JPS5934191Y2 - DA conversion circuit - Google Patents

Description

[Detailed description of the invention] This invention relates to a means for correcting the characteristics of the analog output of a DA conversion circuit to a desired nonlinearity. An object of the present invention is to provide a DA conversion circuit capable of providing a nonlinear analog output having characteristics opposite to the above.

When converting a digital signal into a current or voltage value using a DA converter that converts a digital signal into an analog signal, weighting is performed using a binary system, that is, 1.2, 4,
By adding current or voltage values such as 8..., an analog output is obtained.

Figure 1 shows a conventional DA for obtaining analog output of current value.
This is a circuit diagram of a conversion circuit, showing a case where the number of bits is 4.

In this circuit, when the switching element S1 is turned on by the digital input of the first bit, a current flows;
Hereinafter, when the second bit switching element S2 is turned on, the current 2I flows through the third bit switching element S2.
When bit 3 is turned on, current 4I flows, and when switching element S4 of the fourth bit is turned on, current 8I flows.

Note that the four current sources provided according to the weighting of each bit are a common power source E.

and constant current resistors R1, R2, R3, and R4.

Therefore, the current i is an analog output obtained by adding the above current values.

is io = 84 (8I) +83 (4I) 182 (2
I)+S, (I)...■ It is represented by i in Figure 2.

It exhibits linear characteristics as shown in .

Such a linear analog output is suitable for linear loads, but if you want to control nonlinear loads with it, you may want to correct the nonlinearity of the load by some means to bring it closer to linearity. .

For example, when lighting a light emitting diode with a current output that has been converted to DA, the relationship between the drive current and the light intensity of the light emitting diode is nonlinear. element is used.

However, such nonlinear elements generally have the disadvantage of large variations in temperature characteristics and other characteristics, and lack of stability.Also, there is not always an element with characteristics opposite to a given nonlinear load. In some cases, only insufficient correction or no correction can be made at all.

This idea is to solve this problem,
The analog output of the DA conversion circuit is designed to have desired nonlinear characteristics.

FIG. 3 shows a circuit diagram of an embodiment of the DA converter circuit according to this invention. In response to the digital input of the first bit, a current 2 is caused to flow through the switching element S1, and then a current 2I is caused to flow through the switching element S2 of the second bit. , a current 4I flows through the third bit switching element S3,
This circuit is similar to the conventional circuit in that these current sources include constant current resistors R1, R2, and R3 and a common power source Eo.

However, in the circuit of the embodiment, a power supply E1 is added to increase the above-mentioned current I by J when the fourth bit is turned on, and the switching element 84' is turned on by the digital input of the fourth bit. , the lower bits, the first . Second. The current flowing to the third bit is set to I+J and 2 according to the weighting of each bit.
Increase to (I+J)4(I-t-J).

Next, when the fourth bit turns on, switching element S4
Therefore, a current also flows to the fourth bit itself, but the current value in this case is set to I'=8I...■ in order to maintain continuity with the current added value by the lower bit, and The value of the resistor R4 is determined so that the above current flows using the power source Eo+E1.

The diode D is provided to prevent the power source E from being short-circuited by the switching element 84'.

Therefore, the current i flowing in the circuit of the embodiment after the fourth bit is turned on is i, =S4 I'+53(4(I+J))+52(2
(I-+-J)) +s1(I+J)...■, and its characteristics are shown at 11 in FIG.

That is, the current output i in FIG.

changes to the value of current 11 after the fourth bit is turned on, and its output characteristic becomes nonlinear in the form of a polygonal line.

Although the above embodiment describes the case where the most significant bit is corrected once, this invention is not limited to this, and each bit other than the least significant bit may be corrected multiple times as necessary. Correction can also be made, and furthermore, by changing the value of the current correction value A, a broken line of a desired shape can be obtained.

Figure 4 shows the characteristics of this embodiment when the third and fourth bits are corrected twice and the value of j is changed each time. Compared to the characteristics, more detailed corrections are made to the characteristics.

Furthermore, in the above explanation, the case where a current value is obtained as an analog output has been explained, but in order to obtain a voltage value, for example, the terminal voltage of the load resistor RL can be taken out. It is no different from the case of .

As described above, the DA conversion circuit according to this invention corrects the current or voltage value generated in the lower bits than the specific bit by a desired amount according to the weighting of the binary system when the digital input for a specific bit is turned on. Moreover, by setting the current or voltage value of a specific bit to a value that maintains continuity, the characteristics are changed in a polygonal manner with the operation start point of the specific bit as a boundary. It is something to do.

Therefore, by repeating such correction, it is possible to obtain an analog output with characteristics extremely close to the desired nonlinear characteristics, and furthermore, by increasing the number of bits and the number of corrections, it is possible to further improve the similarity of characteristics. be.

According to this invention, as mentioned above, an analog output having desired nonlinear characteristics can be easily obtained, so by applying an output with opposite characteristics to a nonlinear load such as a light emitting diode, a digital output can be obtained. It is possible to control the illuminance in proportion to the signal, and there is no need to use a separate compensation element, and since the compensation action is performed in the digital circuit, it is possible to control the illuminance in proportion to the signal. Compared to , it is less affected by temperature characteristics, etc., and the stability of operation is improved.

Therefore, it is extremely suitable as a control source when controlling a signal system using a photocoupler that combines a light emitting diode and a photoelectric element such as a CDS. This has the advantage of being highly applicable as a signal system control means.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional DA converter circuit, Figure 2 is a characteristic diagram of analog output between the conventional one and the one based on this invention.
FIG. 3 is a circuit diagram of a DA converter circuit showing an embodiment of this invention, and FIG. 4 is a characteristic diagram of analog output of another embodiment. Eo, El...Power supply, Sl, S2 t S3
t S4 "" Switching element in the DA conversion circuit, R1t R29R3v R49R4...constant current resistance, D...diode, RL...load resistor

Claims (1)

[Scope of utility model registration request] In a DA converter that uses digital input to obtain an analog output in which current or voltage values are added according to the respective weights of multiple bits, a variable means is provided for a common current or voltage source for each bit, and a specific bit is When the digital input to is turned on, the variable means applies a correction value proportional to binary weighting to each current or voltage value of the lower bits than the specific bit, and The current or voltage value is set to a value that maintains continuity with the added value before correction, and the analog output obtained by adding the current or voltage values of the above multiple bits exhibits nonlinear characteristics with respect to the digital input. A DA characterized by being configured in
conversion circuit.