Magnetic sensor circuit

Abstract

To provide a magnetic sensor circuit capable of suppressing change in in-phase output voltage of a Hall element due to temperature while reducing current consumption and improving magnetic detection accuracy.SOLUTION: A magnetic sensor circuit 100 comprises: a Hall element 111 configured to output Hall voltage VH and offset voltage VHos; a switch part 120 configured to convert the Hall voltage VH into AC component and the offset voltage VHos into DC component; a first DC cut filter 130 configured to transmit the Hall voltage VH of AC component and block the offset voltage VHos of DC component, and set in-phase voltage V2C to a prescribed in-phase voltage V3C; an amplifier circuit 140 configured to amplify voltage obtained by adding the offset voltage VAMPos to the Hall voltage VH; a demodulator circuit 150 configured to demodulate the Hall voltage VH of AC component and modulate the offset voltage VAMPos of DC component; and a lowpass filter 160 configured to transmit the Hall voltage VH of DC component and block the offset voltage VAMPos of AC component.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a magnetic sensor circuit. [Background technology]

[0002] There are various types of magnetoelectric conversion methods for converting magnetism into voltage, and a typical example in semiconductor devices is a Hall element.

[0003] A Hall element is a magnetoelectric conversion element that utilizes the Hall effect and outputs a differential voltage proportional to the strength of an applied magnetic field. To use this Hall element as a magnetic sensor, peripheral circuits such as a driver circuit and an amplifier circuit are connected to the Hall element. The drive circuit is equipped with a constant current source or a constant voltage source, and applies a constant current or voltage to the Hall element to generate a drive current. Since the Hall voltage output from the Hall element is very small, an amplifier circuit is connected downstream of the Hall element.

[0004] Various proposals have been made to enable highly accurate magnetic detection in such peripheral circuits. For example, a drive circuit has been proposed that uses an operational amplifier to control the Hall element voltage and suppress temperature changes in the common-mode output voltage of the Hall element (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-97972 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of one aspect of the present invention is to provide a magnetic sensor circuit that can reduce current consumption, suppress temperature-dependent changes in the common-mode output voltage of a Hall element, and improve magnetic detection accuracy. [Means for solving the problem]

[0007] The magnetic sensor circuit according to an embodiment of the present invention includes: a Hall element that receives a drive current from a drive circuit and outputs a Hall voltage and a first offset voltage; a spinning circuit that changes the polarity of the drive current based on a clock signal, converts the Hall voltage into a DC component, and converts the first offset voltage into an AC component, and outputs the converted voltage; a modulation circuit that converts the Hall voltage into an AC component and the first offset voltage into a DC component in a differential voltage output from the spinning circuit based on the clock signal; a first DC cut filter that passes the Hall voltage, which is an AC component, and blocks the first offset voltage, which is a DC component, in the differential voltage output from the modulation circuit, and that can set the common-mode voltage from the modulation circuit to a predetermined common-mode voltage; an amplifier circuit that amplifies a voltage obtained by adding a second offset voltage of a DC component to the Hall voltage of an AC component in the differential voltage output from the first DC cut filter; a demodulation circuit that demodulates the Hall voltage, which is an AC component, into a DC component in the differential voltage output from the amplifier circuit, and modulates the second offset voltage, which is a DC component, into an AC component; a low-pass filter that passes the Hall voltage, which is a DC component, and blocks the second offset voltage, which is an AC component, in the differential voltage output from the demodulation circuit; It has. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to provide a magnetic sensor circuit that can reduce current consumption, suppress temperature-dependent changes in the common-mode output voltage of a Hall element, and improve magnetic detection accuracy. [Brief explanation of the drawings]

[0009] [Figure 1]FIG. 1 is a block diagram showing a magnetic sensor circuit according to an embodiment of the present invention. [Figure 2] FIG. 2 is a circuit diagram showing the Hall sensor unit and modulation circuit shown in FIG. [Figure 3] FIG. 3 is a block diagram showing a magnetic sensor circuit according to a modification of the example of the embodiment shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] This invention is based on the finding that in a drive circuit using an operational amplifier such as that in Patent Document 1, when high-speed switching is performed to remove various offset voltages (unbalanced voltages), the operational amplifier is required to be responsive and consumes a large amount of current.It is thought that a drive circuit such as that in Patent Document 1 can suppress temperature changes in the common-mode voltage of a Hall element, but when an operational amplifier is used in a drive circuit connected to a Hall element, the operational amplifier must respond to instantaneous voltage fluctuations, which requires the operational amplifier to consume a large amount of current.

[0011] A Hall element is a square non-magnetic metal layer formed on a silicon substrate. When a drive current is applied to a pair of opposing sides, a Hall voltage is generated on a pair of perpendicular sides to detect the magnetic field. This Hall element is prone to generating unnecessary offset voltages that affect magnetic detection accuracy.

[0012] The offset voltage of a Hall element is caused by factors such as the piezoelectric effect due to stress and manufacturing variations, and is the voltage output from the Hall element when no external magnetic field is applied to it. The spinning current method is known as a method for eliminating this offset voltage. The spinning current method eliminates the offset voltage based on the output voltage when the direction of the drive current is changed by high-speed switching (when the polarity is changed by 90°). This spinning current method is always used when the Hall element is in operation, as the Hall voltage does not change even when the polarity is changed by 90°.

[0013] Even if the offset voltage of the Hall element is eliminated by this spinning current method, the offset voltage of the operational amplifier in the amplifier circuit that amplifies the differential voltage signal of the Hall element still affects the magnetic detection accuracy.

[0014] The offset voltage of an operational amplifier is the differential voltage output from the operational amplifier divided by the gain of the operational amplifier when no differential voltage signal is input to the operational amplifier. Chopping is a known method for removing this operational amplifier offset voltage. The chopping method involves arranging the components in the order of modulation circuit, operational amplifier, demodulation circuit, and low-pass filter, modulating the offset voltage of the operational amplifier located downstream of the modulation circuit with the demodulation circuit, and then removing the offset voltage as an AC component with the low-pass filter.

[0015] As described above, when various offset voltages are removed by the spinning current method or chopping method, instantaneous voltage fluctuations occur in the Hall element due to high-speed switching. Therefore, if an operational amplifier is used in the drive circuit connected to the Hall element, the operational amplifier must respond to instantaneous voltage fluctuations, and therefore requires a large current consumption.

[0016] Therefore, the magnetic sensor circuit in one embodiment of the present invention does not use an operational amplifier in the drive circuit, but instead arranges a Hall element, a modulation circuit, a DC cut filter, an operational amplifier, a demodulation circuit, and a low-pass filter in this order. This allows the magnetic sensor circuit to remove various offset voltages using the spinning current method and chopping method without increasing current consumption, thereby suppressing temperature-related changes in the common-mode output voltage of the Hall element and improving magnetic detection accuracy.

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and redundant explanations may be omitted.

[0018] (Example of embodiment) FIG. 1 is a block diagram showing a magnetic sensor circuit according to an embodiment of the present invention. The magnetic sensor circuit 100 is a circuit that detects magnetism using a Hall element, and is formed using a semiconductor process. As shown in FIG. 1, the magnetic sensor circuit 100 includes a Hall sensor unit 110 that performs magnetoelectric conversion using a Hall element, a switch unit 120, a DC cut filter 130, an amplifier circuit 140, a demodulation circuit 150, and a low-pass filter 160. The DC cut filter 130 may be referred to as a first DC cut filter.

[0019] FIG. 2 is a circuit diagram showing the Hall sensor unit and modulation circuit shown in FIG. As shown in FIG. 2, the Hall sensor unit 110 includes a Hall element 111 and a drive circuit 112.

[0020] <Hall element> The Hall element 111 is a magnetoelectric conversion element that outputs a Hall voltage proportional to the strength of an external magnetic field when the magnetic field is applied. The equivalent circuit of this Hall element 111 is a bridge circuit formed by four resistors 111a to 111d. Since the resistance values ​​Ra to Rd of the four resistors 111a to 111d change with temperature, the Hall voltage also changes with temperature. Furthermore, the voltage signal of the Hall element 111 includes, in addition to the Hall voltage, an offset voltage (first offset voltage) resulting from the piezoelectric effect due to stress, variations in manufacturing, and the like.

[0021] Therefore, if the polarity of the drive current (direction in which the drive current flows) of the Hall element 111 is indicated by arrow a in FIG. 2, the voltage signals V1P and V1N are expressed by the following equations (1) and (2). V1P=I×(Rb×Rd) / (Rb+Rd)+VH / 2+VHos / 2 …(1) V1N=I×(Rb×Rd) / (Rb+Rd)-VH / 2-VHos / 2 …(2) Here, I is the drive current flowing through the Hall element 111, VH is the Hall voltage output in proportion to the strength of the external magnetic field, and VHos is the offset voltage of the Hall element 111.

[0022] The differential voltage V1D output from the Hall element 111 is expressed by the following equation (3) based on the above equations (1) and (2). V1D=V1P-V1N=VH+VHos …(3)

[0023] The common-mode voltage V1C output from the Hall element 111 is the average voltage of the voltage signals V1P and V1N, and is therefore expressed by the following equation (4). V1C=(V1P-V1N) / 2=[I×(Rb×Rd) / (Rb+Rd)] / 2 …(4) Therefore, the common-mode voltage V1C depends on the resistance values ​​Rb and Rd of the resistors 111b and 111d, and therefore varies with temperature.

[0024] <Drive circuit> The drive circuit 112 is a constant current source using a current mirror circuit, and supplies a drive current for generating the Hall effect in the Hall element 111, thereby driving the Hall element 111 with a constant current.

[0025] Switch unit 120 has the function of changing polarity by 90° in the spinning current method by high-speed switching based on a clock signal, and modulating the Hall voltage of the Hall element in the chopping method. This switch unit 120 includes two switch pairs, spinning circuits 121 and 122, and another two switch pairs, modulation circuits 123 and 124.

[0026] The four switch pairs in the spinning circuits 121, 122 and the modulation circuits 123, 124 are respectively connected to the connection points of the four resistors 111a to 111d of the Hall element 111. These four switch pairs include switches 121a, 122a, 123a, and 124a that are turned on when the clock signal is at an L level, and switches 121b, 122b, 123b, and 124b that are turned off. Furthermore, when the clock signal is at an H level, the switches 121a, 122a, 123a, and 124a of the four switch pairs are turned off, and the switches 121b, 122b, 123b, and 124b are turned on. Switching of these four switch pairs changes the polarity of the drive current flowing from the drive circuit 112 to the Hall element 111, modulating the voltage signal of the Hall element 111. At this time, the Hall voltage VH of the differential voltage signal of the Hall element 111 remains unchanged even if the polarity of the drive current is changed, but the offset voltage VHos is modulated. The spinning circuits 121 and 122 and the modulation circuits 123 and 124 will be described below using equations (5) to (7).

[0027] <Spinning Circuit> The spinning circuits 121 and 122 change the polarity of the drive current flowing through the Hall element 111 to the timing of a predetermined clock signal as indicated by arrows a and b in FIG. 2, and output the Hall voltage VH as a DC component and the offset voltage VHos as an AC component. Therefore, the differential voltage V1D when the polarity of the drive current changes is expressed by the following equation (5) instead of equation (3) when the polarity of the drive current does not change as described above. V1D = V1P - V1N = VH ± VHos … (5) It should be noted that "±" indicates an AC component.

[0028] <Modulation circuit> The modulation circuits 123 and 124 convert the Hall voltage VH into an AC component and the offset voltage VHos into a DC component in the differential voltage output from the spinning circuits 121 and 122 based on the clock signal. Therefore, when the differential voltage V2D and the common-mode voltage V2C are output from the modulation circuits 123 and 124, they are expressed by the following equations (6) and (7). V2D=V2P-V2N=±VH+VHos …(6) V2C=(V2P-V2N) / 2 =[I×(Rb×Rd) / (Rb+Rd)] / 2 …(7)

[0029] When the differential voltage V1D of equation (5) is converted to the differential voltage V2D of equation (6) by the modulation circuits 123 and 124, the Hall voltage VH is modulated to become an AC component, and the offset voltage VHos of the Hall element 111 becomes a DC component. The common-mode voltage V2C in equation (7) is the same as the common-mode voltage V1C of the Hall element 111 shown in equation (4).

[0030] <DCカットフィルタ> Returning to FIG. 1, the DC cut filter 130 is a high-pass filter in which capacitors are connected in series, and outputs voltage signals V3P and V3N by blocking the DC components of the voltage signals V2P and V2N from the modulation circuits 123 and 124 and passing the AC components. Therefore, the differential voltage V3D and the common-mode voltage V3C are expressed by the following equations (8) and (9). V3D = V3P - V3N = ± VH … (8) V3C = (V3P - V3N) / 2 = arbitrary common-mode voltage … (9)

[0031] When the differential voltage V2D of equation (6) becomes the differential voltage V3D of equation (8) by the DC cut filter 130, the DC component "+VHos" of the differential voltage V2D is blocked and the AC component of the differential voltage V2D passes, resulting in "±VH." In other words, even without using an operational amplifier in the drive circuit as in Patent Document 1, the offset voltage VHos of the Hall element 111 can be removed by the DC cut filter 130, and current consumption does not increase. Furthermore, when the DC cut filter 130 converts the in-phase voltage V2C of equation (7) into the in-phase voltage V3C of equation (9), a DC bias component can be added using a constant voltage source or the like after the DC cut filter 130, allowing the in-phase voltage to be set to any desired value. Furthermore, since equation (9) does not include the resistance value of the equivalent resistance of the Hall element 111, the Hall element 111 is less susceptible to temperature changes, and temperature changes in the in-phase voltage of the Hall element 111 can be suppressed.

[0032] <Amplification circuit> The amplifier circuit 140 differentially amplifies the voltage signals V3P and V3N from the DC cut filter 130 using an operational amplifier, and outputs voltage signals V4P and V4N. Therefore, the differential voltage V4D and the common-mode voltage V4C are expressed by the following equations (10) and (11), where A is the gain of the operational amplifier of the amplifier circuit 140 and VAMPos is the offset voltage (second offset voltage) of the operational amplifier of the amplifier circuit 140. V4D=V4P-V4N=±A×VH+A×VAMPos…(10) V4C = (V4P - V4N) / 2 = arbitrary common-mode voltage … (11)

[0033] When the differential voltage V3D of equation (8) becomes the differential voltage V4D of equation (10) by the amplifier circuit 140, the DC component of the offset voltage VAMPos of the operational amplifier is added to the AC component of the Hall voltage VH, and each is amplified by A times.

[0034] <Demodulation circuit> The demodulation circuit 150 demodulates the voltage signals V4P and V4N from the amplifier circuit 140 at the same timing as the modulation circuits 123 and 124, and outputs voltage signals V5P and V5N. Therefore, the differential voltage V5D and the common-mode voltage V5C are expressed by the following equations (12) and (13). V5D=V5P-V5N=A×VH±A×VAMPos…(12) V5C = (V5P - V5N) / 2 = arbitrary common-mode voltage … (13)

[0035] When the differential voltage V4D of equation (10) becomes the differential voltage V5D of equation (12) by the demodulation circuit 150, the Hall voltage VH, which has been amplified by A times, is demodulated to become a DC component, and the offset voltage VAMPos, which has been amplified by A times, is modulated to become an AC component. The common-mode voltage V5C in equation (13) is the same as the common-mode voltage V4C of the Hall element 111 shown in equation (11).

[0036] <Low-pass filter> The low-pass filter 160 cuts off the AC components of the voltage signals V5P and V5N from the demodulation circuit 150 and outputs the voltage signals VOP and VON. Therefore, the differential voltage VOD and the common-mode voltage VOC are expressed by the following equations (14) and (15). VOD = VOP - VON = A × VH … (14) VOC = (VOP - VON) / 2 = arbitrary common-mode voltage … (15)

[0037] When the differential voltage V5D of equation (12) becomes the differential voltage VOD of equation (14) by the low-pass filter 160, the AC component ±A×VAMPos is cut off, and the Hall voltage VH of the Hall element 111 becomes only the DC component amplified by A. In this way, the AC component offset voltage VAMPos can be cut off by the downstream low-pass filter 160 using the chopping method. The common-mode voltage VOC in equation (15) is the same as the common-mode voltage V5C of the Hall element 111 shown in equation (13).

[0038] As described above, the magnetic sensor circuit 100 according to this embodiment can remove the offset voltage VHos of the Hall element 111 by the DC cut filter 130 using the spinning current method. Furthermore, the magnetic sensor circuit 100 can set the AC component output from the DC cut filter 130 to any common-mode voltage, thereby suppressing temperature changes in the common-mode voltage of the Hall element 111. Therefore, there is no risk of an operational amplifier responding quickly to a drive circuit such as that described in Patent Document 1, thereby increasing current consumption. Furthermore, the magnetic sensor circuit 100 can remove the offset voltage of the operational amplifier of the amplifier circuit 140 by chopping.

[0039] (Modification of an example of an embodiment) FIG. 3 is a block diagram showing a magnetic sensor circuit according to a modification of the example of the embodiment shown in FIG. As shown in FIG. 3, the magnetic sensor circuit 200 in the modified example is the same as the magnetic sensor circuit 100 shown in FIG. 1, except that a DC cut filter 170 is further connected between the amplifier circuit 140 and the demodulation circuit 150. The DC cut filter 170 may be referred to as a second DC cut filter. In the magnetic sensor circuit 200, the offset voltage VHos of the Hall element 111 can be further removed by the DC cut filter 170.

[0040] As described above, a magnetic sensor circuit in one embodiment of the present invention includes a Hall element, a modulation circuit, a DC cut filter, an operational amplifier, a demodulation circuit, and a low-pass filter arranged in this order. The Hall element outputs a Hall voltage and an offset voltage. The modulation circuit changes the polarity of the drive current and modulates the Hall voltage using a clock signal. The DC cut filter passes the AC component of the Hall voltage in the differential voltage from the modulation circuit, blocks the DC component of the offset voltage, and can set the common-mode voltage from the modulation circuit to a predetermined common-mode voltage. The amplifier circuit amplifies the voltage obtained by adding the offset voltage of the operational amplifier to the Hall voltage. The demodulation circuit demodulates the AC component of the Hall voltage and modulates the DC component of the offset voltage of the operational amplifier. The low-pass filter passes the DC component of the Hall voltage and blocks the AC component of the offset voltage of the operational amplifier. As a result, this magnetic sensor circuit can reduce current consumption while suppressing changes in the common-mode output voltage of the Hall element due to temperature and improving magnetic detection accuracy.

[0041] Although one embodiment of the present invention has been described above, the present invention is not limited to the embodiment, and various modifications are possible within the scope of the invention. For example, a constant current source using a current mirror circuit is used as the drive circuit, but it may also be a constant current source or constant voltage source that does not use an operational amplifier, or a constant current source or constant voltage source that is connected so that the operational amplifier does not respond quickly using the spinning current method or chopping method. Furthermore, the high-pass filter in which capacitors are connected in series is used as the DC cut filter, but the present invention is not limited to this and any filter that can cut off the DC component of the input voltage may be used. [Explanation of symbols]

[0042] 100, 200 Magnetic sensor circuit 110 Hall sensor section 111 Hall element 120 Switch section 121, 122 Spinning circuit 123, 124 Modulation circuit 130 DC cut filter (first DC cut filter) 140 Amplification circuit 150 Demodulation Circuit 160 Low-pass filter 170 DC cut filter (second DC cut filter) VH Hall voltage VHos offset voltage (first offset voltage) VAMPos offset voltage (second offset voltage)

Claims

1. a Hall element that receives a drive current from a drive circuit and outputs a Hall voltage and a first offset voltage; a spinning circuit that changes the polarity of the drive current based on a clock signal, converts the Hall voltage into a DC component, and converts the first offset voltage into an AC component, and outputs the converted voltage; a modulation circuit that converts the Hall voltage into an AC component and the first offset voltage into a DC component in a differential voltage output from the spinning circuit based on the clock signal; a first DC cut filter that passes the Hall voltage, which is an AC component, and blocks the first offset voltage, which is a DC component, in the differential voltage output from the modulation circuit, and that can set the common-mode voltage from the modulation circuit to a predetermined common-mode voltage; an amplifier circuit that amplifies a voltage obtained by adding a second offset voltage having a DC component to the Hall voltage having an AC component in the differential voltage output from the first DC cut filter; a demodulation circuit that demodulates the Hall voltage, which is an AC component, into a DC component in the differential voltage output from the amplifier circuit, and modulates the second offset voltage, which is a DC component, into an AC component; a low-pass filter that passes the Hall voltage, which is a DC component, and blocks the second offset voltage, which is an AC component, in the differential voltage output from the demodulation circuit; A magnetic sensor circuit comprising:

2. 2. The magnetic sensor circuit according to claim 1, wherein the drive circuit is a constant current source using a current mirror circuit.

3. 2. The magnetic sensor circuit according to claim 1, further comprising a second DC cut filter connected between the amplifier circuit and the demodulator circuit.

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