JPH088787B2 - Integrated circuit with magnetic sensor - Google Patents

Description

Description: [Object of the Invention] (Field of Industrial Application) The present invention relates to an integrated circuit with a built-in magnetic sensor used for detecting a rotor rotational position of a brushless motor.

(Prior Art) As a magnetic sensor, there is a Hall element, and this element utilizes the Hall effect. The Hall effect refers to a phenomenon in which the electric potential distribution on the semiconductor becomes unbalanced due to the Lorentz force acting on the current when a magnetic field is applied to the semiconductor.

FIG. 3 shows the basics of the Hall element. The voltage (Hall voltage) generated in the Y-axis direction when a magnetic field of current IA in the X-axis direction and magnetic flux density B (Wb / m) in the Z-axis direction is applied. ) To V _H
(V) RH; Hall constant (m ³ / C) d; Semiconductor pressure (m). Therefore, in order to increase the sensitivity to the magnetic field, a material having a large Hall constant is selected, and the thickness t of the semiconductor piece is
Would be thin. From this relationship, thin films of InSb and GaAs are often used as the Hall element alone.

On the other hand, a so-called monolithic IC has also been developed in which a Hall element is built into a monolithic integrated circuit (IC) and an amplifier for increasing sensitivity is built in. These are Hall devices configured by using an Si epitaxial layer.

FIG. 4 shows a configuration example of the Hall IC. 1 is a Hall element part using an epitaxial layer, 2 and 3 are input electrodes of the Hall element, 4a and 4b are output terminals, 5 is an isolation region, 6,
Reference numerals 7 and 8 respectively denote a base, an emitter, a collector and a collector buried portion of the transistor.

(Problems to be Solved by the Invention) Since the Hall element alone detects only magnetism, it requires a control circuit such as an amplifier and a power amplifier. The Hall IC is easy to increase the sensitivity, and the output characteristic is easily diversified by only providing the hysteresis characteristic.
However, on the other hand, since the detected output of the Hall element section using the epitaxial layer is small, there is a problem that the operating magnetic flux density is very likely to vary due to the input offset voltage of the differential amplifier that derives this. In other words, due to the input offset voltage of the differential amplifier, a situation may occur in which one differential input is detected but the other differential input cannot be detected. Therefore, careful design is required for the circuit design and the mask pattern design, which causes the price increase.

Therefore, an object of the present invention is to provide a magnetic sensor built-in integrated circuit capable of eliminating the influence of variations in operating magnetic flux density by configuring a magnetic sensor circuit using a monolithic IC.

[Structure of the Invention] (Means for Solving Problems) The present invention relates to a magnetic sensor, a means for supplying a drive current to the magnetic sensor, and a difference in which a detection output of the magnetic sensor is supplied to a differential input. A motion detection amplifier, a switching signal generating means, and a first inverting means for inverting the polarity of the driving current in order to supply the drive current to the magnetic sensor in response to a first output of the switching signal generating means. A second inverting means for alternately inverting the output of the differential detection amplifier in response to the second output of the switching signal generating means, and an output of the second inverting means, and the switching signal A reduction filter having a cutoff frequency set to the output frequency of the generating means is provided so as to cancel the input offset of the detection amplifier equivalently.

(Operation) By the means described above, the polarity of the applied voltage of the Hall element formed inside the IC is alternately switched, and the output of the differential detection amplifier is also switched alternately in synchronization with the switching frequency. As a result, the influence of the input offset of the differential detection amplifier does not affect the output of the low pass filter, and the sensor output can be stably obtained. The reduction filter is for removing switching components.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the basic principle of one embodiment of the present invention. The output electrodes 12 and 13 of the Hall element 11 are connected to the bases of the transistors Q1 and Q2, respectively, which form the differential detection amplifier 16 of the next stage. A driving current is supplied between the driving electrodes 14 and 15 of the Hall element 11, but the polarity thereof is switched by the inverting means 20. That is, the reversing means 20 has the switch parts 20a and 20b, and when the electrode 14 is connected to the power supply line 22 by the switch part 20a, the switch part 20b has the electrode 15a.
To the earth line 23, and conversely connect the electrode 14 to the switch section 20.
When a is connected to the ground line 23, the switch unit 20b is controlled to connect the electrode 15 to the power line 22.

The emitters of the transistors Q1 and Q2 of the operation detection amplifier 16 are connected to the ground line 23 via the constant current source 17.
Further, the collectors of the transistors Q1 and Q2 are connected to the movable contact sides of the switch units 21a and 21b forming the inverting means 21, respectively. Each one fixed contact of the switch units 21a, 21b is commonly connected to the power supply line 22 via the load resistor 18a, and the other fixed contact of each of the switch units 21a, 21b is commonly connected via the load resistor 18b. It is connected to the power supply line 22.

Therefore, the load of the transistors Q1 and Q2 is switched by the inverting means 21, and the output is normally obtained even when the differential input is switched. Then, the transistor side terminals of the load resistors 18a and 18b are connected to the low frequency band fill 19.

The inversion means 20 and 21 are switching signal generation circuits.
Switching control is performed in synchronization with a control pulse from 25.
The low-pass filter 19 is the switching signal generation circuit.
The cutoff frequency is set so as to remove the switch component associated with the switching operation of 25. Further, it is designed to have a pass characteristic for a component of a detection signal required for the system (for example, a signal of an integral multiple of the rotation frequency of the motor).

According to the present invention described above, in terms of the detection capability for the magnetic flux B, it is possible to significantly reduce the factor of variations in the operating magnetic flux density of the magnetic sensor. This is the differential sense amplifier 16
On the other hand, the output of the Hall element is input differentially, and the input amplitude is equivalently expanded.

FIG. 2 shows the configuration of FIG. 1 more specifically. That is, the drive electrode 14 of the Hall element 11 is the transistor Q11, Q
The emitter of the transistor Q11 is connected to the power supply line 22, and the emitter of the transistor Q14 is connected to the ground line 23. And transistor Q11
~ Q14 constitutes the inverting means 20 and the transistor Q
When Q11 and Q12 are turned on, the transistors Q13 and Q14 are turned off, and conversely, when the transistors Q13 and Q14 are turned on, the transistors Q11 and Q12 are turned off.

The output electrodes 13 and 14 of the Hall element 11 are the transistor Q1 and
Connected to the base of Q2. The output of the differential detection amplifier 16 is an inverting means 21 composed of transistors Q21 to Q24.
Causes its output to be inverted. When the transistors Q21 and Q24 are turned on, the transistors Q22 and Q23 are turned off. Conversely, when the transistors Q22 and Q23 are turned on, the transistor Q2 is turned on.
1, Q24 is controlled to turn off. Reduction filter 19
Is composed of a capacitor C1.

[Effects of the Invention] As described above, the present invention has a built-in magnetic sensor in which a factor of variation in operating magnetic flux density due to an input voltage offset or the like of a differential detection amplifier is significantly reduced, and an accurate detection signal is obtained even with respect to temperature change. An integrated circuit can be obtained.
In addition, when applied to Hall ICs, it is possible to use ones that have high precision such as IC mask pattern shape and circuit integrity and are inexpensive in manufacturing process.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an embodiment of the present invention, FIG. 2 is a circuit diagram more specifically showing the circuit of FIG. 1, FIG. 3 is an explanatory view of a Hall element, and FIG. 4 is a Hall element. It is a figure which shows an integrated circuit. 11 ... Hall element, 16 ... Differential detection amplifier, 19 ... Reduction filter, 20, 21 ... Inversion means.

Claims (1)

[Claims] 1. A magnetic sensor, a means for supplying a drive current to the magnetic sensor, a differential detection amplifier for supplying a detection output of the magnetic sensor to a differential input, a switching signal generating means, and the switching signal. Responsive to a first output of the switching means for supplying the drive current to the magnetic sensor in response to the first output of the generating means and for inverting the polarity thereof alternately. Second inverting means for alternately inverting the output of the differential detection amplifier and the output of the second inverting means are supplied, and a low-frequency whose cut-off frequency is set below the output frequency of the switching signal generating means is supplied. An integrated circuit with a built-in magnetic sensor, comprising: a bandpass filter.