JPH0837437A - Digital variable resistor - Google Patents

Abstract

PURPOSE:To obtain the variable resistor in which the resistance is surely and easily adjusted by providing plural resistive elements of series connection connected in parallel to plural short-circuits set to be short-circuited or open depending on a state of an applied signal. CONSTITUTION:A rectangular case 11 is provided with input terminals 12-14 receiving a control signal, a latch terminal 15, a power supply input terminal 16, resistor output terminals 17, 18 and a ground terminal 19. Input terminals A0-A2 correspond to bits of a 3-bit control signal and receive a level corresponding to the control signal. An H level signal is outputted to one of output terminals Y0-Y7, e.g. Y1 and an L signal is outputted to the other terminals depending on the combination of the input terminals A0-A2 receiving the signal. In this case, a light emitting diode D1 of a short-circuit S1 is not lighted. A diode D1 of other short-circuits S0, S2-S7 is lighted. The illuminated light is received by a photo diode D2, an anode and a cathode of the D2 is conductive and short-circuited. Thus, only the resistor R1 is connected between the resistor output terminals 17, 18 and the resistance between the terminals 17, 18 is decided. The combinations of the resistors R0-R7 to be short-circuited are changed depending on the control signal received by the input terminals A0-A2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital variable resistance device which changes a resistance value connected between predetermined terminals by a control signal applied from the outside.

[0002]

2. Description of the Related Art Conventionally, there is, for example, a trimmer potentiometer as a device for changing a resistance value connected between predetermined terminals. Here, the trimmer potentiometer will be described with reference to FIG. FIG. 4 shows an equivalent circuit, for example, a resistor R is connected between the terminals A and C. The tip of the output terminal B slides on the resistor R. According to this configuration, the tip of the output terminal B has the resistance R
For example, the resistance value between the output terminal B and the terminal A changes depending on the position at which the output terminal B is connected. The tip of the output terminal B is connected to the resistor R
When sliding on, it is performed, for example, by rotating an adjusting screw provided on the trimmer potentiometer.

Therefore, when adjusting the level of the optical output of the optical transmitter module using the trimmer potentiometer, the resistance value is changed by rotating the adjusting screw while measuring the optical output with the optical level meter. Then, the adjusting screw is fixed in a state where a predetermined light output is obtained.

For this reason, when the trimmer potentiometer is used, it is necessary to rotate the adjusting screw and fix the adjusting screw. Further, it is difficult to automate the adjustment of the resistance value due to the rotating work and the fixing work of the adjusting screw. In addition, the adjusting screw may move over time, and the set resistance value may change. There are also problems such as an increase in contact resistance and the generation of sliding noise. Further, when it is used as an audio volume or the like and is remotely controlled by a remote controller, a power source such as a servo motor is required, and a circuit for controlling these power sources is also required.

There is also a method of using a D / A converter when the resistance value is changed by an external control signal.
A method of changing the resistance value using the D / A converter will be described with reference to FIG.

The D / A converter is provided with, for example, four input terminals a to d. Resistors having resistance values R, 2R, 4R, and 8R are connected to the input terminals a to d, respectively. The input terminals ad are two operational amplifiers A
1 and A2.

With the above structure, a control signal is applied to the input terminals a to d. At this time, the resistance value connected to the input side of the operational amplifier A1 changes due to the input terminals a to d to which the signal is applied, and the output voltage of the output terminal OUT changes.
Then, the change in the output voltage is converted into the change in the resistance value.

The method using the D / A converter requires a device for converting a change in voltage into a change in resistance value. Also,
Since an operational amplifier is used, the operation tends to become unstable due to the influence of temperature changes and external noise.

[0009]

As described above, in the method using the trimmer potentiometer, it is difficult to automate the work of adjusting the resistance value, and there are problems such as increase in contact resistance and occurrence of sliding noise. . It is also difficult to change the resistance value by remote control.

In addition, the method using the D / A converter requires a device for converting a voltage into a resistance and uses an operational amplifier, so that the operation becomes unstable due to the influence of temperature change and external noise. Cheap.

The present invention solves the above-mentioned drawbacks, and an object of the present invention is to provide a digital variable resistance device in which the resistance value can be adjusted reliably and easily.

[0012]

A digital variable resistance device of the present invention is connected in parallel to a plurality of short-circuit circuits which are short-circuited or open depending on the state of an applied signal, The whole is composed of a plurality of resistance elements connected in series.

Further, the short circuit is composed of a combination of a light emitting diode and a photodiode.

[0014]

According to the above construction, a plurality of short-circuit circuits that are short-circuited or opened by a control signal applied from the outside are provided, and the short-circuit circuits are arranged in parallel and in series as a whole. A plurality of resistance elements are connected. Further, the resistance output terminals are connected to both ends of the plurality of resistance elements connected in series. Then, in accordance with the value of the control signal, one of the plurality of short-circuit circuits is brought into a short-circuited state or an open state, the resistance element connected between the resistance output terminals at both ends is changed, and the resistance value is changed.

According to this structure, since the trimmer potentiometer is not used, the work of adjusting the resistance value can be automated, and there is no problem such as an increase in contact resistance or the occurrence of sliding noise. Further, the resistance value can be changed accurately and easily by remote control. Further, since no operational amplifier is used, there is no influence of temperature change or external noise, and a digital variable resistance device in which resistance value adjustment is reliable and easy can be obtained.

When a light emitting diode and a photodiode are combined as a short circuit, control of a short circuit state and an open state can be reliably performed.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

Reference numeral 11 denotes a rectangular case. The case 11 has input terminals 12 to 14 to which a control signal is input, a latch terminal 15, a power supply input terminal 16, a resistance output terminal 17, and 1.
8 and a ground terminal 19 are provided.

With the above construction, the control signal for setting the resistance value is applied to the input terminals 12-14. Each of the input terminals 12 to 14 corresponds to each bit of the control signal represented by, for example, 3 bits. A power supply voltage of, for example, + 5V is applied between the power supply input terminal 16 and the ground terminal 19.

The resistance output terminals 17 and 18 are connected to the input terminal 12
It is a terminal for outputting a resistance value set by a control signal applied to. A latch signal is input to the latch terminal 15. This latch signal is the resistance output terminal 1
The timing for controlling the resistance value connected between 7 and 18 is determined.

Here, the circuit configuration of the digital variable resistance device housed in the case 11 will be described with reference to FIG. In addition, in FIG. 2, portions corresponding to those in FIG. 1 are denoted by the same reference numerals.

The input terminals 12 to 14 and the latch terminal 15 are connected to the decoder 21. In addition, the decoder 21
A power supply voltage of, for example, +5 V is applied from the power supply input terminal 16 and grounded via the ground terminal 19. The decoder 21 is provided with input terminals A0, A1 and A2 connected to the input terminals 12 to 14 and eight output terminals Y0 to Y7.

The output terminals Y0 to Y7 are short-circuited S0 to S0.
It is connected to S7. The short-circuit circuits S0 to S7 have the same configuration, and are configured by a combination of a light emitting diode and a photodiode. For example, the short circuit S0 will be described. The short circuit S0 includes a light emitting diode D1 and a photodiode D2. The light emitting diode D1 has an anode connected to the power input terminal 16 and a cathode connected to the output terminal Y0. Further, the anode of the photodiode D2 is connected to the resistance output terminal 17, and the cathode is connected to the anode of the photodiode D2 of the short circuit S1 in the next stage. The cathode of the photodiode D2 of the final-stage short circuit S7 is connected to the resistance output terminal 17.

Further, resistors R0 to R7 are connected in parallel to the short circuit circuits S0 to S7, that is, between the anode and cathode of the photodiode D2. The resistors R0 to R7 are connected in series as a whole, and both ends thereof are connected to the resistor output terminal 1
7 and 18 are connected.

The operation of the digital variable resistance device having the above configuration will be described below.

The input terminals A0 to A2 correspond to the respective bits of the 3-bit control signal, and the signals are input to predetermined input terminals A0 to A2 depending on the magnitude of the control signal. Then, depending on the combination of the input terminals A0 to A2 to which the signals are input, a high level signal is output to any one of the output terminals Y0 to Y7, and a low level signal is output to the other.

The input terminals A0 to A2 and the latch terminal 15
FIG. 3 shows the relationship between the signals applied to the output terminals Y0 to Y7 and the signals output from the output terminals Y0 to Y7. In FIG. 3, H means a high level signal and L means a low level signal.

For example, in No. 2, when a high level signal is applied to the latch terminal 15 while a high level signal is applied to the input terminal A0 and a low level signal is applied to the input terminals A1 and A2, the output terminal Y1 becomes high level. Signals and other output terminals Y0, Y2 to Y7 are low level signals.

At this time, the light emitting diode D1 of the short circuit S1 does not emit light because a high level signal is applied to its cathode. However, the light emitting diodes D1 of the other short circuit circuits S0 and S2 to S7 emit light when a low level signal is applied to their cathodes. The light emitted from the light emitting diode D1 is received by the pair of photodiodes D2,
The anode and cathode of the photodiode D2 are electrically connected and short-circuited. Since the light emitting diode D1 of the short circuit S1 does not emit light, the photodiode D2 of the short circuit S1
There is no short circuit between the anode and cathode. In this case, both ends of the resistors R0 and R2 to R7 are short-circuited by the photodiode D2. Therefore, only the resistor R1 is connected between the resistance output terminals 17 and 18, and the resistance value between the output terminals 17 and 18 is determined.

No. 1 in FIG. As shown by 9, when the low level signal is applied to the latch terminal 15, the signals output from the output terminals Y0 to Y7 are all high level signals. At this time, the light emitting diodes of the short circuit circuits S0 to S7 do not emit light, and the short circuit circuits S0 to S7 are open. Therefore, the resistors R0 to R0 are provided between the output terminals 17 and 18.
R7 is connected.

According to the above configuration, the input terminals A0 to A2 are
Resistor R short-circuited by the value of the control signal input to
The combination of 0 to R7 changes. As a result, the resistance connected between the resistance output terminals 17 and 18 changes, and the resistance value changes.

According to the above-mentioned embodiment, no power source is required for adjusting the resistance value. Also, the resistance value can be changed by software, and remote operation and automation can be performed easily and accurately. In addition, there is no sliding noise, vibration, temperature,
Variation of resistance value due to environment such as humidity, gas and external noise is small.

Further, in the above-described embodiment, a decoder to which a 3-bit control signal is input is used as a device for controlling the short circuit. However, the control signal is not limited to 3 bits. It is also possible to use an analog signal as the control signal. In this case, instead of the decoder, for example, an analog signal is converted into a digital signal A.
A / D converter or the like is used.

[0034]

According to the present invention, it is possible to realize a digital variable resistance device capable of reliably and easily adjusting the resistance value.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram illustrating an embodiment of the present invention.

FIG. 3 is a diagram for explaining the operation of the present invention.

FIG. 4 is a diagram illustrating a conventional example.

FIG. 5 is a diagram illustrating another conventional example.

[Explanation of symbols]

 11 ... Case 12, 13, 14 ... Input terminal 15 ... Latch terminal 16 ... Power supply input terminal 17, 18 ... Resistance output terminal 19 ... Ground terminal A0-A2 ... Input terminal Y0-Y7 ... Output terminal S0-S7 ... Short circuit R0 ~ R7 ... Resistor D1 ... Light emitting diode D2 ... Photo diode

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location // H03M 1/74

Claims (2)

[Claims] 1. A plurality of short-circuit circuits which are short-circuited or open depending on the state of an applied signal, and a plurality of resistance elements which are respectively connected in parallel to the plurality of short-circuit circuits and are connected in series as a whole. Digital variable resistance device equipped. 2. The digital variable resistance device according to claim 1, wherein the short circuit is formed of a combination of a light emitting diode and a photodiode.