JPS63222516A - A/d conversion value correction method for a/d conversion circuit - Google Patents

Abstract

PURPOSE:To eliminate the need for a correction circuit for each analog sensor and then to eliminate the need for its adjustment by multiplying a ratio of a theoretical A/D conversion value and a reference A/D conversion value to an A/D conversion value. CONSTITUTION:Let the rated power voltage of an A/D IC 12 be 5V, the relation of Vs/5V=C/F exists with the power voltage Vcc selected at 5V, where Vs is a reference voltage of a constant voltage circuit 10, C is a theoretical A/D conversion, that is, an A/D conversion of Vs with Vcc=5V, and F is a full scale value of the A/D IC 12. Moreover, the A/D conversion value of the reference voltage Vs, that is, the reference A/D conversion value S depends on the fluctuation of the power voltage Vcc and the relation of Vs/Vcc=S/F exist. Thus, the relation of Vcc/5V=C/S exists. Then the error of the A/D conversion due to fluctuation of the power voltage Vcc is corrected by multiplying the C/S with the A/D conversion value.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an A/D that converts an analog signal into a digital signal.
The present invention relates to a method of correcting an A/D conversion value of a conversion circuit.

[Conventional technology]

In recent years, it has become common practice to equip automobiles with electronic fuel injection (EFI) systems or electronic carburetor control (ECC) systems. In these systems, the ECU (electronic control circuit) calculates the control amount based on the values of various operating state parameters detected through various sensors and switches, and the ECU (electronic control circuit) calculates the control amount based on the calculation results.
The CU optimally controls various actuators.

By the way, there are two types of sensors: analog sensors that output detection signals in the form of analog signals, and digital sensors that output detection signals in the form of digital signals.
The CU converts the analog signal output from the analog sensor into a digital signal using an analog-to-digital conversion IC (hereinafter referred to as A/DIC), and performs digital calculations.

At this time, the A/D IC converts the analog signal into a digital signal based on the reference voltage V sit. is the power supply voltage VA of the A/D conversion circuit including the A/D IC! It is proportional to +. The power supply voltage VCC for the microcomputer of the ECU is normally supplied to this power supply voltage v1, and this power supply voltage VCC is applied to each ECU.
Although the voltage value itself at the CU does not change,
Depending on ECLJ, ±10% to ±5 against the average value of 5V
There is a variation of %. Therefore, even if the analog signal value is the same, the A/
The D conversion value, that is, the digital signal value after A/D conversion becomes different. Therefore, A/D conversion requires correction using the power supply voltage VCC.

Therefore, conventionally, the rated power supply voltage V A of the A/D conversion circuit
If DO is 5v, as shown in Figures 6 and 7,
An adjustment was made to weight Vcc15 to the analog signal value. That is, the adjustment method shown in FIG. 6 is a voltage division method applied to, for example, a battery voltage of 1 B, and +8 is
Since it is unrelated (not proportional) to the variation in CC, the battery voltage +B is divided by the fixed resistor 61 and the variable resistor 62 and weighted by Vcc/5, and then supplied to the ^/D IC 63. It is something to do. Also, the seventh
The adjustment method shown in the figure is, for example, the output voltage V of the 02 sensor 71.
. This is an amplification method applied to the operational amplifier 72.
The fixed resistor 73 and the variable resistor 74 generate a voltage that is independent (not proportional) to variations in VCC. After amplifying t by a predetermined amplification factor A and weighting it by vcc15, ^
/DIC75.

[Problem that the invention seeks to solve]

However, the conventional method described above requires a correction circuit for each analog sensor that generates an output signal that does not compensate for variations in VCC, and therefore has the problem that adjustment is time-consuming.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for correcting A/D conversion values of an A/D conversion circuit that eliminates the need for a correction circuit for each analog sensor and therefore also eliminates the need for adjustment thereof. shall be.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for correcting an A/D conversion value of an A/D conversion circuit that converts an analog signal into a digital signal, comprising: First, a reference analog signal having a first predetermined voltage value is applied to the second A/D conversion circuit.
Determine a theoretical A/D conversion value and a reference A/D conversion value, which are A/D conversion values by the A/D conversion circuit when a power supply voltage having a predetermined voltage value and an arbitrary voltage value is applied, respectively, and Next, the A/D of the analog signal when the power supply voltage having the arbitrary voltage value is applied to the A/D conversion circuit.
An A/D conversion value correction method for an A/D conversion circuit is provided, in which an AID conversion value by a D conversion circuit is multiplied by a ratio between the theoretical A/D conversion value and the reference A/D conversion value.

〔Example〕

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

FIG. 1 is a block diagram of an A/D converter to which the method of the present invention is applied. In the figure, reference numeral 10 indicates a constant voltage circuit, and this constant voltage circuit No. 10 supplies a reference analog signal having a reference voltage value V to a multiplexer (MPX) 11.

The multiplexer (MPX) 11 has n-channel selection input terminals, and each of the first to (n-1)th selection input terminals has a (n-1
) voltage value VAI output by each of the analog sensors
Analog sensor signals each having ˜VA(n-1) are input. Further, the reference analog signal is input to the n-th selection input terminal.

12 indicates A/DIC, and this ^/D IC12 has:
The power supply voltage VCC of the microcomputer 13 is applied as the A/D circuit power supply voltage VAII.

The microcomputer 13 is an I10 boat 131, C
It is composed of a PU 132, a ROM 133, a RAM 134, and a bus 135 connecting these. A predetermined area of the ROM 133 stores a program for an A/D conversion value correction routine, which will be described later. In addition, in other predetermined areas of the ROM 133, the rated power supply voltage ■
Theoretical A/D conversion value C, which is the A/D conversion value of the reference voltage value V, by the A/D IC 12 when 1° is applied.
is stored.

Next, the A/D conversion value correction routine executed by the microcomputer 13 will be explained using the flowchart shown in FIG.

First, in step 201, a channel select signal a is sent to the multiplexer 11, and the multiplexer 11
Specify the selection input terminal of. When receiving the channel select signal a, the multiplexer 11 supplies the A/D IC 12 with an analog signal to be input to the selection input terminal designated by the channel select signal a.

Next, in step 202, the A/D IC 12 is
/D conversion start signal S is sent to instruct the start of A/D conversion of the analog signal supplied from the multiplexer 11. Then, in step 203, the A/D IC 12
By receiving the A/D conversion end signal C from A
/D After confirming the completion of A/D conversion in the IC 12, in step 204, the A/D conversion output from the A/DIC 12 is confirmed.
A D conversion conversion value signal is optically transmitted.

Next, in step 205, it is determined whether the selection input terminal of the multiplexer 11 selected in step 201 is the nth selection input terminal.

When the determination result is affirmative (YES), that is, when the n-th selection input terminal is selected, the received A/D conversion value is the reference A/D conversion value of the reference voltage value vs. It is determined that it is a D-converted value, and the process proceeds to step 206, stores the reference A/D-converted value S in the RAM 134, and returns.

On the other hand, if the result of the determination in step 205 (7) is negative (NO), it is determined that the received A/D conversion value is the A/D conversion value of the voltage value V outputted by the analog sensor. , proceed to step 207.

In step 207, the A/D conversion value (C/S)
Performs an operation to multiply . Note that C and S are the theoretical A/S stored in the ROM 133, respectively, as described above.
D conversion value and reference A/
It is a D conversion value.

Here, the meaning of the above calculation will be explained. Now, A/DIC1
If the rated power supply voltage VA11° of 2 is 5V, the power supply voltage ■. , is 5■, the following formula (1) holds true.

V s / 5 V = C / F −−−−・−−
---・-----(1) Here, v3 is the reference voltage value output by the constant voltage circuit 10, and C is the theoretical A/D conversion value, that is, the A/D conversion value of ■3 at vCc-5v. , F is ^
/D is the full scale value of IC12. In addition, the A/D conversion value of the reference voltage value v3, that is, the reference A/D conversion value S changes due to variations in the power supply voltage VCC, and is expressed by the following formula (2)%
Equation % Therefore, by performing the calculation of multiplying the A/D converted value by (C/S), the error in the A/D converted value due to the variation in the power supply voltage VCC is corrected.

Next, the process proceeds to step 208, and the calculated value obtained in step 207 is stored in the RAM 134.

As described above, each of the voltage values VA, ~vA(n-1) input to the multiplexer 11 is input to the A/D IC1
After being A/D converted by 2, it is corrected and output as a digital signal. Therefore, as an example, when measuring battery voltage and o2
As shown in the case of sensors, a correction circuit for each sensor is no longer necessary, and accordingly, adjustment of the correction circuit is also no longer necessary. That is, in FIG. 3, battery voltage terminal B
is divided into A by fixed resistors 31 and 32 and A/D
In FIG. 4, the output voltage of the Ot sensor 41 is directly applied to the A/D IC 42.

FIG. 5 shows a specific circuit diagram of the constant voltage circuit 10 in FIG. 1.

〔Effect of the invention〕

As explained above, the A/D conversion circuit of the present invention
According to the converted value correction method, there is no need for a correction circuit for each analog sensor, and therefore, there is no need for its adjustment. Also,
The optimum correction value can always be obtained even with respect to changes in VCC over time and changes in temperature.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an A/D converter to which the method of the present invention is applied, Fig. 2 is a flowchart showing an A/D conversion value correction routine, and Fig. 3 is a diagram showing the relationship between battery voltage and A/D IC. Figure 4 is a diagram showing the relationship between the Ot sensor and A/DIG, Figure 5 is a specific circuit diagram of the constant voltage circuit lO in Figure 1, and Figure 6 is the conventional circuit diagram. A diagram explaining the pressure adjustment method and FIG. 7 are diagrams explaining the conventional amplification adjustment method. lO... Constant voltage circuit, 11... Multiplexer, 13... Microcomputer.

Claims (1)

[Claims] 1. A method for correcting an A/D conversion value of an A/D conversion circuit that converts an analog signal into a digital signal, which first includes: a reference analog signal having a first predetermined voltage value;
the A/D when a power supply voltage having a second predetermined voltage value and an arbitrary voltage value is applied to the A/D conversion circuit;
A theoretical A/D conversion value and a reference A/D conversion value, which are A/D conversion values by the conversion circuit, are determined, and then a power supply voltage having the arbitrary voltage value of the analog signal is applied to the A/D conversion circuit. The A/D conversion value of the A/D conversion circuit is multiplied by the ratio of the theoretical A/D conversion value and the reference A/D conversion value. Correction method.