JP4313729B2 - Magnetic sensor circuit - Google Patents

Description

  The present invention relates to a technology for compensating for or suppressing temperature dependency of characteristics of a Hall element and its peripheral circuits and variation in characteristics of each product and increasing detection accuracy of a magnetic sensor circuit using the Hall element.

  FIG. 5 is a circuit diagram showing a configuration of a basic magnetic sensor circuit. In FIG. 5, 1 is a power supply terminal, and 2 is a signal output terminal of the magnetic sensor circuit. Reference numeral 3 denotes a Hall element. The Hall element 3 is formed with a pair of excitation current supply terminals and a signal detection terminal. One excitation current supply terminal of the Hall element 3 is connected to the power supply terminal 1 and the other excitation current supply terminal is connected to the ground.

  One signal detection terminal of the Hall element 3 is connected to the non-inverting input terminal (+) of the amplifier 4a, and the other signal detection terminal is connected to the inverting input terminal (−) of the amplifier 4a. The output terminal of the amplifier 4a is connected to one input terminal of the comparator 5a, and the output terminal of the comparator 5a is connected to the signal output terminal 2. The other input terminal of the comparator 5a is connected to the high potential side terminal of the reference voltage source 6 in which the low potential side terminal is connected to the ground.

In the circuit of FIG. 5 having such a structure, the following operation is performed.
An excitation current having a predetermined magnitude is supplied from the power supply terminal 1 to the Hall element. Here, when a magnetic flux that penetrates the Hall element 3 exists, a voltage signal having a magnitude corresponding to the magnetic flux and the excitation current is generated between the signal detection terminals of the Hall element 3. The amplifier 4a amplifies the voltage signal generated in the Hall element 3 and supplies it to the comparator 5a. Then, when the output signal of the amplifier 4a is larger than the threshold set by the reference voltage source 6, the comparator 5a puts the output signal into a state that implies the presence of the magnetic flux. (Here, the state of the output signal that implies the presence of the magnetic flux is the low level of the high level and the low level.)
A magnetic sensor circuit having such a structure and operation is introduced, for example, in FIG.
Japanese Patent Application Laid-Open No. 08-194040

Hall element characteristics have temperature dependence (varies with temperature changes) and variations in semiconductor chip manufacturing processes cause Hall element characteristics to vary from product to product (hereinafter referred to as variations and variations). (Omitted) is well known. As a countermeasure for suppressing fluctuations and variations in characteristics of the Hall element, the following method has been taken as an example.
That is, a resistor having substantially the same characteristics as the Hall element is formed, and the resistor is used as one of the two feedback resistors of the amplifier provided on the output side of the Hall element. The countermeasure is to change the gain of the amplifier according to the variation in the characteristic of the resistance almost the same as that of the Hall element to compensate for the variation based on the characteristic change of the Hall element included in the voltage signal.

  Recent magnetic sensors using Hall elements are being integrated into ICs, and some Hall elements, amplifiers, and comparators are formed on one chip together. Here, when the Hall element is formed using the N-well region of the semiconductor chip, if the resistor is formed using the same N-well region on the same chip, the Hall element has substantially the same characteristics. Resistance is easily obtained. Even if the region formation depth and impurity concentration vary from product to product due to the manufacturing process, the resistance characteristics of the Hall element formed using the same N-well region on the same chip are almost the same. can do. For this reason, if the resistor formed as described above is used, it is possible to compensate for the variation due to the change in characteristics of the Hall element and at the same time suppress the influence of variations in the Hall element.

However, the two feedback resistors of the amplifier originally have the same characteristics as each other in order to suppress fluctuations due to temperature changes in the output signal of the amplifier set to high gain and variations caused by the manufacturing process. Is done. If a resistor with a different characteristic is used for one of the two feedback resistors, the balance will be lost in various parts related to the feedback resistor, resulting in fluctuations and variations in the characteristics of the amplifier instead of the Hall element. There was a problem.
SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic sensor circuit that compensates for variations in characteristics of Hall elements and their peripheral circuits and suppresses variations in characteristics, thereby obtaining a highly accurate detection result.

  In order to achieve the above object, the present invention provides a magnetic sensor circuit that includes a Hall element and an amplifier, and amplifies a voltage signal corresponding to an external magnetic field generated in the Hall element. And a monitor circuit that outputs a monitor signal that changes in accordance with a change in resistance characteristics, and the amplifier that receives the monitor signal and corrects the magnitude of the output signal in accordance with the monitor signal. Alternatively, a Hall element, an amplifier and a comparator are provided, a voltage signal corresponding to the external magnetic field generated in the Hall element is amplified by the amplifier, and the output signal of the amplifier is compared with a predetermined threshold value in the comparator, and the detection result is In a magnetic sensor circuit that generates an output signal, a monitor circuit that has a resistor having substantially the same characteristics as the Hall element, and that outputs a monitor signal whose magnitude changes with changes in the resistance characteristics, and supply of the monitor signal And the comparator for correcting the threshold value according to the monitor signal.

  By using a resistor having the same characteristics as the Hall element, a monitor signal that changes so as to be interlocked with the fluctuation in characteristics of the Hall element can be obtained. By changing the amplification factor of the amplifier or the threshold value of the comparator in accordance with the monitor signal, the compensation for the fluctuation based on the characteristic fluctuation of the Hall element included in the voltage signal is performed. Since resistors with the same characteristics as the Hall elements are provided in the circuit part that generates the monitor signal, elements with almost the same characteristics can be used for the feedback resistance of the amplifier, etc. Can be suppressed. This makes it possible to provide a magnetic sensor circuit that can obtain a highly accurate detection result.

A resistor having the same characteristics as the Hall element is provided, and a control transistor is connected in series to the resistor. The output terminal of the error amplifier is connected to the control terminal of the control transistor, the voltage signal generated at one end of the resistor is input to one input terminal of the error amplifier, and the voltage signal corresponding to the power supply voltage is input to the other input terminal. Configure the connection to input. A monitor circuit is configured by a resistor, a control transistor, and an error amplifier that are substantially connected to the configuration of the constant current circuit.
The current flowing through the control transistor of the monitor circuit is supplied as a monitor signal to an amplifier connected to the Hall element or a comparator for processing an output signal of the amplifier.

In the first aspect of the present invention, a Gm amplifier including a Gilbert cell and first and second current sources is used as an amplifier connected to the Hall element. By supplying a monitor signal to a circuit position that receives a current supply from the second current source of the Gilbert cell, the amplification factor (gain) of the Gm amplifier is changed according to the monitor signal.
The current flowing through the control transistor of the monitor circuit changes according to the characteristic variation of the resistance. Since the resistance has almost the same characteristics as the Hall element, the monitor signal changes so as to be interlocked with the characteristic variation of the Hall element. Therefore, by changing the amplification factor (gain) of the Gm amplifier in accordance with the monitor signal, the variation based on the characteristic change of the Hall element included in the voltage signal is compensated.

In the second aspect of the present invention, as a comparator for processing the output signal of the amplifier, the first and second transistors connected so as to form a differential pair, and the common connection of the first and second transistors A comparator having a current source connected to a point and an active load circuit connected to the first and second transistors, and a structure for extracting an output signal from the connection point of the second transistor and the active load circuit. use. By supplying a monitor signal to the connection point between the first transistor and the active load circuit, the threshold value of the comparator is changed.
The monitor signal changes so as to be interlocked with the fluctuation in characteristics of the Hall element. By changing the threshold value of the comparator in accordance with the monitor signal, the variation based on the characteristic change of the Hall element included in the voltage signal is compensated.

FIG. 1 shows a circuit of a first embodiment of a magnetic sensor circuit according to the present invention.
The magnetic sensor circuit of FIG. 1 uses a variable gain amplifier 4b instead of the fixed gain type, and additionally includes a monitor circuit 7a for supplying a monitor signal to the amplifier 4b, except for the conventional magnetic circuit of FIG. It has the same configuration as the sensor circuit. Here, the circuit portions of the amplifier 4b and the monitor circuit 7a, which are the main points of the magnetic sensor circuit according to the present invention, are specifically configured as shown in FIG.

  The variable gain amplifier 4b shown in FIG. 2 has a Gilbert cell CELL, a first current source IR1, a second current source IR2, and an output circuit OUT, and these components are mutually connected to form a Gm amplifier. It is connected to the. Specifically, the input side of the Gilbert cell CELL is connected to the first and second input terminals IN1 and IN2 to receive a voltage signal from the Hall element, and the output side of the Gilbert cell CELL is the output circuit OC. Is connected to the input side. Circuit positions for receiving two current supplies of the Gilbert cell CELL are connected to the ground via first and second current sources IR1 and IR2, respectively. The output side of the output circuit OC is connected to an output terminal OUT1 for supplying an amplified voltage signal to the comparator 5b. The circuit positions for receiving the supply of drive voltages for the Gilbert cell CELL and the output circuit OC are connected to the power supply terminal 1 a connected to the power supply terminal 1, respectively.

  On the other hand, the monitor circuit 7a shown in FIG. 2 has a resistor Rm1, a control transistor Q1, an error amplifier AMP1, and resistors R1 and R2, and these components are connected to each other so as to form a current source circuit. Specifically, one end of the resistor Rm1 having substantially the same characteristics as the Hall element 3 is connected to the source of the control transistor Q1, and the other end is connected to the ground. The drain of the control transistor Q1 is connected to the amplifier 4b, more specifically, to a circuit position that receives a current supply from the second current source IR2 of the Gilbert cell CELL. The gate of the control transistor Q1 is connected to the output terminal of the error amplifier AMP1, and the inverting input terminal (−) of the error amplifier AMP1 is connected to one end of the resistor Rm1. The resistors R1 and R2 are connected in series between the power supply terminal 1b connected to the power supply terminal 1 and the ground, and the common connection point of the resistors R1 and R2 is connected to the non-inverting input terminal (+) of the error amplifier AMP1. ing.

  The gain of a typical Gm amplifier having a Gilbert cell and two current sources is determined by the ratio of the two currents supplied from the two current sources to the Gilbert cell. The amplifier 4b in the circuit of FIG. 2 is supplied with current from the first current source IR1 at one current supply position of the Gilbert cell CELL, and is supplied with the second current source IR2 and the monitor at the other current supply position of the Gilbert cell CELL. A current is supplied from the circuit 7a. The current supplied from the monitor circuit 7a is a monitor signal. When the magnitude of the monitor signal changes, the amplification factor of the amplifier 4b also changes.

Incidentally, the current (that is, the monitor signal) flowing through the control transistor Q1 of the monitor circuit 7a has a value corresponding to the voltage appearing at one end of the resistor Rm1 when the power supply voltage V _{DD at} the position of the power supply terminal 1b is constant. For example, when the ambient temperature changes, the electric resistance value of the resistor Rm1 varies in the same manner as the Hall element 3. For this reason, the monitor signal changes in conjunction with fluctuations in the characteristics of the Hall element 3. Of course, the amount of change in the characteristics of the Hall element 3 and the amount of change in the monitor signal have a substantially correlated relationship. As described above, since the amplification factor of the amplifier 4b changes according to the monitor signal, the voltage signal supplied from the Hall element 3 to the comparator 5a via the amplifier 4a is included in the amplifier 4a. The variation based on the characteristic change of the Hall element 3 is compensated by the change of the amplification factor.

If the excitation current is directly supplied to the hall element 3 from the power supply terminal 1 as shown in FIG. 1, the magnitude of the voltage signal generated in the hall element 3 when the power supply voltage V _DD fluctuates also changes. Therefore, in the magnetic sensor circuit according to the present invention, as shown in FIG. 2, a voltage corresponding to the power supply voltage V _DD is supplied from a series circuit (= voltage dividing circuit) of resistors R1 and R2 to the non-inverting input terminal (+) of the error amplifier AMP1. Was supplied as a reference voltage. With such a configuration, it is possible to compensate for fluctuations based on fluctuations in the power supply voltage V _DD in the voltage signal.

FIG. 3 shows a circuit of a second embodiment of the magnetic sensor circuit according to the present invention.
The magnetic sensor circuit of FIG. 3 has substantially the same circuit configuration as the conventional magnetic sensor circuit of FIG. 5 except that a monitor circuit 7a that supplies a monitor signal to the comparator 5b is additionally provided. Here, the circuit portions of the comparator 5b and the monitor circuit 7b, which are the main points of the magnetic sensor circuit according to the present invention, are specifically configured as shown in FIG.

  The comparator 5b of FIG. 4 has four transistors Q3, Q4, Q5, Q6 and a current source IR3, which are connected to each other so as to form a differential amplifier. Specifically, the sources of the first transistor Q3 and the second transistor Q4 are commonly connected so as to form a differential circuit, and the common connection point of the sources is connected to the power supply terminal 1c via the current source IR3. ing. The power supply terminal 1 c is connected to the power supply terminal 1. The gate of the first transistor Q3 is connected to the input terminal IN3 connected to the reference voltage source 6, and the gate of the second transistor Q4 is connected to the input terminal IN3 connected to the output terminal of the amplifier 4a.

  The drain of the first transistor Q3 is connected to the ground via the main current path of the transistor Q5, and the drain of the second transistor Q4 is connected to the ground via the main current path of the transistor Q6. The drain and gate of the transistor Q5 are short-circuited, and the gates of the transistors Q5 and Q6 are commonly connected so as to constitute a current mirror type active load circuit. The common connection point of the drains of the transistors Q4 and Q6 is connected to the output terminal OUT2 connected to the signal output terminal 2 of the magnetic sensor circuit.

  On the other hand, the monitor circuit 7b shown in FIG. 4 has a resistor Rm2, a control transistor Q2, an error amplifier AMP2, and resistors R3 and R4, and these components are connected to each other so as to constitute a current source circuit. Specifically, one end of the resistor Rm2 having substantially the same characteristics as the Hall element 3 is connected to the source of the control transistor Q2, and the other end is connected to the ground. The drain of the control transistor Q2 is connected to the comparator 5b, more specifically to the common connection point of the drains of the first transistor Q3 and the transistor Q5. The gate of the control transistor Q2 is connected to the output terminal of the error amplifier AMP2, and the inverting input terminal (−) of the error amplifier AMP2 is connected to one end of the resistor Rm2. Resistors R3 and R4 are connected in series between the power supply terminal 1d connected to the power supply terminal 1 and the ground, and the common connection point of the resistors R3 and R4 is connected to the non-inverting input terminal (+) of the error amplifier AMP2. ing.

Now, in the circuit of FIG. 4, it is assumed that the monitor circuit 7b does not exist and only the comparator 5b exists.
When the voltage signal supplied to the gate of transistor Q4 is very small, most of the current passing through current source IR3 flows into transistor Q4. At this time, since almost no current flows through the transistors Q3, Q5, and Q6, the signal (voltage) appearing at the position of the output terminal OUT2 becomes high level. When the voltage signal supplied to the gate of the transistor Q4 is gradually increased, the signal state of the output terminal OUT2 is eventually inverted from the high level to the low level. The value of the voltage signal located at the boundary where the signal state of the output terminal OUT2 is inverted from the high level to the low level (hereinafter referred to as a threshold value) is equal to the reference voltage supplied to the gate of the transistor Q3. It becomes.

  Here, when the voltage signal supplied to the gate of the transistor Q4 is equal to the threshold value, focusing on the current passing through each transistor, the current passing through the transistor Q4 and the current passing through the transistor Q6 are substantially equal. . Therefore, when the voltage signal is equal to the threshold value, that is, when the signal state of the output terminal OUT2 is located at the boundary where the signal state is inverted from the high level to the low level, the current passing through the transistor Q4 and the transistor Q6 pass. It can be said that the current is almost equal.

With the above in mind, consider the case of the circuit of FIG. 4 in which the comparator 5b and the monitor circuit 7b are provided again.
For example, even if a current flows into the monitor circuit 7b by appropriately setting the characteristics and sizes of the transistors constituting the comparator 5b, {threshold value} = {reference voltage supplied to the gate of the transistor Q4 } Is possible. It is assumed that this is so that it is easy to understand.

  When the resistance value of the resistor Rm2 in the monitor circuit 7b changes due to a temperature change or the like, the current passing through the control transistor Q2, in other words, the monitor signal supplied from the monitor circuit 7b to the comparator 5b, in other words, the comparator 5b. Changes the magnitude of the current flowing into the monitor circuit 7b. Then, the magnitude of the current passing through the transistor Q5 in the comparator 5b changes, and the passing current of the transistor Q6 that forms an active load of the current mirror together with the transistor Q5 also changes. For this reason, the threshold value of the comparator path 5b is shifted in accordance with the amount of change in the current flowing into the monitor circuit 7b.

Specifically, it is assumed that other conditions are the same and only the temperature is increased.
As the temperature increases, the input resistance of the Hall element 3 increases. Then, a voltage signal generated in the Hall element 3 and amplified in the amplifier 4a and then supplied to the gate of the transistor Q4 via the input terminal IN4 becomes small. At this time, the current passing through the transistor Q4 in the comparator 5b increases.

  On the other hand, when the temperature increases, the resistance value of the resistor Rm2 in the monitor circuit 7b increases, and the current passing through the control transistor Q2 decreases. Then, the current passing through the transistor Q5 in the comparator 5b is increased by the amount that the current flowing into the monitor circuit 7b is reduced, and accordingly, the passing current of the transistor Q6 is also increased. Therefore, even if the passing current of the transistor Q4 changes due to the temperature change, the passing current of the transistor Q6 has such a magnitude as to compensate for this. When this is seen not inside the comparator 5b but outside the comparator 5b, even if the voltage signal changes due to a temperature change, the threshold value of the comparator 5b changes so as to compensate for the variation based on the temperature change in the voltage signal. I can say that.

Even if the power supply voltage V _DD changes and the voltage signal fluctuates accordingly, the threshold value of the comparator 5b changes to compensate for the fluctuation as in the case of the temperature change. Naturally, since elements with uniform characteristics can be used for the feedback resistance of the amplifier 4a, it is possible to suppress variations in characteristics among products.

1 is a circuit diagram of a magnetic sensor circuit according to a first embodiment of the present invention. FIG. 2 is a detailed circuit diagram of a main part of the circuit of FIG. 1. The circuit diagram of the magnetic sensor circuit by the 2nd Example of this invention. FIG. 3 is a detailed circuit diagram of a main part of the circuit of FIG. 2. The circuit diagram of the conventional most basic magnetic sensor circuit.

Explanation of symbols

1: Power supply terminal 2: Signal output terminal 3: Hall element 4a: Amplifier 4b: Amplifiers 5a, 5b: Comparator 7a, 7b: Gm amplifier configuration Monitor circuits Rm1, Rm2: Hall element 3 having substantially the same characteristics Resistance

Claims (2)

A hall element, an amplifier and a comparator are provided, a voltage signal corresponding to an external magnetic field generated in the hall element is amplified by the amplifier, and an output signal of the amplifier is compared with a predetermined threshold value in the comparator to detect In the magnetic sensor circuit that produces the resulting output signal,
A monitor circuit comprising a resistor having substantially the same characteristics as the Hall element, and outputting a monitor signal whose magnitude changes in accordance with a change in the resistance characteristics;
First and second transistors connected to form a differential pair, a current source connected to a common connection point of the first and second transistors, and connected to the first and second transistors And a comparator for correcting a threshold value so as to compensate for fluctuations of the voltage signal according to the monitor signal supplied to the main current path of the first transistor ,
A magnetic sensor circuit comprising: The monitor circuit has a resistor having substantially the same characteristics as the Hall element, a control transistor connected in series to the resistor, and an error for controlling a conduction amount of the control transistor according to a voltage generated at one end of the resistor The magnetic sensor circuit according to claim 1, further comprising an amplifier, wherein a current passing through the control transistor is supplied to the comparator as the monitor signal.

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