JP2985815B2 - Constant voltage circuit and DA conversion circuit using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant voltage circuit for dividing a voltage by a resistor to obtain a constant voltage, and more particularly to a constant voltage circuit having a variable resistor and a fixed resistor. The present invention relates to a constant voltage circuit controlled by a comparator for comparing these outputs and a DA (digital / analog) conversion circuit utilizing characteristics of the constant voltage circuit.

[0002]

2. Description of the Related Art An example of a conventional constant voltage circuit is disclosed in
There is a reference voltage generation circuit as disclosed in Japanese Patent Publication No. 175742/1995. This reference voltage generation circuit generates a reference voltage based on the voltage between the base and the emitter of the transistor.

As another example, Robert. A. Peas's document (IEEE 1990, BCTM 9.3-2)
In some cases, a reference voltage is generated based on a bandgap voltage as shown in pages 14 to 218).

[0004]

In this conventional constant voltage circuit, a reference voltage is generated based on characteristics of a transistor element such as a base-emitter voltage and a band gap voltage. To make things
There is a disadvantage that the manufacturing process needs to be finely controlled, and that it is easily affected by variations in the manufacturing process and variations in completed transistors, particularly when a CMOS process is used.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned drawbacks, a constant voltage circuit according to the present invention is configured to obtain a constant voltage output by dividing a voltage between a variable resistance element and a fixed resistance element. And two comparators having the constant voltage output signal as a common input, and a comparator having the output of the amplifier as a comparison input. And the magnitude relationship between the amplified outputs of the two amplifiers is inverted with the required constant voltage value as the boundary input value.

Further, one of the two amplifiers is constituted by a linear amplifier and the other is constituted by a non-linear amplifier, and an input voltage value at which each amplification characteristic curve intersects at one point is set to a required constant voltage value.

Further, of the two amplifiers, one is constituted by a linear amplifier and the other is constituted by a non-linear amplifier, and the amplification characteristic of the linear amplifier is variably controlled so that the input voltage value at which each amplification characteristic curve intersects at one point is obtained. And the required constant voltage value.

The variable resistance element is constituted by a MOS transistor, and the resistance between the source and the drain is controlled by the gate input voltage, so that the resistance is variably controlled.

Further, another fixed resistance element is connected in parallel with the variable resistance element from the constant voltage output terminal side of the fixed resistance element to form a voltage dividing circuit.

Further, the relationship between the digital value input and the constant voltage circuit output in these constant voltage circuits is used for digital-to-analog (DA) conversion to form a DA conversion circuit.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the constant voltage circuit according to the first embodiment of the present invention. In FIG. 1, 1 is a variable resistance element, 2 is a fixed resistance element, 3 is a terminal for outputting a required constant voltage from a voltage dividing point 30, 4 is a linear amplifier, 5 is a non-linear amplifier, 6 is a comparator, 7 is a comparator. The terminals to which the divided voltage is applied are shown. Both the linear amplifier 4 and the non-linear amplifier 5 receive the voltage at the voltage dividing point 30, and the output of each amplifier is used as the comparison input of the comparator 6. The resistance value of the variable resistance element 1 is controlled by the comparison result output signal of the comparator 6.

FIG. 2 shows a linear amplifier 4 and a nonlinear amplifier 5.
5 is a characteristic curve showing the amplification characteristic of the. In FIG. 2, the input voltage Va at point A where these characteristic curves intersect at one point is a required constant voltage value. When the input voltage is smaller than Va,
The output of the linear amplifier is greater than the output of the nonlinear amplifier,
When the input voltage is higher than Va, the magnitude relationship is reversed.

Next, the operation of the constant voltage circuit will be described.
Immediately after the power is turned on, the resistance value of the variable resistance element 1 is sufficiently larger than the resistance value of the fixed resistance element 2, and the voltage at the voltage dividing point 30 is generally smaller than Va, so that the input voltage to the amplifier is also smaller than Va. . At this time, the comparison result output of the comparator 6 becomes an active level, and the resistance value of the variable resistance element 1 becomes sufficiently smaller than the resistance value of the fixed resistance element 2 by the comparison result output signal. The voltage is Va
To a larger value. At this time, since the input voltage of the amplifier also becomes a value larger than Va, the magnitude relation of the output is reversed, and the output of the comparator 6 is also reversed. Then, the resistance value of the variable resistance element 1 becomes a large value again, and the voltage at the voltage dividing point 30 becomes a value smaller than Va. By repeating such inversion operation, the voltage at the voltage dividing point 30 eventually approaches Va and converges. At this time, the output of the comparator 6 is an intermediate level output voltage that is controlled to a variable resistance value such that the voltage of the voltage dividing point 30 becomes Va so that the resistance is divided. This convergence voltage Va becomes a required constant voltage output value.

Next, a second embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram of a constant voltage circuit according to a second embodiment of the present invention. In FIG. 3, reference numeral 41 denotes a digital signal input 8, which is a linear amplifier whose amplification characteristic is controlled, such as selecting a feedback resistance network of an operational amplifier and controlling a feedback resistance value to select a gain. This is a linear amplifier. Other components are the same as those in FIG. By changing the input value of the digital signal, the amplification characteristic straight line of the linear amplifier changes from the straight line 1 to the straight line 2 as shown in FIG. 4, for example, and the intersection with the characteristic curve of the nonlinear amplifier moves from the point A to the point B. I do. Thus, by changing the input voltage at the intersection from Va to Vb, the required constant voltage value can be changed from Va to Vb, and the constant voltage output value can be variably controlled.

Next, a third embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 shows an example in which the constant voltage circuit of FIG. 3 is used as a DA (digital / analog) conversion circuit. A digital signal input to a linear amplifier is converted to a digital input of the DA conversion circuit, and a constant voltage output is converted to DA. FIG. 3 is a block diagram of a DA conversion circuit which is an analog conversion output of the circuit. The relationship between the digital value and the analog value is determined from the amplification characteristic curves of the linear amplifier 41 and the nonlinear amplifier 5.

[0018]

As described above, the constant voltage circuit of the present invention
The input voltage value at the point where the amplification characteristic curves of the linear amplifier and the non-linear amplifier intersect at a single point is set to a required constant voltage value. Therefore, the input voltage value is hardly affected by variations in the characteristics of the transistor elements and the like. Thus, there is an effect that the circuit can be easily configured.

[Brief description of the drawings]

FIG. 1 is a block diagram of a constant voltage circuit according to a first embodiment of the present invention.

FIG. 2 is a characteristic curve diagram of the amplifier of the constant voltage circuit according to the first embodiment of the present invention.

FIG. 3 is a block diagram of a constant voltage circuit according to a second embodiment of the present invention.

FIG. 4 is a characteristic curve diagram of the amplifier of the constant voltage circuit according to the second embodiment of the present invention.

FIG. 5 is a block diagram of a DA conversion circuit according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Variable resistance element 2 Fixed resistance element 3 Constant voltage output terminal 4 Linear amplifier 5 Nonlinear amplifier 6 Comparator 7 Terminal for applying divided voltage 8 Digital signal input 9 Data buffer 10 Digital conversion input 11 Analog conversion output

Claims (9)

(57) [Claims] 1. A constant voltage circuit in which a voltage is divided by a variable resistance element and a fixed resistance element to obtain a constant voltage output, two amplifiers having the constant voltage output signal as a common input, and these amplifiers And a comparator having the output of the comparator as a comparison input, wherein the resistance of the variable resistance element is variably controlled by the output of the comparator, and a required constant voltage value is set as a boundary input value, and the two constant values are used as the boundary input value. A constant voltage circuit characterized in that the magnitude relationship between the amplification outputs of the amplifiers is inverted. 2. One of the two amplifiers is a linear amplifier,
2. The constant voltage circuit according to claim 1, wherein the other is constituted by a non-linear amplifier, and an input voltage value at which each amplification characteristic curve crosses at one point is a required constant voltage value. 3. One of the two amplifiers is a linear amplifier,
The other is constituted by a non-linear amplifier, and by variably controlling the amplification characteristics of the linear amplifier, the input voltage value at which each amplification characteristic curve crosses at one point is set to a predetermined constant voltage value. The constant voltage circuit according to claim 1. 4. One of the two amplifiers is a linear amplifier,
The other is constituted by a non-linear amplifier, and the amplification characteristic of the linear amplifier is variably controlled by digital value input so that the input voltage value at which each amplification characteristic curve intersects at one point is set to a required constant voltage value. The constant voltage circuit according to claim 1, wherein: 5. A variable resistance element comprising a MOS transistor, wherein a resistance value between a source and a drain is controlled by a gate input voltage to variably control the resistance value. The constant voltage circuit according to claim 1, 2, 3, or 4. 6. A voltage dividing circuit in which another fixed resistance element is connected in parallel with the variable resistance element from the constant voltage output terminal side of the fixed resistance element to constitute a voltage dividing circuit. The constant voltage circuit according to claim 1, 2, 3, 4, or 5. 7. The relationship between a digital value input and a constant voltage circuit output in the constant voltage circuit according to claim 4,
A DA converter circuit used for analog (DA) conversion. 8. The DA converter according to claim 7, wherein the constant voltage circuit is the constant voltage circuit according to claim 5. 9. The DA converter according to claim 7, wherein the constant voltage circuit is the constant voltage circuit according to claim 6.