JPH06311036A - A/d converter - Google Patents

Abstract

PURPOSE:To provide an A/D converter easily integrated to be a digital IC. CONSTITUTION:The feedback comparison type A/D converter is provided with a controller 1 outputting digital data, a D/A converter 2 comprising a ladder resistor, a source of a reference voltage 8, resistors 6, 7 averaging voltages, and an analog switch 5 selecting inputs, and the effect of a digital input port of the controller 1 is corrected by data when the analog switch 5 is turned off. Thus, multichannel input is facilitated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an A / D (analog / digital) converter which does not use a comparator.

[0002]

2. Description of the Related Art The structure of a conventional A / D converter will be described with reference to FIG. FIG. 8 is a diagram showing an A / D (analog / digital) conversion device using a ladder resistor which is generally used in the past.

In FIG. 8, reference numeral 1 is a control device composed of a CPU having at least a 1-bit input port (P0) and output ports (P1 to P5) for outputting digital data of a plurality of bits, and 2 is a control device 1. Output port (P1
To P5) and outputs an analog voltage corresponding to the output data, one of the input terminals of the digital / analog converter 3 is connected to the output side of the digital / analog converter 2 and the other is output. The terminal is an analog comparator connected to the input port (P0) of the control device 1. In addition, 4 is a measured voltage (Vx).

Next, the operation of the conventional A / D converter will be described. This A / D conversion device compares the output of the digital / analog converter 2 corresponding to the output data of the control device 1 and the measured voltage 4 by the analog comparator 3, and adjusts the digital output data based on the result. The digital data output from the control device 1 when the input voltage difference of the analog comparator 3 becomes a predetermined value or less is used as the digital conversion data of the measured voltage 4.

[0005]

In the conventional A / D conversion device as described above, the analog comparator 3 performs voltage comparison, and the digital control device 1 instructs the conversion procedure. For this reason, there are problems that the operation speed is limited depending on the analog comparator 3, and that when the IC (integrated circuit) is used, the design is difficult because of the analog / digital mixed circuit.

The present invention has been made in order to solve the above-mentioned problems, and an object thereof is to obtain an A / D conversion device which can be easily made into a digital IC without using an analog comparator.

[0007]

The A / D converter according to claim 1 of the present invention comprises the following means. [1] A control device having an input port for inputting digital data and an output port for outputting digital data of a plurality of bits. [2] A digital / analog converter configured by a ladder resistor, which outputs an analog voltage corresponding to digital data output from the control device, and whose output is applied to an input port of the control device. [3] An analog switch whose output terminal is connected to the output side of the digital / analog converter, whose voltage input terminal is connected to the first resistance, and whose reference voltage input terminal is connected to the second resistance. Then, the control device switches between two input voltages of a voltage to be measured and a reference voltage by the analog switch to input, and the threshold value of the input port when the analog switch is connected to the voltage to be measured. The first equivalent to
Output data, second output data corresponding to the threshold value of the input port when the analog switch is connected to the reference voltage, and the second output data when the analog switch is not connected to either. The measured voltage is calculated from the third output data corresponding to the threshold value of the input port.

An A / D converter according to a second aspect of the present invention is provided with the following means. [1] A control device having an input port for inputting digital data and an output port for outputting digital data of a plurality of bits. [2] A digital / analog converter configured by a ladder resistor, which outputs an analog voltage corresponding to digital data output from the control device, and whose output is applied to an input port of the control device. [3] An analog switch whose output terminal is connected to the output side of the digital / analog converter and whose input terminal is connected to a resistor. Then, in the control device, the analog switch is OF
The measured voltage is calculated from the first output data corresponding to the threshold value of the input port when F and the second output data corresponding to the threshold value of the input port when the analog switch is ON. It is calculated and obtained.

An A / D converter according to a third aspect of the present invention comprises the following means. [1] A control device having an input port for inputting digital data and an output port for outputting digital data of a plurality of bits. [2] A digital / analog converter configured by a ladder resistor, which outputs an analog voltage corresponding to digital data output from the control device, and whose output is applied to an input port of the control device. [3] An analog switch having an output terminal connected to the output side of the digital / analog converter and a plurality of measured voltage input terminals connected to each of a plurality of resistors. Then, the control device switches a plurality of measured voltages by the analog switch and inputs them, and a first threshold voltage corresponding to the threshold value of the input port when the analog switch is connected to the measured voltage. Output data and a second threshold corresponding to the threshold of the input port when the analog switch is not connected to any of the measured voltages.
The voltage to be measured is calculated from the output data of 1.

[0010]

In the A / D conversion device according to the first aspect of the present invention, the analog voltage corresponding to the digital data output from the control device is output by the digital / analog converter configured by the ladder resistor, The output is applied to the input port of the controller. Further, by the control device having an input port for inputting digital data and an output port for outputting digital data of a plurality of bits,
First input data corresponding to a threshold value of the input port when two input voltages of a measured voltage and a reference voltage are switched by an analog switch and the analog switch is connected to the measured voltage. A second output data corresponding to a threshold value of the input port when the analog switch is connected to the reference voltage, and a second output data of the input port when the analog switch is not connected to either. The voltage to be measured is calculated and obtained from the third output data corresponding to the threshold value.

In the A / D converter according to the second aspect of the present invention, the digital / analog converter constituted by the ladder resistor outputs the analog voltage corresponding to the digital data output from the controller, The output is applied to the input port of the controller. In addition, the control device having an input port for inputting digital data and an output port for outputting digital data of a plurality of bits, the first output data corresponding to the threshold value of the input port when the analog switch is OFF, The measured voltage is calculated and obtained from the second output data corresponding to the threshold value of the input port when the analog switch is ON.

In the A / D converter according to the third aspect of the present invention, the analog voltage corresponding to the digital data output from the controller is output by the digital / analog converter configured by the ladder resistor, The output is applied to the input port of the controller. Further, a control device having an input port for inputting digital data and an output port for outputting digital data of a plurality of bits switches and inputs a plurality of measured voltages by an analog switch, and the analog switch is connected to the measured voltage. Corresponding to the first output data corresponding to the threshold of the input port when the analog switch is turned on and the threshold of the input port when the analog switch is not connected to any of the measured voltages. The voltage to be measured is calculated and obtained from the second output data.

[0013]

EXAMPLES Example 1. The configuration of the first embodiment of the present invention will be described with reference to FIG. 1 is a diagram showing a configuration of a first embodiment of the present invention.

Referring to FIG. 1, the first embodiment of the present invention comprises a controller 1, a digital / analog converter 2, an analog switch 5, resistors 6 and 7, and a reference voltage 8 whose output voltage is V _R. It is configured. In addition, 4 is an external measured voltage Vx.

The threshold value of the P0 terminal of the control device 1 is V _T
, Which is connected to the output side of the digital / analog converter 2 and the common terminal of the analog switch 5. Further, the P1 to P5 terminals of the control device 1 are digital output ports and are connected to each bit of the digital input terminals of the digital / analog converter 2.

The analog channel X of the analog switch 5 is connected to the measured voltage 4 via the resistor 6, the analog channel R is connected to the reference voltage 8 via the resistor 7, and the analog channel N is an unconnected terminal. The switching terminals SEL and INH are connected to the digital output ports S1 and S2 of the control device 1, respectively, and switch the channel according to an instruction from the control device 1.

If the resistance values of the resistors 6 and 7 are the same as the output impedance R of the digital / analog converter 2 and the internal resistance of the analog switch 5 is sufficiently smaller than R, the resistance 6 and the analog switch 5 are combined. The impedance R ₁ , the resistance 7 and the combined impedance R ₂ of the analog switch 5 can be approximated as follows.

R ₁ ≈R, R ₂ ≈R

Next, the operation of the first embodiment of the present invention will be described with reference to FIGS. 2, 3 and 4. Figure 2
3 is a flowchart showing the operation of the first embodiment of the present invention. FIG. 3 is a diagram showing an equivalent circuit when the analog switch 5 is connected to N in the first embodiment of the present invention. Further, FIG. 4 is a diagram showing an equivalent circuit when an analog switch is connected to X or R in the first embodiment of the present invention.

In steps 20 to 24, first, when the control device 1 connects the analog switch 5 to N, the first embodiment shown in FIG. 1 is represented by the equivalent circuit shown in FIG. Output data is 0, that is, all output ports P1 to P5 are "L"
When set to level (low level), the input port P0 is also "L"
It becomes a level. The logic level of the input port P0 is checked while incrementing the output data, and the value of the output data when switching from the "L" level to the "H" level (high level) is m _N.

Next, in steps 25 to 29, when the analog switch 5 is connected to R, the first embodiment shown in FIG.
Is represented by the equivalent circuit shown in FIG. However, the connected voltage is the reference voltage 8 (V _R). While incrementing the output data from 0, the logical level of the input port P0 is checked, and the value of the output data when switching from the “L” level to the “H” level is m _R.

In steps 30-34, the analog switch 5 is then connected to X, similarly represented by the equivalent circuit shown in FIG. However, the connected voltage is the measured voltage 4 (V _X ). While incrementing the output data from 0, check the logic level of the input port P0,
The value of the output data when switching from the “L” level to the “H” level is m _X.

In step 35, the measured voltage V _X is obtained from the following equation using the data m _N , m _R and m _X thus obtained and the reference voltage V _R.

V _X = {(2m _N −m _X ) / (2m _N −m _R )} V _R

The first embodiment of the present invention, as described above,
An input port P0 for inputting digital data and an output port P1 for outputting each bit of digital data of a plurality of bits
To P5 and a ladder resistor, which outputs an analog voltage corresponding to the digital data output from the control device 1, the output side of which is connected to the input port P0 of the control device 1 digital / analog. Converter 2
And an analog switch 5 whose output terminal is connected to the output side of the digital-analog converter 2, whose voltage input terminal to be measured is connected to the resistor 6, and whose reference voltage input terminal is connected to the resistor 7. is there.

Then, two input voltages of the measured voltage 4 and the reference voltage 8 are switched by the analog switch 5 and inputted.
Output data corresponding to the threshold value of the digital input port P0 when the analog switch 5 is connected to the measured voltage side and the digital input port P0 when the analog switch 5 is connected to the reference voltage side. The measured voltage 4 is calculated from the output data corresponding to the threshold value and the output data corresponding to the threshold value of the digital input port P0 when the analog switch 5 is not connected to either. To do.

That is, in the first embodiment, the analog switch input is of a 2-input switching type, one is connected to the measured voltage 4 via the resistor 6 and the other is connected to the reference voltage 8 via the resistor 7, and the analog switch is connected. The measured voltage 4 is calculated from the output data corresponding to the threshold value of the digital input port P0 when 5 is OFF, when it is connected to the measured voltage side, and when it is connected to the reference voltage side. I asked for it.

In the first embodiment, the threshold value of the digital input port P0 when the analog switch 5 is OFF,
In addition to the threshold value of the digital input port P0 when the analog switch 5 is connected to the measured voltage side, the threshold value of the digital input port P0 when the analog switch 5 is connected to the reference voltage side is obtained.

When the analog switch 5 is OFF, the analog voltage corresponding to the digital output data is directly applied to the digital input port P0. It is assumed that the output data is changed to check the state change of the digital input port P0, and the output data corresponding to the threshold value V _T is m _N. When the resolution (minimum value of D / A output voltage) of the digital / analog converter 2 is V _B , the digital input port P
The threshold value V _T of 0 is expressed by the following equation.

V _T = V _B · m _N

When the analog switch 5 is connected to the measured voltage side, the analog voltage corresponding to the output data and the voltage obtained by dividing the measured voltage V _X are applied to the digital input port P0. When the output impedance of the digital / analog converter 2 is R, the minimum resolution is V _B , the measured voltage is V _X , and the combined impedance of the resistance 6 and the resistance of the analog switch 5 connected to the measured voltage is R _1. , If the output data corresponding to the threshold value of the digital input port P0 is m _X , the threshold value V _T of the digital input port P0 is expressed by the following equation.

V _T = {R / (R + R ₁ )} V _X + {R ₁ / (R + R ₁ )} V _B · m _X

Further, when the analog switch 5 is connected to the reference voltage side, the output impedance of the digital / analog converter 2 is R, the minimum resolution (D / A output voltage minimum value).
Is V _B , the reference voltage 8 is V _R , and the combined impedance of the resistor 7 connected to the reference voltage 8 and the resistance of the analog switch 5 is R ₂ , output data corresponding to the threshold value of the digital input port P0. Is m _R , the threshold value V _T of the digital input port P0 is given by the following equation.

V _T = {R / (R + R ₂ )} V _R + {R ₂ / (R + R ₂ )} V _B · m _R

From the three equations of the threshold V _T when the analog switch 5 is OFF, when it is connected to the measured voltage side, and when it is connected to the reference voltage side, the threshold V _T and the resolution If V _B is erased, the measured voltage V _X can be calculated by the following equation.

V _X = {{(R + R ₁ ) m _N −R ₁ m _X } / {(R + R ₂ ) m _N −R ₂ m _R }} · V _R

Example 2. Reference In Embodiment 1 voltage V _R
However, the power supply voltage of the circuit is clear (usually,
5 V is used), the output impedance of the digital output port of the control device 1 is sufficiently smaller than the output impedance R of the digital / analog converter 2, and the rate of fluctuation of the power supply voltage is sufficiently smaller than the required accuracy,
It is not necessary to use the reference voltage.

FIG. 5 is a diagram showing the configuration of the second embodiment of the present invention. In the circuit shown in FIG. 5, the reference voltage 8 and the resistor 7 are removed from the circuit shown in FIG. 1, and the analog switch 5A has only one channel ON / OFF circuit, and accordingly, the channel switching signal line from the controller 1 is changed. Is one.

Next, the operation of the second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a flowchart showing the operation of the second embodiment of the present invention.

In steps 70 to 74, first, when the analog switch 5A is turned off, the second embodiment is represented by the equivalent circuit shown in FIG. At this time, the resolution V _B of the output voltage of the digital / analog converter 2 is represented by the following equation, where V _C is the power supply voltage and k is the number of digital input data bits of the digital / analog converter 2.

V _B = 2 ^−k × V _C

While the output data is incremented from 0, the logic level of the input port P0 is checked, and "L"
The output data when the level is switched to the "H" level is m _N.

Next, in steps 75 to 79, when the analog switch 5A is turned on, the second embodiment is changed to FIG.
It is represented by the equivalent circuit shown in. However, the connected voltage is the measured voltage V _X. The logical level of the input port P0 is checked while incrementing the output data from 0, and the value of the output data when switching from the "L" level to the "H" level is m _X.

In step 80, the data m _N , m _X obtained as described above and the digital / analog converter 2
The measured voltage V _X is obtained from the following equation using the resolution V _B or the power supply voltage V _C of

V _X = (2m _N −m _X ) V _B = (2m _N −m _X ) × 2 ^−k × V _C

The second embodiment of the present invention, as described above,
An input port P0 for inputting digital data and an output port P1 for outputting each bit of digital data of a plurality of bits
To P5 and a ladder resistor, which outputs an analog voltage corresponding to the digital data output from the control device 1, the output side of which is connected to the input port P0 of the control device 1 digital / analog. Converter 2
And an analog switch 5A whose output terminal is connected to the output side of the digital / analog converter 2 and whose measured voltage input terminal is connected to the resistor 6.

Output data corresponding to the threshold value of the digital input port P0 when the analog switch 5A is OFF, and output data corresponding to the threshold value of the digital input port P0 when the analog switch 5A is ON. It is characterized in that the voltage to be measured is calculated from the above.

Analog switch 5 used in the second embodiment
A is an analog element, but a transistor (ON / OF
Since only the F operation) is used, it is relatively easy to embed it in a digital IC, and it becomes easy even when multi-channel input is used.

According to the second embodiment, when the analog switch 5A is OFF, the analog voltage corresponding to the digital output data is directly applied to the digital input port P0. It is assumed that the output data is changed to check the state change of the digital input port P0, and the output data corresponding to the threshold value V _T is m _N. When the resolution of the digital / analog converter 2 (minimum value of D / A output voltage) is V _B , the threshold V _T of the digital input port P0 is expressed by the following equation.

V _T = V _B · m _N

When the analog switch 5 is turned on, the analog voltage corresponding to the output data and the voltage obtained by dividing the measured voltage V _X are applied to the digital input port P0. When the output impedance of the digital / analog converter 2 is R, the minimum resolution is V _B , the measured voltage is V _X , and the combined impedance of the resistor 6 connected to the measured voltage and the resistance of the analog switch 5A is R _1. , If the output data corresponding to the threshold value of the digital input port P0 is m _X , the threshold value V _{T of the} digital input port P0
Is expressed by the following equation.

V _T = {R / (R + R ₁ )} V _X + {R ₁ / (R + R ₁ )} V _B · m _X

When the analog switch 5A is OFF and when O
If V _T is erased from the formula of the threshold V _T when N, the measured voltage V _X can be obtained by performing the calculation of the following formula.

V _X = {m _N + (R ₁ / R) (m _N −m _X )} V _B

By using the Schmitt circuit as the digital input port P0 in the above-described first and second embodiments, it is possible to reduce the increase in current consumption near the threshold value.

Example 3. A third embodiment of the present invention will be described with reference to FIG. FIG. 7 shows the configuration of the third embodiment of the present invention. The third embodiment is a multi-channel input A / D converter. For the measured voltages 41 to 49,
The analog switch 5B is a multi-channel switching type of X1 to X9, and resistors 61 to 69 are connected between each input terminal of the analog switch 5B and each terminal of the voltage to be measured. The channel switching signal line of the analog switch 5B also requires a plurality of bits.

The operation of the third embodiment is the same as that of the second embodiment described above, in which the output data m _X is measured and the measured voltage V _X is calculated by switching to each of the channels X1 to X9.

In the third embodiment, the Schmitt circuit 9 is inserted before the digital input port P0. In a normal CMOS input circuit having an inverter structure, a large through current may flow in the CMOS internal circuit near the threshold value. Therefore, the Schmitt circuit 9 is inserted in the digital input section to prevent an excessive current.

The third embodiment of the present invention, as described above,
It has a multi-channel input switching type analog switch 5B corresponding to a plurality of measured voltages 41 to 49, and resistors 61 to 69 for connecting each input channel of the analog switch 5B and each measured voltage 41 to 49. . And
The plurality of measured voltages 41 to 49 are analog-to-digital converted by the same procedure as in the first and second embodiments.

By the way, in the above description of each embodiment,
Although the output data m _N , m _X , and m _R corresponding to the threshold value are obtained by incrementing from 0, they may be obtained by other dichotomy or the like.

[0061]

As described above, the A / D converter according to claim 1 of the present invention includes a controller having an input port for inputting digital data and an output port for outputting digital data of a plurality of bits, and a ladder. A digital / analog converter configured by a resistor to output an analog voltage corresponding to digital data output from the control device, the output of which is applied to an input port of the control device;
The output terminal is connected to the output side of the digital / analog converter, the voltage-under-measurement input terminal is connected to the first resistor,
An analog switch having a reference voltage input terminal connected to the second resistor is provided, and the control device switches between the two input voltages of the voltage to be measured and the reference voltage by the analog switch and inputs the voltage. The first output data corresponding to the threshold value of the input port when connected to the measured voltage, and the threshold value of the input port when the analog switch is connected to the reference voltage. Since the measured voltage is calculated from the corresponding second output data and the third output data corresponding to the threshold value of the input port when the analog switch is not connected to either, The voltage to be measured can be obtained by an arithmetic expression unrelated to the threshold value of the digital input circuit, the cost of the device can be reduced, and the digital IC can be easily formed. There is an effect that.

As described above, the A / D converter according to the second aspect of the present invention includes a controller having an input port for inputting digital data and an output port for outputting digital data of a plurality of bits, and a ladder resistor. A digital / analog converter configured to output an analog voltage corresponding to digital data output from the control device, the output of which is applied to an input port of the control device;
An analog switch having an output terminal connected to an output side of the digital-analog converter and an input terminal connected to a resistor;
The first corresponding to the threshold value of the input port in the case of FF
Output voltage and the second output data corresponding to the threshold value of the input port when the analog switch is ON, the voltage to be measured is calculated and obtained, so that it does not depend on the threshold value of the digital input circuit. The voltage to be measured can be obtained by an arithmetic expression, the cost of the device can be reduced, and the digital IC
There is an effect that it can be easily realized.

As described above, the A / D conversion device according to the third aspect of the present invention includes a control device having an input port for inputting digital data and an output port for outputting digital data of a plurality of bits, and a ladder resistor. A digital / analog converter configured to output an analog voltage corresponding to digital data output from the control device, the output of which is applied to an input port of the control device;
An analog switch having an output terminal connected to the output side of the digital / analog converter and having a plurality of measured voltage input terminals connected to each of a plurality of resistors; and the control device having a plurality of measured voltages. Is switched by the analog switch and input, first output data corresponding to the threshold value of the input port when the analog switch is connected to the measured voltage, and the analog switch Since the voltage to be measured is calculated from the second output data corresponding to the threshold value of the input port when not connected to any of the above, it is an arithmetic expression irrelevant to the threshold value of the digital input circuit. With this, the measured voltage can be calculated and obtained, the cost of the device can be reduced, and multi-channel input and digital IC can be easily achieved. To.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a flowchart showing the operation of the first embodiment of the present invention.

FIG. 3 is a diagram showing an equivalent circuit when the analog switch according to the first embodiment of the present invention is at N.

FIG. 4 is a diagram showing an equivalent circuit when the analog switch according to the first embodiment of the present invention is at X or R.

FIG. 5 is a diagram showing a configuration of a second embodiment of the present invention.

FIG. 6 is a flowchart showing the operation of the second embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of a third embodiment of the present invention.

FIG. 8 is a diagram showing a conventional A / D conversion device.

[Explanation of symbols]

 1 Control Device 2 Digital / Analog Converter 4, 41, 49 Measured Voltage 5, 5A, 5B Analog Switch 6, 61, 69 Resistor 7 Resistor 8 Reference Voltage 9 Schmitt Circuit

Claims (3)

[Claims] 1. A control device having an input port for inputting digital data and an output port for outputting digital data of a plurality of bits, and an analog voltage corresponding to the digital data output from the control device, the analog voltage being constituted by a ladder resistor. A digital / analog converter whose output is applied to the input port of the control device and an output terminal of which are connected to the output side of the digital / analog converter, and whose measured voltage input terminal is the first resistor And an analog switch having a reference voltage input terminal connected to the second resistor, wherein the control device switches between the two input voltages of the voltage to be measured and the reference voltage by the analog switch to input the voltage. A first voltage corresponding to the threshold value of the input port when the analog switch is connected to the measured voltage;
Output data, second output data corresponding to the threshold value of the input port when the analog switch is connected to the reference voltage, and the second output data when the analog switch is not connected to either. An A / D conversion device, characterized in that the measured voltage is calculated from third output data corresponding to a threshold value of an input port. 2. A control device having an input port for inputting digital data and an output port for outputting digital data of a plurality of bits, and an analog voltage corresponding to the digital data output from the control device, the analog voltage being constituted by a ladder resistor. And a digital / analog converter whose output is applied to the input port of the control device, and an analog switch whose output terminal is connected to the output side of the digital / analog converter and whose input terminal is connected to a resistor. The control device corresponds to a first output data corresponding to a threshold value of the input port when the analog switch is OFF, and a threshold value of the input port when the analog switch is ON. An A / D conversion device, characterized in that the voltage to be measured is calculated from the second output data. 3. A control device having an input port for inputting digital data and an output port for outputting digital data of a plurality of bits, and an analog voltage corresponding to the digital data output from the control device, the analog voltage being constituted by a ladder resistor. A digital / analog converter whose output is applied to the input port of the control device; an output terminal connected to the output side of the digital / analog converter; and a plurality of measured voltage input terminals An analog switch connected to each of the resistors, wherein the control device inputs a plurality of measured voltages by switching with the analog switch, and the input when the analog switch is connected to the measured voltage. The first equivalent to the port threshold
Of the measured voltage and the second output data corresponding to the threshold value of the input port when the analog switch is not connected to any of the measured voltages. An A / D conversion device characterized by: