JP5658715B2 - Hall electromotive force signal detector - Google Patents

Description

  The present invention relates to a Hall electromotive force signal detection device, and more particularly, to a Hall electromotive force signal detection device capable of performing highly accurate correction processing for magnetic sensitivity.

Conventionally, as a magnetic sensor semiconductor integrated circuit incorporating a Hall element, a current sensor that detects a magnetic field generated by a current, a rotation angle sensor that detects rotation of a magnet, a position sensor that detects movement of a magnet, and the like have been known. Yes.
It is known that the magnetic sensitivity (the magnitude of the Hall electromotive force per unit magnetic field) of such a Hall element varies with temperature. Therefore, in order to correct the magnetic sensitivity of the Hall element with high accuracy, it is necessary to correct the influence of temperature. Furthermore, it is known that the magnetic sensitivity of the Hall element changes not only by the influence of temperature but also by stress (piezo Hall effect).

Further, in applications of current detection and position detection using various magnetic field detections, non-contact magnetic sensors using Hall elements are used for reasons of durability and reliability.
FIG. 1 is a configuration diagram showing an example of a non-contact magnetic sensor using a silicon monolithic Hall element. A Hall element 2 that detects a magnetic field from the outside and converts it into a voltage in the silicon substrate 1, an A / D (analog / digital) converter 3 such as a ΔΣ (delta sigma) modulator, and various correction processes. A signal processing circuit including a digital arithmetic circuit 4 having a filter function and a D / A (digital / analog) converter 5 is incorporated.

  In such a signal processing circuit, many circuit techniques for reading an accurate magnetic field strength have been proposed. It is known that a Hall electromotive force signal output in proportion to the magnetic field strength and an offset signal independent of the magnetic field are included in the output of the Hall element, and only the Hall electromotive force signal is detected with high accuracy. As a method, for example, in Non-Patent Document 1, the Hall electromotive force signal and the offset signal are separated into a DC signal and an AC signal, respectively, by using signal processing called spinning current that switches the direction of the drive current of the Hall element. It is known to reduce the offset.

2A and 2B are diagrams showing a state in which the direction of the drive current of the Hall element is switched in order to detect the offset signal, and FIG. 3 shows a waveform in which the offset signal is superimposed on the Hall electromotive force signal. FIG.
By switching the direction of the drive current between the 0 degree direction and the 90 degree direction as shown in FIGS. 2A and 2B, the signal output from the Hall element is a direct current as shown in FIG. The waveform is obtained by superimposing an AC offset signal (a signal independent of a magnetic field) on a Hall electromotive force signal (a signal output in proportion to the magnetic field intensity). In other words, the relationship is as follows.

Hall element output at 0 degree direction driving = Vh — 0 deg [(Vh — 0 deg +) − (Vh — 0 deg−)]
Hall element output at 90 degrees direction driving = Vh_90 deg [(Vh_90 deg +) − (Vh_90 deg−)]
By smoothing this signal with a filter, it is possible to cancel the offset signal superimposed on the Hall electromotive force signal and detect only the Hall electromotive force signal. In other words, the relationship is as follows.

Hall electromotive force signal = (Vh — 0 deg + Vh — 90 deg) / 2
In addition, it is generally known that a Hall element for detecting a magnetic field changes in magnetic sensitivity in accordance with environmental changes such as stress of the package material and temperature. For example, Patent Document 1 relates to magnetic field, stress, and temperature. 2. Description of the Related Art A correction circuit that takes in signals into an A / D converter and corrects magnetic sensitivity based on stress and temperature information is known.

Further, for example, Patent Document 2 discloses that the stress applied to the Hall element is reduced by devising the package material and the package structure.
In addition, with respect to the problem that the magnetic sensitivity of the Hall element changes with temperature, correcting the magnetic sensitivity by providing a one-chip microcomputer for controlling the power supply voltage of the Hall element is disclosed in Patent Document 3, for example. Has been.

  Further, for example, in Patent Document 4, when an analog video signal is sampled by a sampling device such as an A / D converter, noise called “folding noise” generated along with sampling is reduced. It is disclosed that a pre-filter is provided in front of the A / D converter so that video signals of a plurality of types of formats can be sampled without generating aliasing noise.

US Pat. No. 6,362,618 (B2) JP 2008-292182 A JP 2009-139213 A JP 2002-185323 A

R S Popovic Hall Effect Devices (ISBN-10: 0750300965) Inst of Physics Pub Inc (1991/05)

  In order to read accurate magnetic field information based on the Hall electromotive force signal, it is necessary to correct the magnetic sensitivity based on the correction signal having stress information and temperature information applied to the Hall element as described above. Considering that the stress and temperature inside the circuit are not uniform, it is desirable to place the Hall element, the detection element for the correction signal, and their signal processing circuit together at the same position, and to perform high-accuracy correction It is necessary to share a circuit such as an A / D converter used for detecting the Hall electromotive force signal and the correction signal.

In general, an A / D converter has a factor that increases noise called aliasing noise that accompanies sampling, and a countermeasure for preventing aliasing is also required in a signal processing circuit for Hall electromotive force signals.
4A to 4C are diagrams for explaining aliasing noise, FIG. 4A is a diagram showing sample timing and a noise waveform after sampling, and FIG. 4B is a noise spectrum. FIG. 4C is a diagram illustrating a noise spectrum when the anti-folding filter is used.

  The aliasing noise is a phenomenon in which when sampling is performed, the noise is concentrated in a low frequency band below the sample frequency, and the noise cannot be reduced by the filter. In order to prevent the aliasing noise, a method of providing an antialiasing filter having a low-pass characteristic before the input of the A / D converter is generally used. However, in the signal processing of the Hall element, the above-described Non-Patent Document 1 is used. When the spinning current method as described above and the anti-aliasing filter are used together, there is a further problem that an error occurs in the calculation result of the Hall electromotive force signal.

The reason for this will be described below.
5 (a) and 5 (b) are diagrams showing the output of the Hall element before and after the anti-folding filter, FIG. 5 (a) is the output of the Hall element before passing through the anti-aliasing filter, and FIG. The output of the Hall element after passing through the anti-folding filter is shown.
As shown in FIG. 5 (a), the output from the Hall element includes an AC offset signal superimposed on the DC Hall electromotive force signal. As shown in b), the output of the offset signal has a dull edge.

  If the A / D converter takes in the time until the offset signal converges to a certain value, an error (hereinafter referred to as a settling error) occurs in the calculation result of the Hall electromotive force signal. It is necessary to stop sampling in the A / D converter until it converges to a certain value. However, in this case, useless time is generated in signal processing.

  The present invention has been made in view of such a problem, and an object of the present invention is to detect the Hall electromotive force signal by using the Hall electromotive force signal and a signal different from the Hall electromotive force signal. An object of the present invention is to provide a Hall electromotive force signal detecting device capable of effectively reducing a settling error and effectively using a waiting time for avoiding a settling error in signal processing.

The present invention has been made to achieve such an object. The invention according to claim 1 is directed to a Hall element that outputs a signal including a Hall electromotive force signal that fluctuates according to a magnetic field strength, and the Hall. An electrical signal output circuit that outputs a second electrical signal different from the electromotive force signal, a switch circuit that switches an energization direction of a drive current supplied between the plurality of electrodes of the Hall element, and the switch circuit, An anti-aliasing filter having a cut-off frequency of fc having a low-pass characteristic, and a signal from one of the anti-aliasing filter and the second electrical signal connected to the anti-aliasing filter and the electric signal output circuit. A time-division switch circuit that outputs in a time-division manner and an analog signal of the Hall electromotive force signal and the second electric signal connected to the time-division switch circuit. An A / D converter that converts to a digital signal and outputs in a time-division manner, and the time-division switching circuit includes the second division within a time of 1 / fc from switching of the energization direction of the drive current of the switch circuit. And the Hall electromotive force signal is not output .

Also, the invention according to claim 2, in the invention described in claim 1, comprising a correction calculation circuit connected to the A / D converter, the correction operation circuit the hole electromotive force signal and / or said The magnetic sensitivity of the Hall electromotive force signal is corrected.

According to a third aspect of the present invention, in the invention of the second aspect , the correction arithmetic circuit is configured to generate the Hall electromotive force signal based on the second electric signal digitally converted by the A / D converter. And / or correcting the magnetic sensitivity of the Hall electromotive force signal.
According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the electric signal output circuit includes a temperature detection element and outputs a second electric signal including temperature information. It is characterized by.

According to a fifth aspect of the invention, in the invention of the fourth aspect , the temperature detecting element is disposed in the vicinity of the Hall element, and the electric signal output circuit is temperature information relating to a temperature in the vicinity of the Hall element. The second electrical signal including the signal is output.
The invention according to claim 6 is the invention according to any one of claims 1 to 5 , wherein the electrical signal output circuit includes a stress detection element and outputs a second electrical signal including stress information. It is characterized by.

According to a seventh aspect of the invention, in the sixth aspect of the invention, the stress detection element is disposed in the vicinity of the Hall element, and the electrical signal output circuit is stress information relating to stress in the vicinity of the Hall element. The second electrical signal including the signal is output.

  According to the present invention, in the signal processing of the Hall element, the A / D converter that samples the Hall electromotive force signal samples a signal different from the Hall electromotive force signal at a predetermined time from the timing when the energization direction of the Hall element is switched. By doing so, it is possible to effectively use the waiting time for avoiding settling errors for signal processing. For example, by sampling a correction signal for correcting the Hall electromotive force signal at a predetermined time from the timing at which the energization direction of the Hall element is switched, it is possible to reduce the settling error and reduce the waiting time for avoiding the settling error. It can be effectively used for signal processing of correction signals.

It is a block diagram which shows an example of the non-contact magnetic sensor using a silicon monolithic Hall element. (A), (b) is a figure which shows the state which switches the direction of the drive current of a Hall element in order to isolate | separate a Hall electromotive force signal and an offset signal. It is a figure which shows the waveform with which the offset signal was superimposed on the Hall electromotive force signal. (A) thru | or (c) is a figure for demonstrating aliasing noise. (A), (b) is a figure which shows the output of the Hall element before passing through the anti-folding filter and the output of the Hall element after passing through the anti-aliasing filter. It is a circuit block diagram for demonstrating the Example of the Hall electromotive force signal detection apparatus which concerns on this invention. (A) thru | or (f) is a figure which shows each signal waveform of the circuit structure in FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 6 is a circuit configuration diagram for explaining an embodiment of the Hall electromotive force signal detection device according to the present invention, and FIGS. 7A to 7F show signal waveforms of the circuit configuration in FIG. It is. In the figure, 21 is a Hall element, 22 is a chopper switch circuit, 23 is a clock generation circuit, 24 is an oscillation circuit, 25 is an anti-folding filter, 26 is a time-division switch circuit, 27 is an A / D converter, and 28 is a digital filter. , 29 is a correction arithmetic circuit, 30 is a D / A converter, and 31 is a temperature detection element.

The Hall electromotive force signal detection apparatus according to the embodiment of the present invention is a Hall electromotive force signal detection apparatus configured to perform temperature correction on a Hall electromotive force signal based on a temperature that affects the magnetic sensitivity of the Hall element 21.
The chopper switch circuit 22 switches the energization direction of the drive current supplied between the plurality of electrodes of the Hall element 21 based on the polarity of the chopper clock signal shown in FIG. 7B, and from the output V1 signal from the Hall element The Hall electromotive force signal and the offset signal are separated. This chopper clock signal is a signal generated by the clock generation circuit 23 based on the oscillation signal from the oscillation circuit 24.

The anti-folding filter 25 is connected to the chopper switch circuit 22 and obtains the V1 signal shown in FIG. 7 (e), and is used to prevent the anti-aliasing noise that occurs with sampling. The anti-folding filter 25 is a low-pass filter having a low-pass characteristic.
The time division switch circuit 26 is connected to the chopper switch circuit 22 and the anti-folding filter 25, and outputs the V2 signal from the temperature detection element 31 and the V1 signal from the anti-folding filter 25 in a time division manner. is there.

The A / D converter 27 is connected to the time division switch circuit 26 and converts the analog signals of the V1 signal and the V2 signal into digital signals.
The digital filter 28 is connected to the A / D converter 27 to obtain a magnetic field signal B and a temperature signal T applied to the Hall element 21.
The correction calculation circuit 29 corrects the magnetic sensitivity from the magnetic field signal B based on the temperature signal T from the digital filter 28. The correction arithmetic circuit 29 outputs a temperature-corrected magnetic field signal Bcal.

The A / D converter 27 is provided so as to share a signal processing circuit for the V1 signal and the V2 signal. Thereby, as the signal processing of the Hall element, it is possible to perform highly accurate correction processing for magnetic sensitivity by sharing the magnetic field and temperature signal detection circuit with one A / D converter.
The chopper switch circuit 22 is used to periodically switch the direction of the bias current of the Hall element 21 in accordance with the polarity of the chopper clock (frequency f chop) to separate the Hall electromotive force signal and the offset signal.

V1 output from the chopper switch circuit 22 is controlled to be a signal in which an AC offset signal is superimposed on a DC Hall electromotive force signal.
The V1 signal passes through a detection path that passes through the anti-aliasing filter 25 having a low-pass characteristic (cutoff frequency fc), and the V2 signal passes through a detection path that does not pass through the anti-aliasing filter 25. Each signal is input to the division switch circuit 26.

  In the time division switch circuit 26, the V1 signal is selected as an output when φ1 shown in FIG. 7C is high, and the V2 signal is output when φ2 shown in FIG. 7D is high. Selected for output. Further, these signals are sampled by the A / D converter 27 at the fsamp frequency by the sample clock signal shown in FIG. 7A from the clock generation circuit 23, and subjected to analog / digital conversion. The / D converter 27 outputs a V1 output converted to a digital signal when φ1 is high, and outputs a V2 converted to a digital signal when φ2 is high.

Further, the correction arithmetic circuit 29 corrects the magnetic sensitivity from the magnetic field signal B based on the temperature signal T, calculates the magnetic field signal Bcal robust to the temperature change, and outputs it as an analog signal V _HOUT through the D / A converter 30. Is done.
Robustness or robustness means an internal mechanism or property that prevents a system from changing due to the influence of disturbances such as stress and environmental changes, and a design that has robustness is robust. Optimizing design and robustness is called robust optimization. The adjective “robust” meaning “robust” is the origin of the word, and it may be said to be robustness, toughness, robustness, strength, etc.

  The structural features of this embodiment of the present invention are that the A / D converter 27 uses a common circuit in a time-division configuration for the signal processing of the magnetic field signal and the temperature signal, and the detection path of the magnetic field signal. Is provided with a chopper switch circuit 22 and an anti-folding filter 25, and the time when φ2 for sampling the temperature signal is high is provided at a predetermined time from the timing at which the polarity of the chopper clock is switched.

The advantage of using a common circuit is that the influence of stress and temperature non-uniformity inside the circuit is eliminated, and magnetic sensitivity can be corrected with high accuracy. Further, the advantages of synchronizing the timing at which φ2 becomes high with the timing at which the polarity of the chopper clock is switched will be described in detail below.
The V1 signal that passes through the anti-folding filter 25 is used to finally calculate the magnetic field signal B as described above. The magnetic field signal B is a signal for detecting a current and a position. In general, the Hall electromotive force signal detection apparatus requires high accuracy and low noise performance, and the anti-folding filter 25 is used. However, if sampling is performed in a state where the output is not completely settled when the chopper is switched, there is a problem that the settling error described above occurs.

In the present invention, the A / D converter 27 is configured to stop sampling of the V1 signal for a time corresponding to several sample clocks when φ1 becomes low, thereby reducing settling errors in Hall electromotive force detection. In addition, by performing the sampling of the V2 signal by using a common A / D converter, it is possible to perform highly accurate correction calculation and accurately detect the magnetic field strength.
Further, the anti-aliasing filter may be provided for the detection path of the V2 signal. However, as described above, the V2 signal is a signal used for calculating the temperature signal T, and the temperature change is a change in the surrounding environment. Since it is only necessary to detect a gradual change, if the number of times of averaging is increased when performing smoothing with a digital filter, the necessary accuracy can be easily realized without using an anti-aliasing filter.

  In general, it is desirable to set the cutoff frequency of the anti-aliasing filter 25 used for preventing aliasing noise to be equal to or lower than a frequency of 1/2 · fsamp called a Nyquist frequency. The reason for this is that the aliasing noise is a phenomenon in which a high-frequency noise component is sampled, so that the noise is concentrated in a frequency band of 1/2 · fsamp or less. This is because the occurrence of aliasing noise can be suppressed to almost zero.

Even when the present invention is implemented, in order to sufficiently reduce the aliasing noise, the cutoff frequency fc of the aliasing prevention filter 25 is preferably set to ½ · fsamp or less. Therefore, it is preferable to adjust the interval necessary for stopping the sampling of the V1 signal to be 1 / fc or more from the time when the chopper is switched, at which the V1 signal is sufficiently settled.
Generally, in high-precision magnetic detection applications, it is required to suppress the detection error to 1% or less. However, if a 1 / fc sampling stop period is provided, an error due to insufficient settling is suppressed to 0.2% or less. be able to. (If the time of the sample stop period is T, the settling error is estimated by e ^{−2π · fc · T} · 100% when the anti-aliasing filter is a low-pass filter having a general primary characteristic)

  Although the embodiments of the present invention have been described above, other various modifications can be easily made. For example, an embodiment in which a stress detection element is used instead of a temperature detection element to perform stress correction for magnetic sensitivity, and an embodiment in which a temperature detection element and a stress detection element are provided at the same time, and temperature and stress correction for magnetic sensitivity are simultaneously performed. Easy to analogize.

Furthermore, the gist of the present invention is to effectively use the time during which sampling of the Hall electromotive force signal is stopped, and it can be easily applied to purposes other than correction of magnetic sensitivity.
For example, instead of the signal used to correct the magnetic sensitivity, the voltage value applied to the Hall element is sampled by an A / D converter, and failure diagnosis such as disconnection or short circuit is performed from that value. Is possible.

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Hall element 3 A / D (analog / digital) converter 4 Digital arithmetic circuit 5 D / A (digital / analog) converter 11 Hall element 12 Current source 13 A / D converter 21 Hall element 22 Chopper switch Circuit 23 Clock generation circuit 24 Oscillation circuit 25 Anti-folding filter 26 Time division switch circuit 27 A / D converter 28 Digital filter 29 Correction arithmetic circuit 30 D / A converter 31 Temperature detection element

Claims (7)

A Hall element that outputs a signal including a Hall electromotive force signal that varies according to the magnetic field strength;
An electrical signal output circuit for outputting a second electrical signal different from the Hall electromotive force signal;
A switch circuit for switching the direction of driving current supplied between the plurality of electrodes of the Hall element;
An anti-aliasing filter having a cut-off frequency of fc connected to the switch circuit and having a low-pass characteristic;
A time-division switch circuit connected to the anti-folding filter and the electric signal output circuit, and outputting one of the signal from the anti-folding filter and the second electric signal in a time-division manner;
An A / D converter connected to the time division switch circuit, converting the analog signal of the Hall electromotive force signal and the second electric signal into a digital signal, and outputting the digital signal in a time division manner;
The time-division switch circuit outputs the second electric signal and does not output the Hall electromotive force signal within a time of 1 / fc after switching of the energization direction of the drive current of the switch circuit. Electromotive force signal detection device. A correction arithmetic circuit connected to the A / D converter;
The Hall electromotive force signal detection device according to claim 1, wherein the correction arithmetic circuit corrects the Hall electromotive force signal and / or the magnetic sensitivity of the Hall electromotive force signal. The correction arithmetic circuit corrects the Hall electromotive force signal and / or the magnetic sensitivity of the Hall electromotive force signal based on the second electric signal digitally converted by the A / D converter. Item 3. The hall electromotive force signal detection device according to Item 2 . It said include an electrical signal output circuit is a temperature detecting element, the Hall electromotive force signal detection apparatus according to any one of claims 1 to 3, characterized in that for outputting a second electrical signal including temperature information. Said temperature detecting element is disposed near the Hall element, the electrical signal output circuit according to claim 4, characterized in that for outputting a second electrical signal including temperature information regarding the temperature in the vicinity of the Hall element Hall electromotive force signal detection device. It said include an electrical signal output circuit stress detection element, the Hall electromotive force signal detection apparatus according to any one of claims 1 to 5, characterized in that for outputting a second electrical signal including stress information. Said stress detecting element is disposed near the Hall element, the electrical signal output circuit according to claim 6, characterized in that for outputting a second electrical signal including stress information about stress in the vicinity of the Hall element Hall electromotive force signal detection device.

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