JPS5933929A - Digital/analog converting circuit - Google Patents

Abstract

PURPOSE:To form the entire input/output characteristics as the N-power characteristic, by using N-set of D/A converters whose maximum value of the output is set by a reference input. CONSTITUTION:Input terminals D0-D3 (4-bit) of the D/A converters 1, 2 are connected in common, an output terminal OUT of the D/A converter 1 is connected to a reference input terminal Ref- of the D/A converter 2, a 0V voltage is applied to a reference input terminal Ref- of the D/A converter 1, a 5V voltage is applied to a reference input terminal Ref+ of the D/A converter 1 via a resistor R1, a 0V voltage is applied to a reference input Ref+ of the D/A converter 2, a 0V voltage is applied to the output terminal OUT of the D/A converter 1 and the reference input Ref- of the D/A converter 2 via a resistor R3, a 0V voltage is applied to the output terminal OUT of the D/A converter 2 via a resistor R4. The output Vout of the D/A converter 2 is VOUT=KX(D/15)<2>, where D is the input digital amount.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a digital-to-analog conversion circuit.

With the recent development of microcomputers, fields that were traditionally processed using analog circuits have been replaced with digital processing.
It is common practice to aim for higher functionality. In such cases, the final processed digital quantities must be converted into analog quantities. For example, a welding power source must specify voltage and current values, but in the case of a welding robot, the microcomputer in the robot controller digitally processes what voltage and current values to give. Ru. In order to indicate these digital current and voltage values with a meter, etc., they must be converted into analog quantities using a digital-to-analog conversion circuit.

Conventional configurations and their problems In a typical digital-to-analog converter (DAC), when an input is given in binary numbers, an output is obtained in the form of current or voltage, and the relationship between them is linear. In this type of DAC, the output resolution is determined by the lowest unit of the input binary number, and the output is extremely stable and has excellent reproducibility. In addition to this DAC, there are also DACs that use operational S/g null amplifiers to have functional characteristics such as exponential functions and square root functions. In practice, it is a little difficult because of the involvement of

In the field of DAC application, there is no difference in resolution at the output,
There are many cases where an amount proportional to the output value is sufficient. For example, in the above-mentioned command current value to the welding power source, it is meaningless to control using the difference as a basic unit, and it is better to use small current increments when the current value is small, and large current increments when the current value is large. This is a practical control. however,
Reproducibility,! Variations between J1 products must be strictly controlled.

In order to do this, it is required to combine the two advantages described in the conventional example. If a normal DAC is used with emphasis on accuracy, it will require a bit length equal to the maximum current value divided by the minimum increment value, and this will be an extremely wasteful use where the current value is large. Since DACs with a large bit length are expensive, the cost increases relative to the desired functionality.

OBJECTS OF THE INVENTION It is an object of the present invention to provide an inexpensive digital-to-analog conversion circuit that can make output resolution proportional to output value, has excellent reproducibility, has little variation between products.

Structure of the Invention The digital-to-analog conversion circuit of the present invention uses N DACs (N is an integer of 2 or more) whose maximum output value can be set by a reference input, and uses the output of the first stage DAC to convert the output of the second stage DAC. The reference input of the second stage DAC is determined as the reference input of the third stage DAC.
By determining a reference input of C and sequentially performing this process up to the Nth stage, the overall input/output characteristics are made to be N-th power characteristics.

Let me explain in more detail. Generally, a DAC has a reference input that determines the maximum output value, and the required maximum output level 1a is determined by this reference input.On the other hand, it is preferable to give a binary input and distribute the reference input proportionally. In the present invention, the DACs are arranged in series, the binary inputs are common, and the reference input is controlled by the output of the preceding DAC, which is a common usage. By doing this, for example, when two DACs are connected in series, the overall output becomes a multiplication of human power. Therefore, if N DACs are arranged in series, it becomes the Nth power.

DESCRIPTION OF EMBODIMENTS In the following embodiments, a digital-to-analog conversion circuit having square-law characteristics will be described.

Figure 1 is a 4-bit DAC used in the company example,
Digital Kugata has an input terminal. -D3 as a binary number, the reference potential V- is given to the reference input terminal Ref-, and the reference potential 7h is given to the reference input terminal Ref+, so that the reference input terminal Ref+ is the same as the reference input terminal Ref-. A current I is passed through the current limiting resistor R to the reference input terminal Ref+. flows in. At this time, the output terminal OU of the DAC
The inflow current I into T is I=Io・1no−・Song (1) ■. =02...Given by (2). D is the input digital quantity.

From equation .(.1), it can be seen that even if the binary input is constant, if the reference potential V+ or V- is changed, the output will be liquefied.

As shown in FIG. 2, the digital-to-analog conversion circuit of the embodiment has input terminals of DACs 1 and 2. -D3 are connected in common, the output terminal OUT of DAC1 is connected to the reference input terminal Ref- of DAC2, and the reference input terminal R of DAC1 is connected.
Applying the voltage of QV to ef-, the reference input terminal Re of the DAC
A voltage of 5V is applied to f+ via a resistor R□, a voltage of QV is applied to the reference input terminal Ref1 of DAC2, and a voltage of OV is applied to the output terminal OUT of DAC1 and the reference input terminal Ref- of DAC2 via a resistor R3. , and a voltage of oV is applied via the output terminal OUTK resistor R4 of the DAC2.

In FIG. 2, the final output is given as a negative value, but this is to simplify the explanation of the circuit, and if an operational amplifier is used here, this voltage value can be arbitrary. Further, in order to simplify the explanation below, the resistance values of the resistors R to R4 are all assumed to be the same R, but they do not need to be the same.

Find the relationship between the human output of this digital-to-analog conversion circuit. First, regarding the front-stage DAC 1, the following holds true: (4) o = 5/R. For the latter stage DAC2K, vOUT=R
-12...Song (5) l2=Io2・■・・・・・・(6) Io2= Vl/R・・−・−(71 v1= Rx T 1・−・−f8] is established. I , I is the reference 01 02 current of DAC1 and DAC2. By sequentially substituting the above equations, can be obtained.

Since D is the input percentage and vOUT is the output, it is a square characteristic.

Figure 3 shows this as Gwa 7. The resolution at the output is given by the differential coefficient 1.D of equation (9), which satisfies the intent of the invention.

In this way, the digital-to-analog conversion circuit of this embodiment gives the same binary input to DAC1 and DAC2K, and the reference voltage of DAC2 in the subsequent stage is given by the output of DAC1 in the previous stage, so the resolution of the output is It can be made proportional to the square of the square, and unlike conventional systems that use operational amplifiers, the resolution can be strictly determined, resulting in excellent reproducibility.
is inexpensive because it does not require a large number of bits.

Effects of the Invention The digital-to-analog converter circuit of the present invention can make the output resolution proportional to the Nth power of the output and make the input/output characteristics Nth power characteristics, and also reduces reproducibility and variations between products. It has the advantage of being less expensive and less expensive.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a DAC used in an embodiment of the present invention, Figure 2 is a circuit diagram of a digital-to-analog conversion circuit, and Figure 3 is a circuit diagram of a digital-to-analog conversion circuit.
The figure shows the person's output characteristics. 1.2...DAC%Do~D3...Input terminal, R
ef-...Reference input terminal, OUT...Output terminal Fig. 1 □D Fig. 3

Claims (1)

[Claims] The digital input terminals of each bit of N digital-to-analog converters (N is an integer of 2 or more) whose maximum output value can be set by the reference input are connected in common, and the Digital-to-analog conversion circuit with cascade connection between reference input terminal and output terminal.