JPH0358628A - D/a converter - Google Patents

Abstract

PURPOSE:To correct dispersion in the resistance by providing plural switching elements in parallel connection with a prescribed resistive element among plural resistive elements and a storage element storing a data controlling properly the switching element. CONSTITUTION:A data controlling on/off of switching elements 5-10 is written in a storage element 4 and the on/off of the switching elements varies the resistance. Then at the design, the resistors are selected as R=R20=R21, 2R=R 11+R12=R14+R15=R17+R18=R22. Then the switching elements 5, 7, 9 are turned off and the switching elements 6, 8, 10 are to be turned on in the absence of dispersion due to diffusion in the resistance. When the dispersion is caused in the increasing direction of the resistance, all the switching elements 5-10 are turned on. Thus, the resistance dispersed due to diffusion is corrected and a highly accurate D/A converter is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a D/A converter, and particularly to a ladder-type D/A converter that is most suitable for applications requiring a highly accurate output level.

[Conventional technology]

To begin with, a D/A converter is a circuit that inputs multiple digital signals and outputs and supplies a current or voltage representing the corresponding analog value.There are various types, but the ladder type D The /A converter is one of them, and a conventional example of a 3-bit converter is shown in FIG. In Figure 2, book D/
The configuration of the A converter is as follows: digital input signals I4, I5
, I6 are received by inverters 24, 25.26, the outputs of these inverters 24, 25.26 are used as reference voltage sources, and resistive elements 2 with a resistance value of 2R are connected to these, respectively.
7, 28.29 and these resistance elements 27, 28.29
A resistance element 30, 31 with a resistance value R, a resistance element 32 with a resistance value 2R, and an output terminal 33 are provided.

For example, if a digital signal such that (I4, I5, I6) is (0, 1.1) is input, the equivalent circuit shown in FIG. 3 is obtained. In the figure, ■ is a reference voltage source. First, the combined resistance of the resistive elements 29 and 32 is equal to a resistor having a resistance value of 2R connected in parallel to the contact i-GND, so according to Ohm's law, it becomes l R l . Similarly, the combined resistance value of resistance elements 28, 29, 31.32 is also
It becomes l B + .

Therefore, the combined resistance between the contact g and GND is 2R. From the above results, the following formula is obtained.

If the output voltage V out is determined in the same manner for other digital input signals (I4, I5, I6), the output level as shown in the truth value display in FIG. 4 will be obtained.

[Problem to be solved by the invention]

When the above-described conventional ladder-type D/A converter is built into a semiconductor integrated circuit, the resistance value differs from the designed resistance value due to variations during diffusion. Therefore, an error occurs between the predicted output level and the actual output level. Moreover, it has the disadvantage that this error cannot be corrected after diffusion.

SUMMARY OF THE INVENTION An object of the present invention is to provide a D/A converter in which the above-mentioned drawbacks are solved and variations in resistance values can be corrected.

Means for Solving Problem C] The D/A converter of the present invention has first to nth reference voltage sources each receiving a digital signal and outputting a reference voltage;
A series body of a plurality of resistance elements each having one end connected to the output of the first to nth reference voltage sources, and (n-1) resistance elements connecting the other ends of the series body. Prepare,
a resistance element is provided between the other end of the series body connected to the nth reference voltage source and ground, and the other end of the series body connected to the first reference voltage source is used as an output terminal; ] connected in parallel with a predetermined resistance element among the plurality of resistance elements;
The present invention is characterized in that it includes a switching element to an n-th switching element, and a storage element that stores data for appropriately controlling the switching element.

? Example〕 Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing a 3-bit ladder type D/A converter as a D/A converter according to an embodiment of the present invention. In the same figure, in this embodiment, digital input signals II, I2, I
The outputs of inverters 1, 2.3, which respectively receive 3, are used as reference voltage sources, and resistance elements 11, 14 are connected in series thereto.
, 15; 12, 16, 17; 13, 18. 19, and the resistance elements 20, 2 connected between the other ends of these resistance elements.
1, and a resistance element 22 whose one end is connected to GND, switching elements 5 to 10 connected in parallel to each of the resistance elements 14 to 17, and a memory element 4 made of, for example, FROM. This memory element 4 has
Data for controlling on/off of the switching elements 5 to 10 can be written therein.

At this time, the total resistance between contact a and contact b is R. Then, when both switching elements 5 and 6 are turned off, R o ”
R l■ + R l 2 + R + 3. Also, Sui 5-1? When only the switching element 6 is turned on, a short circuit occurs between contact a' and contact b, resulting in Ro'': R11+R1■.

However, it is assumed that the resistance of the switching element can be ignored. The same applies in the explanation below. In this way, the resistance value can be varied by switching the switching element between on and off. Therefore, at the time of design, R=R20=R21, 2R=R1
1+R12=R14+R15=Rl7+R1 8=R2
Set it to 2. Then, if there is no variation in diffusion, switching elements 5, 7.9 may be turned off and switching elements 6, 8.10 may be turned on. Further, when the diffusion varies in the direction of increasing the resistance value, all of the switching elements 5 to 10 are turned on.

On the other hand, when the diffusion varies in the direction of decreasing, all switching elements 5 to 10 may be turned off.

Furthermore, since the way of diffusion varies between contacts a and b, between contacts C and contacts d, and between contacts e and f, the switching elements can be turned on and off accordingly.

6- Then, by writing control data for the switching elements 5 to 10 connected in parallel to the resistance elements 14 to 19 into the memory element 4, an accurate output level can always be obtained once tested. By increasing the number of resistance elements connected in parallel with the data output line of the memory element 4 and the switching element, and dividing each resistance value into smaller values, finer adjustment can be made and accuracy can be further improved.

By configuring in this way, it is possible to correct the resistance value that varies due to diffusion, and a highly accurate D/A converter can be obtained.

〔Effect of the invention〕

As described above, the present invention has the effect of providing a highly accurate D/A converter by being able to adjust the output level after completion of diffusion.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a D/A converter according to an embodiment of the present invention, Figure 2 is a circuit diagram of a conventional D/A converter, and Figure 3 shows (I4, I5, I6) of Figure 2. To each (“I L I+,”
FIG. 4 is a diagram showing the relationship between the input data and the output level of the circuit of FIG. 2. 1, 2, 3, 24, 25.26... Inverter, 4... Writable storage element, 5 to 10
......Switching element, 23.33...
・Output terminals, 11 to 22. 27 to 32...
Resistance element.

Claims (1)

[Claims] first to nth reference voltage sources each receiving a digital signal and outputting a reference voltage; a series body of a plurality of resistance elements each having one end connected to the output of the first to nth reference voltage sources; (n-1) resistance elements connecting the other ends of the series body, the resistance element being provided between the other end of the series body connected to the n-th reference voltage source and ground; , the other end of the series body connected to the first reference voltage source serves as an output terminal, and first to nth switching elements are connected in parallel with a predetermined resistance element among the plurality of resistance elements; ,
A D/A converter comprising: a memory element that stores data for appropriately controlling the switching element.