JPH0591040U - A / D converter - Google Patents

Abstract

(57) [Abstract] [Purpose] By making the ground potential of each operational amplifier common to each other, individual ground voltage fluctuations due to noise are eliminated, and zero adjustment is not required, and the maximum value of the digital output signal can be easily adjusted. An A / D conversion device configured to perform the above is provided. [Configuration] In order to amplify the input analog signal,
At least one operational amplifier 1 connected in series with each other
2, 14 and the analog signal from the operational amplifier are A / D
A reference voltage terminal including an A / D converter 16 for conversion and to be input to each operational amplifier is connected to a reference voltage power source of the A / D converter via resistors 13 and 15, respectively. , A / D converter 10.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an A / D conversion device that amplifies an input analog signal and then performs A / D conversion.

[0002]

[Prior Art]

 Conventionally, such an A / D converter is configured as shown in FIG. 3, for example. In the figure, in the A / D conversion device 1, an analog signal to be A / D converted is input from an external input terminal 2 through a resistor between the inverting input terminal 3a and the non-inverting input terminal 3b, and The terminal 3b is grounded via a resistor, and the output terminal 3c is fed back to the inverting input terminal 3a via the variable resistor 4, and the output of the first operational amplifier 3 is It is input to the inverting input terminal 5a via a resistor, the non-inverting input terminal 5b is grounded via a resistor, and is connected to a constant voltage power source (not shown) via a variable resistor 6, and its output is low. The second operational amplifier 5 which is fed back to the inverting input terminal 5a through the resistor 7 and the output of the second operational amplifier 5 are connected to the analog input terminal 8a, and the reference voltage input terminal 8b is connected to the ground. Are connected, and an A / D converter 8 to output a digital signal A / D converted from the output terminal 8c to the external output terminal 9.

According to the A / D conversion device 1 thus configured, the analog signal input to the external input terminal 2 is amplified by the first operational amplifier 3 and the second operational amplifier 5, respectively, and then A The digital signal is converted by the / D converter 8 and output from the external output terminal 9. Here, the variable resistor 4 adjusts the amplification factor of the first operational amplifier 3, and the variable resistor 6 performs zero adjustment.

[0004]

[Problems to be solved by the device]

 However, in the A / D converter 1 having such a configuration, it is necessary to perform zero adjustment of the operational amplifier separately with reference to its ground voltage, and in the case of a circuit configuration in which a large number of opamps are connected in series, The operation of zero adjustment was troublesome because it was necessary to perform zero adjustment for each operational amplifier. Also, since the ground voltage of each operational amplifier may fluctuate due to clock noise, drops, etc., the reference voltages will fluctuate differently, causing fluctuations in the input signal to the A / D converter. As a result, the accurate A / D conversion cannot be performed, and as a result, the digital output signal is accompanied by an error due to the change as shown in FIG. When adjusting the maximum value of the digital output signal, first perform the zero adjustment of the digital output signal, and then adjust the amplification factor by operating the variable resistor 4, and then perform the zero adjustment of the digital output signal. Since it is necessary to check the above, there is a problem that the workability is poor and adjustment takes time.

In view of the above points, the present invention eliminates individual ground voltage fluctuations due to noise by making the ground potential of each operational amplifier common to each other, and eliminates the need for zero adjustment to maximize the maximum value of the digital output signal. It is an object of the present invention to provide an A / D conversion device that can be easily adjusted.

[0006]

[Means for Solving the Problems]

 According to the present invention, it includes at least one operational amplifier connected in series to amplify an input analog signal and an A / D converter for A / D converting the analog signal from the operational amplifier. In the A / D conversion device, the reference voltage terminal to be input to each operational amplifier is configured to be connected to the reference voltage power source of the A / D converter via a resistor.

[0007]

[Action]

 According to the above configuration, the reference voltage of each operational amplifier is set based on the A / D conversion reference voltage of the A / D converter, and therefore each reference voltage may change due to noise or the like. Since it can be held constant at all times, zero adjustment of each operational amplifier becomes unnecessary and highly accurate A / D conversion can be performed. Since zero adjustment is not required when adjusting the maximum value of the digital output signal, the maximum value is adjusted simply by adjusting the amplification factor, improving workability and making adjustments in a short time. Is performed.

[0008]

【Example】

 FIG. 1 shows an embodiment of an A / D converter according to the present invention. In this A / D converter 10, an analog signal to be A / D converted is input from an external input terminal 11 via a resistor between an inverting input terminal 12a and a non-inverting input terminal 12b, and an output terminal 12c thereof is connected to a variable resistor 13a. It has a first operational amplifier 12 which is fed back to the inverting input terminal 12a through the output of the first operational amplifier 12, and the output of the first operational amplifier 12 is input to the inverting input terminal 14a through a resistor and its output. Has a second operational amplifier 14 that is fed back to the inverting input terminal 14a via a resistor 15, and the output of the second operational amplifier 14 is connected to the analog input terminal 16a and its output terminal And an A / D converter 16 which outputs a digital signal A / D-converted to the external output terminal 17.

The above-mentioned configuration is similar to that of the conventional A / D converter 1 shown in FIG. 3, but in the A / D converter 10 according to the present invention, the reference voltage input of the A / D converter 16 is input. The terminal 16b is connected to a constant voltage power supply 18 that supplies a reference voltage, and the non-inverting input terminal 12b of the first operational amplifier 12 and the non-inverting input terminal 14b of the second operational amplifier 14 are respectively connected via resistors. It is connected to the constant voltage power source 18.

The A / D converter 10 according to the present invention is configured as described above, and the analog signal input to the external input terminal 11 is amplified by the first operational amplifier 12 and the second operational amplifier 14, respectively. After that, it is converted into a digital signal by the A / D converter 16 and output from the external output terminal 17.

Here, since the reference voltage of each operational amplifier 12, 14 is set based on the voltage of the constant voltage power supply 18 which gives the A / D conversion reference voltage of the A / D converter 16, Since the reference voltage does not fluctuate due to noise or the like and can always be held constant, zero adjustment of each operational amplifier 12, 14 is unnecessary, and the reference voltage of the A / D converter 16 is not zero. Therefore, as shown in FIG. 2, since it is not necessary for A / D conversion to process a minute signal near zero, more accurate A / D conversion can be performed.

Further, when adjusting the maximum value of the digital output signal from the external output terminal 17, it is not necessary to perform zero adjustment of the operational amplifiers 12 and 14. Therefore, in the illustrated case, the variable resistor 13 of the operational amplifier 12 is used. The maximum value adjustment can be easily performed by just adjusting.

[0013]

[Effect of the device]

 As described above, according to the present invention, the reference voltage of each operational amplifier is set based on the A / D conversion reference voltage of the A / D converter. Since it does not fluctuate, it can always be kept constant, so that zero adjustment of each operational amplifier is unnecessary and highly accurate A / D conversion can be performed. Also, since zero adjustment is not necessary when adjusting the maximum value of the digital output signal, the maximum value can be adjusted by simply adjusting the amplification factor, improving workability and reducing the work time. Adjustments are made. Thus, according to the present invention, by making the ground potential of each operational amplifier common to each other, individual ground voltage fluctuations due to noise are eliminated, zero adjustment becomes unnecessary, and the maximum value of the digital output signal can be easily adjusted. Therefore, an extremely excellent A / D conversion device is provided.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an A / D conversion device according to the present invention.

FIG. 2 is a graph showing an input and an output in the A / D converter of FIG.

FIG. 3 is a circuit diagram showing an example of a conventional A / D conversion device.

FIG. 4 is a graph showing an input and an output in the A / D converter of FIG.

[Explanation of symbols]

 10 A / D conversion device 11 External input terminal 12 Operational amplifier 13 Variable resistance 14 Operational amplifier 15 Resistance 16 A / D converter 17 External output terminal 18 Constant voltage power supply

Claims (1)

[Scope of utility model registration request] 1. The system includes at least one operational amplifier connected in series with each other for amplifying an input analog signal, and an A / D converter for A / D converting the analog signal from the operational amplifier. In the A / D converter, the reference voltage terminal to be input to each operational amplifier is
An A / D conversion device, characterized in that each is connected to a reference voltage power supply of the converter via a resistor.