity passage of the magnetic pole with this Hall element by the change of the magnetic field,
The specified rotation angle of the engine is detected.

In this case, the output voltage from the Hall element is as small as several tens of mV and its voltage amplitude is small even in a state where the magnetic field acting on the Hall element changes relatively greatly.
Further, when the Hall element is in a state where current is consumed for detecting the output signal due to the principle of the Hall effect, the output voltage from the Hall element is remarkably reduced.
Therefore, in the signal processing circuit to which the output signal from this Hall element is supplied, impedance conversion is performed in order to set an almost infinite impedance as shown in FIGS. 3 and 4, for example. And an amplifier that amplifies the subsequent signal. Then, the amplified output signal is compared with a reference voltage Vref that sets a predetermined threshold level, and is converted into a logical amplitude level, and the presence or absence of a magnetic field is detected by the converted logical output. That is, by setting the reference voltage Vref in correspondence with a desired magnetic field threshold level Bref, for example, the proximity passing state of magnetic poles is detected.

FIG. 3 shows an example of a processing circuit in which a large impedance is set in order to extract the output signal from the Hall element as described above. The output terminals a and b of the Hall element 11 are shown in FIG.
The output voltage signal during is fed to an impedance converter 12 which is set to an impedance of approximately infinity. The output signal from the impedance converter 12 is amplified by an amplifier 13, and then a predetermined set reference voltage Vref by a comparator 14.
And the comparison logic output is output as a Hall voltage detection signal. That is, when the Hall element 11 detects a magnetic field strength equal to or higher than a predetermined level, the output signal from the comparator 14 becomes a high level and the increase state of the magnetic field strength is detected.

Further, in the case of FIG. 4, a differential amplifier 17 in which the detection signal from the Hall element 11 is used as both an impedance converter and an amplifier by the OP amplifiers 15 and 16 is constructed, and its output signal is compared. It is designed to be supplied to 14.

However, in the processing circuit for the detection signal from the Hall element configured as described above, at least one circuit element is required for each of the impedance converter, the amplifier, and the comparator, and the circuit configuration is required. It gets complicated.

[Problems to be Solved by the Invention] The present invention has been made in view of the above points, and is intended to reliably detect a detection signal from a Hall element by a processing circuit having a sufficiently simple circuit configuration. In addition, it is an object of the present invention to provide a Hall voltage processing device that can effectively set the magnetic field threshold level to be detected with some arbitrariness and can be effectively used as, for example, a rotation speed detection mechanism of an engine.

[Means for Solving the Problems] That is, in the Hall voltage processing device according to the present invention, impedance conversion is performed by the first and second transistors configured to connect the output terminals from the Hall element to the respective bases. The circuit is configured, and the first and second transistors are set so that a constant current is supplied respectively. Then, a resistance for level shifting is connected to the first transistor circuit, and the threshold level set by the resistance is compared with the output voltage from the Hall element supplied to the impedance conversion circuit. A circuit is used for comparison, and an output signal for detecting a change in the magnetic field strength acting on the Hall element is obtained from the comparison circuit.

[Operation] In the Hall element voltage processing device configured as described above, the output potential difference appearing between the output terminals of the Hall element is set between the emitters of the first and second transistors. Further, since a constant current is applied to the resistance portion, a predetermined potential difference is set, and the potential difference generated in the resistance portion and the first difference
And the Hall voltage generated in the second transistor portion is compared and output. Therefore, this comparison logic output detects the Hall voltage by using the potential difference set in the resistance portion as a threshold voltage, and the resistance level of the detection magnetic field can be arbitrarily set by this resistance. Is.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 shows its configuration. The Hall element 21 detects, for example, the near passage of a magnet by the change of the magnetic field strength, and a voltage signal corresponding to the magnetic field strength is provided between its output terminals a and b. Is output. The output terminals a and b of the Hall element 21 are connected to the bases of the first and second transistors 22 and 23, respectively. The first and second transistors 22 and 23 form an impedance conversion circuit 24.
Constant current circuits 25 and 26 are set in the emitter circuits of the transistors 22 and 23, respectively.
Is set so that a constant current Icc is applied to each of them.

In addition, the emitter of the first transistor 22 has a resistor
27 is connected and set in series, and the constant current Icc flows through the resistor 27 so that a potential difference corresponding to the resistance value R is set between both ends c and d points. Then, the potential difference between the point d and the point e of the emitter of the second transistor 23 is detected by the comparison circuit 28, and the logic output f is obtained from the comparison circuit 28.

That is, the minute output voltage Vin generated between the output terminals of the hall element 21 is supplied to the impedance conversion circuit 24. Also, the resistor 27 constitutes a level shift circuit, and from the relationship between the current Icc flowing through the resistor 27 and the resistance value R, a potential difference of Vref = Icc × R is set between both ends cd of this resistor. Then, the potential Vref is level-shifted. Therefore, the point d input to the comparison circuit 28
The potential difference between and e is "Vin-Vref".

Therefore, the comparison circuit seen from the output terminal side of the Hall element 21
The logic outputs of 28 are in a state equivalent to those having an apparent threshold voltage Vref.

FIG. 2 (A) shows the relationship between the magnetic flux density B of the magnetic field acting on the Hall element 21 and the output voltage of the Hall element 21, and the magnetic flux density B and the output voltage of the Hall element 21 are direct. Have a relationship. Then, the magnetic field threshold level Bref is set with respect to the voltage Vref, and the low level as shown in FIG. 2B from the comparison circuit 28 corresponds to the magnetic field threshold level Bref. And a logic output that changes to a high level binary value is obtained.

In this case, the threshold voltage Vref is
By adjusting and setting the constant current value set by 25 and the value R of the resistor 26, it becomes possible to set an arbitrary value. That is, the magnetic field threshold level Br for obtaining the logical output
ef can be easily adjusted with arbitrariness.

Although the means for setting the magnetic field threshold level Bref can be configured simply, the setting voltage Vref and the magnetic field threshold level Bref have a linear relationship, and therefore the degree of freedom of setting is great. Further, in order to compensate the temperature characteristic of the Hall element 21, an element having a certain temperature coefficient can be adopted for the resistor 27 or the constant current circuits 25 and 26. Therefore, the temperature compensation of the Hall element 21 can be easily carried out in the state of good accuracy, and the magnetic field strength detecting device with high reliability can be easily constructed.

In this case, if the resistor 27 and the constant current circuits 25 and 26 are formed on the same semiconductor chip, it becomes easy to make the temperature characteristic of the threshold voltage zero, and the Hall element 21 and its signal processing circuit. If all the parts are formed on the same semiconductor chip, the hall sensor can be formed at an extremely low cost.

Furthermore, the output signal from the comparison circuit 28 causes a constant current circuit.
If it is configured to change the constant current value Icc of 25, it can be set to have a hysteresis function. Therefore, a more reliable magnetic field detection mechanism is configured, and, for example, the reliability of the detection signal of the rotation speed detection mechanism is further improved.

Here, the constant current circuits 25 and 26 may be configured by resistors when the setting accuracy is not a particular problem.

[Advantages of the Invention] As described above, the Hall voltage processing device according to the present invention is
It can be configured by a simple impedance conversion circuit including individual transistors, and can be very effective in configuring an engine rotation speed detection device for an automobile, for example. Further, in this Hall voltage processing device, the magnetic field threshold level can be easily adjusted and set, and the temperature characteristics can be easily compensated. , Which is extremely effective for further improving reliability.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram for explaining a Hall voltage processing device according to an embodiment of the present invention, FIG. 2 is a diagram for explaining the relationship between the Hall element output and the processing output with respect to the magnetic flux density, and FIG.
FIG. 4 and FIG. 4 are diagrams showing examples of conventional processing circuits. 21 …… Hall element, 21, 23 …… Transistor, 24 …… Impedance conversion circuit, 25, 26 …… Constant current circuit, 27 ……
Resistance (for level shift), 28 …… Comparison circuit.

Claims (1)

[Claims] 1. A first and second transistor, which constitutes an impedance conversion circuit and is base-controlled by a pair of output voltages of a Hall element, and a resistor for level shift, which is connected and set to the first transistor circuit. A constant current circuit set so that a constant current flows through each of the first and second transistor circuits, and a threshold level set by the resistor,
A comparison circuit for comparing the output level of the Hall element supplied to the impedance conversion circuit is provided, and the detection output of the change in the magnetic field strength acting on the Hall element is obtained from this comparison circuit. Characteristic Hall voltage processing device.