JPS61170139A - Digital-analog converter - Google Patents

Abstract

PURPOSE:To attain simple constitution and to improve the reliability by providing a constant current source, a load resistor connected in series therewith and a switch circuit and using a digital signal given to the switch circuit externally to changeover the switch circuit thereby controlling the number of load resistors. CONSTITUTION:The titled A/D converter consists of the constant current source 1, 7 resistors 2-8 connected in series and the switch circuit 9, digital signal lines i, j, k are connected to the input side of the switch circuit 9 and lines (a-h) are connected to the output side. The line (a) at the output side is connected to a connecting point between the constant current source 1 and the resistor 2 and connected to an output line (l). The the lines b, c...g are connected respectively to connecting points between the resistors 2 and 3, between the resistors 3 and 4, between the resistors 7 and 8, respectively and the line (h) is connected to the other terminal of the resistor 8. Thus, simple constitution is attained by utilizing that the flowing current is unchanged even when the load resistor of the constant current source is varied and the reliability is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a digital/analog converter (hereinafter referred to as a D/A converter) in a data processing device or the like.

Conventional technology Conventionally, the D/A converter in this building had multiple constant current sources.
It has been common to have a circuit that obtains an analog output corresponding to the digital quantity by controlling a current switch using a digital quantity supplied from the outside and selectively connecting the output of a constant current source to a current adder.

Therefore, in order to increase the resolution, many constant current sources are required. Therefore, the total number of components is large, and a lot of time is required for adjustment, which has the disadvantage of lowering reliability and increasing cost.

Problems to be Solved by the Invention The purpose of the present invention is to solve the above-mentioned drawbacks, namely, the number of components is large and adjustment requires a lot of time, resulting in decreased reliability and high cost. An object of the present invention is to provide a D/A converter.

Means for Solving the Problems The present invention d In order to solve the above-mentioned problems, one constant current source, a plurality of resistors connected in series, and a digital signal applied from the outside are used to control the resistors. This configuration employs a switch circuit that is selectively connected as a load resistance of a constant current source.

Operation Since the present invention is configured as described above, the switch circuit changes the added resistance value of the resistors connected in series according to an external digital signal to become the load resistance of the constant current source, and converts the analog value proportional to the load resistance value. It generates a voltage value on the output side.

Example Next, embodiments of the present invention will be described with reference to the drawings.

Referring to FIG. 1 showing an embodiment of the present invention, the D/A converter of the present invention includes a constant current source 1, seven resistors 2 to 8 connected in series, and a switch circuit 9. The switch circuit 9 has digital signal lines i, j, and k connected to its input side, and lines a to h connected to its output side. A line a on the output side is connected to a connection point between a constant power source l and a resistor 2, and further connected to an output line l. Then the lines b#C#...g are connected to resistors 2 and 3, respectively. Resistance 3 and 4. . . . A wire is connected to the other end of the resistor 8 at the connection point between the resistors 7 and 8.

Table 1 shows the inputs i, j, and output side of the switch circuit 9.
The relationship between a and h is shown, logic 0.1 is shown for digital inputs i and j, G is the ground potential, and areas without markings are open.

Table 1 Next, the operation of this embodiment will be explained with reference to FIG. 1 and Table 1.

First, the current of the constant current source 1 is assumed to be ■, and the resistance values of the resistors 2 to 8 are assumed to be R, -R. Now' tJ *k)=(0゜0
, O) are input, since a becomes the ground potential, l becomes the ground potential. Then ('1j@k)=(0,
0, 1) is input, b becomes the ground potential, so
Current ■ from constant current source 1 flows through 2. If the potential difference between l and the ground potential at this time is V/, then V/=R,
Becomes XI. Then (ttj*k)=(o*lt o
) is input, the current from l flows through 2 and 3 because C becomes the ground potential.

At this time, V/=(R20R3)I.

Considering the following in the same way, the relationship V'/='I x ΣRi holds true. Σ几i is a value determined by digital input. Therefore, it is possible to obtain a D/A converter that outputs a voltage having a certain relationship with the digital input.

The above is an explanation of the operation of this embodiment. By taking advantage of the fact that the flowing current does not change even if the load resistance of the constant current source is varied, it can be made into a simple II configuration, which is highly reliable and inexpensive. Effects of the Invention As explained above, according to the present invention, one constant current source, a load resistor connected in series with the constant current source, and a switch circuit are provided, and a switch can be connected from the outside. By adopting a simple configuration in which the number of connected load resistors is controlled by switching the switch circuit using a digital signal applied to the circuit,
This has the effect of providing a highly reliable and inexpensive /A converter.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention. l... Constant current source, 248... Resistor, 9
...Switch circuit, a-h...Output side line, t-k...Digital input line, l...
・−・Output line.

Claims (1)

[Claims] It is characterized by being composed of one constant current source, a plurality of resistors connected in series, and a switch circuit that selectively connects the resistor as a load resistance of the constant current source according to an externally applied digital signal. digital/analog converter.