JP2008182508A - A/d conversion apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a digital value of an input voltage accurately, even if an interval from switching a signal at a multiplexer portion to executing an A/D conversion is shortened. <P>SOLUTION: A calculation formula of a measurement error resulted from a response delay of a sensor output voltage by an input circuit given from a sensor to an A/D converter 4 and from a voltage change by a redistribution of a charge is calculated from the relational expression of a circuit, and the correction for an A/D conversion value is carried out, based on the calculation formula. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an A / D conversion device, and more particularly, to an A / D conversion device that has a multiplexer unit in front of an A / D conversion unit and can switch an input signal for A / D conversion by the multiplexer unit.

  In a control apparatus that uses analog signals (voltage signals) that are outputs of a large number of sensors and is used in a control system for an internal combustion engine in recent years, a single A / D conversion unit can be used to control a plurality of sensors. In some cases, an A / D converter configured to perform A / D conversion of the analog signal is used. As an A / D converter of this type, one analog signal is selected from a plurality of analog signals in a time-division manner using a multiplexer section having an internal switch, and the selected analog signals are sequentially A / D converted. Some are configured to convert to a digital value.

  In such an A / D conversion device, there is a capacitor disposed between the switch in the multiplexer unit and the A / D conversion unit, a charge capacitance due to an inherent parasitic capacitance, etc. (hereinafter referred to as a switching unit capacitance). Immediately after switching the analog signal selected by the multiplexer unit (analog signal output from the multiplexer unit to the A / D conversion unit), the charge accumulated in the switching unit capacitor by the analog signal before switching by the multiplexer unit is transferred by the multiplexer unit. This will affect the analog signal input after switching.

  For this reason, when the switching time from when the analog signal is switched by the multiplexer unit to when the A / D conversion unit performs A / D conversion is short, between the analog signal output by the sensor and the A / D converted digital value An error (residual capacity error) occurs.

  It is conceivable to lengthen the switching time so that such a residual capacity error does not occur. However, if the switching time is lengthened, the sampling interval of the sensor must be lengthened accordingly, and there is a problem that it becomes impossible to cope with A / D conversion of the analog signal of the sensor whose change in the physical quantity to be measured is fast.

  As one of countermeasures against such a problem, there is a method of increasing the capacitance of the input circuit unit capacitor by installing an input circuit unit capacitor between the multiplexer unit and the plurality of sensors. In this measure, when the analog signal input by the multiplexer unit is switched, the charge stored in the switching unit capacitor is redistributed with the input circuit unit capacitor, and the charge stored in the switching unit capacitor is given to the input analog signal. The influence can be reduced.

  Also, the previous digital conversion value converted by the A / D conversion unit, the current digital conversion value, the sampling time interval in the A / D conversion unit, and the analog input portion of the A / D conversion unit from the multiplexer unit There is an A / D converter that calculates a digital value of an input analog signal from a time constant (for example, Patent Document 1).

JP 2000-22540 A

  In an environment where the influence of external noise is large, such as an internal combustion engine control system, an electric resistance element is installed between the sensor and the multiplexer unit in order to improve the S / N ratio of the signal, and the input circuit unit capacitor Is used as a combination filter circuit to reduce the influence of noise.

  In such a system, when the input circuit section capacitor is increased, the time constant of the filter circuit increases. Thus, when the change rate of the physical quantity measured by the sensor is fast and the change of the sensor output voltage is fast, the change rate of the voltage after passing through the filter circuit is slower than the change of the sensor output voltage. As a result, the digital value obtained by A / D converting the voltage after passing through the filter circuit includes a measurement error with the sensor output voltage.

  An A / D converter as described in Patent Document 1 corrects a response delay of a sensor output voltage caused by an input circuit from a sensor to an A / D converter, and is more sensitive than a switch inside a multiplexer unit. The circuit installed on the side is not considered.

  However, when the input circuit unit capacitor is installed on the sensor side of the switch inside the multiplexer unit, it is accumulated in the switching unit capacitor between the switching unit capacitor and the input circuit unit capacitor, apart from the response delay of the input voltage. As a result, a voltage change occurs due to the redistribution of charges, and an error occurs in the A / D conversion result.

  In order to reduce the above error, instead of simply correcting the response delay with the previous sampling value as the initial value, including the voltage change due to redistribution when the switch built in the multiplexer is switched. It is necessary to correct.

  In addition, when mass-producing A / D converters, generally, variations in circuit element characteristics occur. When such a variation occurs, the control calculation unit cannot detect the variation in characteristics. As a result, an error occurs in the correction amount calculated by the control calculation unit. Variations in the characteristics of circuit elements can be reduced by increasing the accuracy of production equipment and selecting production products, but this leads to increased costs.

  The present invention has been made in view of the problems to be solved, and the object of the present invention is to delay the response of the sensor output voltage by the input circuit from the sensor to the A / D converter and to redistribute the charge. A / D can accurately obtain the digital value of the input voltage even if the interval between the signal switching at the multiplexer unit and the A / D conversion is shortened by eliminating the measurement error due to the voltage change due to It is to provide a D conversion device.

  In order to achieve the above object, an A / D converter according to the present invention includes a multiplexer unit that sequentially selects one analog signal from a plurality of analog signal inputs, and the analog signal selected by the multiplexer unit. An A / D conversion device including an A / D conversion unit for converting to a digital value, wherein a first analog signal before switching an analog signal selected by the multiplexer unit is converted by the A / D conversion unit. A digital value of 1 and a second digital value obtained by converting the second analog signal after switching the analog signal selected by the multiplexer unit by the A / D conversion unit and an analog signal selected by the multiplexer unit The time from switching to A / D conversion by the A / D converter, and the time of the input unit from the analog signal source to the A / D converter The analog signal response characteristics according to the above, the capacitance from the signal source of the analog signal to the input section of the multiplexer section, and the charge distribution characteristics by the capacitance ratio from the input section of the multiplexer section to the A / D conversion section, And correction calculation means for correcting and calculating the two digital values.

  In order to achieve the above object, an A / D converter according to the present invention includes a multiplexer unit that sequentially selects one analog signal from a plurality of analog signal inputs, and the analog unit selected by the multiplexer unit. An A / D converter that converts a signal into a digital value and an A / D converter that includes a non-volatile storage device, before switching an analog signal selected by the multiplexer unit under a predetermined condition set in advance The A / D converter converts the third digital value obtained by converting the third analog signal by the A / D converter and the fourth analog signal after switching the analog signal selected by the multiplexer. Calculated by a correction amount calculation unit that calculates a correction amount from a fourth digital value, the third digital value, the fourth digital value, and the correction amount calculation unit. A storage processing unit that stores the relationship with the correction amount in the nonvolatile storage device, and a first analog signal that is converted by the A / D conversion unit before the analog signal selected by the multiplexer unit is switched. The digital value and the second digital value converted by the A / D converter after the second analog signal after switching the analog signal selected by the multiplexer is stored in the nonvolatile storage device. A read processing unit that reads a correction amount, and a correction calculation unit that corrects the second digital value using the correction amount read by the read processing unit.

  According to the present invention, there is a capacitor disposed between the switch inside the multiplexer unit and the A / D conversion unit, a switching unit capacitance such as an inherent parasitic capacitance, and the capacitor is installed on the sensor side of the multiplexer unit. In the A / D converter, even if the interval from when the signal is switched in the multiplexer unit to when the A / D conversion is performed is short, the digital value of the input voltage can be obtained with high accuracy.

Hereinafter, an embodiment of an A / D conversion device of the present invention will be described with reference to the drawings.
FIG. 1 shows an embodiment of an A / D converter according to the present invention.
The A / D converter 1 receives analog voltages Vin (1) to Vin (n) output from n sensors 100 (1) to 100 (n), and the input analog voltages Vin (1) to Vin (1) to Vin (n) is converted into a digital value.

  The A / D conversion device 1 includes an input circuit unit 2, a multiplexer unit 3, an A / D conversion unit 4, and a calculation unit 5. The A / D converter 1 inputs analog voltages Vin (1) to Vin (n) output from n sensors 100 (1) to 100 (n) to the input circuit unit 2 in parallel.

  The input circuit section 2 includes input circuit section capacitors Cin (1) to Cin (n) for each sensor signal input section, and the input analog voltages Vin (1) to Vin (n) are output voltages Vm ( 1) to Vm (n) are input to the multiplexer unit 3.

  The multiplexer unit 3 has a built-in switching circuit, and sequentially selects one of the output voltages Vm (1) to Vm (n) of the input circuit unit 2 and inputs it to the A / D conversion unit 4. The multiplexer unit 3 has a switching unit capacitor Cmpx. The voltage across the switching unit capacitance Cmpx is Vmpx.

  Hereinafter, a case where the multiplexer unit 3 selects the output voltage Vm (m) based on the analog voltage Vin (m) from an arbitrary m-th sensor 100m will be described.

  The A / D conversion unit 4 converts the voltage Vmpx (m) across the multiplexer unit 3 into a digital value ADin (m).

  The calculation unit 5 performs a required calculation using the digital value ADin (m). The result calculated by the calculation unit 5 is output as an analog voltage using, for example, a D / A converter separately attached to the calculation unit, and is used for drive control of an actuator connected to the D / A converter. . The arithmetic unit 5 also controls timing for switching the switches of the multiplexer unit 3 and measures the time for switching the switches.

  FIG. 2 shows an example of the behavior of the voltage Vmpx across the switching unit capacitance Cmpx in the A / D conversion device 1. A solid line A in FIG. 2 indicates that the output voltage Vm (m) of the mth sensor signal from the output voltage Vm (m-1) of the m-1st sensor signal at the time point T (m-1) in the multiplexer unit 3. The behavior of the voltage Vmpx at both ends when the input signal to be selected is switched is shown.

  At time T (m−1), the multiplexer unit 3 selects an input signal for selecting from the output voltage Vm (m−1) based on the m−1th sensor signal to the output voltage Vm (m) based on the mth sensor signal. Immediately after switching, the charge accumulated in the switching unit capacitor Cmpx and the charge accumulated in the input circuit unit capacitor Cin (m) are distributed, and the voltage Vmpx across the multiplexer unit 3 becomes Vdist (m).

  Thereafter, the both-ends voltage Vmpx gradually approaches the analog voltage Vin (m) of the sensor output according to the response characteristics of the circuit configured between the sensor 100 (m) and the A / D conversion unit 4. At the time T (m) when the sampling interval Tint (m) has elapsed from the time (m−1), the value of the voltage Vmpx at both ends of the multiplexer unit 3 is A / D converted by the A / D conversion unit 4 and A / D conversion value (digital value) ADin (m) is acquired.

  Thereafter, the multiplexer unit 3 switches the input signal to be selected from the output voltage Vm (m) based on the mth sensor signal to the output voltage Vm (m + 1) based on the m + 1th sensor signal.

  Here, when the sampling interval Tint (m) is long, the both-ends voltage Vmpx converges to the analog voltage Vin (m) of the sensor output as indicated by the broken line B, and the A / D conversion unit 4 The analog voltage Vin (m) is subjected to A / D conversion on the converged both-end voltage Vmpx, and the A / D conversion value ADin (m) becomes a value corresponding to the sensor output analog voltage Vin (m).

  On the other hand, as shown in FIG. 2, when the sampling interval Tint (m) is short, A / D conversion is performed before the voltage Vmpx at both ends converges to the analog voltage Vin (m) of the sensor output. As a result, the A / D conversion value ADin (m), which is a digital value of the A / D conversion result, has an error e with respect to the analog voltage Vin (m) of the sensor output to be measured. Become. For this reason, when it is desired to measure at a fast sampling interval, an error occurs in the A / D conversion result.

  FIG. 3 shows an error with respect to the analog voltage Vin (m) output from the sensor 100 (m) when the analog voltage Vin (m-1) output from the sensor 100 (m-1) is 0 V and the sampling interval is constant. The characteristic of e (equivalent to the difference between the analog voltage Vin (m) and the A / D conversion value ADin (m)) is shown.

  As shown in FIG. 3, the error e is an analog voltage Vin (m−1) output from the sensor 100 (m−1) and an analog voltage Vin (m) output from the next sensor 100 (m). The larger the difference from Vin (m), the larger the difference. Since the error e changes depending on the voltage change of the both-end voltage Vmpx, the error e changes if there is a variation in the characteristics of the circuit elements, such as when the A / D converter 1 is produced in large quantities.

  FIG. 4 shows an example of the voltage behavior of the both-end voltage Vmpx when the characteristics of the circuit element are changed. In contrast to the behavior A of the voltage Vmpx at both ends when the characteristics of the circuit element are the same as the design value, the behavior C of the voltage Vmpx at the both ends is different from the behavior A when the characteristics of the circuit element are different from the design values. become.

  As a result, when the circuit element characteristics are different from the design value with respect to the A / D conversion value ADin (m) of the analog voltage Vin (m) when the circuit element characteristics are the same as the design value, the analog voltage The A / D conversion value of Vin (m) becomes a value ADinE1 (m) different from ADin (m).

  Further, when the power supply voltage used for the A / D conversion unit 4 is different from the design value, an error occurs in the A / D conversion result due to the amount of deviation of the power supply voltage.

  FIG. 5 shows an example of the voltage behavior of the both-end voltage Vmpx when the power supply voltage used for the A / D converter 4 is different from the design value. When the power supply voltage used for the A / D converter 4 is different from the design value, the behavior A of the both-end voltage Vmpx when the power supply voltage used for the A / D converter 4 is the same as the design value. The behavior E of the voltage Vmpx is different from the behavior A.

  As a result, the A / D conversion unit uses the A / D conversion value ADin (m) of the analog voltage Vin (m) when the power supply voltage used for the A / D conversion unit 4 is the same as the design value. When the supplied power supply voltage is different from the design value, the A / D conversion value of the analog voltage Vin (m) is a value ADinE2 (m) different from ADin (m). However, this error is not an error depending on the presence of the switching unit capacitance Cmpx. Even if the sampling time is increased, the A / D conversion value is not ADin (m) but another ADinE2 (m). End up.

  A first embodiment of an A / D conversion device according to the present invention, which makes it possible to accurately output a digital value of the A / D conversion value ADin (m) even when there is an error as described above, will be described below. .

  In the first embodiment, the calculation unit 5 of the A / D conversion apparatus 1 shown in FIG. 1 includes a correction calculation unit 41 as shown in FIG. The correction calculation unit 41 calculates a digital value ADin_comp (m) corresponding to the analog voltage Vin (m) output from the sensor 100 (m).

  In the present embodiment, the charge accumulated in the switching unit capacitor Cmpx at the time T (m−1), the distribution characteristic of the charge accumulated in the input circuit unit capacitor Cin (m), and the time T (m−1). ) To the time delay T (m), the response delay characteristic expression by the circuit time constant is solved, and the A / D converted digital value ADin (m before the input signal (analog signal) is switched by the multiplexer unit 3. -1), the digital value ADin (m) after A / D conversion after switching the input signal (analog signal) by the multiplexer unit 3, and the sampling interval Tint (m), corresponding to the analog voltage Vin (m). Obtain an arithmetic expression for calculating the voltage.

  Here, the analog voltage Vin (m−1) is the first analog signal, the analog voltage Vin (m) is the second analog signal, the digital value ADin (m−1) is the first digital value, and the digital value ADin ( m) is the second digital value, and the sampling interval Tint (m) corresponds to the time from when the analog signal selected by the multiplexer unit 3 is switched to when the A / D conversion unit 4 performs A / D conversion. .

  The correction calculation unit 41 follows the calculation formula obtained in advance, the digital value ADin (m−1) A / D converted before switching the input signal by the multiplexer unit 3, and A after switching the input signal by the multiplexer unit 3. A voltage corresponding to the analog voltage Vin (m) of the sensor 100 (m) after switching is calculated from the digital value ADin (m) converted by / D and the sampling interval Tint (m), and this is A / D converted. Then, the A / D conversion value ADin_comp (m) is output. The voltage calculation corresponding to the analog voltage Vin (m) may be performed using a conversion table in which the result of the calculation formula is stored in advance.

  As a result, in the A / D conversion device 1 in which capacitors (input circuit unit capacitors Cin (1) to Cin (n)) are installed on the sensor side of the multiplexer unit 3, the multiplexer unit 3 switches the signal. Even if the interval until the A / D conversion is performed is short, the influence of the electric charge accumulated in the switching unit capacitance Cmpx by the input voltage (sensor voltage) Vin (m−1) before switching the signal in the multiplexer unit 3. It is possible to obtain a digital value ADin (m) having no error in the input voltage Vin (m) after being switched by the multiplexer unit 3.

  However, the arithmetic expression in the first embodiment becomes more complex as the number of elements of the circuit configured between the sensor and the A / D converter 4 increases.

  Therefore, in a system in which the calculation load cannot be increased, the calculation cannot be performed using an arithmetic expression. Further, when there is a variation in circuit element characteristics during mass production as described above, it is between the input voltage (sensor voltage) Vin (m) calculated by the arithmetic expression and the A / D conversion value ADin_comp (m). There is a concern that the error will increase.

  Therefore, Embodiments 2 and 3 for obtaining the A / D conversion value ADin_comp (m) of the input voltage Vin (m) in consideration of the above-described variation in circuit element characteristics during mass production will be described below.

  In the second embodiment, as shown in FIG. 7, a correction amount learning unit 51, a correction calculation unit 52, and power are supplied to the calculation unit 5 of the A / D conversion device 1 shown in FIG. An EEPROM 53, which is a non-volatile memory that retains the stored value even if not present, calculates an A / D conversion value ADin_comp (m) corresponding to the input voltage Vin (m).

  In the second embodiment, before measuring the sensor value, specific voltages Ain (m−1) and Ain (m) are input to the input circuit unit 2 from the outside, and the correction amount learning unit shown in FIG. 51 is used to learn the correction amount.

  The correction amount learning unit 51 according to the second embodiment illustrated in FIG. 8 includes a reference voltage calculation unit 61, a correction amount calculation unit 62, and an EEPROM storage processing unit 63.

  FIG. 9 is a flowchart illustrating a procedure when the correction amount learning unit 51 of the second embodiment learns the correction amount.

  When learning of the correction amount is started, the external specific voltages Ain (m−1) and Ain (m) are both set to the predetermined voltage 1 as a predetermined condition (step S101), and the reference voltage calculation unit 61 uses the A The / D conversion value ADin (m) is set as the digital value AdinR (step S102).

  Next, the external specific voltage Ain (m−1) is set to the predetermined voltage 2 and the external specific voltage Ain (m−1) is set to the predetermined voltage 1 (step S103), and the A / D conversion value ADin (m) at this time Is the digital value AdinC, and the correction amount calculator 62 subtracts the digital value AdinC from the digital value AdinR as the correction amount.

  Then, the EEPROM storage processing unit 63 writes the correction amount calculated as the correction amount corresponding to the A / D conversion values ADin (m−1) and ADin (m) at this time into the EEPROM 53.

  If the number of sets of the predetermined voltage 1 and the predetermined voltage 2 that have been subjected to the above processing is equal to or less than the predetermined value 3, the predetermined voltage 1 and the predetermined voltage 2 are changed (step S107), and steps S101 to S106 are repeated. carry out. When the number of sets reaches a predetermined value of 3 or more, the learning process is terminated.

  With the above processing, the correction amount required when the external specific voltage Ain (m−1) and the external specific voltage Ain (m) are a combination of arbitrary values is converted into the A / D conversion value ADin (m−1). Are stored in the EEPROM 53 in association with ADin (m).

  In this correction amount learning process, the external specific voltage Ain (m−1) is the third analog signal, the external specific voltage Ain (m) is the fourth analog signal, and ADin (m−1) is the third digital value. A / D conversion value ADin (m) corresponds to the fourth digital value.

  The process shown in FIG. 9 is performed at a predetermined sampling interval Tint.

  FIG. 10 shows details of the correction calculation unit 52 that is actually performed when measuring the sensor value.

  The correction calculation unit 52 includes an EEPROM read processing unit 81, a sampling interval correction calculation unit 82, and a final correction calculation unit 83.

  When the apparatus is actually used, the EEPROM read processing unit 81 includes the A / D conversion value ADin (m−1) that is the first digital value and the A / D conversion value ADin (m) that is the second digital value. The correction amount stored in the EEPROM 53 is read according to the value.

  The sampling interval correction calculation unit 82 determines whether the time from when the analog signal selected by the multiplexer unit 3 is switched to when the A / D conversion unit 4 performs A / D conversion is different from the sampling interval Tint of the correction amount learning process. The correction amount read by the read processing unit 81 is further corrected using the sampling interval Tint (m), and the correction result is passed to the final correction calculation unit 83.

  The final correction calculator 83 corrects the A / D conversion value ADin (m) using the correction result to calculate the A / D conversion value ADin_comp (m).

  As a result, even if the interval from when the signal is switched in the multiplexer unit 3 to the time when the A / D conversion is performed is short, the circuit element characteristic variation, the A / D conversion unit 4 power supply voltage variation, the sampling interval Even if there is variation, the digital value of the input voltage can be obtained with high accuracy.

  In other words, according to the second embodiment, correction necessary for calculating the digital value of the input voltage even if there are variations in the characteristics of circuit elements, variations in the power supply voltage of the A / D converter 4 and variations in the sampling interval. The amount can be stored, and the digital value of the input voltage can be obtained with high accuracy by performing correction using the stored correction amount.

  In the third embodiment, as in the second embodiment, before the sensor value is measured, specific voltages Ain (m−1) and Ain (m) are input from the outside to the input circuit unit 2 and shown in FIG. The correction amount learning unit 51 is used to learn the correction amount.

  A correction amount learning unit 51 according to the third embodiment illustrated in FIG. 11 is an Ain reference voltage reading unit 91, a correction amount calculation unit 92, and a nonvolatile memory that holds a stored value without supplying power. EEPROM 53.

  FIG. 12 is a flowchart illustrating a procedure when the correction amount learning unit 51 of the third embodiment learns the correction amount.

  When learning of the correction amount is started, the external specific voltage Ain (m−1) is set to the predetermined voltage 2 and the external specific voltage Ain (m) is set to the predetermined voltage 1 (step S201).

  Next, the value of a predetermined voltage set to the external specific voltage Ain (m) according to the time from the start of the process is stored in advance by the Ain (m) reference voltage reading unit 91, and is The voltage set to the external specific voltage Ain (m) is read out as a reference voltage (step S202).

  Next, the correction amount calculation unit 92 sets a difference between the reference voltage and the A / D conversion value ADin (m) as a correction amount (step S203).

  Next, as EEPROM saving processing, the correction amount calculated as the correction amount corresponding to the A / D conversion values ADin (m−1) and ADin (m) at this time is written in the EEPROM 53 (step S204).

  If the number of sets of the predetermined voltage 1 and the predetermined voltage 2 that have been subjected to the above processing is equal to or less than the predetermined value 3, the predetermined voltage 1 and the predetermined voltage 2 are changed (step S206), and steps S201 to S205 are repeated. carry out. When the number of sets reaches a predetermined value of 3 or more, the learning process is terminated.

  With the above processing, the correction amount required when the external specific voltage Ain (m−1) and the external specific voltage Ain (m) are a combination of arbitrary values is converted into the A / D conversion value ADin (m−1). Are stored in the EEPROM 53 in association with ADin (m).

  In this embodiment, the external specific voltage Ain (m−1) is the third analog signal, the external specific voltage Ain (m) is the fourth analog signal, ADin (m−1) is the third digital value, The A / D conversion value ADin (m) corresponds to the fourth digital value.

  The process shown in FIG. 11 is also performed at a predetermined sampling interval Tint.

  In the third embodiment, the correction calculation unit 52 that is performed when actually measuring the sensor value may be the same as that of the second embodiment.

  Even in the third embodiment, it is possible to store the correction amount necessary for calculating the digital value of the input voltage even if there are variations in characteristics of circuit elements, variations in the power supply voltage of the A / D converter 4, and variations in the sampling interval. Thus, the digital value of the input voltage can be obtained with high accuracy by performing correction using the stored correction amount.

The summary of the embodiment of the A / D converter according to the present invention is summarized as follows.
(1) The calculation formula of the measurement error caused by the delay in response of the sensor output voltage by the input circuit from the sensor to the A / D converter and the voltage change due to the charge redistribution is obtained from the relational expression of the circuit. Based on the correction.

(2) The digital value of the input voltage after switching the signal is calculated by the multiplexer unit 2 in which the measurement error caused by the response delay of the sensor output voltage and the voltage change due to the charge redistribution is eliminated.
In this case, after producing the A / D converter, under a predetermined condition, the input voltage before switching the signal by the multiplexer unit 3, the input voltage after switching the signal by the multiplexer unit 3, and the necessary correction amount Store the relationship in the storage device.
Next, when the A / D conversion device is actually used, a necessary correction amount is calculated from the input voltage value before switching the signal in the multiplexer unit and the input voltage value after switching the signal in the multiplexer unit. Read out from the storage device built in. Then, the digital value of the input voltage that eliminates the measurement error due to the input circuit capacitor is calculated by correcting the A / D conversion value of the input voltage after the signal is switched by the multiplexer unit 3 using the read correction amount. .

(3) Here, as one method for calculating the necessary correction amount, when the input voltage before switching the signal in the multiplexer and the input voltage after switching the signal in the multiplexer are the same value In addition, there is a method of combining the input voltage before switching the signal in the multiplexer unit and the case where the input voltage after switching the signal in the multiplexer unit is set to a different value.

  In this method, when the input voltage before switching the signal at the multiplexer unit 3 and the input voltage after switching the signal at the multiplexer unit 3 are set to the same predetermined value A, the input after switching the signal at the multiplexer unit 3 In the multiplexer unit 3 when the A / D conversion value ADinR of the voltage and the input voltage before switching the signal in the multiplexer unit 3 are the predetermined value B, and the input voltage after switching the signal in the multiplexer unit is the predetermined value A. A difference between the A / D conversion value ADinC of the input voltage after the signal is switched is calculated as a necessary correction amount.

(4) As another method, as the predetermined condition, the input voltage before the signal is switched by the multiplexer unit 3 and the input voltage after the signal is switched by the multiplexer unit are set to different predetermined voltage values. There is a way. In this method, a voltage input in advance is stored in a storage device, and a difference between the stored digital value and a digital value obtained by A / D converting the input voltage after switching signals by the multiplexer unit 3 is necessary. There is a method of calculating as a correction amount.
The necessary correction amount is calculated by repeatedly changing the predetermined value A and the predetermined value B so that the input voltage before switching the signal in the multiplexer unit and the input after switching the signal in the multiplexer unit 3 are used. It is possible to save the relationship between the voltage and the necessary correction amount.

(5) As one of the predetermined conditions, an interval at which sampling is performed by the A / D converter 4 is used. The sampling interval in the A / D conversion unit 4 affects the correction amount. Therefore, by calculating the necessary correction amount with a constant sampling interval, it is possible to calculate the necessary correction amount without variation due to the sampling interval. When the sampling interval when actually using the A / D converter is different from the predetermined condition, the correction amount is adjusted according to the sampling interval.

  When an input signal for A / D conversion is switched using a multiplexer unit and high-speed A / D conversion is performed, the A / D conversion device according to the present invention is very effective and is likely to be used.

The block diagram which shows the whole structure of one Embodiment of the A / D converter by this invention. The graph which shows the voltage waveform of the switching part capacity | capacitance part of the multiplexer part of an A / D converter. The graph which shows an A / D conversion error characteristic. The graph which shows the voltage waveform of the multiplexer part switching part capacity | capacitance part when a circuit element characteristic varies. The graph which shows the voltage waveform of the multiplexer part switching part capacity | capacitance part when the power supply voltage of an A / D conversion part varies. The block diagram of the calculating part of Embodiment 1 of the A / D converter by this invention. The block diagram of the calculating part of Embodiment 2 of the A / D converter by this invention. FIG. 9 is a block diagram of a correction amount learning unit of a calculation unit according to the second embodiment. 9 is a correction amount learning flowchart according to the second embodiment. FIG. 6 is a block diagram of a correction calculation unit according to the second embodiment. FIG. 10 is a block diagram of a correction amount learning unit according to the third embodiment. 12 is a correction amount learning flowchart according to the third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 A / D converter 2 Input circuit part 3 Multiplexer part 4 A / D converter part 5 Calculation part 41 Correction calculation part 51 Correction amount learning part 52 Correction calculation part 53 EEPROM
61 Reference voltage calculation unit 62 Correction amount calculation unit 63 EEPROM storage processing unit 81 EEPROM read processing unit 82 Sampling interval correction calculation unit 83 Final correction calculation unit 91 Ain (m) reference voltage read unit 92 Correction amount calculation unit

Claims (7)

A / D conversion device comprising: a multiplexer unit that sequentially switches and selects one analog signal from a plurality of analog signal inputs; and an A / D conversion unit that converts the analog signal selected by the multiplexer unit into a digital value Because
A first digital value obtained by converting the first analog signal before switching the analog signal selected by the multiplexer unit by the A / D conversion unit and a second digital value after switching the analog signal selected by the multiplexer unit. A second digital value obtained by converting the analog signal by the A / D conversion unit, a time from when the analog signal selected by the multiplexer unit is switched to when A / D conversion is performed by the A / D conversion unit, and the analog signal Response characteristics of the analog signal by the circuit of the input unit from the signal source to the A / D conversion unit, the capacitance from the signal source of the analog signal to the input unit of the multiplexer unit, and the A / D from the input unit of the multiplexer unit A / D comprising correction calculation means for correcting and calculating the second digital value based on a charge distribution characteristic depending on a capacity ratio to the D converter. Conversion apparatus. A multiplexer unit that sequentially switches and selects one analog signal from a plurality of analog signal inputs, an A / D conversion unit that converts the analog signal selected by the multiplexer unit into a digital value, and a nonvolatile memory device A / D conversion device,
Under a predetermined condition set in advance, a third digital value obtained by converting the third analog signal before switching the analog signal selected by the multiplexer unit by the A / D conversion unit, and an analog signal selected by the multiplexer unit A correction amount calculation unit that calculates a correction amount from a fourth digital value obtained by converting the fourth analog signal after switching by the A / D conversion unit;
A storage processing unit that stores a relationship between the third digital value, the fourth digital value, and the correction amount calculated by the correction amount calculation unit in the nonvolatile storage device;
A first digital value obtained by converting the first analog signal before switching the analog signal selected by the multiplexer unit by the A / D conversion unit and a second digital value after switching the analog signal selected by the multiplexer unit. A read processing unit that reads out the correction amount stored in the nonvolatile storage device from the value of the second digital value obtained by converting the analog signal by the A / D conversion unit;
An A / D conversion apparatus comprising correction calculation means for correcting and calculating the second digital value using the correction amount read by the read processing unit.   The A / D converter according to claim 2, wherein the predetermined condition is a combination when the values of the third analog signal and the fourth analog signal are the same and different.   3. The A / D converter according to claim 2, wherein the predetermined condition is a voltage value in which values of the third analog signal and the fourth analog signal are set in advance.   The A / D converter according to claim 2, wherein the predetermined condition is that the values of the third analog signal and the fourth analog signal are performed in a plurality of combinations.   3. The predetermined condition is characterized in that a sampling interval, which is a time from when an analog signal selected by the multiplexer unit is switched to when A / D conversion is performed by the A / D conversion unit, is a predetermined time. The A / D conversion device described.   When the time from when the analog signal selected by the multiplexer unit is switched to when the A / D conversion unit performs A / D conversion is different from the predetermined time when the apparatus is actually used, the correction amount is calculated using the sampling interval. The A / D converter according to claim 6, wherein the A / D converter is corrected.

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