JP3403127B2 - A / D conversion circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an A / D conversion circuit for converting an input analog signal and outputting it as a digital signal, and more particularly to a technique for reducing the processing in the MPU and increasing the speed.

[0002]

2. Description of the Related Art FIG.
It is a block diagram which shows the structure of the A / D conversion circuit which converts into the digital value which was scaled by the calculation process of (it calls MPU). In the figure, reference numeral 100 denotes an analog signal S10 which is a digital signal (hereinafter referred to as a raw digital value) S11.
A / D conversion unit for converting into an analog signal S10
A switch for notifying that a reference analog signal for error correction has been input to the switch 102, and a switch 102 for notifying whether the reference analog signal is an offset value or a gain value.
Reference numeral 3 denotes a non-volatile memory for storing and holding the raw digital value S11 when the reference analog signal is input.
Reference numeral 4 denotes an MPU for scaling the raw digital value S11 based on the offset value and gain value stored in the non-volatile memory 103 and outputting the digital value S12. There are two types of input of the reference analog signal: an offset value and a gain value.

Generally, the raw digital value converted by the A / D converter shown in FIG. 14 is the A / D due to the variation of the parts constituting the A / D converter and the change of the ambient temperature.
An error occurs due to a change in the characteristics of the components that make up the conversion unit. Therefore, in any device, correction must be performed so that when the same analog value is input, it is converted into the same digital value. As this correction method, there are a method of correcting a component error and a characteristic change due to a volume resistance, and a correction by a scaling process described below.
The merit of the scaling process is that the correction can be performed even if the resolution of the A / D converter and the resolution of the digital value S12 do not match. Accordingly, by setting the resolution of the A / D conversion unit higher than the resolution of the digital value S12, it is possible to make it difficult for an error generated in the A / D conversion unit to appear in the digital value S12 due to noise or the like.

Next, the scaling process will be described. Figure 1
Reference numeral 5 indicates the characteristic of converting an analog signal input to the A / D converter into a raw digital value, and
The raw digital value converted by the converter is 0-4000.
It is a figure which shows the process which carries out scaling to the digital value of (resolution 4000). In the figure, 105 is a switch 1
01 and the switch 102, the offset value (hereinafter referred to as Voffset) of the input reference analog signal converted by the A / D conversion unit 100 is the raw digital value (Doffset), and 106 is similarly notified. The gain value (Vgain) of the reference analog signal is the A / D conversion unit 10
Is a raw digital value (Dgain) converted by 0,
Doffset and Dgain are stored and held in the non-volatile memory 103.

Using the Doffset and Dgain, the MPU 10
4 is A when an arbitrary analog signal (Vin) is input
Raw digital value (Din) converted by the / D converter
Then, the scaling value (Ds) is calculated by the following calculation formula. Ds = (Din-Doffset) / {(Dgain-Doffset) / resolution} (Formula 1) Here, Din is a raw digital value for an arbitrary analog signal (Vin).

FIG. 16 is a schematic block diagram of a D / A converter for converting a digital signal into a digital value suitable for the resolution of an analog output by calculation of MPU. In the figure, reference numeral 110 executes a calculation process for converting an input arbitrary digital signal S13 according to the resolution of an analog output, and a digital value (hereinafter referred to as a conversion digital value) converted so as to match the resolution of the analog output. (Referred to as value) MPU for outputting S14, 111 is a D / A for converting the converted digital value S14 into an analog signal S15.
A conversion unit 112 is a switch for entering an analog output adjustment mode for changing the D / A conversion characteristic of the device, 11
3 is a switch for selecting offset adjustment or gain adjustment when the adjustment mode is entered by the switch 112, 11
Reference numeral 4 denotes a switch for increasing / decreasing and adjusting the analog output by increasing / decreasing the conversion digital value in the adjustment mode. Reference numeral 115 denotes the conversion digital value S14 when the switch 113 is set to SET during offset adjustment and gain adjustment.
Is a non-volatile memory that stores and holds.

FIG. 17 shows a digital signal 0-4000.
It is a figure which shows the process for converting (resolution 4000) into analog output 0-10V. Generally, the resolution of the D / A converter 111 is higher than that of the digital signal S13. Therefore, it is necessary to convert the digital signal S13 into a value that matches the resolution of the D / A converter. In the figure, 116 is a converted digital value (Dooff) when the value of the digital signal is 0, and the switch 11
2 enters the adjustment mode and switches 113 and 114
Is a value when an arbitrary analog value (offset analog value, 0 V in this example) is increased / decreased and the switch 113 is set to the SET position. Similarly, 117 is a converted digital value (Do) when the analog output outputs an arbitrary analog value (gain analog value, 10 V in this example).
gain). Dooff and Dogain are stored and held in a non-volatile memory.

The MPU obtains a converted digital value (Da) for the arbitrarily input digital value (A) by using the following formula using Dooff and Dogain. Da = A * {(Dogain-Dooff) / resolution} + Dooff (Equation 2) The D / A converter executes the conversion of the D / A conversion characteristic shown in FIG. 17, and converts the analog value (Vout) to the converted digital value (Da). ) Is output.

[0009]

In the conventional A / D conversion circuit, when an analog signal to be A / D converted is input,
Scaling processing is performed as software processing inside the MPU, and is output as a digital value. for that reason,
The time required for processing depends on the processing capacity of the MPU.
In order for U to execute (Equation 1) at high speed, the performance of MPU must be improved. That is, in order to improve the responsiveness from the input of an analog signal to the output of a digital value, a highly functional MPU is required, and this highly functional MPU becomes very expensive. there were.

It is an object of the present invention to provide a method and a circuit for increasing the speed of A / D conversion without depending on the performance of MPU. Furthermore, A / is not affected by errors due to component variations (initial errors) and changes in ambient temperature.
A method and a circuit for D conversion are provided.

[0011]

An A / D conversion circuit according to the present invention uses an A / D conversion unit for converting an input analog signal into a raw digital value and a reference analog signal for the A / D conversion.
Using the reference digital value converted by the D converter,
Control means for calculating beforehand an A / D conversion value corresponding to the digital value to be output for each digital value, and the A / D conversion value calculated by this control means is stored in a format in which the address corresponds to the digital value. Data table and A
And a comparison circuit for comparing the raw digital signal converted from the analog signal by the / D conversion unit with the A / D conversion value in the data table and outputting the address having the matched contents as a digital value. .

Further, the calculation by the control means uses a reference digital value composed of Dgain and Doffset converted from the analog signal when the test command is input as a reference analog signal, and stores it in the address AD of the data table A / D converted value Din is Din = {(Dgain-Doffset) / resolution} × AD + Dof
It is obtained by fset.

Furthermore, the A / D conversion value output when the reference voltage is input to the A / D conversion unit is compared with the theoretical A / D conversion value that will be output corresponding to the reference voltage in advance. Then
The circuit error of the A / D converter is detected and the error is automatically corrected.

[0014]

[0015]

[0016]

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1. FIG. 1 is a block diagram showing an A / D conversion circuit according to the present invention. The difference between FIG. 14 and FIG. 1 described in the item of the prior art is that the MPU 4 is converted by the A / D conversion unit 1 at that time by inputting a test command S1 associated with a switch operation from the user to the MPU 4, for example. The data table is calculated based on the raw digital value S3, and the data table is stored in the memory 3. In addition, during normal A / D conversion (other than when a test command is issued), the raw digital value S3 is compared with the data table stored in the memory 3 by the comparison circuit 2, and the digital value S4 is output.

In the figure, 1 is an A / D converter for converting an analog signal S2 into a raw digital value S3, and 2 is a raw digital value S3 converted by the A / D converter 1 and a memory 3.
A comparison circuit for comparing the contents of the data table stored in and outputting the coincident address as a digital value S4,
Reference numeral 3 denotes a memory in which a data table is stored, which is composed of a non-volatile memory. Reference numeral 4 is an MPU corresponding to a control means for creating a data table based on the raw digital value S3 when the test command S1 is input.

Next, the data table stored in the memory 3 will be described with reference to the schematic view of the data table in FIG. As a method of storing the A / D converted value (raw digital value S3) in the data table, a raw digital value corresponding to the digital value n is stored for the address n of the nonvolatile memory 3. That is, when the raw digital value and the A / D converted value of the data table are compared, the storage format is determined so that the matching address can be output as it is as the digital value S4.

In the data table, the test command S1 is MP
When input to U4, the raw digital value S3 corresponding to the analog signal S2 input to the A / D converter 1 at that time is used as a reference A / D conversion value, and MP is calculated based on this reference A / D conversion value.
Created by U4. Here, the reference A / D conversion value is
Similar to Doffset and Dgain shown in FIG. 15, the test command S
When 1 is input to the MPU 4, the input analog signal S2 is the offset value (Voffs) of the reference analog signal.
et) or a gain value (Vgain), and the offset value (Voffset) and the gain value (Vgain) are converted by the A / D converter 100 to obtain a raw digital value (Doffset) and a raw digital value. (Dga
in). In addition, the non-volatile memory is used as the memory for storing the data table based on the test A based on the test command S1 every time the power of the circuit and the device is turned on / off.
This is because the / D conversion value is input and the MPU 4 does not create a data table. However, power ON / O
The volatile memory may be used as the data table storage memory if the reference A / D conversion value is input and executed based on the test command S1 every time the FF is performed and the data table is created by the MPU 4. In addition, a nonvolatile memory for storing the reference A / D conversion value is provided separately from the memory for storing the data table, and when the power is turned on / off, the MPU 4 uses the reference A / D conversion value stored in the nonvolatile memory. By creating the data table, it is possible to avoid the input execution of the reference A / D conversion value based on the test command S1 every time the power is turned on / off, and therefore the data table storage memory can be a volatile memory. When a non-volatile memory is used as the data table storage memory, the MPU 4 does not need to create a data table based on the reference A / D conversion value every time the power is turned on / off. The non-volatile memory for storing the converted value can be omitted.

In the formula for calculating the data table, assuming that AD is the address of the data table, the data (Din) stored in the AD address is: Din = {(Dgain-Doffset) / resolution} * AD + Doffset (Formula 3) Will start from address 0.). When the test command S1 is input, the MPU 4 executes calculations for the number of resolutions and stores the data table in the memory 3
To store. The resolution referred to here corresponds to the number of bits of a digital value included in the A / D conversion circuit, and is (Dgain-D
offset) is the number of divisions between. In addition, power supply ON
It goes without saying that the calculation for the number of resolutions may be performed when / OFF.

Next, the comparison circuit 2 will be described. The comparator circuit 2 compares the raw digital value S3 with the contents of the data table, and determines the matched memory address as the digital value S.
Output as 4. By using a two-branch comparison method as a comparison method, a digital value can be output by performing z + 1 (times) times for finding a matching address having a digital resolution of z bits. When the comparison circuit is configured by hardware, generally, the time required for one comparison is about 100 nS. Therefore, the time required to find a coincident address with a 12-bit digital resolution is 13 (times) × about 100 (nS / times) = about 1.3 (μS), and the scaling processing is performed at high speed without depending on the performance of the MPU.

According to the present embodiment, in the test mode when the test signal S1 is input, the MPU 4 previously stores the raw digital value S3 (Dgain, Doffset) in the data table.
Since the A / D converted value is calculated and stored based on, the raw digital value S3 output from the A / D conversion unit 1 and the A / D stored in the data table are stored in the normal mode other than the test mode. Since only the D conversion values are compared and the coincident address is output as the digital value S4, the scaling process can be performed at high speed without imposing a load on the MPU 4. Here, by comparing the A / D converted value stored in the data table with the raw digital value,
By outputting the address of the matched data table as a digital value, the processing can be performed by hardware, and as in the conventional case, the processing can be performed at higher speed regardless of the performance of the MPU, and the analog signal can be input. The responsiveness from the output of the digital value to the output of the digital value is improved, and the A / D conversion can be performed at high speed without using a high-performance MPU.

Embodiment 2. In the present embodiment, in addition to the first embodiment, an initial error correction function that corrects variations (initial errors) of components in the device and the circuit, and temperature drift correction that corrects errors of the device and the circuit due to changes in ambient temperature. It is a combination of functions and. FIG. 3 is a block diagram showing the configuration of the second embodiment of the present invention. In order to correct the error, the reference voltages 1 and 2 which are sufficiently more accurate than the specifications of the device and the circuit are provided.

First, the initial error correction function will be described. The reference voltages 1 and 2 are predetermined voltages, and are provided with a voltage lower than or near the lower limit of the analog input signal range (referred to as reference voltage 1) and a voltage closer to the upper limit or upper limit (referred to as reference voltage 2). . The voltages of the reference voltages 1 and 2 are predetermined, and the theoretical values of the A / D conversion values corresponding to the reference voltages 1 and 2 are incorporated in the firmware in which the operation of the A / D conversion circuit is programmed. .

The MPU4 switches SW1 when the power is turned on,
The A / D converted values of the reference voltages 1 and 2 are taken in, the difference (error) between the value pre-installed in the firmware and the A / D converted value of the reference voltages 1 and 2 when the power is turned on is calculated, and output from the comparison circuit 2. The corrected digital signal S4 is corrected by this error and a corrected digital signal is output.
In the comparison circuit 2, during normal operation in which no test command is input, the A / D conversion value that the MPU 4 has previously calculated and stored in the data table and the raw digital value S3 output from the A / D conversion unit 1 Is the same as in the above-described first embodiment in that the matched address is output as the digital value S4. The factor of the initial error is
This is the variation in the components of the A / D conversion unit. In this example, the analog input signal and the reference voltages 1 and 2 are the same A / D converter 1
Therefore, it is possible to correct the initial error when the analog signal is input by the above correction.

A method of correcting the initial error will be described with reference to the diagram showing the error of the A / D conversion characteristic shown in FIG. The A / D conversion characteristics change as shown in FIG. 4 due to variations in the components of the A / D conversion unit. At this time, the A / D conversion value of the reference voltage 1 changes to D1 → D1 ′ and the A / D conversion value of the reference voltage 2 changes to D2 → D2 ′.

The correction is realized by recreating the data table by the following calculation. If X = (D1 ′) − (D1) Y = (D2′−D1 ′) / (D2-D1), the data (Din) stored in the AD address of the data table is obtained by modifying (Equation 3) below. It is obtained by the formula. Din = [{(Dgain−Doffset) / resolution} / Y] × AD +
(Doffset-X)

Since the initial error is a variation in the characteristics of the parts, the correction process of the initial error is performed once when the power is turned on, a data table is created in consideration of the initial error, and the above-mentioned processing is performed based on the data table. The operation of the first embodiment is performed.

Next, the temperature drift correction function will be described. The A / D converter 1 is easily affected by changes in ambient temperature. Therefore, in the present embodiment, the lower limit of the analog input signal range or a voltage close to the lower limit (reference voltage 1) and the upper limit or a voltage close to the upper limit (reference voltage 2).
The MPU 4 switches SW1 to the reference voltages 1 and 2 to obtain the amount of change from the A / D conversion values corresponding to the reference voltages 1 and 2 incorporated in the firmware of the A / D conversion circuit.

The data table is created by the initial error correction function, and by correcting the amount of change described above, it is possible to correct an error (temperature drift error) due to a change in ambient temperature.

A method of correcting the temperature drift error will be described with reference to the diagram showing the error of the A / D conversion characteristic shown in FIG.
The A / D conversion characteristic changes as shown in FIG. 5 due to the change in ambient temperature. At this time, the A / D conversion value of the reference voltage 1 changes to D1 → D1 ′ and the A / D conversion value of the reference voltage 2 changes to D2 → D2 ′.

The correction is (change of A / D conversion value of reference voltage 1) = (D1 ')-
(D1) is calculated, A'is returned to A, then (change in inclination) = (D2'-D1 ') / (D2-D1) is calculated, and B'is returned to B. This is shown in FIG. 6 as a diagram.

Specifically, the MPU 4 executes the following processes (1) to (3). C = (A / D conversion value)-{(D1 ')-(D1)} is calculated. "Data table address A that matches" C "
Search for D "D = AD / {(D2'-D1 ') / (D2-D1)}
The output MPU 4 corrects an error due to a change in ambient temperature by using D as a correction digital value.

According to the present embodiment, when the power is turned on, the initial error correction for the characteristic variation of the parts is performed, the data table is corrected, and the digital value output from the data table is set to the ambient temperature. Since the MPU calculates to correct the error due to the change, in addition to the effect of the first embodiment described above, accurate A / D conversion can be performed.

Embodiment 3. FIG. 7 is a block diagram of the D / A conversion device according to the present embodiment. In the figure,
6 is an MPU that outputs a digital offset value and a digital gain value as a test digital value S7 to the D / A converter 7, for example, by inputting a test command S6 by a switch input by the user. In the input test mode, an analog signal is generated based on the test digital value S7, and the test command S
In the normal mode where 6 is not input, a D / A converter that generates an analog signal based on a digital conversion value, and 8 is a non-volatile memory in which a data table is stored.

Here, it is usually necessary to perform offset / gain adjustment for the D / A conversion characteristic, and this adjustment is executed as follows by inputting the test command S6. When the test command S6 is input, the D / A converter 7 receives an MP
The test digital value S7 output from U6 is input, and this test digital value S7 is increased / decreased by the UP / DOWN command input to the MPU 6 by the adjustment of the switch and the like by the user similarly to the test command S6, whereby D / The analog signal output from the A converter also increases or decreases.

Here, when the test command S6 is input to perform the offset adjustment for outputting the reference voltage V1 when the offset digital value is shown in FIG. 8 and the gain adjustment for outputting the reference voltage V2 when the gain digital value is shown. To
Based on the input of a predetermined fixed offset digital value, the D / A converter 7 outputs the reference voltage V1. Based on the UP / DOWN command input to the MPU 6, the reference digital value S7 is used as the test digital value S7. Increase or decrease the conversion value D1. Further, when the test command S6 is input, the D / A converter 7 outputs the reference voltage V2 based on the input of a predetermined fixed gain digital value, so that the UP / DOWN input to the MPU 6 is input.
Based on the command, the reference digital conversion value D2 is increased or decreased as the test digital value S7. Then, the reference digital conversion values D1 and D2 are stored in the non-volatile memory 8 when the test command S6 is completed. This turns the power on / O
It is not necessary to perform the offset / gain adjustment every time the FF is performed, and the data table can be created based on the reference digital conversion values D1 and D2 stored in the nonvolatile memory when the power is turned on.

By thus determining D1 and D2, the digital conversion value D corresponding to the digital value A is obtained.
a can be derived by Da = [(D2-D1) / {(gain digital value)-(offset digital value)}] * {(A-offset digital value)} + D1 (Equation 4). The MPU 6 executes calculation for the number of resolutions and stores the digital conversion value Da corresponding to the derived digital value A in the non-volatile memory 8 as a data table. Here, the configuration of the data table stored in the nonvolatile memory 8 is the “address” of the memory.
= “Digital value”, “data” = “digital conversion value corresponding to digital value”. For example, when the digital conversion value when the digital value is 100 is 2400 according to (Equation 4), 240 is stored in the 100th address of the memory.
0 will be stored.

16 and 7 described in the section of the prior art.
The difference is that M is based on the reference digital conversion values D1 and D2.
The PU 6 obtains the digital converted value Da corresponding to the digital value A by (Equation 4), creates the data table shown in FIG. 9 in the memory, and when the digital value to be D / A converted is input, The data table is accessed using the digital value as the memory address, and the digital conversion value stored at the address corresponding to the digital value is D
The point is that the MPU 6 does not need to calculate the digital conversion value for each D / A conversion by sending it to the / A conversion unit.

Normal D / A conversion other than when a test command is issued is M
Based on the digital value A input to PU6, MPU
6 accesses the data table of the non-volatile memory 8,
As shown in FIGS. 10 and 11, the address A corresponding to the digital value A is read, and the data stored at the address, that is, the digital conversion value Da is D / A.
Output to the conversion unit 7. Then, the D / A conversion unit 7 takes in the output data of the memory at this time and performs D / A conversion, thereby outputting an analog signal. That is, by performing the same operation as the read of the memory, the digital conversion value Da stored in the address A of the data table is stored.
Can be output and the calculation for obtaining the digital conversion value Da of the MPU 6 can be omitted.

According to the present embodiment, when the analog output corresponding to the digital value A is output, the MPU
It is not necessary to perform the calculation of (Equation 4) for each conversion, and the digital conversion value can be obtained only by performing the same operation as the reading of the memory. That is, the processing can be performed at high speed without imposing a load on the MPU. In general, the memory access time is several tens of nanoseconds, and D / A conversion can be performed in this time, which does not depend on the performance of the MPU.

Fourth Embodiment In the present fourth embodiment, an A / D conversion circuit with an error correction function for correcting the variation of the parts described in the second embodiment and the error influence of the ambient temperature change is provided, and the A / D conversion circuit with the error correction function is provided. On the basis of the error-corrected corrected digital signal of (1), the initial error due to the variation of parts in the D / A conversion circuit and the error due to the influence of the fluctuation of the ambient temperature are corrected.

FIG. 12 is a block diagram showing the configuration of the present invention. In the figure, 8 is an A / D conversion circuit with an error correction function, 9 is a D / A conversion circuit for converting an input digital signal into an analog signal, and 10 is a correction calculation of an error of a D / A conversion unit. It is MPU.

Generally, in the D / A conversion circuit 9, an initial error due to variations in parts and an error due to the influence of fluctuations in ambient temperature occur. Therefore, the D / A described in the third embodiment
The analog signal output from the conversion circuit 9 is switched to the switch S.
By switching W2, it is input to the A / D conversion circuit 8 with the error correction function described in the second embodiment, and the error-corrected corrected digital signal is taken out. As described in the second embodiment, the A / D conversion circuit also has an initial error due to component variations and an error due to a change in ambient temperature, but it is corrected, and the error is corrected. The corrected digital signal is output.

The corrected digital signal output from the A / D conversion circuit 8 with the error correction function and the digital value before being converted by the D / A conversion circuit 9 (the D / A conversion circuit performs the D / A conversion).
By comparing it with the digital value input to be converted, the variation becomes an error of the D / A conversion circuit 9.

When the digital value S is input to the D / A conversion circuit 9, the digital value S changes to the digital value S1 due to an error inside the D / A conversion circuit, and D / A conversion is performed. Here, if the digital value S1 is D /
Assuming that the A-converted analog value is T1, the error is corrected when the analog value T1 is A / D converted by the A / D conversion circuit 8 with an error correction function.
A digital value S1 corresponding to is output from the A / D conversion circuit 8 with an error correction function. That is, the D / A conversion circuit 9
The error generated in the D / A conversion circuit 9 can be detected by comparing the original digital value S input to the A and the digital value S1 converted by the A / D conversion circuit 8 with an error correction function. it can.

Based on this, the digital value input to the D / A conversion circuit 9 is corrected to obtain the D / A
The error of the conversion circuit unit 9 can be removed, and the D / A conversion circuit 9 having no error can be realized as a whole.

Next, the correction method will be described by taking as an example the case where an error of the D / A conversion circuit 9 causes an error of the A / D conversion characteristic as shown in FIG. D / A conversion circuit 9
13 shows the A / D conversion characteristics converted by the A / D conversion circuit with no error due to the variation of the parts and the change of the ambient temperature.
It changes like.

The MPU 10 performs error correction as follows. Switch SW2 to the A / D conversion circuit side 8 with error correction function, and set D1 and D2 as the test digital values to MPU10.
Output to the D / A conversion circuit 9. A / D conversion circuit 8 and D
By keeping the resolutions of the A / A conversion circuits 9 the same,
Since the error is corrected in the A / D conversion circuit 8, D /
When the A conversion circuit 9 has no error, the A / D conversion values are D1 and D2. If there is an error in the D / A conversion circuit 9,
As shown in FIG. 13, the A / D conversion value changes from D1 → D1 ′ D2 → D2 ′. Based on this change, the MPU 10 recalculates the digital value into a corrected digital value by the following calculation formula, and outputs it to the D / A conversion circuit 9. (Corrected digital value) = {(digital value)-(D1-
D1 ')} / {(D2'-D1') / (D2-D1)} +
D1 By converting this corrected digital value into an analog value by the D / A conversion circuit 9 as in the third embodiment, an analog output without error can be obtained. The timing of switching the switch SW2 may be properly corrected in accordance with a temperature change, as well as performing switching correction when the power is turned on in order to detect an initial error due to variations in parts.

[0051]

According to the present invention, since it is not necessary for the MPU to execute the scaling processing for A / D conversion, the MP
It is possible to speed up the scaling process of A / D conversion without depending on the performance of U.

Further, since the error correction of the A / D conversion is automatically performed, the error correction for each device and the error correction in the actual use environment (temperature) are unnecessary.

[0053]

[0054]

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of an A / D conversion unit of an A / D conversion device of the present invention.

FIG. 2 is a diagram showing the contents of a data table of an A / D conversion device.

FIG. 3 is a configuration diagram showing a configuration of an A / D conversion unit of an automatic error correction A / D conversion device.

FIG. 4 is a graph showing an initial error of A / D conversion characteristics.

FIG. 5 is a graph showing an error in A / D conversion characteristics.

FIG. 6 is a graph showing error correction of A / D conversion characteristics.

FIG. 7 is a configuration diagram showing a configuration of a D / A conversion unit of the D / A conversion device of the present invention.

FIG. 8 is a graph showing a digital value conversion method of the D / A conversion device.

FIG. 9 is a diagram showing the contents of a data table of the D / A conversion device.

FIG. 10 is a diagram showing a digital value conversion method of a D / A conversion device.

FIG. 11 is a digital value conversion timing chart of the D / A conversion device.

FIG. 12 is a diagram showing an automatic error correction D / A conversion device.

FIG. 13 is a graph showing error correction of D / A conversion characteristics.

FIG. 14 is a configuration diagram showing a configuration of an A / D conversion unit of a conventional A / D conversion device.

FIG. 15 is a graph showing scaling of A / D conversion.

FIG. 16 is a configuration diagram showing a configuration of a D / A conversion unit of a conventional D / A conversion device.

FIG. 17 is a graph showing digital value correction of D / A conversion.

[Explanation of symbols]

1 A / D converter, 2 comparison circuit, 3 data table, 4 MPU, 5 non-volatile memory, 6 MPU, 7
D / A converter, 8 data table, 9 non-volatile memory.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-8-330958 (JP, A) JP-A-3-19428 (JP, A) JP-A-6-204868 (JP, A) JP-A-5- 152953 (JP, A) JP-A-11-98014 (JP, A) JP-A-5-327499 (JP, A) Actual Kaihei 1-149133 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03M 1/00-1/88

Claims (3)

(57) [Claims] 1. A digital value to be output using an A / D conversion section for converting an input analog signal into a raw digital value and a reference digital value converted by the A / D conversion section for a reference analog signal. And a data table in which the A / D conversion value calculated by this control means is stored in a format corresponding to the digital value. And a comparator circuit for comparing the raw digital signal converted from the analog signal by the A / D converter and the A / D converted value in the data table and outputting the address having the matched contents as a digital value. A characteristic A / D conversion circuit. 2. The calculation by the control means uses a reference digital value composed of Dgain and Doffset converted from an analog signal when a test command is input as a reference analog signal, and stores it in an address AD of a data table.
The A / D conversion circuit according to claim 1, wherein the D conversion value Din is obtained by Din = {(Dgain-Doffset) / resolution} * AD + Doffset. 3. The A / D conversion value output when the reference voltage is input to the A / D conversion unit is compared with the theoretical A / D conversion value that will be output corresponding to the reference voltage in advance. And above A
3. The A according to claim 1, wherein a circuit error of the D / D converter is detected and the error is automatically corrected.
/ D conversion circuit.