JPH0915272A - Voltage measuring circuit - Google Patents

Abstract

PURPOSE: To measure voltage with a resolution higher than that inherent in an analog-to-digital converter. CONSTITUTION: An analog-to-digital converter 21 converts a voltage Vx to be measured with a specified voltage unit, and outputs a first converted value. A digital-to-analog converter 23 converts this first converted value, and gives it to a differential amplifier circuit 10 which amplifies the voltage Vx and a first voltage difference at a specified amplification factor, and outputs a second voltage difference. Another analog-to-digital converter 22 converts the second voltage, and outputs a second converted value. A control part 24 operates a digital value equivalent to the subject voltage Vx on the basis of both these first and second converted values and the specified amplification factor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage measuring circuit for converting a voltage into a digital value and measuring it.

[0002]

2. Description of the Related Art Conventionally, when measuring a voltage with a digital value, an A / D converter having a required resolution (bit width) is usually used.

[0003]

Therefore, if the resolution of the A / D converter on hand is less than the desired resolution, an A / D converter with a higher resolution must be obtained. The present invention has been made under such circumstances, and an object thereof is to obtain a digital value corresponding to a voltage to be measured with a resolution higher than the predetermined resolution by using an A / D converter having a predetermined resolution. It is to provide a voltage measurement circuit.

[0004]

The voltage measuring circuit of the present invention includes an input terminal for inputting a voltage to be measured and a first voltage converting circuit for measuring a voltage applied to the input terminal according to a first resolution. An A / D converter, a D / A converter that converts the conversion value output from the first A / D converter according to the first resolution, a measured voltage applied to the input terminal, and the D / A converter using a differential input as an input voltage for amplifying the output voltage at a predetermined amplification rate, and a second A / A converter for converting the output voltage of the differential amplifier circuit according to a second resolution.
D converter, first conversion value output from the first A / D converter, second conversion value output from the second A / D converter, and the differential amplifier circuit And a calculation means for calculating a digital value corresponding to the measured voltage based on the predetermined amplification factor of.

Further, the present invention is characterized in that the first A / D converter, the second A / D converter, and the D / A converter are built in one one-chip microcomputer. There is.

[0006]

The first A / D converter converts the measured voltage in a predetermined voltage unit determined based on the first resolution and outputs the first converted value. The D / A converter converts the first conversion value based on the first resolution and supplies the first conversion value as a first voltage to the differential amplifier circuit. The differential amplifier circuit amplifies the voltage to be measured and the first voltage as a differential input at a predetermined amplification factor and outputs a second voltage. The second A / D converter is
The second corresponding to a voltage value below the predetermined voltage unit
The second converted value is output based on the second resolution based on the second resolution. The calculating means calculates the value of the voltage to be measured from the first conversion value, the second conversion value, and the amplification factor of the differential amplifier circuit, so that the first resolution is higher than the first resolution of the first A / D converter. A digital value corresponding to the measured voltage is obtained with high resolution.

The first A / D converter and the second A / D converter
When the / D converter and the D / A converter are built in one one-chip microcomputer, the voltage measuring circuit can be configured without increasing the number of parts.

[0008]

Next, the present invention will be described with reference to the drawings. 1 is a circuit diagram showing an embodiment of the voltage measuring circuit of the present invention, FIG. 2 is an operation flowchart, and FIG.
FIG. 4 is a characteristic diagram of a differential amplifier circuit.

The terminals tx and tx are the measured voltage V to be measured.
It is an input terminal for inputting x. Operational amplifier N
Positive and negative symmetrical voltages + Vcc and -Vcc are supplied as power supplies to 1 and N2, respectively, and an output terminal is connected to an inverting input terminal to form a high input impedance buffer circuit.

The differential amplifier circuit 10 shown by the chain double-dashed line in the figure is
An operational amplifier N3 supplied with a voltage Vp as an operating power supply,
It is composed of input resistors R1, R3, R4 and a feedback resistor R2. C1 to C4 are noise prevention capacitors. Here, the resistance value of the differential amplifier circuit 10 is R
If the relationship of 1 = R3, R2 = R4 is set,
The input / output characteristics and the amplification factor are expressed by equation (1) and (2)
It is shown by the formula.

(Equation 1) (Eo: output voltage, Ei1: non-inverting input voltage, Ei2: inverting input voltage)

(Equation 2) (A: amplification rate)

The one-chip microcomputer 20 shown by the one-dot chain line in the figure has analog input terminals t1 and t, respectively.
A first A / D converter 21 and a second A / D connected to
D converter 22 and D connected to the analog output terminal t3
The A / A converter 23 and a control means 24 that controls each of these parts and executes an arithmetic operation to be described later are incorporated. The control means 24 includes a CPU, a storage means including a ROM containing a control program and a RAM for storing and holding data, a peripheral I / F element for exchanging data and control commands with each section. A / D converters 21 and 2
2. The D / A converter 23 and the control means 24 are connected to each other by a data bus DB and a control bus CB.

In this embodiment, the A / D converter 21,
22 and the resolution (bit width) Wb of the D / A converter 23 are 8 bits. In addition, A / D converters 21, 22 and D
The operating voltage of the / A converter 23 is 0V and 5V. That is, the input range of the A / D converters 21 and 22 is 0V to 5V.
V, and the output range of the D / A converter 23 is 0V to 5V
Becomes Therefore, the A / D converters 21 and 22 and the D / A converter 23 perform A / D conversion and D / A conversion at the unit voltage ΔV determined by the operating voltage and resolution.
Here, the unit voltage ΔV is 5V / 256 bits = 19.53m
V / bit.

According to the above configuration, the voltage Vx to be measured passes through the buffer N1 and the one-chip microcomputer 2
0 through the analog input terminal t1 and the A / D converter 21
And the non-inverting input terminal of the differential amplifier circuit 10. On the other hand, the output voltage of the D / A converter 23 of the one-chip microcomputer 20 is the output terminal t
3 and is supplied to the inverting input terminal of the differential amplifier circuit 20 via the buffer N2. The differential amplifier circuit 10 outputs to the A / D converter 22 via the analog input terminal t2 of the one-chip microcomputer 20, the voltage amplified by a predetermined amplification rate based on the difference between the output voltages of the buffers N1 and N2. give.

Next, the operation of the voltage measuring circuit will be described with reference to the circuit diagram of FIG. 1 and the flowchart of FIG.
It is assumed that the measured voltage Vx is applied to the input terminals tx and tx. First, the control unit 24 commands the A / D converter 21 receiving the measured voltage Vx output from the buffer N1 via the analog input terminal t1 to start the A / D conversion operation via the control bus CB. Yes (step S1).

When the A / D conversion operation by the A / D converter 21 is completed, the control unit 24 holds the first conversion value d1 output from the A / D converter 21 in the storage means (step S2). ).

At this time, the A / D converter 21 performs conversion with the unit voltage ΔV (19.53 mV / bit) described above. Therefore, the error voltage Ve corresponding to the quantization error below the voltage unit is truncated.

Next, the control section 24 controls the first conversion value d.
1 is supplied to the D / A converter 23 via the data bus DB and the D / A converter 23 is instructed to start the D / A conversion operation (step S3).

Therefore, the D / A converter 23 outputs from the analog output terminal t3 the analog voltage Va1 generated by performing the D / A conversion with the unit voltage ΔV described above (step S4).

The analog voltage Va1 is supplied to the inverting input terminal of the differential amplifier circuit 10 via the buffer N2.
At this time, the non-inverting input terminal of the differential amplifier circuit 10 is supplied with the measured voltage Vx via the buffer N1.

Therefore, the differential amplifier circuit 10 amplifies the difference voltage obtained by subtracting the voltage Va1 from the measured voltage Vx (corresponding to the error voltage Ve described in step S2) and outputs it as the second voltage Va2. It This voltage Va2 is A
It is input to the / D converter 22 (step S5). The relationship between the amplification factor A of the differential amplifier circuit 10 and the error voltage Ve will be described later.

The control unit 24 controls the A / D converter 22.
To start the A / D conversion operation (step S6).
As a result, the A / D converter 22 inputs the second conversion value d2, which is the A / D conversion result, to the control unit 24 (step S
7).

Next, the control unit 24 controls the first conversion value d1 already stored in the storage means and the A / D converter 22.
A digital voltage value Vdx corresponding to the measured voltage Vx is calculated from the second conversion value d2 supplied from the above based on the following equation (3) (step S8), and the voltage value V
Predetermined processing is executed based on dx (step S9), and a series of measurement operations ends.

Now, the formula for calculating the voltage value Vdx will be described. When the power supply voltage of the differential amplifier circuit 10 is 0 V and 5 V, the output voltage is generated with 2.5 V as the reference voltage. That is, when the difference voltage obtained by subtracting the input voltage of the inverting terminal from the input voltage of the non-inverting terminal is 0V, the output voltage is 2.5V. The A / D converter 22 has operating voltages of 0V and 5V and a resolution of 8 bits, so that the digital output value is 1/2 of "FFH" when the analog input voltage is 2.5V. It becomes "80H" (128D). Therefore, the voltage value Vdx is expressed by the following equation (3).

(Equation 3)

Next, the relationship between the error voltage Ve and the amplification factor A of the differential amplifier circuit 10 will be described with reference to FIG.
In FIG. 3, the horizontal axis represents the differential input voltage (Ei1
-Ei2) is taken, and the vertical axis represents the output voltage Eo and the output value of the A / D converter 22. As shown
The operating range required for the differential input voltage of the differential amplifier circuit 10 may have a width of the unit voltage ΔV with 0 V as the center.

Further, in order for the A / D converter 22 to have a wide resolution when converting the error voltage Ve, the amplification factor A of the differential amplifier circuit 10 ensures the linearity of the output voltage of the operational amplifier N3. Within the above range, it is preferable to set as large as possible in the operating range of the differential input voltage.

As described above, according to this embodiment, the measured voltage Vx is measured by the A / D converter 22 with 8-bit resolution. At this time, the first conversion value d1 is measured in the unit of the unit voltage ΔV determined by the 8-bit resolution. Next, the error voltage Ve below the unit voltage ΔV is amplified by the differential amplifier circuit 10 with the amplification factor A and digitally converted by the 8-bit A / D converter 23, and the second conversion value d2 is measured. The control unit 24 controls the first conversion value d1,
Based on the second conversion value d2 and the amplification factor A, the voltage value Vdx corresponding to the measured voltage Vx is converted into the first A / D converter 21.
Can be obtained with a resolution higher than 8 bits, which is the bit width of.

The first A / D converter 21 and the second A / D converter 21
The resolution (bit width Wb) of the A / D converter 22 may be different, but the resolutions of the first A / D converter 21 and the D / A converter 23 need to match. Further, the resolution of the first A / D converter 21 and the second A / D converter 22 is not limited to 8 bits.

In this embodiment, since the one-chip microcomputer 20 incorporating the A / D converters 21, 22 and the D / A converter 23 is used, the voltage measuring circuit can be constructed inexpensively without increasing the number of parts. However, it goes without saying that each of the converters 21, 22, and 23 may be composed of an individual IC.

[0029]

As described above in detail, according to the voltage measuring circuit of the present invention, the first A / D converter has the predetermined voltage unit in which the measured voltage is determined based on the first resolution. And outputs the first converted value. The D / A converter converts the first conversion value based on the first resolution and supplies the first conversion value as a first voltage to the differential amplifier circuit. The differential amplifier circuit receives the measured voltage and the first voltage as a differential input, amplifies the voltage with a predetermined amplification factor, and outputs a second voltage. The second A / D converter outputs the second voltage corresponding to a voltage value lower than the predetermined voltage unit to the second voltage based on the second resolution.
Output the converted value of. Therefore, the calculation means is the first
By calculating the value of the voltage to be measured from the converted value, the second converted value, and the amplification factor of the differential amplifier circuit, with a resolution higher than the first resolution of the first A / D converter. A digital value of voltage can be obtained.

The first A / D converter and the second A / D converter
When the / D converter and the D / A converter are built in one one-chip microcomputer, the voltage measurement circuit can be configured at low cost without increasing the number of parts.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a voltage measuring circuit of the present invention.

FIG. 2 is an operation flowchart in the embodiment.

FIG. 3 is a characteristic diagram of the differential amplifier circuit in the example.

[Explanation of symbols]

 10 differential amplifier circuit 21 1st A / D converter 22 2nd A / D converter 23 D / A converter 24 control part (arithmetic means) tx input terminal Vx measured voltage

Claims (2)

[Claims] 1. An input terminal for inputting a measured voltage, a first A / D converter for converting the measured voltage applied to the input terminal according to a first resolution, and the first A / D converter. A D / A converter for converting the converted value output from the D / D converter according to the first resolution, and the measured voltage applied to the input terminal and the output voltage of the D / A converter as differential inputs. A differential amplifier circuit that amplifies with a predetermined amplification factor, a second A / D converter that converts an output voltage of the differential amplifier circuit according to a second resolution, and an output from the first A / D converter Corresponding to the voltage to be measured based on a first converted value, a second converted value output from the second A / D converter, and a predetermined amplification factor of the differential amplifier circuit. A voltage measuring circuit, comprising: an arithmetic means for calculating a digital value. 2. The first A / D converter, the second A / D converter, and the D / A converter are incorporated in one one-chip microcomputer.
The voltage measurement circuit described.