JP2006135683A - Analog signal measuring apparatus and analog signal measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform stable measurement by preventing output signals from being largely varied and saturated due to the influence of the temperature drift of a sensor and external noise. <P>SOLUTION: Analog input signals 10 measured by adding and subtracting offset components 11 are converted to digital output signals 13 by an A/D converter 2, and in the case that the condition of updating the offset components is satisfied, the offset components are newly calculated on the basis of the output signals 13 outputted from the A/D converter 2, and the calculated offset components are updated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an analog signal measuring device and an analog signal measuring method for measuring a sensor signal.

  In recent years, with the spread of mobile phones and PDAs, the need for navigation systems for pedestrians has increased, and various sensors such as pedometers and electronic compass that can be mounted on portable devices for measuring the current position and direction of travel of pedestrians. The demand for measurement by is increasing.

  In measurement using a sensor, a method of converting an analog signal from a sensor into a digital signal and performing computation by digital signal processing is generally seen.

  However, when the number of input bits of the A / D converter that converts an analog signal into a digital signal is limited, the output signal of the sensor is easily affected by temperature drift and offset fluctuation due to external noise, and the A / D converter There is a problem of overflowing beyond the measurement range, and how to measure stably is a problem.

  For such a problem, it is conceivable to increase the measurement range of the A / D converter. However, such an A / D converter is expensive, leading to an increase in the cost of the measuring apparatus, and 1 in the analog circuit portion. The voltage accuracy per bit becomes strict and the burden on circuit design increases.

  As a method for converting an analog signal into a digital signal without increasing the measurement range of the A / D converter and measuring the signal without overflowing, for example, a technique disclosed in Patent Document 1 is disclosed. In this technique, when the measurement signal exceeds the measurement range of the A / D converter, the offset is added to or subtracted from the measurement signal, and measurement is performed with the measurement signal within the measurement range of the A / D converter.

  However, in the above technique, when the measurement signal exceeds the measurement range of the A / D converter, the offset value is added and the measurement range is moved, so it is unclear how much the measurement range has been exceeded. The signal remains essentially saturated. Therefore, it is difficult to apply this technique to an application for measuring a rapid change in signal as seen in a sensor.

  Therefore, the object of the present invention is to prevent the output signal from fluctuating and saturating due to temperature drift of the sensor, the influence of external noise, etc., and capable of performing stable measurement, and an analog signal measuring device, and The present invention relates to an analog signal measurement method.

JP 2002-135119 A

  According to the present invention, in analog signal measurement for measuring an analog input signal from a sensor, an analog input signal is measured by adding and subtracting an offset component, and the measured analog input signal is converted into a digital output signal by an A / D converter. When the condition for converting and updating the offset component is satisfied, a new offset component is calculated based on the output signal output from the A / D converter, and the calculated offset component is updated. As a result, it is possible to prevent the output signal from fluctuating and saturating due to the temperature drift of the sensor or the influence of external noise, thereby making it possible to always measure the input signal stably.

  The present invention includes an input signal measuring means for measuring an analog input signal by adding / subtracting an offset component to / from an analog input signal, and an A / A for converting the analog input signal measured by adding / subtracting the offset component to a digital signal. It is determined whether or not a condition for updating the offset component and the D converter is satisfied, and if the condition for the update is satisfied, a new one is created based on the output signal from the A / D converter. An analog signal measuring apparatus is configured by including an offset calculating unit that calculates an offset component and an offset updating unit that updates the calculated offset component.

  The offset calculation means is configured to change the new offset so that a difference between an output signal from the A / D converter and a predetermined value set within a measurement range of the A / D converter is minimized at regular intervals. Components may be calculated.

  The offset calculation means may make the fixed period shorter than a period of a frequency that is twice the upper limit frequency of the frequency band to be measured.

  When the output signal from the A / D converter exceeds a threshold value set within the measurement range of the A / D converter, the offset calculation means is within the measurement range of the threshold value and the A / D converter. The new offset component may be calculated so that the difference from the set predetermined value is minimized.

  The offset calculation means calculates a change range of the output signal based on a distribution of output signals from the A / D converter measured in the past, and calculates the center of the change range of the output signal and the A / D. The new offset component may be calculated so that the difference from a predetermined value set within the measurement range of the converter is minimized.

  The offset calculation means predicts a change in the output signal in the next predetermined period from a change in the output signal from the A / D converter measured in the predetermined period, and the change in the predicted output signal is The new offset component may be calculated so as to be within the measurement range of the A / D converter.

  The predetermined value may be the center of the measurement range of the A / D converter.

  The input signal measuring means may include a D / A converter and an analog subtracter.

  The present invention relates to an input signal measuring step for measuring an analog input signal by adding / subtracting an offset component to / from an analog input signal, and a signal conversion for converting the analog input signal measured by adding / subtracting the offset component to a digital signal A process and whether or not a condition for updating the offset component is satisfied, and if the update condition is satisfied, a new offset is generated based on the output signal from the A / D converter. An analog signal measuring method is provided by including an offset calculating step for calculating a component and an offset updating step for updating the calculated offset component.

  In the offset calculation step, the new offset is set so that the difference between the output signal from the A / D converter and a predetermined value set within the measurement range of the A / D converter is minimized at a certain period. It is good also as a method of calculating a component.

  The offset calculating step may be a method characterized in that the fixed period is shorter than a period of a frequency that is twice the upper limit frequency of the frequency band to be measured.

  In the offset calculating step, when the output signal from the A / D converter exceeds a threshold value set in the measurement range of the A / D converter, the offset value is within the measurement range of the A / D converter. The new offset component may be calculated such that the difference from the set predetermined value is minimized.

  The offset calculating step calculates a change range of the output signal based on a distribution of output signals from the A / D converter measured in the past, and calculates the center of the change range of the output signal and the A / D. The new offset component may be calculated so that the difference from a predetermined value set within the measurement range of the converter is minimized.

  The offset calculation step predicts a change in the output signal in the next predetermined period from a change in the output signal from the A / D converter measured in the predetermined period, and the change in the predicted output signal is The new offset component may be calculated so as to be within the measurement range of the A / D converter.

  The present invention provides an analog signal measurement program capable of executing the above-described analog signal measurement method by a computer.

  The present invention provides a computer-readable recording medium on which the analog signal measurement program described above is recorded.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First example]
A first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows a schematic configuration of an analog signal measuring apparatus according to the present invention.
This analog signal measuring device is roughly divided into an offset addition / subtraction unit 1, an A / D converter 2, a calculation unit 3, and an offset calculation unit 4.

  The offset addition / subtraction unit 1 is for measuring an analog signal 10 input from the outside, and an offset value 11 is added to or subtracted from the input analog signal 10 (hereinafter referred to as addition / subtraction for short). The analog signal 12 is obtained. The analog signal 12 measured in this way is output to the A / D converter 2.

  In the A / D converter 2, the analog signal 12 obtained by adding / subtracting the offset value 11 is converted into an output signal 13 of a digital signal and output to the calculation unit 3 and the offset calculation unit 4.

  The offset calculation unit 4 newly calculates the difference between the calculated value obtained from the tendency or distribution of the input output signal 13 and a predetermined value such as the center of the measurement range of the A / D converter 2. A correct offset value 11 is calculated. The newly calculated offset value 11 is output to the offset addition / subtraction unit 1 and the calculation unit 3.

  The calculation unit 3 performs desired data processing based on the input digital output signal 13 and the offset value 11 from the offset calculation unit 4.

  The offset calculation unit 4 also needs to set an initial offset value as an initial offset value 11 in advance, such as the midpoint of the measurement range, at the start of measurement.

  Further, the offset calculation unit 4 generates a new offset value 11 every fixed period or whenever the output signal 13 from the A / D converter 2 exceeds a threshold set within the measurement range of the A / D converter 2. May be calculated.

(Analog signal measurement processing)
FIG. 2 shows a flowchart of processing for measuring an analog signal.
The offset calculation unit 4 sets an initial offset value as the initial offset value 11 (step S1), and outputs the set offset value 11 to the offset addition / subtraction unit 1 and the calculation unit 3 (step S2).

  Then, the offset addition / subtraction unit 1 adds / subtracts the offset value 11 to the analog signal 10 to become an analog signal 12, which is sent to the A / D converter 2. In the A / D converter 2, the analog signal 12 is converted into a digital signal to become an output signal 13, which is output to the calculation unit 3 and the offset calculation unit 4 and measured (step S3).

Then, the computing unit 3 calculates the true analog signal 10 input from the outside based on the input output signal 13 and the offset value 11 at that time (step S6).
It is determined whether a condition for updating the set offset value 11 is satisfied (step S4).

  If the condition for updating the offset value 11 is satisfied, the offset calculation unit 4 newly calculates the offset value 11 based on the output signal 13 input at that time (step S5).

  The calculated new offset value 11 is output to the offset addition / subtraction unit 1 and the calculation unit 3 (step S2).

  Then, a new output signal 13 is measured under the new offset value 11, and is output to the calculation unit 3 and the offset calculation unit 4 (step S3).

The arithmetic unit 3 calculates the true analog signal 10 input from the outside from the input new offset value 11 and the output signal 13 measured based on the offset value 11 (step S6).

  On the other hand, when the condition for updating the offset value 11 is not satisfied (step 4), the output signal 13 is measured with the current offset value 11 without newly calculating the offset, and the calculation unit 3 and the offset It outputs to the calculation part 4 (step S3).

Then, the arithmetic unit 3 calculates the true analog signal 10 input from the outside from the input output signal 13 and the offset value 11 at that time (step S6).
Based on the output result of the true analog signal 10 calculated in this way, the processing unit 3 performs data processing (step S7).

  Further, in the present invention, in the analog signal measuring apparatus shown in FIG. 1, the analog signal measuring method including the calculation process of the offset value 11 can be configured as an analog signal measuring program that can be executed by a computer.

  Furthermore, the analog signal measurement program executed by the analog signal measurement device can be recorded on a computer-readable recording medium.

[Second example]
A second embodiment of the present invention will be described with reference to FIGS. In addition, about the same part as the 1st example mentioned above, the description is abbreviate | omitted and the same code | symbol is attached | subjected.

  In this example, an example in which a magnetic field is measured using the magnetic sensor 100 is shown.

  FIG. 3 shows a configuration example of an analog signal measuring device in the case where the analog signal 10 output from the magnetic sensor 100 is measured.

  The analog signal measuring device includes a magnetic sensor 100, a subtracter 20, a D / A converter 21, an A / D converter 2, a calculation unit 3, an offset calculation unit 4, an offset update condition setting unit 22, And a storage unit 23. The subtracter 20 and the D / A converter 21 constitute an offset addition / subtraction unit 1. The storage unit 23 stores the offset value 11 and the sensor output data value 24.

  As the magnetic sensor 100, for example, a Hall element can be used, and a compound semiconductor system such as InSb, InAs, and GaAs, or a Si monolithic Hall element is preferable.

  Further, when the signal output from the magnetic sensor 100 is small, it is conceivable that the signal is amplified by an amplifier (not shown) and then input to the subtracter 20.

  The arithmetic unit 3 calculates the true output of the magnetic sensor 100 from the output signal 13 from the A / D converter 2 and the offset value 11 and outputs it as a sensor output data value 24 to the storage unit 23 and performs desired data processing. I do.

  The D / A converter 21 converts the offset value 11, which is a digital signal from the offset calculation unit 4, into an analog signal and outputs it to the subtracter 20.

  The offset update condition setting unit 22 calculates the offset value 11 at regular intervals or whenever the output signal 13 of the A / D converter 2 exceeds the offset output adjustment threshold set within the measurement range of the A / D converter 2. It is possible to set conditions such as

  The offset calculation unit 4 newly calculates the offset value 11 according to the conditions set by the offset update condition setting unit 22 and outputs the offset value 11 to the D / A converter 21, the storage unit 23, and the calculation unit 3. Further, the initial offset value 11 is read from the storage unit 23.

  The storage unit 23 can store an initial offset value 11, a newly calculated offset value 11, and a sensor output data value 24 that is a true output of the magnetic sensor 100 calculated by the calculation unit 3.

  The output of the magnetic sensor 100 that is the analog signal 10 is input to the subtracter 20, and the output of the magnetic sensor 100 is subtracted from the output of the D / A converter 21 by the subtracter 20 to become the analog signal 12, and the A / D converter 2 is output.

  The analog signal 12 input to the A / D converter 2 is converted into an output signal 13 of a digital signal and output to the calculation unit 3 and the offset calculation unit 4.

  The offset calculation unit 4 calculates the offset value 11 based on the update condition set by the offset update condition setting unit 22 and outputs it to the D / A converter 21, the calculation unit 3, and the storage unit 23.

  In the D / A converter 21, the calculated offset value 11 is converted from a digital signal to an analog signal and output to the subtracter 20.

  The arithmetic unit 3 calculates the true output of the magnetic sensor 100 from the output signal 13 of the A / D converter 2 and the calculated offset value 11 and outputs the true output as the sensor output data value 24 to the storage unit 23 and also stores it. An arithmetic process such as calculating a geomagnetic signal from the sensor output data value 24 stored in the unit 23 is performed.

(Analog signal measurement processing)
FIG. 4 shows a flowchart of a process for updating the offset value 11 at regular intervals and measuring the analog signal 10 that is the true output of the magnetic sensor 100.

  The offset calculation unit 4 reads the initial offset value 11 stored in the storage unit 23 and sets it as an offset initial value (step S1), and the set offset value 11 is set to the D / A converter 21, the calculation unit 3, Each is output to the storage unit 23 (step S2).

  In the D / A converter 21, the input offset value 11 is converted from a digital signal to an analog signal and output to the subtracter 20, and the subtracter 20 outputs the output of the D / A converter 21 from the output of the magnetic sensor 100. Subtract and output to the A / D converter 2 as an analog signal 12. Then, it is converted into a digital signal by the A / D converter 2 to become an output signal 13, which is output to the calculation unit 3 and the offset calculation unit 4 and measured (step S10).

  Then, the arithmetic unit 3 calculates the true output of the magnetic sensor 100 based on the input output signal 13 and the offset value 11 at that time, and outputs the true output to the storage unit 23 as the sensor output data value 24 ( Step S6).

Then, it is determined whether a certain period has elapsed (step S11).
When the fixed period has elapsed, the offset calculation unit 4 newly calculates an offset value 11 based on the output signal 13 input at that time (step S5).

  For example, the new offset value 11 is calculated so that the difference between the output signal 13 from the A / D converter 2 and a predetermined value within the measurement range of the A / D converter 2 is minimized at regular intervals. This predetermined value may be the center of the measurement range of the A / D converter 2.

  The calculated new offset value 11 is output to the D / A converter 21, the calculation unit 3, and the storage unit 23, respectively (step S2).

  Then, the output signal 13 is measured under the new offset value 11, and is output to the calculation unit 3 and the offset calculation unit 4 (step S10).

  The arithmetic unit 3 calculates the true output from the magnetic sensor 100 from the input new offset value 11 and the output signal 13 measured under the offset value 11, and outputs the sensor output data to the storage unit 23. The value is output as 24 (step S6).

  On the other hand, when the fixed period has not elapsed (step S11), the output signal 13 is measured with the current offset value 11 without calculating the new offset value 11, and the calculation unit 3 and the offset calculation unit are measured. 4 (step S10).

  Then, the arithmetic unit 3 calculates the true output of the magnetic sensor 100 from the input output signal 13 and the offset value 11 at that time, and outputs it as the sensor output data value 24 to the storage unit 23 (step S6). .

  Based on the true output of the magnetic sensor 100 and the sensor output data value 24 thus calculated, data processing is performed by the computing unit 3 (step S7).

  FIG. 5 shows how the output signal 13 from the A / D converter 2 changes when the offset value 11 is updated every measurement cycle.

  A solid line in FIG. 5 represents a change in the output signal 13 from the A / D converter 2, and a dotted line represents a change in the output signal 13 when the offset value 11 is not changed. In FIG. 5, the offset calculation unit 4 represents a state where the difference between the center of the measurement range of the A / D converter 2 and the output signal 13 is minimized for each measurement cycle.

  A magnetic signal with a large fluctuation that overflows beyond the measurement range of the A / D converter 2 moves to the vicinity of the center of the measurement range of the A / D converter 2 by adding or subtracting the offset value 11 for each measurement period. It turns out that it measures so that it may not overflow.

  In FIG. 5, the offset value 11 is calculated and updated for each measurement cycle. However, the offset value 11 can be updated once every several measurement cycles, not necessarily every measurement cycle.

When the output of the magnetic sensor 100 is V _HE and the output of the D / A converter 21 having an offset value 11 that is updated by addition or subtraction at regular intervals is O _DA (m), the signal input to the A / D converter 2 V _AD is
V _AD = V _HE −O _DA (m) (1)
It becomes. However, m is an integer greater than or equal to 0 representing the cycle in which the offset value 11 is calculated, and O _DA (0) = I ₀ (I ₀ represents the offset initial value). When the measurement range of the A / D converter 2 is R _AD with voltage (V) and L _AD with code display (LSB), the output code (LSB) of the A / D converter 2 is
C _AD = L _AD / R _AD (V _HE −O _DA (m)) (2)
It becomes.

Here, after a fixed period has elapsed (m = 1), the output of the magnetic sensor 100 is V _HE (1) (= V _AD (1) + I ₀ , where V _AD (1) is an A / D converter when the fixed period has elapsed. 2), the offset value 11O _DA (1) is the output code C _AD (1) (= L _AD / R _AD · V _AD ( 1)) is set to be the center L _AD / R _AD · V _C (V _C is a voltage representing the center of the measurement range of the A / D converter 2) of the measurement range of the A / D converter 2,
C _AD (1) −L _AD / R _AD V _C = L _AD / R _AD (V _HE (1) −O _DA (1) −V _C ) = 0
That is,
O _DA (1) = V _HE (1) −V _C (= V _AD (1) + I ₀ −V _C ) (3)
And changed.
The code input to the D / A converter 21 at this time is
P _DA (1) = (V _HE (1) −V _C ) / ΔV _DA (4)
It has become. However, ΔV _DA represents the output voltage (V / LSB) per 1 LSB input of the D / A converter 21.

Further, 1LSB of the A / D converter 2 and 1LSB of the D / A converter 21 are not necessarily equal (1 / ΔV _DA ≠ L _AD / R _AD ), and 1 LSB of the D / A converter 21 is the A / D converter 2 It is useful to prevent the output signal 13 from exceeding the measurement range of the A / D converter 2.

  For example, when 1 LSB of the D / A converter 21 corresponds to 20 LSB of the A / D converter 2, the output signal 13 shifted by 100 LSB from the center of the measurement range of the A / D converter 2 corresponds to 5 LSB of the D / A converter 21. By outputting this from the D / A converter 21, the output signal 13 can be moved to the center of the measurement range of the A / D converter 2.

However, when the output signal 13 is shifted by 115 LSB from the center of the measurement range of the A / D converter 2, the D / A converter 21 outputs 5 LSB, and the output signal 13 is 15 LSB from the center of the measurement range of the A / D converter 2. The D / A converter 21 outputs 6LSB or the output signal 13 deviates by 10 LSB from the center of the measurement range of the A / D converter 2. In FIG. 5, the deviation between the output signal 13 for each measurement period and the center of the measurement range of the A / D converter 2 represents the state.
The actual _CAD (1) and _PDA (1) are measured or output with the rounding error corrected as follows.
C _AD (1) = rint {L _AD / R _AD (V _HE (1) −O _DA (1))} (5)
P _DA (1) = print {(V _HE (1) −V _C ) / ΔV _DA } (6)
Here, lint () is a rounding operator.

In the measurement until the next fixed period elapses after the first cycle, the signal V _AD ′ input to the A / D converter 2 is V _AD ′ = when the output of the magnetic sensor 100 is V _HE ′. V _HE '-O _DA (1) (7)
It becomes. Thereafter, every time a certain period elapses, the output of the D / A converter 21 is reset, and the output signal 13 of the A / D converter 2 moves to the center of the measurement range of the A / D converter 2.
When the m-th fixed period has elapsed, the output O _DA (m) of the D / A converter 21 is
O _DA (m) = V _HE (m) −V _C (8)
And changed. However, V _HE (m) is the output of the magnetic sensor 100 when a certain period has passed m times,

Can also be expressed as However, V _AD (n) represents a signal input to the A / D converter 2 when the n-th fixed period has elapsed.
The code display of O _DA (m) is
P _DA (m) = {V _HE (m) −V _C } / ΔV _DA (10)
It becomes.

As before, the actual P _DA (m) is of course corrected to an integer.
P _DA (m) = rint {(V _HE (m) −V _C ) / ΔV _DA } (11)
There are various types of magnetic field measurement using the magnetic sensor 100 described above, and in particular, in the environment where every magnetic field varies in various directions, such as in an urban area, a minute magnetism such as geomagnetism is observed. Suitable for use.

[Third example]
A third embodiment of the present invention will be described with reference to FIGS. In addition, about the same part as the 2nd example mentioned above, the description is abbreviate | omitted and the same code | symbol is attached | subjected.

  Similar to the second example described above, a case where the magnetic sensor 100 is used will be described. The configuration of the analog signal measurement device other than the acceleration sensor is the same as the configuration of FIG. 3 of the second example described above.

  This example is an example in which the offset value 11 is newly calculated when an offset adjustment threshold set within the measurement range of the A / D converter 2 is exceeded as an update condition of the offset value 11.

(Analog signal measurement processing)
FIG. 6 shows that every time the output signal 13 of the A / D converter 2 exceeds the offset adjustment threshold set within the measurement range of the A / D converter 2, the offset value 11 is updated, and the true output of the magnetic sensor 100 is obtained. The flowchart of the process which measures a certain analog signal 10 is shown.
The offset calculation unit 4 reads the initial offset value 11 stored in the storage unit 23 and sets it as the offset initial value (step S1).

  Then, an offset adjustment threshold value is set within the measurement range of the A / D converter 2 (step S20).

  The set offset value 11 is output to the D / A converter 21, the calculation unit 3, and the storage unit 23, respectively (step S2).

  In the D / A converter 21, the input offset value 11 is converted from a digital signal to an analog signal and output to the subtracter 20, and the subtracter 20 outputs the output of the D / A converter 21 from the output of the magnetic sensor 100. Subtract and output to the A / D converter 2 as an analog signal 12. Then, it is converted into a digital signal by the A / D converter 2 to become an output signal 13, which is output to the calculation unit 3 and the offset calculation unit 4 and measured (step S10).

  Then, the arithmetic unit 3 calculates the true output of the magnetic sensor 100 based on the input output signal 13 and the offset value 11 at that time, and outputs the true output to the storage unit 23 as the sensor output data value 24 ( Step S6).

  When the output signal 13 from the A / D converter 2 exceeds the offset adjustment threshold (step 21), a new value is set so as to move the offset adjustment threshold to a predetermined value within the measurement range of the A / D converter 2. An offset value 11 is calculated (step S5).

  The calculated new offset value 11 is output to the D / A converter 21, the calculation unit 3, and the storage unit 23, respectively (step S2).

  Then, the output signal 13 is measured under the new offset value 11, and is output to the calculation unit 3 and the offset calculation unit 4 (step S10).

  The arithmetic unit 3 calculates the true output from the magnetic sensor 100 from the input new offset value 11 and the output signal 13 measured under the offset value 11, and outputs the sensor output data to the storage unit 23. The value is output as 24 (step S6).

  On the other hand, if the output signal 13 from the A / D converter 2 does not exceed the offset adjustment threshold value (step S21), the output signal 13 of the A / D converter 2 is measured with the current offset value 11 kept unchanged. And output to the calculation unit 3 and the offset calculation unit 4 (step S10).

  Then, the arithmetic unit 3 calculates the true output from the magnetic sensor 100 from the input output signal 13 and the offset value 11 at that time, and outputs the true output to the storage unit 23 as the sensor output data value 24 (step). S6).

Based on the true output of the magnetic sensor 100 and the sensor output data value 24 thus calculated, data processing is performed by the computing unit 3 (step S7).
Step S1 can be exchanged with step S20, and step S2 can be exchanged with step S20.

FIG. 7 shows that the output signal 13 of the A / D converter 2 becomes the center L _C (= L _AD / R _AD V _C ) within the measurement range of the A / D converter 2 when the offset adjustment threshold value is exceeded. The state of measurement is shown as follows.

Further, the offset adjustment threshold values are L _H and L _L , and their positions are indicated by dotted lines within the measurement range of the A / D converter 2.

  After the start of measurement, the output signal 13 indicated by a solid line initially fluctuates within the measurement range of the A / D converter 2 in FIG.

However, when the output signal 13 exceeds _{L H,} the offset calculating section 4 calculates an offset value 11 as the center of a new measuring range of the A / D converter 2 to _{L H, R AD / L AD} (L _H− L _C ) is added to the output of the D / A converter 21.

When viewed from the side of the output signal 13, the measurement range of the A / D converter _2, L H -L _C upwards to appear to shift (in FIG. 7 (B)).

Again, the output signal 13 exceeds _{L H,} further adding _R AD _/ L AD the _(L H -L _C) to the output of the D / A converter 21, to move the measurement range of the A / D converter 2 (Fig. (C) in 7).

When the output signal 13 moves downward from L _L , R _AD / L _AD (L _C −L _L ) is further subtracted from the output of the D / A converter 21 to lower the measurement range of the A / D converter 2 downward. It is moved ((D) in FIG. 7).

  In this way, measurement can be continued so that the output signal 13 from the A / D converter 2 does not exceed the measurement range of the A / D converter 2 and overflow.

  In this method, since the threshold value for changing the measurement range of the A / D converter 2 is smaller than the measurement range of the A / D converter 2, unlike the method of Patent Document 1, there is a signal measurement omission. Clearly not.

If the output of the A / D converter 2 exceeds L _H , the output O _DA of the D / A converter 21 is added with R _AD / L _AD (L _H −L _C ), so that the offset initial value D / If the output from the A converter 21 is I _O ,
O _DA = I _O + R _AD / L _AD (L _H −L _C ) (12)
It becomes.

Similarly, beyond the upper m times _{L H,} assuming that exceeds downward the n times _{L L,} the output _O DA (m + n) of the D / A converter 21, m times _{R AD / L AD (L H} -L C ) Add and subtract n times R _AD / L _AD (L _C -L _L )
O _DA (m + n) = I _O + R _AD / L _AD {mL _H + nL _L − (m + n) L _C } (13)
It becomes.

  As described above, when the offset value 11 is updated, when the offset adjustment threshold set within the measurement range of the A / D converter 2 is exceeded, the offset value 11 can be newly calculated. In this case, an analog signal having a large fluctuation that overflows beyond the measurement range of the A / D converter 2 is moved to a vicinity of a predetermined value within the measurement range of the A / D converter 2 and measured so as not to overflow. Can do.

[Fourth example]
A fourth embodiment of the present invention will be described with reference to FIGS. In addition, about the same part as the 2nd example mentioned above, the description is abbreviate | omitted and the same code | symbol is attached | subjected.

  FIG. 8 shows a configuration example of an analog signal measuring device that measures the analog signal 10 output from the acceleration sensor 200. The configuration of the analog signal measurement device other than the acceleration sensor 200 is the same as the configuration of FIG. 3 of the second example described above.

  The analog signal 10 from the acceleration sensor 200 is input to the subtracter 20, and the output of the D / A converter 21 is subtracted by the subtracter 20 to become an analog signal 12, which is output to the A / D converter 2.

  The analog signal 12 input to the A / D converter 2 is converted into an output signal 13 of a digital signal and output to the calculation unit 3 and the offset calculation unit 4.

  The offset calculation unit 4 calculates the offset value 11 based on the update condition set by the offset update condition setting unit 22 and outputs it to the D / A converter 21, the calculation unit 3, and the storage unit 23.

  The offset value 11 calculated by the D / A converter 21 is converted from a digital signal to an analog signal and output to the subtracter 20.

  The arithmetic unit 3 calculates the true output of the acceleration sensor 200 from the output signal 13 of the A / D converter 2 and the calculated offset value 11, and outputs the true output to the storage unit 23 as the sensor output data value 24. Calculation processing such as step count calculation is performed from the sensor output data value 24 stored in the unit 23.

  FIG. 9 shows how the output signal 13 of the A / D converter 2 fluctuates by the acceleration sensor 200 when the measurement range of the A / D converter 2 is not fluctuated.

A / D converter 2 has a measurement range around the C _G.

However, when the acceleration sensor 200 is walking with a terminal mounted in a centrifugal force is applied, the output of the acceleration sensor 200 may swing about for example the C _{G 'as} shown in FIG.

  At this time, if a signal that swings up and down as shown in FIG. 9 is input, an overflow occurs.

FIG. 10 shows how the output signal 13 of the A / D converter 2 is changed by the acceleration sensor 200 when the measurement range of the A / D converter 2 is changed.
In FIG. 10, rather than measure around the C _G, by measuring around the C G _', it is possible to measure without overflowing.

However, there is a way to hold and shaked terminal, in order to join the way of the centrifugal force is changed, also does not mean that always swings around the C _{G '.}

In this case, the offset update condition is set as follows, and the offset value 11 is updated by the offset calculation unit 4, whereby measurement can be performed without overflowing from the measurement range of the A / D converter 2.
(I) The midpoint of the output signal 13 is calculated from the maximum value and the minimum value of the output signal 13 of the A / D converter 2 measured at a fixed period, and the midpoint is the center of the measurement range of the A / D converter 2 And
(Ii) The average value of the output signal 13 of the A / D converter 2 measured at a constant period is calculated, and the value is set as the center of the measurement range of the A / D converter 2.
(Iii) The output signal 13 of the A / D converter 2 measured at a constant period is input to the LPF, and the value obtained by removing the high frequency component is set as the center of the measurement range of the A / D converter 2.
(Iv) The center point of the oscillation of the output signal 13 is calculated from the distribution of the output signal 13 of the A / D converter 2 measured at a fixed period, for example, a histogram, and the value is the center of the measurement range of the A / D converter 2 And
(V) The center of the output range of the A / D converter 2 is moved by the method described in the second example or the third example.

First, (i) will be described. Assuming that the maximum value and the minimum value of the output of the acceleration sensor 200 measured in the m-th fixed cycle are V _MAX (m) and V _MIN (m), respectively.
V _MAX (m) = V _ADMAX (m) + O _DA (m−1) (14)
V _MIN (m) = V _ADMIN (m) + O _DA (m−1) (15)
It is. However, V _ADMAX (m) and V _ADMIN (m) represent the maximum value and the minimum value of the signal input to the A / D converter 2 during the m-th fixed period.
The midpoint V _MID (m) of the two values V _MAX (m) and V _MIN (m) is
V _MID (m) = (V _ADMAX (m) + V _ADMIN (m)) / 2 + O _DA (m−1) (16)
It becomes. Therefore, the offset may be calculated so that the value obtained by subtracting the output of the new D / A converter 21 from this value becomes the center V _C of the measurement range of the A / D converter 2. The newly calculated offset value 11O _DA (m) output from the D / A converter 21 is O _DA (m) = V _MID (m) −V _C (17)
That is, if the offset initial value is I ₀ ,

Next, (ii) will be described.
The output Vm (t) (= V _AD (t) + O _DA (m−1), V _AD (t) of the acceleration sensor 200 at time t within the period measured in the m-th fixed period (length T) is The average value V _AVE (m) of the signal input to the A / D converter 2 at time t is

However, T = t ₂ −t ₁ . The newly calculated offset value 11O _DA (m) output from the D / A converter 21 is O _DA (m) = (V _AVE (m) −V _C ) (20)
It becomes.

In the method (iii), the fluctuation of the DC component is calculated by passing through the LPF. If the measurement signal obtained by passing the output signal 13 within the m-th fixed period through the LPF is L _LPF (m) in code display, it is output by the D / A converter 21 which is newly calculated. The offset value 11O _DA (m) is
O _DA (m) = L _LPF (m) R _AD / L _AD + O _DA (m−1) −V _C (21)
That is,

It becomes.

  Note that the above description is based on the assumption that the LPF is disposed after the A / D converter 2, but it may be disposed before the A / D converter 2.

Finally, the method (iv) will be described.
If walking with a mounted terminal acceleration sensor 200, the output signal 13 as mentioned above, may have a center of not vibrate at C _G by centrifugal forces. If the output signal 13 is in the form of a normal distribution distributed around a certain point, the average value is the center of vibration of the output signal 13. However, in practice, the distribution is not necessarily normal as shown in FIG. 11A, and may be distribution as shown in FIG. 11B.

Accordingly, in the case where the acceleration sensor 200 vibrates with a distribution as shown in FIG. 11B, if a simple average value is used as the center of vibration, there is a possibility that a deviation from the center actually vibrating occurs.
Therefore, in the case of such a distribution, the center of the spread of the distribution is set as the center of vibration of the output signal 13.

The equation for calculating the offset value 11 in this case is obtained by substituting the distribution end points into V _ADMAX (m) and V _ADMIN (m) in the method (i). The distribution is calculated and calculated by the offset calculation unit 4.

(Analog signal measurement processing)
FIG. 12 shows a flowchart of an analog signal measurement process for updating the offset value 11 based on the distribution of FIG.
The offset calculation unit 4 reads the initial offset value 11 stored in the storage unit 23 and sets it as an offset initial value (step S1), and the set offset value 11 is set to the D / A converter 21, the calculation unit 3, Each is output to the storage unit 23 (step S2).

  In the D / A converter 21, the input offset value 11 is converted from a digital signal to an analog signal and output to the subtracter 20, and the subtracter 20 performs D / A from the analog signal 10 that is the output of the acceleration sensor 200. The output of the converter 21 is subtracted and output to the A / D converter 2 as an analog signal 12. Then, it is converted into a digital signal by the A / D converter 2 to become an output signal 13, which is output to the calculation unit 3 and the offset calculation unit 4 and measured (step S10).

The arithmetic unit 3 calculates the true output of the acceleration sensor 200 based on the input output signal 13 and the offset value 11 at that time, and outputs the true output to the storage unit 23 as the sensor output data value 24 ( Step S6).
Then, it is determined whether a certain period has elapsed (step S11).

  When the fixed period has elapsed, the offset calculation unit 4 calculates a distribution from the output signal 13 input so far (step S30).

An offset value 11 is newly calculated from the end point of the calculated distribution (step 31).
The calculated new offset value 11 is output to the D / A converter 21, the calculation unit 3, and the storage unit 23, respectively (step S2).

Then, the output signal 13 is measured under the new offset value 11, and is output to the calculation unit 3 and the offset calculation unit 4 (step S10).
The arithmetic unit 3 calculates a true output from the acceleration sensor 200 from the input new offset value 11 and the output signal 13 measured based on the offset value 11, and outputs the sensor output data to the storage unit 23. The value is output as 24 (step S6).

  On the other hand, when the fixed period has not elapsed (step 11), the output signal 13 is measured with the current offset value 11 without calculating the new offset value 11, and the calculation unit 3 and the offset calculation unit 4 (step S10).

  Then, the arithmetic unit 3 calculates the true output of the acceleration sensor 200 from the input output signal 13 and the offset value 11 at that time, and outputs it as the sensor output data value 24 to the storage unit 23 (step S6). .

Based on the true output of the acceleration sensor 200 calculated in this way and the sensor output data value 24, the calculation unit 3 performs data processing (step S7).
In the offset calculation procedures (i), (ii), and (iii), steps S30 and S31 in the flowchart (iV) may be rewritten as necessary procedures for the respective methods.

  As described above, when the acceleration sensor 200 is applied as input means of the analog signal measuring apparatus, the use of the acceleration sensor 200 includes a pedometer or the like.

  However, when walking, the terminal on which the acceleration sensor 200 is mounted may have an acceleration twice or more than the gravitational acceleration, and the magnitude of the offset value of the acceleration sensor 200 is normally 1G when stationary. However, when the terminal is shaken, a centrifugal force may be applied. In such a case, the magnitude of the offset value that becomes the center of vibration becomes larger than 1G. Further, when the terminal is held in the hand, the center of vibration of the signal of each axis of the acceleration sensor 200 is changed by changing the hand holding posture.

  In order to accurately measure such a signal with a large output fluctuation without overflow, an A / D converter 2 having a large measurement range and a large number of input bits is required.

  However, even in such a case, by using this analog signal measuring device, it is possible to perform measurement without preparing an A / D converter 2 having such a large measurement range.

[Fifth Example]
A fifth embodiment of the present invention will be described with reference to FIGS. In addition, about the same part as the 1st example mentioned above and the 2nd example, the description is abbreviate | omitted and the same code | symbol is attached | subjected.

  In this example, the offset value 11 is calculated by estimating the center of the fluctuation range of the output signal 13 in the next period from the change in the output signal 13 within a certain period.

  FIG. 13 shows a method for calculating the offset value 11. The configuration of the analog signal measuring apparatus is the same as the configuration of FIG. 1 of the first example, the configuration of FIG. 3 of the second example, or the configuration of FIG. 8 of the fourth example. The sensor connected to the analog signal measuring device is constituted by the magnetic sensor 100 or the acceleration sensor 200.

  The thick line in FIG. 13 shows the behavior of the output signal 13 when the measurement range of the A / D converter 2 is not changed. The thin solid line represents the fluctuation of the output signal 13 when measurement is performed while changing the measurement range of the A / D converter 2, and the dotted line represents the expected fluctuation of the output signal 13 at the time of the white circle. The black circle represents the center of the fluctuation range of the predicted output signal 13.

  Due to the temperature drift gradually from the measurement start point, the measurement value, that is, the output signal 13 fluctuates upward within the measurement range of the A / D converter 2. Changes in the output signal 13 from the measurement start point to the measurement point after the fixed period elapses after the elapse of a certain period, for example, an average value of dozens of measurement values from the measurement start point and dozens of measurements after the elapse of the fixed period Inclination is calculated from the average value of the values, the fluctuation range of the measurement value after the next fixed period elapses, and the center of the fluctuation range is moved to the center of the measurement range of the A / D converter 2 The offset value 11 is calculated.

(Analog signal measurement processing)
FIG. 14 estimates the center of the fluctuation range of the output signal 13 in the next period from the change of the output signal 13 within a certain period, updates the offset value 11, and measures the analog signal 10 which is the output of the sensor. The flowchart of a process is shown.

  The offset calculation unit 4 reads the initial offset value 11 stored in the storage unit 23 and sets it as a read offset initial value (step S1), and the set offset value 11 is stored in the D / A converter 21, the calculation unit 3, and the storage. Each is output to the unit 23 (step S2).

  In the D / A converter 21, the input offset value 11 is converted from a digital signal to an analog signal and output to the subtracter 20. The subtracter 20 converts the analog signal 10 that is the output of the sensor from the D / A converter 21. Is output to the A / D converter 2 as an analog signal 12. Then, it is converted into a digital signal by the A / D converter 2 to become an output signal 13, which is output to the calculation unit 3 and the offset calculation unit 4 and measured (step S10).

  Then, the arithmetic unit 3 calculates the true output of the sensor based on the input output signal 13 and the offset value 11 at that time, and outputs it as the sensor output data value 24 to the storage unit 23 (step S6). ).

Then, it is determined whether a certain period has elapsed (step S11).
When a certain period has elapsed, the offset calculation unit 4 obtains the slope of the change in the measured value between the average value of the measured values after the start of measurement and the average value of the measured values after the lapse of the certain period. (Step S40).

  Then, the fluctuation range of the measurement value in the next fixed cycle is predicted, and the offset value 11 is newly calculated so as to move the center of the fluctuation range to the center of the measurement range of the A / D converter 2 (step) S41).

  The calculated new offset value 11 is output to the D / A converter 21, the calculation unit 3, and the storage unit 23, respectively (step S2).

  Then, the output signal 13 is measured under the new offset value 11, and is output to the calculation unit 3 and the offset calculation unit 4 (step S10).

  The arithmetic unit 3 calculates a true output from the sensor from the input new offset value 11 and the output signal 13 measured based on the offset value 11, and outputs the sensor output data value 24 to the storage unit 23. (Step S6).

  On the other hand, when the fixed period has not elapsed (step 11), the output signal 13 is measured with the current offset value 11 without calculating the new offset value 11, and the calculation unit 3 and the offset calculation unit 4 (step S10).

  Then, the arithmetic unit 3 calculates the true output of the sensor from the input output signal 13 and the offset value 11 at that time, and outputs it as the sensor output data value 24 to the storage unit 23 (step S6).

  Based on the true output of the sensor and the sensor output data value 24 calculated in this way, data processing is performed by the calculation unit 3 (step S7).

If the length of the fixed period is T and the average value of the measurement values near the measurement start point input to the A / D converter 2 in the mth period is V (m), the mth period and the m + 1th period The center V _EC (m) of the fluctuation range of the measured value after the elapse of the (m + 1) th cycle, which is predicted from the average value V (m + 1) of the measured values near the start point,
V _EC (m) = {V (m + 1) −V (m)} / T × (½) T + V (m + 1) (23)
It becomes. Accordingly, the output of O _DA (m−1) that is the output of the D / A converter 21 in the m-th cycle is updated, and V _EC (m) is changed to the center V _C of the measurement range of the A / D converter 2. In order to move the measured value, the calculation is performed as follows. The output of the D / A converter 21 in the m + 1th cycle is O _DA (m) = V _EC (m) + O _DA (m−1) −V _C (24)
That is,

It becomes.

  In the above description, the (m + 1) -th cycle that is the next cycle of the m-th cycle is considered. However, from the fluctuation range of the measured value of the m-th cycle, a change in the measured values of the m + 2 and subsequent cycles may be predicted. . That is, in the equation (23), (1/2) T is calculated as (3/2) T, (5/2) T, and the present invention is not limited to predicting the next cycle.

  In general, the output voltage of a sensor tends to fluctuate due to temperature drift after power is turned on. If the sensor is sensitive to temperature, the measured value may exceed the measurement range of the A / D converter 2 due to temperature drift.

  However, by using the analog signal measuring apparatus according to this example, the newly calculated offset value 11 is subtracted from the output of the sensor, and the measurement range of the A / D converter 2 is moved, so that the measurement value is A / D converter 2 can be brought close to a predetermined value within the measurement range.

[Sixth example]
A sixth embodiment of the present invention will be described with reference to FIGS. In addition, about the same part as the 1st example-the 5th example mentioned above, the description is abbreviate | omitted and the same code | symbol is attached | subjected.

  In this example, in the example of calculating the offset value 11 to be added to or subtracted from the analog signal 10 that is an input signal for every fixed period, particularly, the points to be noted in the calculation process of the offset value 11 will be described. The configuration of the analog signal measuring apparatus is the same as the configuration of FIG. 1 of the first example, the configuration of FIG. 3 of the second example, or the configuration of FIG. 8 of the fourth example.

  15 to 17, when the output signal 13 that is a measurement signal is an AC signal, the offset value 11 is calculated at a constant period, and the output signal 13 is moved to the center of the measurement range of the A / D converter 2. The state of the measurement by the difference of the length of a fixed period is shown.

  FIG. 15 shows an example where the frequency cycle of the measurement signal is the same as the fixed cycle for calculating the offset value 11.

  FIG. 16 is an example in the case where the constant period is the same as the period of twice the frequency of the measurement signal.

FIG. 17 shows an example where the fixed period is the same as the period of the frequency four times that of the measurement signal.
In both cases, the measurement range of the A / D converter 2 is twice the amplitude of the measurement signal.

  FIG. 15 shows an example in which the constant period is the same as the frequency of the signal to be measured. For example, when the maximum value or the minimum value of the output signal 13 is the center of the measurement range of the A / D converter 2, Between the time of calculating 11 and the next time of calculating the offset value 11, the midpoint overflows from the midpoint of the vibration width of the measurement signal between the maximum value and the maximum value.

FIG. 16 shows a state in which the offset value 11 is calculated at a frequency cycle twice the frequency of the measurement signal, and the measurement value is moved to the center of the measurement range of the A / D converter 2.
In this case, the measurement signal overflows while moving from the midpoint of the signal vibration width to the minimum value and from the midpoint of the signal vibration width to the maximum value in the next cycle.

FIG. 17 shows a state in which the offset value 11 is calculated at a frequency period four times the frequency of the measurement signal, and the measurement value is moved to the center of the measurement range of the A / D converter 2.
In this case, the measurement signal does not overflow.

  As described above, it is necessary to change the cycle for calculating the offset value 11 in accordance with the measurement signal.

  When the measurement range of the A / D converter 2 is larger than four times the amplitude of the measurement signal, the measurement signal does not overflow.

  However, conversely, when the measurement range of the A / D converter 2 is smaller than four times the amplitude of the measurement signal, the measurement signal overflows, so the period for calculating the offset value 11 is the frequency of the measurement signal. It is desirable that the period is shorter than twice the frequency.

  In the above description, as shown in FIGS. 15 to 17, the case where the measurement signal is a sine wave has been described.

  Even in such a case, as described above, it is desirable that the fixed period for calculating the offset value 11 is shorter than the period of the frequency that is twice or more the upper limit frequency of the frequency component of the measurement signal.

The upper limit frequency corresponds to, for example, f _BW when the measurement signal has a frequency band including a gain (amplitude Am, frequency f) as shown in FIG.

  By paying attention to the above points, it is possible to measure an amplitude that exceeds the measurement range of the A / D converter 2 without overflowing.

(Modification 1)
In the first to sixth examples described above, an amplifier is added between the magnetic sensor 100, the acceleration sensor 200, and the subtractor 20, or between the subtractor 20 and the A / D converter 2, thereby increasing the signal amplitude. It is good also as a structure which adjusts and measures thickness.

(Modification 2)
In the above each embodiment has been mainly setting the V _C is the center of the measurement range of the A / D converter 2 as a predetermined value.

  However, it does not necessarily have to be central. For example, a signal that greatly fluctuates above the measurement range of the A / D converter 2 is brought below the center, so that stable measurement can be realized more reliably.

(Modification 3)
Further, only one of the offset output adjustment threshold values in the third example described above may be set.

(Modification 4)
When the offset output adjustment threshold value L _L or L _H of the third example is exceeded, R _AD / L _AD (L _H −L _C ) is output to the output of the D / A converter 21 as the offset value 11. or 60% of the _{R AD / L AD (L C} -L L), 80%, is 120%, a method of adding or subtracting a voltage such as 140%.

(Modification 5)
In the case of using the magnetic sensor 100 as in the first to third examples described above, the D / A converter 21 is not necessarily essential as means for adding the offset value 11.

  There are a method of applying an offset magnetic field to the magnetic sensor 100 by an external magnetic field generating means, such as passing a current through the coil, or a method of changing the operating point by changing the bias condition of the magnetic sensor 100. Applicable to the invention.

It is a block diagram which shows schematic structure of the analog signal measuring device which is the 1st Embodiment of this invention. It is a flowchart which shows the analog signal measurement process which is the 1st Embodiment of this invention. It is a block diagram which shows the structural example of the analog signal measuring device in the case of measuring the analog signal output from the magnetic sensor which is the 2nd Embodiment of this invention. It is a flowchart which shows the analog signal measurement process which is the 2nd Embodiment of this invention. It is explanatory drawing which shows the mode of the change of the output signal of an A / D converter in the case of updating an offset value for every measurement period. It is a flowchart which shows the analog signal measurement process which is the 3rd Embodiment of this invention. It is explanatory drawing which shows the mode of a measurement when the output signal of an A / D converter exceeds the threshold value for offset adjustment. It is a block diagram which shows schematic structure of the analog signal measuring device in the case of measuring the analog signal output from the acceleration sensor which is the 4th Embodiment of this invention. It is explanatory drawing which shows the fluctuation | variation of the output signal of the A / D converter by an acceleration sensor when not changing the measurement range of an A / D converter. It is explanatory drawing which shows the fluctuation | variation of the output signal of the A / D converter by an acceleration sensor when changing the measurement range of an A / D converter. It is explanatory drawing which shows the vibration distribution of the output signal of an acceleration sensor. It is a flowchart which shows the analog signal measurement process which calculates the offset value based on the vibration distribution of the acceleration sensor which is the 4th Embodiment of this invention. It is explanatory drawing which shows a mode that the center of the fluctuation range of the signal in the following period is estimated from the change of the output signal in a fixed period, and an offset value is calculated, which is the fifth embodiment of the present invention. FIG. 9 is a flowchart showing an analog signal measurement process for estimating an offset value by estimating the center of a fluctuation range of a signal in the next period from a change in an output signal within a certain period, which is a fifth embodiment of the present invention. is there. It is explanatory drawing which shows the example in case the frequency period of a measurement signal and the fixed period which calculates an offset value are the same which is the 6th Embodiment of this invention. It is explanatory drawing which shows the example in case the fixed period which calculates offset which is the 6th Embodiment of this invention is the same as the period of the frequency twice as high as the frequency of a measurement signal. It is explanatory drawing which shows the example in case the fixed period which calculates offset which is the 6th Embodiment of this invention is the same as the period of the frequency 4 times the frequency of a measurement signal. It is explanatory drawing which shows the gain characteristic of a measurement signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Offset addition / subtraction part 2 A / D converter 3 Operation part 4 Offset calculation part 10 Analog signal 11 Offset value 12 Analog signal 13 Output signal 20 Subtractor 21 D / A converter 22 Offset update condition setting part 23 Storage part 24 Sensor output data value 100 magnetic sensor 200 acceleration sensor

Claims (16)

Input signal measuring means for measuring the analog input signal by adding / subtracting an offset component to / from the analog input signal;
An A / D converter that converts the analog input signal measured by adding and subtracting the offset component into a digital signal;
It is determined whether or not a condition for updating the offset component is satisfied. If the update condition is satisfied, a new offset component is calculated based on an output signal from the A / D converter. Offset calculating means for
An analog signal measuring apparatus comprising offset updating means for updating the calculated offset component. The offset calculating means includes
Calculating the new offset component so that the difference between the output signal from the A / D converter and a predetermined value set within the measurement range of the A / D converter is minimized at regular intervals. The analog signal measuring apparatus according to claim 1, wherein The offset calculating means includes
3. The analog signal measuring apparatus according to claim 2, wherein the fixed period is shorter than a period of a frequency that is twice the upper limit frequency of a frequency band to be measured. The offset calculating means includes
When the output signal from the A / D converter exceeds a threshold value set within the measurement range of the A / D converter, the threshold value and a predetermined value set within the measurement range of the A / D converter The analog signal measuring apparatus according to claim 1, wherein the new offset component is calculated so that the difference between the two is minimized. The offset calculating means includes
Based on the distribution of the output signal from the A / D converter measured in the past, the change range of the output signal is calculated, and within the center of the change range of the output signal and the measurement range of the A / D converter. The analog signal measuring apparatus according to claim 1, wherein the new offset component is calculated so that a difference from a set predetermined value is minimized. The offset calculating means includes
A change in the output signal in the next predetermined period is predicted from a change in the output signal from the A / D converter measured within a predetermined period, and the change in the predicted output signal is measured by the A / D converter. The analog signal measuring apparatus according to claim 1, wherein the new offset component is calculated so as to be within a range.   The analog signal measuring apparatus according to claim 1, wherein the predetermined value is a center of a measurement range of the A / D converter. The input signal measuring means includes
8. The analog signal measuring device according to claim 1, further comprising a D / A converter and an analog subtractor. An input signal measuring step for measuring the analog input signal by adding / subtracting an offset component to / from the analog input signal;
A signal conversion step of converting the analog input signal measured by adding and subtracting the offset component into a digital signal;
It is determined whether or not a condition for updating the offset component is satisfied. If the update condition is satisfied, a new offset component is calculated based on an output signal from the A / D converter. Offset calculating step to
An analog signal measurement method comprising: an offset update step of updating the calculated offset component. The offset calculation step includes
Calculating the new offset component so that the difference between the output signal from the A / D converter and a predetermined value set within the measurement range of the A / D converter is minimized at regular intervals. 10. The analog signal measuring method according to claim 9, wherein The offset calculation step includes
The analog signal measurement method according to claim 10, wherein the fixed period is shorter than a period of a frequency twice the upper limit frequency of a frequency band to be measured. The offset calculation step includes
When the output signal from the A / D converter exceeds a threshold value set within the measurement range of the A / D converter, the threshold value and a predetermined value set within the measurement range of the A / D converter The analog signal measurement method according to claim 9, wherein the new offset component is calculated so that the difference between the two is minimized. The offset calculation step includes
Based on the distribution of the output signal from the A / D converter measured in the past, the change range of the output signal is calculated, and within the center of the change range of the output signal and the measurement range of the A / D converter. 10. The analog signal measuring method according to claim 9, wherein the new offset component is calculated so that a difference from a set predetermined value is minimized. The offset calculation step includes
A change in the output signal in the next predetermined period is predicted from a change in the output signal from the A / D converter measured within a predetermined period, and the change in the predicted output signal is measured by the A / D converter. The analog signal measurement method according to claim 9, wherein the new offset component is calculated so as to be within a range.   15. An analog signal measurement program capable of executing the analog signal measurement method according to claim 9 by a computer.   The computer-readable recording medium which recorded the analog signal measurement program of Claim 15.

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