JP3254897B2 - A / D converter - 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 converter (analog / digital converter) for measuring a voltage value of an externally supplied voltage to be measured.

[0002]

2. Description of the Related Art As an example of a conventional A / D converter, for example,
For example, there is one shown in FIGS. This has a period T
Clock pulse V₀And input a substantially triangular wave
Voltage V ₁And triangular wave generator 1
Output voltage V₁And the measured voltage V given from outside_INWhen
Are compared and input, and a substantially square wave voltage determined by these
V_TwoOp amp 2 as a comparator that outputs
Output voltage V of amplifier 2_TwoAnd the voltage to be measured V_INDesi
And a microcomputer 3 for measuring the
Have been.

[0003] Each configuration will be described below. The triangular wave generator 1 uses an integrating circuit composed of an operational amplifier 11, a capacitor 12, and resistors 13 to 17, and the operational amplifier 11
The clock pulse V is applied to the inverting input terminal 11a of the
₀ , a reference voltage _Vref determined by the resistors 14 and 15 is input from the non-inverting input terminal 11b, and a substantially triangular voltage V having a period T around the reference voltage _Vref is output from the output terminal 11c. Outputs ₁ .

That is, when the clock pulse V ₀ is high (“H”), the capacitor 12 is gradually charged, so that the voltage V ₁ decreases. Further, when the clock pulses V ₀ is low ( "L"), the capacitor 12 is gradually discharged, the voltage V ₁ was rises. Thus, voltages V _1, since repeated lowered and raised above, as shown in FIG. 4, is of a substantially triangular waveform of the reference voltage V _ref period T centered line.

[0005] Next, the operational amplifier 2, when the voltages V ₁ is input to the inverting input terminal 2a, voltages V ₁ and the non-inverting input terminal 2b
To the measured voltage V _IN input to the output terminal 2c.
And outputs the voltage V ₂ of the substantially square wave from.

[0006] That is, the voltage V _2, as shown in FIG. 4, when the voltages V ₁ is smaller than the measured voltage V _IN becomes "H", when the voltages V ₁ is greater than the measured voltage V _IN "L"
, Resulting in a substantially square waveform.

The microcomputer 3 inputs the voltage V ₂ and measures the time T ₁ from the lower limit of the voltage V ₁ to coincidence with the voltage V _IN , thereby obtaining the voltage V _IN.
Measure the digital value of. Note that the range of the measured voltage V _{IN that} can be measured is from the maximum value V _max of the voltage V ₁ to the minimum value V _max.
Range up to _min .

[0008]

[SUMMARY OF THE INVENTION] aforementioned A / D conversion apparatus, when measuring the measured voltage V _IN from a smaller voltage, reduce the minimum value V _min of the voltages V ₁ by lowering the reference voltage V _ref However, since the minimum value _Vmin has a limit, the measurement of the measured voltage V _IN also has a limit.

[0009] That is, the operational amplifier 11, as shown in FIG. 5, in general the output side is constituted by the transistors 41, 42 and 43, a transistor for decreasing the voltage V ₁ 41 and 42
Is completely turned on, since the voltage V _BE between the beta and the emitter of the transistor 41 and the voltage V _CES between the collector and the emitter of the transistor 42 are V _BE ≠ 0 and V _CES ≠ 0, the voltage V ₁ (= V _BE + V _CES ) cannot be reduced to about 0.8 V or less, and as shown in part A in FIG.
V is the limit.

For this reason, the clock pulse V0 becomes "H".
From and inverted to "L", the voltage V1, the capacitor 12
Undershoot under the influence of (see B in FIG. 6)
Thereafter, since the transistor 43 is turned on, the operation is quickly restored.

Therefore, since the voltage V ₁ becomes a curved line and does not have a normal good linearity when the voltage V ₁ is about 0.8 V or less as shown in a part C in FIG. 6, the time interval of “H” of the voltage V ₂ And the voltage V to be measured by the microcomputer 3 becomes smaller.
_IN measurement becomes difficult.

The present invention has been made in view of such a point, and an object of the present invention is to make a voltage output from a triangular wave generator have good linearity.
An object of the present invention is to provide an A / D converter capable of measuring a minute value of a voltage to be measured more accurately.

[0013]

In order to achieve the above object, an A / D converter according to the present invention comprises an inverting input of an operational amplifier.
A capacitor is connected between the
The clock pulse input to the inverting input terminal of the amplifier is
The voltage of the operational amplifier
A triangular wave generator output from the output terminal , a comparator for comparing and inputting the output voltage of the triangular wave generator with the voltage to be measured supplied from the outside and outputting a substantially square wave voltage, and an output voltage of the comparator And a microcomputer for measuring a digital value of the voltage to be measured,
The configuration is such that a resistor is provided between the output terminal of the triangular wave generator and the ground.

[0014]

According to the structure of the present invention, when the output voltage of the triangular wave generator rises after the undershoot occurs, it is difficult for the output voltage to rapidly rise due to the resistor, so that the resistance value of the resistor is adjusted. Thus, the voltage can be made a waveform having a rising gradient with good linearity.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. Note that the same components as those of the above-described conventional example are denoted by the same reference numerals, and description thereof will be omitted.

The difference from the conventional example is that a pull-down resistor 18 as a resistor is provided between the output terminal 11c of the operational amplifier 11, which is a component of the triangular wave generator 1, and the ground.

Next, the operation of this embodiment will be described with reference to FIG. Here, the triangular wave generator 1 will be described, and the description will be made in a state where the reference voltage _Vref is lowered.

The triangular wave generator 1 is connected to an inverting input terminal 11a of an operational amplifier 11 via a resistor 13 and outputs a clock pulse
Enter ₀ to output the substantially triangular voltage V ₁ of the period T from the output terminal 11c.

That is, when the clock pulse V ₀ is “L”, the capacitor 12 is gradually discharged, so that the voltage V ₁ increases. When the clock pulse V ₀ is “H”, since the capacitor 12 is gradually charged, the voltage V
₁ decreases until it reaches the limit value (part A in FIG. 2).
When the clock pulse V ₀ is inverted from “H” to “L”, the voltage V ₁ undershoots due to the influence of the capacitor 12 (part B in FIG. 2), and then the capacitor 12 is gradually discharged. Therefore, it rises (C section in FIG. 2). Accordingly, the voltage V ₁ repeats the above-described falling and rising, and thus has a substantially triangular waveform having a period T as shown in FIG.

In this embodiment, the pull-down resistor
By adjusting the 18 resistance of, when the voltages V ₁ rises after that caused an undershoot, it is possible to make it difficult rapidly return the voltages V ₁ as in the conventional example (see FIG. 6), the voltage can V ₁ is adjusted to the slope of the voltages V ₁ after the cause undershoot, as a result, it is possible to make the voltages V ₁ and the waveform of a good rising gradient linearity.

[0021] From the above, this embodiment can be the waveform of a good rising slope linearity of the voltages V ₁ after the voltages V ₁ caused the undershoot, the measured voltage V _IN is a small also, the time interval of "H" of the voltage V ₂ becomes larger compared with the conventional example, as a result, it is possible to measure the minute value of the measured voltage V _iN by a microcomputer.

[0022]

According to the A / D converter of the present invention, when the output voltage of the triangular wave generator rises after an undershoot occurs, the output voltage is hardly rapidly increased by the resistor. By adjusting the resistance value, the voltage can be made into a waveform having a rising gradient with good linearity. As a result, even if the voltage to be measured is minute, it can be measured more accurately by the microcomputer.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention.

FIG. 2 is an operation waveform diagram of the voltage.

FIG. 3 is a circuit diagram of a conventional example.

FIG. 4 is an operation waveform diagram of the voltage.

FIG. 5 is a partial circuit diagram showing an internal configuration of an operational amplifier of the triangular wave generator.

FIG. 6 is an operation waveform diagram of the voltage.

[Explanation of symbols]

1 Triangular wave generator 2 Operational amplifier 3 Microcomputer 18 Pull-down resistor V ₁ voltage V ₂ voltage V _IN measured voltage

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03M 1/00-1/88

Claims (1)

(57) [Claims] 1. Between an inverting input terminal and an output terminal of an operational amplifier
Is connected to the inverting input of the operational amplifier.
The clock pulse input to the end is charged and discharged by the capacitor.
Output from the output terminal of the operational amplifier as a substantially triangular waveform voltage.
A triangular wave generator, a comparator for comparing and inputting an output voltage of the triangular wave generator with a voltage to be measured supplied from the outside and outputting a substantially square-wave voltage, and a voltage for measuring the same by inputting the output voltage of the comparator. And a microcomputer for measuring the digital value of the A / D signal, wherein a resistor is provided between the output terminal of the triangular wave generator and ground.
Conversion device.