JP3171247B2 - Multi-function arithmetic circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-function arithmetic circuit, and more particularly to an arithmetic circuit having functions such as signal conversion, addition, and size adjustment using differential signals and single signals as input signals.

[0002]

2. Description of the Related Art For example, in a modulation / demodulation device used in a digital cellular phone or the like, in order to obtain good modulation and demodulation characteristics, a differential signal is converted into a single signal (also called a single-ended signal). A function such as addition of another single signal to one single signal and adjustment of the signal amplitude is required. Such a function is conventionally provided by the differential input terminals 102A, 102B as shown in the block diagram of FIG.
Differential conversion circuit 102 that converts a differential signal input from the multiplexor into a single signal, an addition circuit 104 that adds a single signal from an input terminal 112 to an output signal of the differential single conversion circuit 102, and a gain adjustment circuit 106 Are realized by an arithmetic circuit 108 in which the differential
Each circuit of the addition circuit 104 and the gain adjustment circuit 106 is configured using at least one operational amplifier.

[0003]

Therefore, in the conventional arithmetic circuit 108, since an operational amplifier is used for each circuit block, the power consumption of the entire arithmetic circuit 108 is large.
Further, the occupied area on the semiconductor chip or the circuit board has also been increased. In particular, in battery-powered electronic devices and the like, there is a strong demand for low power consumption in order to extend the battery life, and reducing power consumption is an important issue. Furthermore, as a result of the configuration in which operational amplifiers are connected in multiple stages, there is a disadvantage that noise increases. Further, the differential single conversion circuit 102
When it is necessary to select and output one of the single signal 110 output from the external signal and the single signal 112 input from the outside, it is necessary to provide a selector in the addition circuit 104 or the like. Therefore, there is a problem that characteristics such as amplification errors and distortions are deteriorated due to the nonlinearity of the selector.

Accordingly, a main object of the present invention is to reduce the number of operational amplifiers used, thereby realizing low power consumption, miniaturization, and reduction of noise, and furthermore, deterioration of characteristics such as amplification error and distortion. It is an object of the present invention to provide a multi-function arithmetic circuit capable of selecting a signal while minimizing the signal.

[0005]

In order to achieve the above object, the present invention provides an operational amplifier and a first resistor connected between a first input terminal and a non-inverting input terminal of the operational amplifier. And a series circuit comprising first and second switch means;
A series circuit composed of a second resistor and a second switch connected between the input terminal of the operational amplifier and an inverting input terminal of the operational amplifier; a third input terminal and a non-inverting input terminal of the operational amplifier; And a third resistor connected between
A series circuit comprising a fourth resistor and a fourth switch connected between a reference potential point and an inverting input terminal of the operational amplifier; and a non-inverting circuit of the operational amplifier. A first variable resistor connected between an input terminal and the reference potential point; a second variable resistor connected between an inverting input terminal of the operational amplifier and an output terminal of the operational amplifier; It is characterized by having.

In the multifunction operation circuit according to the present invention, the first and second switch means are turned on, the third and fourth switch means are turned off, and the first and second variable resistors are set to appropriate resistance values. If set, a differential amplifier circuit having the first and second input terminals as differential input terminals is formed, and the differential signal input to the first and second input terminals includes only those differential components. Is amplified and converted into a single signal, and output from the output terminal of the operational amplifier. At this time, the amplification degree can be changed by the first and second variable resistors, so that the magnitude of the signal can be adjusted. In addition, the first and second
When the switch means is turned off and the third and fourth switch means are turned on, a non-inverting amplifier circuit having the third input terminal as an input is formed, and a single signal input from the third input terminal is amplified. It is output from the output terminal of the operational amplifier.
At this time, the amplification degree can be changed by the second variable resistor,
The magnitude of the single signal can be adjusted.

When all of the first to fourth switch means are turned on, the circuit functions as a differential amplifier circuit and a non-inverting amplifier circuit, and the differential signal input to the first and second input terminals and , And the single signal input to the third input terminal are added and output from the output terminal of the operational amplifier. When the first and second switch means are turned on and the third and fourth switch means are turned off as described above, even if a single signal is input to the third input terminal, the signal is not applied. Only the differential signal is selectively output without being added. On the contrary, the first and second switch means are turned off,
When the third and fourth switch means are turned on, only the single signal input to the third input terminal is selectively output.

Further, the present invention provides a series circuit comprising an operational amplifier, a first variable resistor connected between a first input terminal and a non-inverting input terminal of the operational amplifier, and first switch means. A series circuit including a second variable resistor and a second switch connected between a second input terminal and an inverting input terminal of the operational amplifier; a third input terminal and a serial circuit of the operational amplifier; A series circuit comprising a third variable resistor and a third switch connected between the non-inverting input terminal and a fourth circuit connected between a reference potential point and the inverting input terminal of the operational amplifier; A series circuit comprising a variable resistor and fourth switch means, a first resistor connected between the non-inverting input terminal of the operational amplifier and the reference potential point, and an inverting input terminal of the operational amplifier. An output terminal of the operational amplifier; A second resistor connected therebetween, a first capacitor connected between the non-inverting input terminal of the operational amplifier and the reference potential point, and an inverting input terminal and an output terminal of the operational amplifier. A second capacitor connected therebetween.

Therefore, the multifunction operation circuit of the present invention has the same basic circuit configuration as the multifunction operation circuit of the invention and can realize the same functions as those of the multifunction operation circuit. Since the first and second capacitors are respectively connected in parallel to the second resistor,
It operates as a differential amplifier circuit or a non-inverting amplifier circuit having primary filter characteristics. As a result, the signal band is limited, and the phase rotation in a high band can be suppressed, so that it is not necessary to use an unnecessarily wide operational amplifier. Therefore, an operational amplifier with low power consumption can be used, and power consumption can be further reduced.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an example of a multi-function operation circuit according to the present invention. As shown in FIG. 1, the multi-function operation circuit 2 according to the present embodiment includes an operational amplifier 4 and a A second resistor 18 and a second resistor 18 connected between a second input terminal 14 and an inverting input terminal 16 of the operational amplifier 4; And a series circuit comprising switch means 20.

The multi-function operation circuit 2 includes a third resistor 24 and a third switch means 26 connected between the third input terminal 22 and the non-inverting input terminal 8 of the operational amplifier 4.
And a fourth resistor 30 connected between the reference potential point 28 and the inverting input terminal 16 of the operational amplifier 4.
And a series circuit comprising the fourth switch means 32. Further, the multi-function arithmetic circuit 2 includes a first variable resistor 34 connected between the non-inverting input terminal 8 of the operational amplifier 4 and the reference potential point 28, the inverting input terminal 16 of the operational amplifier 4 and the operational amplifier 4. And a second variable resistor 36 connected between the output terminal 5 and the second output terminal 5.

The first to fourth switch means 12,
In the present embodiment, 20, 26 and 32 are constituted by MOS transistors. The first and second variable resistors 34 and 36 are respectively provided with resistors 38 and 40 having a plurality of taps (not shown) and one terminal of the first and second variable resistors 34 and 36. Switch means 44 and 46 for selectively connecting 42 to any of the taps, and switch means 44 and 46 in the present embodiment are constituted by MOS transistors.

The resistance values of the first and second resistors 10, 18 are substantially equal to each other, and the third and fourth resistors 24,
The resistance values of 30 are also substantially equal to each other. Then, the ratio between the resistance value of the first variable resistor 34 and the resistance value of the first resistor 10, the resistance value when the first switch means 12 is turned on, and the switch constituting the first variable resistor 34 The ratio of the resistance value when the means 44 is turned on is substantially equal to the ratio between the resistance value of the first variable resistor 34 and the resistance value of the third resistor 24 and the ratio when the third switch means 26 is turned on. Is substantially equal to the ratio of the resistance value when the switch means 44 constituting the first variable resistor 34 is turned on.

Further, first and second switch means 1
The on-state resistances of the second and second switch means 26 and 32 are substantially equal, and the switches constituting the first and second variable resistors 34 and 36 are substantially equal. The on-state resistance values of the means 44 and 46 are substantially equal. Then, the first and second variable resistors 34 and 36 are switched by the switch means 44 and 46 so that they always have the same resistance value. The reference potential point 28 is an output terminal of a constant voltage power supply (not shown) in this embodiment.

In the multi-function operation circuit 2 configured as described above, the first and second switch means 12 and 20 are turned on, the third and fourth switch means 26 and 32 are turned off, and the first and second switch means are turned off. By setting the variable resistors 34 and 36 of the first and second input terminals 6 and 14 to appropriate resistance values,
Is formed as a differential input terminal, and the differential signal input to the first and second input terminals 6 and 14 is
Only those differential components are amplified and the in-phase components are removed, converted into a single signal, and output from the output terminal of the operational amplifier 4 through the output terminal 48 of the multi-function operation circuit 2. At this time, the amplification degree is a value obtained by dividing the resistance value of the first variable resistor 34 by the resistance value of the first resistor 10 (the resistance value of the second variable resistor 36 is changed by the resistance value of the second resistor 18). Therefore, the magnitude of the signal can be adjusted by setting the amplification degree by the first and second variable resistors 34 and 36.

The first and second switch means 1
2, 20 off, third and fourth switch means 26,
When the switch 32 is turned on, a non-inverting amplifier circuit having the third input terminal 22 as an input is formed. The single signal input from the third input terminal 22 is amplified without inverting the phase, and the output of the operational amplifier 4 is output. Output from terminal. At this time, the amplification degree is determined by changing the resistance value of the first variable resistor 34 to the third resistor 24.
Therefore, the amplification degree can be selected by the first and second variable resistors 34 and 36 to adjust the magnitude of the single signal.

The first to fourth switch means 1
When all 2, 20, 26, and 32 are turned on, the circuit functions as a differential amplifier circuit and a non-inverting amplifier circuit, and the differential signal input to the first and second input terminals 6, 14 and
The single signal input to the third input terminal 22 is added and output from the output terminal of the operational amplifier 4.

When the first and second switch means 12 and 20 are turned on and the third and fourth switch means 26 and 32 are turned off as described above, the third input terminal 22 is independently connected to the third input terminal 22. Even if a signal is input, the signal is not added, and only the differential signal is selectively output. Conversely, the first
When the second switch means 12 and 20 are turned off and the third and fourth switch means 26 and 32 are turned on, only the single signal input to the third input terminal 22 is selectively output. .

Further, first to fourth switch means 1
When all 2, 20, 26, and 32 are turned off, the multi-function operation circuit 2 becomes a voltage follower circuit, and the reference potential point 28 input to the non-inverting input terminal 8 of the operation amplifier 4 through the first variable resistor 34. The voltage is output from the operational amplifier 4 through the output terminal 48 with a low impedance almost as it is. As described above, the multi-function operation circuit 2 according to the present embodiment can also function as a voltage follower.

In this embodiment, since only one operational amplifier 4 is used, the power consumption is significantly reduced and the occupied area is reduced as compared with the conventional multi-function operation circuit. In addition, since only one operational amplifier 4 as a noise source is included, noise is reduced and SN
The ratio improves. In addition, a signal can be selected by switching the first to fourth switch means 12, 20, 26, and 32, and the ON resistance value of each switch means can be set as described above. Can be minimized. Further, if the switch means is constituted by a MOS transistor, there is no problem of non-linearity, and no signal distortion occurs.

The amplification of the multi-function operation circuit 2 is determined by the resistance ratio as described above, and therefore, the on-resistance of each switch means affects the amplification of the multi-function operation circuit 2. Therefore, in the present embodiment, as described above, the ratio of the on-resistance value of the switch is also adjusted to the resistance ratio of each resistor, so that the switching means does not cause an error in the amplification degree. As a method of eliminating the influence of the switching means on the amplification, a method of reducing the ON resistance value of the switching means to such a degree that the amplification is not affected may be considered. The switching means is a MOS transistor as in this embodiment.
In the case of using a transistor, the size of the transistor may be increased to reduce the on-resistance value. However, in that case, the parasitic capacitance generated in the MOS transistor also becomes large, and characteristic deterioration such as signal distortion occurs. Therefore, the size of the transistor cannot be made very large, and a method of appropriately setting the ratio of the on-resistance values as in the present embodiment is more realistic than reducing the on-resistance value of the switch means.

Next, a second embodiment will be described. In the multi-function operation circuit 2, the resistance values of the first and second variable resistors 34 and 36 are changed in order to adjust the amplification degree. Therefore, when viewed from the operational amplifier 4, the load changes depending on the amplification degree set. Therefore,
By using an operational amplifier whose bias point changes according to the magnitude of the load in place of the operational amplifier 4, even if the resistance values of the first and second variable resistors 34 and 36 are set to be small, they are more than necessary. The load current can be prevented from flowing, and the current consumption in the operational amplifier 4 can be suppressed to reduce the power consumption of the entire multi-function operation circuit 2.
As the operational amplifier whose bias point changes depending on the size of the load, an operational amplifier including an AB class amplifier circuit or the like can be used.

Next, a third embodiment will be described. FIG. 2 is a circuit diagram showing a multi-function operation circuit according to the third embodiment. In the figure, the same elements as those in FIG. 1 are denoted by the same reference numerals, and a description thereof will be omitted here. As shown in FIG. 2, the multifunction operation circuit 50 according to the third embodiment includes first and second variable resistors 34 and 36.
Is different from the multifunction operation circuit 2 in that first and second capacitors 52 and 54 are connected in parallel to the multifunction operation circuit 2. As a result of connecting the first and second capacitors 52 and 54 in this manner, the high frequency component of the signal to be amplified is suppressed. The frequency of the signal to be suppressed depends on the first and second capacitors 5.
2, 54 capacitors and first and second variable resistors 3
4, 36, etc., and these values are
The signal is set to a value such that a signal having a frequency as low as possible is suppressed as long as the signal input from the first to third input terminals 6, 14, 22 is not attenuated. As a result, the signal band is limited and the phase rotation in the high frequency band can be suppressed, so that it is not necessary to use an unnecessarily wide operational amplifier 4. Since the wideband operational amplifier generally consumes a large amount of power, the elimination of such an operational amplifier 4 leads to a further reduction in the power consumption of the entire circuit.

Next, a fourth embodiment will be described. FIG. 3 is a circuit diagram showing a multi-function operation circuit 2 according to the fourth embodiment. In the drawings, the same elements as those in FIGS. 1 and 2 are denoted by the same reference numerals. As shown in FIG. 3, the multi-function operation circuit 56 according to the third embodiment includes an operational amplifier 4 and
A series circuit comprising a first variable resistor 58 and a first switch means 12 connected between the first input terminal 6 and the non-inverting input terminal 8 of the operational amplifier 4;
4 and the second switch means 20 connected between the second variable resistor 60 and the inverting input terminal 16 of the operational amplifier 4.
And a series circuit comprising:

The multi-function operation circuit 56 is connected to the third variable resistor 62 and the third switch means 26 connected between the third input terminal 22 and the non-inverting input terminal 8 of the operational amplifier 4. And a series circuit comprising a fourth variable resistor 64 and a fourth switch means 32 connected between the reference potential point 28 and the inverting input terminal 16 of the operational amplifier 4.

The multi-function operation circuit 56 includes a first resistor 66 connected between the non-inverting input terminal 8 of the operational amplifier 4 and the reference potential point 28, and an inverting input terminal 16 of the operational amplifier 4. A second resistor 68 connected between the output terminal of the operational amplifier 4 and a first capacitor 7 connected between the non-inverting input terminal 8 of the operational amplifier 4 and the reference potential point 28;
0, and a second capacitor 72 connected between the inverting input terminal 16 and the output terminal of the operational amplifier 4.

The first and second resistors 66 and 68 have substantially equal resistance values, and the first and second capacitors 70 and 72 also have substantially equal capacitance. The first and second variable resistors 58 and 60 are operated in conjunction with each other and set to substantially the same value. The same applies to the third and fourth variable resistors. These variable resistors are, specifically, the first and second variable resistors 3 described above.
As in the case of 4, 36, it can be constituted by a resistor with a tap and a MOS transistor.

Since the first and second capacitors 70 and 72 are connected in parallel to the first and second resistors 66 and 68, the multifunction operation circuit 56 has a differential filter having a first-order filter characteristic. It is a dynamic amplifier circuit (or a non-inverting amplifier circuit), and suppresses a high frequency component of a signal to be amplified, as in the case of the multi-function operation circuit 50. The frequency of the signal to be suppressed is determined by the capacitance of the first and second capacitors 70 and 72, the resistance of the first and second resistors 66 and 68, and the like, and these values are the first to third inputs. The signal is set to a value that suppresses a signal having a frequency as low as possible within a range in which a signal input from the terminals 6, 14, and 22 is not attenuated.

As a result, the signal band is restricted and the phase rotation in the high frequency band can be suppressed, so that it is not necessary to use an unnecessarily wide operational amplifier 4. Therefore, as in the case of the multi-function operation circuit 50, further lower power consumption can be achieved. In the multi-function operation circuit 56, the first and second resistors 6
Reference numerals 6 and 68 denote fixed resistors, and since the adjustment of the amplification is performed by the first to fourth variable resistors, the frequency characteristics do not change even if the amplification is changed. Therefore, the cutoff frequency can be set to a value closer to the frequency of the input signal than in the case of the multi-function operation circuit 50, which is more effective in reducing power consumption. In setting the amplification degree and the like, the first to fourth switch means 12, 20, 2,
By including the on-resistance values of 6, 32 in the resistance values of the first to fourth variable resistors respectively connected in series, necessary differential amplification characteristics and the like can be secured.

[0030]

As described above, in the multi-function operation circuit according to the present invention, the first and second switch means are turned on and the third switch means is turned on.
And the fourth switch means are turned off, and the first and second switch means are turned off.
Is set to an appropriate resistance value, a differential amplifier circuit having the first and second input terminals as differential input terminals is formed, and the differential amplifier input to the first and second input terminals is formed. The dynamic signal is converted into a single signal by amplifying only those differential components and output from the output terminal of the operational amplifier. At this time, the amplification degree can be changed by the first and second variable resistors, so that the magnitude of the signal can be adjusted.
Further, when the first and second switch means are turned off and the third and fourth switch means are turned on, a non-inverting amplifier circuit having the third input terminal as an input is formed. The single signal is amplified and output from the output terminal of the operational amplifier. At this time, the amplification degree can be changed by the second variable resistor, and the magnitude of the single signal can be adjusted.

When all of the first to fourth switch means are turned on, the circuit functions as a differential amplifier circuit and a non-inverting amplifier circuit, and the differential signal inputted to the first and second input terminals and , And the single signal input to the third input terminal are added and output from the output terminal of the operational amplifier. Further, when the first and second switch means are turned on and the third and fourth switch means are turned off as described above, even if a single signal is input to the third input terminal, the signal is not applied. Only the differential signal is selectively output without being added. On the contrary, the first and second switch means are turned off,
When the third and fourth switch means are turned on, only the single signal input to the third input terminal is selectively output.

Since the multi-function operation circuit of the present invention is configured using only one operation amplifier, the power consumption is significantly reduced and the occupied area is reduced as compared with the conventional multi-function operation circuit. In addition, since only one operational amplifier, which is a noise source, is included, noise is reduced and S
The N ratio is improved. In addition, a signal can be selected by switching the first to fourth switch means, and an error in the amplification degree can be minimized by appropriately setting the on-resistance value of each switch means. Each switch means can be constituted by, for example, a MOS transistor. In this case, there is no problem of non-linearity, and no signal distortion occurs. That is, according to the present invention, a signal can be selected without causing an error in amplification degree or signal distortion.

Further, in the multi-function operation circuit of the present invention, since the first and second capacitors are connected in parallel to the first and second resistors, respectively, the differential amplifier having the first-order filter characteristic is provided. It operates as a circuit or a non-inverting amplifier circuit. As a result, the signal band is limited, and the phase rotation in a high band can be suppressed, so that it is not necessary to use an unnecessarily wide operational amplifier. for that reason,
An operational amplifier with low power consumption can be used, and power consumption can be further reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a multi-function operation circuit according to the present invention.

FIG. 2 is a circuit diagram showing a multifunction operation circuit according to a third embodiment.

FIG. 3 is a circuit diagram showing a multi-function operation circuit according to a fourth embodiment.

FIG. 4 is a block diagram illustrating an example of a conventional multi-function operation circuit.

[Explanation of symbols]

2... Multi-function arithmetic circuit, 4... Operational amplifier, 6.
, Non-inverted input terminal, 10 ... first resistor, 12 ... first switch means, 14 ... second input terminal, 16 ... inverted input terminal, 18 ... 2 resistors, 20 second switch means, 22 third input terminal, 24 third resistor, 26 third switch means, 28 reference potential point, 30 ... the fourth resistor, 3
2... 4th switch means, 34... 1st variable resistor, 36... 2nd variable resistor, 38.
... Resistor 42, one terminal 44 switch means 46 switch means 48 output terminal 50
... Multi-function operation circuit, 52 ... First capacitor, 54 ...
... second capacitor, 56 ... multi-function operation circuit, 58 ...
... a first variable resistor, 60 ... a second variable resistor, 62
... Third variable resistor, 64... Fourth variable resistor, 6
6 first resistor, 68 second resistor, 70
First capacitor, 72... Second capacitor, 102
...... Differential single conversion circuit, 104 ... Addition circuit, 106 ...
... Gain adjustment circuit, 108 arithmetic circuit, 110 single signal, 112 single signal.

Claims (13)

(57) [Claims] An operational amplifier; a series circuit comprising a first resistor and first switch means connected between a first input terminal and a non-inverting input terminal of the operational amplifier; A series circuit composed of a second resistor and a second switch connected between an input terminal and an inverting input terminal of the operational amplifier; and a third circuit connected to a third input terminal and a non-inverting input terminal of the operational amplifier. A series circuit comprising a third resistor and third switch means connected therebetween; a fourth resistor and a fourth switch connected between a reference potential point and an inverting input terminal of the operational amplifier. A first series resistor connected between a non-inverting input terminal of the operational amplifier and the reference potential point; an inverting input terminal of the operational amplifier and an output terminal of the operational amplifier. Second possible connected between A multi-function arithmetic circuit comprising a variable resistor. 2. The multi-function operation according to claim 1, wherein a differential signal is input to the first and second input terminals, and a single signal is input to the third input terminal. circuit. 3. The method according to claim 1, wherein the first to fourth switch means are M
2. The multi-function operation circuit according to claim 1, wherein the multi-function operation circuit comprises an OS transistor. 4. The first and second variable resistors each include a resistor having a plurality of taps, and one terminal of the first and second variable resistors is selectively connected to one of the taps. 2. The multi-function arithmetic circuit according to claim 1, further comprising switch means connected to said multi-function arithmetic circuit. 5. The multi-function operation circuit according to claim 4, wherein said switch means comprises a MOS transistor. Wherein said resistance values of the first and second resistors etc. properly in <br/> each other, the resistance value of the third and fourth resistors rather equal to each other, the first The ratio between the resistance value of the variable resistor and the resistance value of the first resistor, the resistance value when the first switch means is turned on, and the resistance when the switch means constituting the first variable resistor is turned on. etc. properly the ratio of values, the first and the ratio of the resistance value and the resistance value of the third resistor of the variable resistor, said third switch means oN when the resistance value and the first variable wherein etc. properly the ratio of the resistance value at the on-state of the switching means constituting the resistor, the resistance value of the oN state of the first and second switching means
Etc. properly, the resistance value of the ON state of the third and fourth switching means
Etc. properly, the first and second multi-function arithmetic circuit according to claim 5, wherein the resistance value of the ON state of the switching means constituting the variable resistor is characterized by equal correct. 7. The first and second variable resistors are connected to each other.
Multifunctional arithmetic circuit according to claim 1, characterized in that it is set to a value equal to. 8. The multifunction operation circuit according to claim 1, wherein said reference potential point is an output terminal of a constant voltage power supply. 9. The multi-function arithmetic circuit according to claim 1, wherein a bias point of the operational amplifier changes according to a magnitude of a load. 10. The multi-function arithmetic circuit according to claim 9, wherein said operational amplifier is constituted by an AB class amplifier circuit. 11. A first capacitor connected between a non-inverting input terminal of the operational amplifier and the reference potential point,
2. The multi-function arithmetic circuit according to claim 1, further comprising a second capacitor connected between an inverting input terminal and an output terminal of the operational amplifier. 12. A series circuit comprising an operational amplifier, a first variable resistor connected between a first input terminal and a non-inverting input terminal of the operational amplifier, and first switch means; A series circuit comprising a second variable resistor and second switch means connected between the input terminal of the operational amplifier and an inverting input terminal of the operational amplifier; a third input terminal and a non-inverting input terminal of the operational amplifier A series circuit consisting of a third variable resistor and third switch means connected between the third variable resistor and a third variable resistor connected between a reference potential point and an inverting input terminal of the operational amplifier; A series circuit comprising fourth switch means; a first resistor connected between the non-inverting input terminal of the operational amplifier and the reference potential point; an inverting input terminal of the operational amplifier and the operational amplifier; Connect to output terminal A second resistor, a first capacitor connected between the non-inverting input terminal of the operational amplifier and the reference potential point, and a capacitor connected between the inverting input terminal and the output terminal of the operational amplifier. And a second capacitor. Wherein said first and second resistors to one another
It has equal correct resistance value, the first and second capacitors multifunctional arithmetic circuit according to claim 12, wherein it has an equal correct capacity each other <br/> physician.