JPH04255115A - Analog/digital converter - Google Patents

Abstract

PURPOSE:To convert an input voltage in excess of a reference voltage into an accurate digital value. CONSTITUTION:The analog/digital(A/D) converter is provided with a voltage generating circuit 9 generating a known voltage Vd and a subtraction amplifier circuit 7 generating voltage Vc, which subtracts the known voltage Vd from an input voltage Va to generate the voltage Vc. When an A/D converter 3 converts the voltage Vc into a digital value, a CPU 5 adds the converted digital value from the voltage Vc and the digital value of the said known voltage Vd to calculate a digital value of the input voltage Va.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog/digital conversion device for converting an analog value of an input voltage into a digital value.

0003

2. Description of the Related Art In recent years, various analog/digital converters (hereinafter simply referred to as A/D converters) for converting analog values of input voltages into digital values have been proposed. For example, when the power supply voltage is 5V, an 8-bit A/D converter uses the power supply voltage of 5V as a reference voltage, and outputs a maximum of 255 counts of digital values when the input voltage is 5V. When the input voltage is 0 to 5V, a digital value of 0 to 255 counts is output according to this input voltage. For example, when the input voltage is 3V, a digital value of 153 counts is output as shown in the following equation.

255×3÷5=153
...(
1) As such a conventional A/D conversion device, one shown in FIG. 6 is known.

[0005] When the input voltage Va is 5V or less, the A/D converter 10
3 and 0 to 25 depending on the input voltage Va as described above.
Convert to 5 count digital value. Also, CPU10
5 determines that the input voltage Va is 5V or more,
By controlling the analog multiplexer 101, the resistors R1 and R
The voltage Vc divided by 2 is input to the A/D converter 103. That is, Vc=Va×R2÷(R1+R2)
...(2) Above (
2) The voltage Vc divided as shown in the formula is applied to the A/D converter 103.
and converted to a digital value. The CPU 105 calculates the digital value of the input voltage Va by multiplying the digital value of the voltage Vc by the reciprocal of the voltage division ratio of the resistors R1 and R2.

[0006]

[Problems to be Solved by the Invention] However, when the input voltage Va, which is higher than the reference voltage Vb as shown in the curve a in FIG. 7, is divided by the resistors R1 and R2 as described above, the voltage shown in the curve b in FIG. As shown, the amount of change in input voltage is reduced by voltage division. Therefore, the input voltage Va is
, R2 to divide the pressure and convert it into a digital value,
There were cases where errors occurred. For example, if the input voltage Va is 1
To explain specifically the case where the voltage is 3V and the voltage division ratio is 1/3, the voltage V divided by the resistors R1 and R2
The digital value of c is calculated as follows.

(13÷3÷5)×255=220
(3) Therefore, the digital value of the input voltage Va=13V is calculated as shown in the following equation (4) by multiplying the value obtained by the above equation (3) by the reciprocal 3 of the above voltage division ratio. 220×3=660
…
...(4) Next, calculate the true digital value of input voltage Va = 13V, (13÷5) x 255 = 663
...(5) As is clear from a comparison of equations (4) and (5) above, the method of dividing the voltage using resistors R1 and R2 and converting it into a digital value is a true digital value with input voltage Va = 13V. value is 663
The count is 660, which is 3 counts less than the actual count.

[Configuration of the invention]

[0009]

[Means for Solving the Problems] In order to solve the above problems, the first invention of the present application provides subtraction means for subtracting a predetermined voltage lower than an input voltage from the input voltage; The object of the present invention is to include a converting means for converting the voltage into a digital value, and an adding means for adding a digital value corresponding to a predetermined voltage value subtracted by the subtracting means to the digital value converted by the converting means. do.

A second invention of the present application includes a subtraction means for subtracting a predetermined voltage from an input input voltage, and a voltage subtracted by the predetermined voltage by the subtraction means and the input voltage, respectively, and the subtraction means subtracts a predetermined voltage from the input voltage. a selection means that outputs the voltage from the subtraction means when the voltage is greater than the predetermined voltage, and outputs the input voltage when it is smaller; and a conversion means that converts the voltage input from the selection means into a digital value. and addition means for adding a digital value corresponding to a predetermined voltage value subtracted by the subtraction means to the digital value converted by the conversion means when the voltage from the subtraction means is selected by the selection means. The gist is:

[0011]

[Operation] When the input voltage is equal to or higher than the reference voltage, the A/D converter of the first invention of the present application subtracts a predetermined voltage lower than the input voltage from the input voltage and converts it into a digital value. After conversion, by adding a digital value corresponding to the predetermined voltage value subtracted by the subtraction means to the digital value of the converted voltage, it is possible to accurately calculate the digital value of the input voltage that is equal to or higher than the reference voltage. can.

[0012] In addition to the first invention, the A/D conversion device of the second invention of the present application converts the input voltage into a digital value and directly outputs the value when the input voltage is lower than the reference voltage. This is how it was done.

[0013]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the overall configuration of an A/D conversion device to which the present invention is applied will be explained with reference to FIG.

The A/D conversion device to which the present invention is applied includes an analog multiplexer 1, an A/D converter 3, and a CPU 5.

The analog multiplexer 1 is a multi-input analog signal switching means, and when the input voltages Va, Vc, and Vd are input, the analog multiplexer 1 outputs a control signal 5A from the CPU 5.
Depending on the voltage, one of the voltages is selected and switched and outputted to the A/D converter 3. Protection diodes D1 and D2 are connected to the input side of the A/D converter 3. The A/D converter 3 is an 8-bit converter that converts the analog value of the voltage input from the analog multiplexer 1 into an 8-bit digital value, and sends the converted digital value signal to the CPU.
Output to 5. This A/D converter 3 is a conversion means that converts the voltage Vc subtracted by a subtraction means described later into a digital value.

The CPU 5 determines whether the input voltage Va is equal to or higher than a reference voltage, for example 5V, based on the digital value signal input from the A/D converter 3. When the CPU 5 determines that the input voltage Va is equal to or higher than the reference voltage, the CPU 5 sends a control signal 5A to the analog multiplexer 1 to select the voltage Vc. Furthermore, when the CPU 5 inputs the digital value signal of the voltage Vc converted by the A/D converter 3, the CPU 5 takes into account the amplification factor of the subtraction amplifier circuit and the voltage Vd generated by the voltage generation circuit, which will be explained later. Calculate the digital value of voltage Va. That is, the CPU 5 is an addition means that adds the digital value of the voltage Vc subtracted by the subtraction means and the digital value of the known voltage Vd. A/D converter 3,
A power supply voltage Vb, for example 5V, is applied to the cathode side of the CPU 5 and the diode D1, and a power supply voltage Vbb, for example 15V, is applied to the analog multiplexer 1.

Next, the circuit configuration on the input side of the analog multiplexer 1 will be explained. A subtraction amplifier circuit 7 and a voltage generation circuit 9 are connected to the input side of the analog multiplexer 1. The subtraction amplifier circuit 7 receives the input voltage V which is the voltage to be measured.
This is subtraction means for subtracting a known voltage Vd from a. The input voltage Va is directly input to the analog multiplexer 1, and is also applied to the non-inverting input terminal of the operational amplifier 11 via the resistor R3. Further, the non-inverting input terminal of the operational amplifier 11 is connected to ground via a resistor R5. The inverting input terminal of the operational amplifier 11 is connected to the output terminal of the operational amplifier 11 via a resistor R5. This operational amplifier 1
1 is connected to the analog multiplexer 1 via a resistor R7, and the voltage Vc is connected to the analog multiplexer 1 through the resistor R7.
Output to. Further, the inverting input terminal of the operational amplifier 11 is connected to the output terminal of the operational amplifier 13 via a resistor R3. The output terminal of operational amplifier 13 is connected to the inverting input terminal. A resistor R is connected between the power supply voltage Vbb and ground.
11 and R13 are connected in series. This resistance R11
The connection point between R13 and R13 is connected to the non-inverting input terminal of the operational amplifier 13. Operational amplifiers 11 and 13 are supplied with power supply voltage Vbb.

Next, the operation will be explained. First, the input voltage V
The effect when a is lower than the reference voltage will be explained.

When an input voltage Va lower than the reference voltage is input to the A/D converter 3 via the analog multiplexer 1,
As shown in equation (1) above, depending on the input voltage Va,
It is converted into a digital value of 255 counts. If the digital value input from the A/D converter 3 is less than 255 counts, the CPU 5 determines that the input voltage Va is less than the reference voltage and inputs the digital value input from the A/D converter 3. Output as a digital value of voltage Va.

Next, the operation when the input voltage Va is higher than the reference voltage, for example 13V, will be explained. As mentioned above, the input voltage Va is input to A via the analog multiplexer 1.
When input to the /D converter 3, it is converted into a digital value according to the input voltage Va. When the digital value inputted from the A/D converter 3 is the maximum count of 255, the CPU 5 determines that the input voltage Va is the reference voltage or higher than the reference voltage. When the CPU 5 determines that the input voltage Va is the reference voltage or higher than the reference voltage, the CPU 5 sends a control signal 5A to the analog multiplexer 1 to select the voltage Vc. Here, voltage Vc will be explained. First, power supply voltage Vbb is divided by resistors R11 and R13. The voltage division ratio R1 due to these resistors R11 and R13
3/(R11+R13) is set to 12/15, for example, and the divided voltage shown in the following equation (6) is applied to the operational amplifier 1.
It is applied to the non-inverting input terminal of No. 3.

Vbb×R13/(R11+R13)=15×(1
2/15)
=12
...(6) When the divided voltage shown in equation (6) above is applied to the non-inverting input terminal of the operational amplifier 13, a voltage Vd equal to this divided voltage is applied to the operational amplifier 13.
The signal is output from the analog multiplexer 1 to the inverting input terminal of the operational amplifier 11 via the resistor R3. In the operational amplifier 11, the input voltage Va is applied to the non-inverting input terminal, and from this input voltage Va the above voltage V is applied.
After subtracting d, it is amplified by a predetermined amplification factor (R5/R3) to generate voltage Vc. Here, the amplification factor (R5/R3) by the resistors R5 and R3 is set to 2, for example, and the voltage Vc shown in the following equation (7) is applied to the analog multiplexer 1.

Vc=(Va-Vd)×(R5/R3)
=(13-12)×2 =2

(7) As described above, when the voltage Vc is input to the A/D converter 3 via the analog multiplexer 1, it is converted into a digital value according to the voltage Vc. That is, 2÷5×255=102
…
...(8) As shown in the above equation (8), the A/D converter 3 is
The signal converted to a digital value of 102 counts is sent to the CPU 5.
Output to. As shown in the following equation (9), the CPU 5
By dividing the digital value of 102 counts input from the /D converter 3 by the same value as the amplification factor (R5/R3), and then adding the digital value of the known voltage Vd=12V, the digital value of the input voltage Va is calculated. Calculate the value.

102÷2+12÷5×255=663
...(9) Here, when adding the digital value of the known voltage Vd, the voltage Vd is selected by the analog multiplexer 1 and the A/D
The digital value input to the converter 3 and converted by the A/D converter 3 may be used. Alternatively, the digital value of the known voltage Vd may be stored in advance in a memory such as a RAM. , read from this memory and obtain the known voltage V
The configuration may be such that the digital values of d are added.

In the above embodiment, the known voltage Vd is subtracted from the input voltage Va and then amplified by the amplification factor (R5/R3) to generate the input voltage Vc. However, the amplification factor (R5 /R3) can be set to an appropriate value by selecting the resistance values of resistors R5 and R3. For example, by selecting the resistance values of resistors R5 and R3 to be equal, the amplification factor is set to 1, and the voltage obtained by subtracting the known voltage Vd from the input voltage Va is used as the input voltage Vc to output the A/ It is given to the D converter 3.

As described above, when the known voltage Vd is subtracted from the input voltage Va, the change in the subtracted voltage can be made the same as the change in the input voltage Va, as shown in FIG. . Then, from the input voltage Va, a known voltage V
The configuration is such that the input voltage Vc is generated by subtracting d and then amplifying it by the amplification factor (R5/R3), so as shown in FIG.
can be expanded according to the input voltage V with high accuracy.
The digital value of a can be calculated.

Next, another embodiment of the present invention will be described with reference to FIG. This embodiment has a voltage generation circuit 9 that generates a known voltage Vd, and a subtraction amplifier circuit 7 that generates an input voltage Vc, and subtracts the known voltage Vd from the input voltage Va and amplifies the input voltage Vd. When generating Vc, the voltage Vd generated by the voltage generating circuit 9 and the amplification factor of the subtraction amplifier circuit 7 are made variable to expand the range of input voltage Va that can be digitally converted.

More specifically, in the subtraction amplifier circuit 7, the inverting input terminal of the operational amplifier 11 is connected to the voltage generation circuit 9 via a resistor R3, and is also connected to a resistor circuit 15. Further, a non-inverting input terminal of the operational amplifier 11 is connected to the resistor R3 and the resistor circuit 17. In the voltage generation circuit 9, the inverting input terminal of the operational amplifier 13 is connected to ground via a resistor R9, and is also connected to a resistor circuit 19. The resistance value of this resistance circuit 19 is controlled by the control signal 5B of the CPU 5, and the resistance value of the resistance circuit 19 is controlled by the control signal 5B of the CPU 5.
The resistance values of and 17 are controlled by the control signal 5C of the CPU 5.

Next, referring to FIG. 5, the resistance circuit 15,
The circuit configuration of 17 and its peripheral parts will be explained. Resistance circuit 15
are resistors R15a, R15b, R15 connected in series
c, R15d, and R15e, a switch S15a connected in parallel with the resistor R15b, a switch S15b connected in parallel with the resistor R15c, a switch S15c connected in parallel with the resistor R15d, and a switch S15c connected in parallel with the resistor R15e. and a switch S15d. These switches S15a, S15b, ..., S15d are operated by the control signal 5C from the CPU 5, and the corresponding resistor R15b
, R15c, . . . , R15e, the combined resistance value of the resistance circuit 15 is determined.

Similarly, the resistance circuit 17 includes resistors R17a, R17b, R17c, R17d, and R1 connected in series.
7e and a switch S1 connected in parallel with the resistor R17a.
7a and a switch S1 connected in parallel with the resistor R17b.
7b and switch S1 connected in parallel with resistor R17c.
7c and switch S1 connected in parallel with resistor R17d.
7d. These switches S17a, S1
7b,..., S17d are operated by the control signal 5C from the CPU 5, and the corresponding resistors R17a, R17b...R17
By short-circuiting d, the combined resistance value of the resistance circuit 17 is determined. Here, resistors R15a,..., R15e, R1
The respective resistance values of 7a,..., R17e are set to the same value, and the combined resistance value of the resistance circuit 15 and the combined resistance value of the resistance circuit 17 are set to the same value by the control signal 5C from the CPU 5. be done.

The circuit configuration of the resistor circuit 19 is also similar to that of the resistor circuits 15 and 17, and includes a plurality of resistors connected in series and a plurality of switches connected in parallel with each resistor. The combined resistance value of the resistance circuit 19 is determined by operating the switch in accordance with the control signal 5B from the CPU 5 and short-circuiting the corresponding resistance.

Further, the circuit configurations other than those shown above are the same as those shown in FIG. 1, and are given the same reference numerals and detailed explanations will be omitted.

Next, the operation of the embodiment shown in FIGS. 4 and 5 will be explained. First, the voltage Vd generated by the voltage generation circuit 9 will be explained using a mathematical formula.

Vd=Vbb×R13÷(R11+R13)×A1
...(10) However, A1 is the amplification factor of the operational amplifier 13, and the control signal 5B from the CPU 5
It is determined according to the combined resistance value of the resistance circuit 19 based on . Therefore, voltage Vd is determined based on control signal 5B from CPU5.

Next, the voltage Vc generated by subtracting the known voltage Vd generated by the voltage generating circuit 9 from the input voltage Va by the subtracting amplifier circuit 7 and amplifying it will be explained using a mathematical formula.

Vc=(Va-Vd)×A2
...(11
) However, A2 is the amplification factor of the operational amplifier 11, and the following (
It is expressed as the ratio between the resistance R3 and the combined resistance R15 of the resistance circuit 15, as shown in equation 12).

A2=R15/R3
…
...(12) The composite resistance R15 of the resistance circuit 15 is CP
Since it is controlled by the control signal 5C from U5, the voltage V
c is expanded according to the amplification factor A2 determined based on the control signal 5C from the CPU 5. The voltage Vc generated in this way is passed through the analog multiplexer 1 to the A/
The signal is supplied to the D converter 3 and converted into a digital value. C.P.
When U5 receives the digital value signal of the voltage Vc from the A/D converter 3, it outputs a control signal 5A to the analog multiplexer 1. As a result, when the analog multiplexer 1 selects the known voltage Vd in response to the control signal 5A from the CPU 5, the known voltage Vd is converted into a digital value by the A/D converter 3 and provided to the CPU 5. The CPU 5 calculates the input voltage Va based on the digital value signal of the input voltage Vc and the known digital value signal of the voltage Vd, taking into account the amplification factor A1 of the operational amplifier 13 and the amplification factor A2 of the operational amplifier 11. Calculate the digital value.

As described above, in the embodiment shown in FIGS. 4 and 5, the voltage Vd generated by the voltage generation circuit 9 and the amplification factor of the subtraction amplifier circuit 7 are changed in accordance with the control signal from the CPU 5. With this configuration, the amount of change in the input voltage Va can be expanded as shown in FIG. Further, the amplification factor A1 of the operational amplifier 13 and the amplification factor A of the operational amplifier 11
By setting 2 to an appropriate value, the range of input voltage Va that can be digitally converted can be expanded.

The embodiments shown in FIGS. 4 and 5 are constructed so that the voltage Vd generated by the voltage generation circuit 9 and the amplification factor A2 of the subtraction amplifier circuit 7 are changed in accordance with the control signals 5B and 5C. However, the present invention is not limited to this, and either one may be changed. That is, if either the voltage Vd generated by the voltage generation circuit 9 or the amplification factor A2 of the subtraction amplifier circuit 7 is configured to be changed, the circuit configuration can be simplified.

[0039]

As described above, according to the present invention, a known voltage is subtracted from an input voltage, the subtracted voltage is converted into a digital value, and the converted digital value and the known voltage are Since the configuration is configured such that the digital value of the input voltage is added, it is possible to accurately calculate the digital value of the input voltage higher than the reference voltage.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment according to the present invention.

FIG. 2 is a waveform diagram of a voltage obtained by subtracting a known voltage Vd from an input voltage Va.

FIG. 3 is a waveform diagram of the input voltage Vc generated by the subtraction amplifier circuit.

FIG. 4 is a circuit diagram of another embodiment according to the present invention.

5 is a circuit diagram showing the circuit configuration of the resistor circuits 15 and 17 and their peripheral parts in the embodiment shown in FIG. 4; FIG.

FIG. 6 is a circuit diagram of a conventional example.

FIG. 7 is a waveform diagram of an input voltage and a divided voltage obtained by dividing this input voltage for explaining the operation of the conventional example.

[Explanation of symbols]

3 A/D converter 5 CPU 7 Subtraction amplifier circuit 9 Voltage generation circuit 11, 13 Operational amplifier

Claims (2)

[Claims] 1. Subtraction means for subtracting a predetermined voltage lower than an input voltage from the input voltage; conversion means for converting the voltage subtracted by the subtraction means into a digital value; an addition means for adding a digital value corresponding to a predetermined voltage value subtracted by the subtraction means to the digital value obtained by the subtraction means. 2. Subtraction means for subtracting a predetermined voltage from the input voltage, and inputting the input voltage and the voltage subtracted by the predetermined voltage by the subtraction means, so that the input voltage becomes the predetermined voltage. a selection means that outputs the voltage from the subtraction means when the voltage is greater than the voltage, and outputs the input voltage when it is smaller; a conversion means that converts the voltage input from the selection means into a digital value; and the selection means and an addition means for adding a digital value corresponding to a predetermined voltage value subtracted by the subtraction means to the digital value converted by the conversion means when the voltage from the subtraction means is selected. /Digital conversion device.