JP2001111358A - Analog operational amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of any error in an analog operational amplifier circuit itself by preventing the generation of any error in the values of an input resistance RA and a feedback resistance RB due to environmental changes or inter-part individual difference or the like and by preventing the generation of any deviation because of the inequality of input offset voltage Vid and reference voltage Vref due to the generation of voltage fluctuation in the input offset voltage Vid or reference voltage Vref itself. SOLUTION: This analog operational amplifier circuit is provided with an operational amplifier, an inversion amplifier having an input terminal connected to the inversion input terminal of the operational amplifier and an output terminal negative feedback-connected with the inversion input terminal, and a filter circuit arranged between the input terminal of the inversion amplifier and the non-inversion input terminal of the operational amplifier for removing the AC signal components of an input signal inputted from the input terminal and for outputting it to the non-inversion input terminal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog operational amplifier circuit capable of maintaining a constant DC offset voltage between input and output signals of an inverting amplifier without adjustment.

[0002]

2. Description of the Related Art FIG. 7 is a circuit diagram showing a conventional analog operational amplifier circuit. In the figure, I is an input terminal, O is an output terminal, OP is an operational amplifier, RA is an input resistance, and RB is a feedback resistance. In the illustrated example, the output terminal O and the operational amplifier O
A negative feedback connection is made between the inverting input terminal of P through a feedback resistor RB, and an input terminal I is connected to the inverting input terminal via an input resistor RA to form an inverting amplifier as an analog operational amplifier circuit. ing.

Next, the operation will be described. Here, an operation for keeping the offset voltage between input and output signals constant will be described. Ideally, when the input voltage is set to zero in the operational amplifier, the output voltage is also set to zero. However, actually, due to the irregularity of the input differential circuit (the error voltage generated between the inverting input terminal (-) and the non-inverting input terminal (+)), the output is high even though the input voltage is zero. DC voltage may be generated instead of zero. Since this DC voltage (hereinafter referred to as an offset voltage) is included in the output voltage after being multiplied by the gain, it generally causes a large error or the like. For this reason, in the above-described inverting amplifier in the analog operational amplifier circuit, a DC power supply for adjusting a variable offset voltage is connected to the non-inverting input terminal, and the potential difference between the inverting input terminal and the non-inverting input terminal becomes zero. Adjustment (offset voltage adjustment) as described above suppresses the influence of the offset voltage.

The adjustment of the offset voltage will be described quantitatively. The offset voltage Vod included in the output signal Vo output from the output terminal O is a voltage difference between the inverting input terminal and the non-inverting input terminal of the operational amplifier OP. A value obtained by adding the reference voltage Vref applied to the non-inverting input terminal of the operational amplifier OP to the product multiplied by the gain of the circuit is output. If the input offset voltage included in the input signal Vi is Vid, it is expressed by Expression (1). be able to. Vod = − (RB / RA) (Vid−Vref) + Vref (1)

Accordingly, from the equation (1), the reference voltage Vref
Is equal to the input offset voltage Vid, the input offset voltage Vid and the output offset voltage Vod become equal, so that the input / output offset voltage of this circuit can always be kept constant.

[0006]

Since the conventional analog operational amplifier circuit is constructed as described above, the input resistance RA and the feedback resistance R are affected by environmental changes and individual differences between components.
When an error occurs in the value of B or when a voltage fluctuation occurs in the input offset voltage Vid or the reference voltage Vref itself, the input offset voltage Vid and the reference voltage Vref do not become equal, and a slight shift occurs, and as a result, the circuit There is a problem that it becomes a major factor of the error of the above.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and is free from the effects of component variations, environmental changes, etc., and can maintain a constant offset voltage between input and output signals without adjustment. It is an object to obtain a simple analog operational amplifier circuit.

[0008]

According to the present invention, there is provided an analog operational amplifier circuit comprising an operational amplifier, an input terminal connected to an inverting input terminal of the operational amplifier, and an output terminal connected to the inverting input terminal and negative feedback. And a filter circuit provided between the input terminal of the inverting amplifier and the non-inverting input terminal of the operational amplifier to remove an AC signal component of an input signal input from the input terminal and output the signal to the non-inverting input terminal. Things.

An analog operational amplifier circuit according to the present invention comprises:
It comprises a plurality of filters having different characteristics, and includes a filter circuit for switching the plurality of filters having different characteristics to vary the response to an input signal and the input / output characteristics.

An analog operational amplifier circuit according to the present invention comprises:
It comprises a filter having variable characteristics, and includes a filter circuit that changes the characteristics of the filter to change the response to an input signal and the input / output characteristics.

An analog operational amplifier circuit according to the present invention comprises:
The filter includes a filter having a variable time constant, and a filter circuit that changes a time constant of the filter to change a transient response characteristic of the filter of the non-inverting input terminal.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. FIG. 1 is a circuit diagram of an analog operational amplifier circuit according to a first embodiment of the present invention. In the figure,
I is an input terminal, O is an output terminal, OP is an operational amplifier, R
A is an input resistance and RB is a feedback resistance. In the example shown,
The output terminal O and the inverting input terminal of the operational amplifier OP are connected in negative feedback via a feedback resistor RB, and the input terminal I and the inverting input terminal are connected via an input resistor RA to form an inverting amplifier. I have. F1 is a filter (filter circuit) that connects the input terminal I and the non-inverting input terminal of the operational amplifier OP and removes an AC signal component included in the input signal Vi. The filter F1 controls the input signal Vi so that the response characteristic of the output signal to the input signal Vi does not deteriorate.
The one having a frequency characteristic suitable for a desired signal included in.

Next, the operation will be described. The present invention relates to an analog operational amplifier circuit having a function of maintaining a constant offset voltage between input and output signals without adjustment, and therefore, this function will be particularly described here. The input signal Vi input to the input terminal I is input to the non-inverting input terminal of the operational amplifier OP after the AC signal component is removed by the filter F1. Assuming that this input voltage is Vp, the input voltage Vp can be replaced with the reference voltage Vref of the conventional circuit. As a result, Vref = V
By substituting p, it can be expressed as in the following equation (2). Vod = − (RB / RA) (Vid−Vp) + Vp (2)

If it is assumed that the characteristic of the filter F1 is a low-pass filter capable of sufficiently removing the AC signal component contained in the input signal Vi, the input voltage Vp
Represents the input offset voltage Vi included in the input signal Vi.
Only d should appear. Therefore, Vp =
By substituting Vid, equation (3) is obtained, and the output offset voltage Vod and the input offset voltage Vid become equal. Vod = − (RB / RA) (Vid−Vid) + Vid (3) ∴Vod = Vid As described above, the difference between the input offset voltage Vid and the output offset voltage Vod is eliminated, and the offset voltage between the input and output signals becomes constant. Will be kept.

As described above, according to the first embodiment, the operational amplifier OP, the input terminal I connected to the inverted input terminal of the operational amplifier OP, and the output terminal O connected negatively to the inverted input terminal (-). Which is provided between an input terminal I of the inverting amplifier and a non-inverting input terminal (+) of the operational amplifier OP to remove an AC signal component of the input signal Vi input from the input terminal I. Since a filter F1 as a filter circuit for outputting to the non-inverting input terminal is provided, the input offset voltage included in the input signal Vi is input to the non-inverting input terminal, the input / output offset voltage difference is automatically erased, and there is no adjustment. The offset voltage between input and output signals can be kept constant. In addition, compared to a case where the reference voltage Vref derived from another power supply is adjusted to be equal to the input offset voltage included in the input signal Vi, the influence of voltage fluctuation due to environmental changes, individual differences between components, and the like is reduced. The effect of not receiving is obtained.

In the first embodiment, the filter F1
Is a low-pass filter, but the same effect as in the above embodiment can be obtained by using a band-pass filter, a notch filter, a composite filter, or the like in order to improve the response characteristics of the output signal to the input signal Vi. Play.

Embodiment 2 FIG. In the first embodiment described above, the response characteristic of the output signal to the input signal is improved by the frequency characteristic of the filter connected to the non-inverting input terminal. However, it is very difficult to create a complicated characteristic with one filter. Difficult. Therefore, in the second embodiment, a plurality of filters having different characteristics are switched and controlled to cope with a complicated input signal.

FIG. 2 is a circuit diagram of an analog operational amplifier circuit according to a second embodiment of the present invention. In the figure, F
, Fn are filters for removing an AC signal component included in the input signal Vi. These filters are connected in parallel, and the switches S1, S2,.
The filter circuit is configured so that cutting control can be performed by using Sn. Further, in this filter circuit, the number of filters and switches connected in parallel may be any number according to the purpose, and the characteristics of the filters connected in parallel may be any characteristics according to the purpose. Note that the same components as those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted.

Next, the operation will be described. Input signal Vi
, The filters F2, F3,.
, Fn are switched by switches S1, S2, ..., Sn. Thus, if a filter having a frequency characteristic matching a desired signal included in the input signal Vi is connected, the response characteristic of the output signal to the input signal Vi can be improved. These filters F2 and F
3,..., Fn may be switched each time so as to fix to a certain filter according to the purpose of use of the circuit, or automatically by detecting the characteristics of the input signal Vi to obtain a desired signal. May be controlled so as to be switched. In addition,
The principle of the automatic elimination of the input / output offset voltage difference performed through the switched filter is the same as that of the first embodiment, and thus the duplicated description will be omitted. By switching the filter to be used according to the purpose of use of the circuit, it is possible to cope with the case where the input signal Vi is a complex signal showing various waveforms.

FIG. 3 is a waveform diagram showing a specific example in a case where the input signal is a complicated signal, and FIG.
(B) shows the waveform of the output signal of the analog operational amplifier circuit when a low-pass filter is used as the filter circuit, and (c) shows the waveform of the output signal of the analog operational amplifier circuit when the band-pass filter is used as the filter circuit. ing. In the example of FIG. 3, the input signal Vi is input as a mixed wave of the low frequency component f _L and the high frequency component f _H as shown in FIG.

Here, for example, when only the input offset voltage which is a DC voltage component included in the input signal Vi is input to the non-inverting input terminal of the operational amplifier OP, the filters F2, F3,. Any one of Fn is connected as a low-pass filter, and switching to the low-pass filter removes both the low-frequency component f _L and the high-frequency component f _H. As a result, as shown in (b), the low frequency component f _L and the high frequency component f _H are inverted as output signals of the circuit, and when the gain of the inverting amplifier is changed, the low frequency component f _L and the high frequency component f _L are changed. Each of _H is affected by a gain change. Further, for example, when the purpose of use of the circuit is changed (or when the low-frequency component f _L is to be removed by noise), only the high-frequency component f _H included in the input signal Vi is removed to remove the non-operation of the operational amplifier OP. when entering the inverting input terminal, filter F2, F3 of the filter circuit, ..., should be tied to any of Fn as a band-pass filter, a high frequency component f _H by switching this bandpass filter Remove. As a result, as shown in (c), the high frequency component f _H is inverted as the output signal of the circuit, and the low frequency component f _L is output in a form reproducing the input waveform. At this time, if the gain of the inverting amplifier is changed, the low frequency component f _L always reproduces the input waveform, but the high frequency component f _H changes according to the gain change.

As described above, by connecting filters having various characteristics so as to be switchable, it is possible to extract and amplify a desired signal component from the input signal Vi by switching the filters according to the purpose of use of the circuit. it can.

In the above description, a mixed wave composed of a plurality of different frequency components is shown as the input signal Vi. However, a mixed wave of signals having different waveform components can be handled by a combination of filters having different characteristics as described above. Can be.

As described above, according to the second embodiment, instead of the filter circuit of the first embodiment, a plurality of filters F2, F3,..., Fn having different characteristics are provided. A plurality of filters F2, F3,.
.., Fn, and respond to the input signal Vi;
And a filter circuit that makes the input / output characteristics variable, so that the same effects as in the first embodiment can be obtained, and the input signal Vi has a complicated signal (for example, a mixed wave or a waveform of a plurality of signals having different frequencies). Even in the case of a mixed wave of a plurality of different signals, the filter can be flexibly handled by switching the filters according to the purpose of use of the circuit.
In addition, the response characteristics of the output signal to the input signal Vi can be improved by combining filters having various characteristics according to the purpose of use of the circuit.

The filters F2, F3,..., Fn used in the second embodiment include low-pass filters and band-pass filters as in the first embodiment.
A notch filter, a composite filter, or the like may be used.

Embodiment 3 FIG. In the second embodiment, switching control is performed with one of a plurality of filters having different characteristics according to the purpose of use of the circuit. However, the analog operational amplifier circuit according to the third embodiment changes the characteristics of the filter itself. It is assumed that.

FIG. 4 is a circuit diagram of an analog operational amplifier circuit according to Embodiment 3 of the present invention. In the figure, F4 is a filter (a variable characteristic filter or filter circuit) whose characteristics can be changed by external control. As the filter F4, for example, there is a filter in which the voltage level of an input signal to be removed is variable by external control. Note that the same components as those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted.

Next, the operation will be described. Input signal Vi
, The characteristics of the filter F4 are changed by external control. This characteristic may be controlled so as to fix the characteristic of the filter in accordance with the purpose of use of the circuit, or when the input signal Vi changes periodically as described later, the filter is adjusted in accordance with the period of the change. Control may be performed so that the characteristics change. The filter F after the characteristic change
The description of the automatic erasing operation of the input / output offset voltage difference performed through the fourth embodiment is the same as that of the first embodiment, and thus the description thereof is omitted.

Thus, for example, the response characteristics of the output signal to the input signal Vi can be improved by setting the frequency characteristics to match the desired signal included in the input signal Vi. Further, it is possible to cope with a case where the input signal Vi is a complicated signal showing various waveforms. Specifically, the input signal Vi shown in FIG. 3 has a low frequency component f _L and a high frequency component f _L.
In the case of a mixed wave with _H , a desired signal can be obtained in the same manner as in the second embodiment by changing the characteristic according to the purpose of use of the circuit.

Further, the configuration according to the third embodiment can cope with more complicated input signals than that shown in the second embodiment. This will be described below.
FIGS. 5A and 5B are waveform diagrams showing another specific example when the input signal is a complex signal. FIG. 5A shows the waveform of the input signal, and FIG. 5B shows the filter F4 in which only the high frequency component f _H is removed. (C) shows the waveform of the output signal of the analog operational amplifier circuit when the low frequency component f _L and the high frequency component f _H of the input signal Vi are removed. . In the example of FIG. 5, as shown in FIG. 5A, the input signal Vi has a waveform in which the low frequency component f _L and the high frequency component f _H appear periodically. If it tries to cope with such input signal Vi in the configuration according to the second embodiment, such as when you want to output only high frequency component f _H which appears for example periodically, to switch the filter in accordance with the this period However, it is not preferable because it is strongly affected by individual differences in filter performance. Therefore, as described above, in the third embodiment, the characteristic itself of the filter F4 is changed by external control to correspond to the period change of the input signal Vi. This will be specifically described below.

For example, a high-frequency component f _H that appears periodically
If you want to output only the frequency characteristic of the filter F4 to synchronously controlled so as to remove only the high frequency component f _H in accordance with the above period. As a result, the offset voltage between the input and output signals is kept equal as shown in FIG.
Only the high frequency component f _H is extracted and inverted and amplified. Further, for example, when it is desired to output both the low-frequency component f _L and the high-frequency component f _H that appear periodically, the frequency characteristics of the filter F4 are adjusted according to the above-described cycle to obtain the low-frequency component f _L and the high-frequency component f _H. to synchronize control to remove both the f _H. As a result, as shown in (c), the offset voltage between the input and output signals is kept equal, and both the low frequency component f _L and the high frequency component f _H are periodically inverted and amplified. As described above, by changing the characteristics of the filter according to the purpose of use of the circuit, it is possible to extract and amplify various signal components from a complicated input signal Vi that cannot be handled by the configuration of the second embodiment.

As described above, according to the third embodiment, instead of the filter circuit of the first embodiment, a filter F4 having variable characteristics is used, and the characteristics of the filter F4 are changed to reduce the input signal Vi. Since the filter circuit having the variable response and input / output characteristics is provided, the same effects as those of the first embodiment can be obtained, and the filter circuit is affected by individual differences in filter performance as compared with the configuration according to the second embodiment. Instead, it is possible to flexibly cope with a more complicated input signal Vi (for example, a signal whose frequency changes periodically) by changing the characteristics of the filter according to the purpose of use of the circuit. Further, since the number of stages of the filter is not increased, it is advantageous in cost as compared with the configuration of the second embodiment.

Embodiment 4 FIG. In the fourth embodiment, the transient response characteristic of the output, which is a problem in the first embodiment, is improved.

FIG. 6 is a circuit diagram of an analog operational amplifier circuit according to Embodiment 4 of the present invention. In the figure, C1 is a capacitor (filter circuit), R1 is a resistor (filter circuit), and the input terminal I is connected to the non-inverting input terminal of the operational amplifier OP via the resistor R1, and one end of the capacitor C1 is grounded. A low-pass filter (filter circuit) is formed by connecting the end between the non-inverting input terminal and the resistor R1. S3 is a switch (filter circuit) that short-circuits both ends of the resistor R1 when closed. Note that the same components as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.

Next, the operation will be described. In the first to third embodiments, the response characteristic of the output signal is improved by the frequency characteristic of the filter connected to the non-inverting input terminal. However, the response characteristic is simply configured only by the combination of the resistor R1 and the capacitor C1. A simple filter circuit as shown in FIG. 4 cannot produce complicated characteristics. Therefore, both ends of the resistor R1, which is a time constant portion of the filter circuit, are bridged by the switch S3, and the switching operation is controlled to change the transient response characteristic of the circuit.

In addition, the time constant may be appropriately varied by external control. Further, the above configuration may be incorporated into the configurations according to the second and third embodiments to improve the transient response characteristics.

As described above, according to the fourth embodiment, a filter having a variable time constant is used in place of the filter circuit of the first embodiment, and the time constant is changed to change the transient in the filter at the non-inverting input terminal. Since the filter circuit having variable response characteristics is provided, the same effects as in the first embodiment can be obtained, and the transient response characteristics of the circuit can be improved.

As described above, the filter circuit in the configuration of the present invention not only automatically eliminates the input / output offset voltage difference by inputting the input offset voltage included in the input signal to the non-inverting input terminal, but also provides the filter circuit. Is changed as shown in the second to fourth embodiments, it is also possible to remove noise included in the input signal and extract a desired signal. Further, in the present invention, the input resistor RA and the feedback resistor RB are not essential components. Even when these values are 1, the same effects as those of the above-described embodiment can be obtained.

[0039]

As described above, according to the present invention, an inverting amplifier having an operational amplifier, an input terminal connected to the inverting input terminal of the operational amplifier, and an output terminal connected to the inverting input terminal and the negative feedback is provided. A filter circuit provided between the input terminal of the inverting amplifier and the non-inverting input terminal of the operational amplifier to remove an AC signal component of the input signal input from the input terminal and output the signal to the non-inverting input terminal; The input offset voltage included in the signal is input to the non-inverting input terminal, the input / output offset voltage difference is automatically erased, and the offset voltage between the input / output signals can be kept constant without adjustment.

In addition, compared to the case where the reference voltage derived from another power supply and the offset voltage included in the input signal are adjusted to be equal, there is an influence of a voltage change due to an environmental change, an individual difference between components, and the like. There is no effect.

According to the present invention, a filter circuit is provided which comprises a plurality of filters having different characteristics and switches the plurality of filters having different characteristics to vary the response to the input signal and the input / output characteristics. Is a complex signal (for example, a mixed wave of a plurality of signals having different frequencies or a mixed wave of a plurality of signals having different waveforms). There is an effect that can be. Further, by combining filters having various characteristics according to the purpose of use of the circuit, there is an effect that the response characteristics of the output signal to the input signal can be improved.

According to the present invention, a filter circuit is provided which comprises a filter having variable characteristics and changes the characteristics of the filter to change the response to an input signal and the input / output characteristics. Even if the input signal is more complicated (for example, a mixed wave of a plurality of signals having different frequencies or a mixed wave of a plurality of signals having different waveforms) without being affected by the individual difference of the filter, By changing the characteristics of the filter according to the purpose of use, there is an effect that the filter can be flexibly handled. Also,
Since the number of filter stages is not increased, the above paragraph 004
There is an effect that it is advantageous in terms of cost as compared with the first configuration.

According to the present invention, since a filter circuit having a variable time constant and changing the time constant of the filter to change the transient response characteristic of the filter of the non-inverting input terminal is provided, the transient of the circuit is provided. There is an effect that the response characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an analog operational amplifier circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of an analog operational amplifier circuit according to a second embodiment of the present invention.

3A and 3B are waveform diagrams illustrating a specific example in a case where an input signal is a complex signal, where FIG. 3A is a waveform of an input signal, FIG. 3B is a waveform of an output signal when a low-pass filter is used, and FIG. () Shows the waveform of the output signal when a band-pass filter is used.

FIG. 4 is a circuit diagram of an analog operational amplifier circuit according to a third embodiment of the present invention.

5A and 5B are waveform diagrams showing another specific example when the input signal is a complex signal, and FIG.
(B) the waveform of the output signal in the case of removing only high-frequency components f _H in the filter F4, (c) is output in the case where removal of the low frequency component f _L and the high frequency component f _H of the input signal Vi 4 shows a signal waveform.

FIG. 6 is a circuit diagram of an analog operational amplifier circuit according to a fourth embodiment of the present invention.

FIG. 7 is a circuit diagram showing a conventional analog operational amplifier circuit.

[Explanation of symbols]

C1 capacitor (filter circuit), F1, F2, F
3,..., Fn filter (filter circuit), F4
Filter (variable characteristic filter, filter circuit), I
Input terminal, O output terminal, OP operational amplifier, R1 resistor (filter circuit), RA input resistor, RB feedback resistor, S1, S2,..., Sn switch (filter circuit), S3 switch (filter circuit).

Continued on the front page F-term (reference) 5J066 AA01 AA47 CA13 FA20 HA25 HA29 HA38 KA25 KA41 KA42 MA13 TA01 TA06 5J091 AA01 AA47 CA13 FA18 FA20 HA25 HA29 HA38 KA25 KA41 KA42 MA13 TA01 TA06 5J100 AA02 BA01 BC07 CA31 EA41

Claims (4)

[Claims] 1. An inverting amplifier having an operational amplifier, an input terminal connected to an inverting input terminal of the operational amplifier, and an output terminal connected to the inverting input terminal in negative feedback. An analog operational amplifier circuit provided between the non-inverting input terminal and a filter circuit for removing an AC signal component of an input signal input from the input terminal and outputting the signal to the non-inverting input terminal. 2. A filter circuit comprising a plurality of filters having different characteristics, wherein a plurality of filters having different characteristics are switched to change a response to an input signal and input / output characteristics. An analog operational amplifier circuit as described. 3. The analog operation according to claim 1, wherein the filter circuit comprises a filter having a variable characteristic, and changes a characteristic of the filter to change a response to an input signal and an input / output characteristic. Amplifier circuit. 4. The filter circuit according to claim 1, wherein the filter circuit comprises a filter having a variable time constant, and the time constant of the filter is changed to change a transient response characteristic of the filter at the non-inverting input terminal. The analog operational amplifier circuit according to claim 3.