JPH0130324B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a range switching amplifier that switches and changes the gain according to the range of change of an input signal.

Generally, in electronic devices that input electrical signals from the outside and display, convert, or amplify them, the user of the device is allowed to select from several types of input ranges for his/her own benefit. There is. For example, mmV, 10mmV, 100mmV, 1V or 1m/
seconds, 5 m/sec, 10 m/sec, g/cm ² , 100 g/cm ² ,
The input signal can be displayed, converted, or amplified by switching according to the input range, such as kg/cm ² .

Conventionally, such range switching is performed by supplying an input signal from an input terminal 11 to amplifiers 12, 13, and 14 having different gains, for example, as shown in FIG.
The outputs of 14 are switched by a switch 15 and one of them is supplied to a main electronic circuit 16 for displaying or converting. The output of the main electronic circuit 16 is supplied to an output terminal 17 as required.

Alternatively, as shown in FIG. 2, the input signal from the input terminal 11 is supplied to the variable gain amplifier 18, and the variable gain amplifier is connected between the input and output terminals of the operational amplifier 19 by a changeover switch 20 that connects resistors 21, 22, and 23. By selecting and connecting one of them, the amplification gain is changed, and the output of the variable gain amplifier 18 is supplied to the main electronic circuit 16. Alternatively, as shown in FIG. 3, the input signal of the input terminal 11 is supplied to the variable attenuator 24, and the attenuation output is taken out by switching the different attenuation rate taps of the variable attenuator 24 using the changeover switch 25. is configured to supply.

These conventional range switching means have the following drawbacks. That is, in order to obtain highly accurate and stable gain in each range, amplifiers 12, 13, 14,
Operational amplifiers, resistors, and attenuators 24 that constitute 18
It is necessary to use resistors that have high accuracy in their characteristics and constants such as resistance values.
As the number of switching ranges increases, the number of such high-precision elements increases, resulting in a disadvantage that the device becomes expensive. Furthermore, as the number of switching ranges increases, the number of switching contacts of the switching switches 15, 20, and 25 increases, reducing reliability and increasing the price.Furthermore, semiconductor switches can be used as switches, but In this case, there were drawbacks such as the switch circuit becoming complicated.

An object of the present invention is to provide a range switching amplifier that has a small number of constituent elements, does not require an increase in the number of elements even if there are many switching ranges, and can be made stable and highly accurate at a relatively low cost. It's about doing.

According to this invention, by using a microcomputer, it is possible to output any analog value from the microcomputer through a DA converter, and the gain of the variable gain amplifier is controlled by the output of the DA converter. In addition, in order to set the corresponding range, a digital signal is set in the DA converter from the microcomputer, and the converted reference signal is supplied to the variable gain amplifier, and the output of the variable gain amplifier and the reference value are set. The gain of the variable gain amplifier is controlled according to the comparison result. Such control is automatically performed by a microcomputer. In this way, a gain corresponding to the range is set in the variable gain amplifier, and an input signal is supplied to the amplification by switching with the output of the DA converter set by the microcomputer.

For example, as shown in FIG. 4, a microcomputer 26 is provided, and the microcomputer 26 is configured to be able to set digital values for each of the DA converters 27 and 28. The DA converter 27 converts the set digital signal into an analog signal to generate a reference signal, and the reference signal is switched with the input signal from the input terminal 11 by the changeover switch 29 and sent to the variable gain amplifier 31. Supplied. Also DA converter 2
8 converts the digital signal set by the microcomputer 26 into an analog signal and supplies it to the variable gain amplifier 31 as a signal for controlling its gain.

In this embodiment, the reference signal for the DA converter 27 can be manually set by inputting it to the microcomputer 26 using the setting device 32. In other words, the desired range can be set using the setting device 32. be made possible.
The gain of the variable gain amplifier 31 is controlled by voltage, that is, it is a voltage controlled variable gain amplifier, and for example, μA757 manufactured by Fairchild, Inc. of the United States can be used.

The amplified output of the variable gain amplifier 31 is selectively supplied to the comparator 34 and the main electronic circuit 16 by a switch 33 in this example. In the comparator 34, the reference value given to the terminal 35 and the variable gain amplifier 3
1, and the comparison result is input to the microcomputer 26. The comparison results are judged by the microcomputer 26 and DA
By changing the set digital value for converter 28, the output of amplifier 31 is controlled to match the reference value at terminal 35. The microcomputer 26 also performs switching control for the switches 29 and 33.

In this configuration, the input range of the main electronic circuit 16 is 0 to 10V, and a voltage of 10V is applied as a reference value to the terminal 35, and the setting device 32 inputs one digit to the input terminal 11 corresponding to 0 to 9. The range is
Assume that 10 different values can be set corresponding to 10V, 5V, 1V, etc.

In this device, for example, the input signal range is
In the case of 1V, when a value corresponding to this is set by the setter 32, the microcomputer 26 reads the input from the setter and sets the corresponding value in the DA converter 27. The microcomputer 26 also controls connecting the switch 29 to the output side of the DA converter 27 and the switch 33 to the input side of the comparator 34. As a result, a 1V analog signal is output from the DA converter 27 and input to the variable gain amplifier 31. The output of variable gain amplifier 31 is compared with 10V at terminal 35 by comparator 34. The output of the comparator 34 is checked by the microcomputer 26 and the set value of the DA converter 28 is changed to control the gain of the variable gain amplifier 31 so that the output of the variable gain amplifier 31 becomes 10V. When this becomes 10V, comparator 34
The output of the DA converter 28 is inverted, for example, becomes a high level, and the microcomputer 26 knows that both inputs of the comparator 34 match, stops changing the set value for the DA converter 28, and also switches the switch 29 to the input terminal 11. The switch 33 is connected to the main electronic circuit 16 on the side.
Switch to the side. As a result, an input signal from the input terminal 11 is converted into a signal of 0 to 10 V for a range of 0 to 1 V and is input to the main electronic circuit 16. The settings on the setting device 32 can be changed not only to one digit but also to two digits.
If you use digits, you can switch the range in 100 steps, and you can set almost any gain.

In FIG. 4, a comparator 34 is provided and the comparison result is taken into the microcomputer 26.
The microcomputer 26 performs such a comparison operation.
You can also do it internally. For example, as shown in FIG. 5, when the switch 29 is connected to the output side of the DA converter 27, that is, when the range is set, the output of the variable gain amplifier 31 is connected to the output side of the AD converter 27.
6 converts it into a digital signal and imports it into the microcomputer 26.
The digital value from the AD converter 36 is compared with the built-in reference value, which corresponds to 10V in the previous embodiment, and the digital value of the DA converter 28 is changed according to the result. Thus, the DA converter 28 is controlled to change until the output digital signal from the AD converter 36 matches the digital reference value corresponding to the internal 10V. In this way, the microcomputer 26 can perform the comparison operation when setting the range. In this example, the switch 29 is switched to the input terminal 11 side, and the input signal from the input terminal 11 is amplified by the variable gain amplifier 31, converted to a digital signal by the AD converter 36, and inputted to the microcomputer 26. This is a case in which the processing in the main electronic circuit 16 in FIG.

In the above description, the range is set by operating the setter 32, but the range may be changed automatically. For example, as shown in FIG. 6 with the same reference numerals attached to parts corresponding to those in FIG.
The microcomputer 26 periodically monitors the state of the output of the comparator 34, and when it detects that the input signal from the input terminal 11 exceeds the currently set range, it switches the switch 29 to change the current setting. A digital reference signal corresponding to the next range different from the current range is set in the DA converter 27, its output is supplied to the variable gain amplifier 31, and the output is compared with the reference value at the terminal 35 by the comparator 34. According to the result, the digital signal of the DA converter 28 is changed, and the amplification gain of the variable gain amplifier 31 is changed and set to a new range. This newly set range is output from the microcomputer 26 to the terminal 38 as range information. Note that these range switching amplifiers may be inserted not only in the input section of the electronic device but also in the middle of the circuit of the electronic device.

As described above, in the range switching amplifier according to the present invention, even if the number of switching ranges increases, the number of constituent elements does not increase, and the DA converter 27,
28. It is only necessary to use a relatively small number of elements such as the comparator 34, which are stable and highly accurate, and this is not related to the number of switching ranges. Therefore, the device of the present invention is advantageous when there are many switching ranges. Become something. Furthermore, if necessary, the switch 29 can be automatically switched to the DA converter 27 side using a microcomputer for calibration.
Even if the gain or the like drifts, it can be easily corrected, and it is also possible to configure such a correction to be performed automatically.

[Brief explanation of drawings]

1 to 3 are block diagrams showing conventional range switching devices, FIG. 4 is a block diagram showing an example of a range switching amplifier according to the present invention, and FIGS. 5 and 6 are block diagrams showing a range switching amplifier according to the present invention, respectively. FIG. 3 is a block diagram showing another example of the amplifier. 11: Input terminal, 16: Main electronic circuit, 17: Output terminal, 26: Microcomputer, 27,2
8: DA converter, 31: Variable gain amplifier, 34:
Comparator, 32: Setting device, 35: Reference value input terminal,
36: AD converter.

Claims (1)

[Claims] 1. A variable gain amplifier that can change the gain, a first DA converter that converts an input digital signal into an analog signal and supplies it to the variable gain amplifier as a signal for controlling its gain, and an input digital signal. a second DA converter that converts the input signal to an analog signal and outputs it as a reference signal; a switch that switches between the input signal to be amplified and the reference signal and supplies it to the variable gain amplifier; and a comparison means for setting a reference digital signal in the second DA converter, and a comparison means for comparing the second DA converter with the second DA converter, and
A range switching amplifier comprising a microcomputer that changes the digital signal given to the 1DA converter.