JPWO2018180111A1 - Noise removal circuit - Google Patents

Abstract

A voltage difference signal between the first input signal terminal (1) and the second input signal terminal (2) is attenuated at a predetermined ratio and converted into a voltage signal based on the voltage of the reference voltage terminal (3). And has an attenuator function of outputting to an output signal terminal (4), and in-phase between the first input signal terminal (1) and the second input signal terminal (2) and the reference voltage terminal (3). The noise removal circuit (100) for removing the noise input at the output signal terminal (4) from the output signal output from the output signal terminal (4) has one end connected to the first input signal terminal (1) and the other end connected to the first input signal terminal (1). A first resistor (5) connected to the output signal terminal (4), one end is connected to a path connecting the output signal terminal (4) and the other end of the first resistor (5), and the other end is a reference. A second resistor (6) connected to the voltage terminal (3), and a voltage difference between the reference voltage terminal (3) and the second input signal terminal (2). Comprising a current converter (7), a - is converted into a current, voltage and outputs a current signal to an output signal terminal (4).

Description

  The present disclosure relates to a noise removal circuit.

  When an arbitrary voltage signal is detected in a noise environment, noise generated between the ground potential of the input signal and the ground potential of the signal detection circuit is applied to both the positive and negative input signal terminals of the signal detection circuit in the same phase and the same amplitude (common). A technique for removing common mode noise with a subtraction circuit configuration using an operational amplifier is disclosed in order for the signal detection circuit to correctly detect an input signal even when the signal is superimposed by (mode noise). (For example, see Patent Documents 1 and 2).

U.S. Pat. No. 8,803,595 U.S. Pat. No. 5,568,561

  However, the circuits using the operational amplifiers disclosed in Patent Documents 1 and 2 have a subtraction circuit configuration on the assumption that feedback control is performed, and an operational amplifier having a finite circuit delay time naturally has a target value above an arbitrary frequency band. On the other hand, the feedback control cannot be followed, and the feedback control may be deviated and the subtraction function may not be performed. For this reason, the circuit configurations of Patent Documents 1 and 2 have a problem that a sufficient common mode noise removing effect cannot be obtained in a high frequency band.

  The present disclosure is intended to solve such a conventional problem, and an object of the present disclosure is to provide a noise elimination circuit that can effectively eliminate common mode noise with a simple circuit configuration.

  To achieve the above object, a noise elimination circuit according to an embodiment of the present disclosure attenuates a difference voltage signal between a first input signal terminal and a second input signal terminal at a predetermined ratio, and An attenuator function of converting the voltage of the voltage terminal into a voltage signal with reference as a reference and outputting the voltage signal to an output signal terminal; A noise removing circuit for removing noise input in-phase from the output signal output from the output signal terminal, one end of which is connected to the first input signal terminal, and the other end of which is the output signal. A first resistor connected to a terminal, a second resistor connected at one end to a path connecting the output signal terminal and the other end of the first resistor, and a second end connected to the reference voltage terminal; , The difference voltage between the reference voltage terminal and the second input signal terminal Converted into a current, a voltage and outputs a current signal to the output signal terminal - characterized in that comprises a current converter, a.

  According to the present disclosure, a noise removing circuit that can effectively remove common mode noise with a simple circuit configuration is realized.

FIG. 1 is a circuit configuration diagram of the noise removal circuit according to the embodiment. FIG. 2 is a circuit configuration diagram showing an example of a general noise removal circuit. FIG. 3 is a circuit configuration diagram showing another example of a general noise removal circuit. FIG. 4A is a circuit configuration diagram illustrating an example of the voltage-current converter according to the embodiment. FIG. 4B is a circuit configuration diagram showing another example of the voltage-current converter according to the embodiment.

  Based on the findings of the present inventors, an outline of one embodiment of the present disclosure is as follows.

  A noise removal circuit according to an embodiment of the present disclosure attenuates a difference voltage signal between a first input signal terminal and a second input signal terminal at a predetermined ratio, and uses a voltage of a reference voltage terminal as a reference. It has a function of an attenuator that converts the voltage into a voltage signal and outputs the voltage signal to an output signal terminal, and suppresses noise input in phase between the first input signal terminal, the second input signal terminal, and the reference voltage terminal. A noise removing circuit for removing an output signal output from the output signal terminal, wherein one end is connected to the first input signal terminal and the other end is connected to the output signal terminal. A resistor, one end of which is connected to a path connecting the output signal terminal and the other end of the first resistor, and the other end of which is connected to the reference voltage terminal; 2 is converted to a current, Characterized in that comprises a current converter, a - voltage for outputting a current signal to the signal terminal.

  According to this, the noise elimination circuit of the present disclosure has a simple circuit configuration including at least two resistors and a voltage-current converter, and does not use an operational amplifier. And common-mode noise can be sufficiently removed up to a high frequency band. As described above, according to the noise removing circuit of the present disclosure, common mode noise can be effectively removed with a simple circuit configuration.

  The voltage-current converter may not have a negative feedback loop for returning an output signal to an input signal terminal.

  In the noise elimination circuit of the present disclosure, there is no risk of oscillation because there is no negative feedback loop that causes oscillation. Therefore, a phase compensation circuit or the like is not required, and the circuit can be simplified. In the case of a semiconductor integrated circuit, the chip area can be reduced.

  Further, a ground potential of a first ground point is applied to the second input signal terminal, a ground potential of a second ground point is applied to the reference voltage terminal, and the voltage-current converter is A negative input signal terminal to which the ground potential of the first ground point is applied by being connected to the second input signal terminal; and a ground potential of the second ground point which is connected to the reference voltage terminal. And a positive-polarity input signal terminal to which is applied.

  According to this, noise existing between the ground potential at the first ground point and the ground potential at the second ground point can be removed from the output signal output from the output signal terminal. Further, the mutual conductance of the voltage-current converter can be set to be the reciprocal of the resistance value of the first resistor without depending on the resistance value of the second resistor. Specifically, in the noise elimination circuit of the present disclosure, the condition for removing the noise component does not include the second resistor, but the input / output voltage gain is determined by the resistance of the first resistor and the resistance of the second resistor. It can be changed by the ratio with the value. Accordingly, when the input / output voltage gain of the input / output signal, that is, the attenuation ratio (predetermined ratio) is changed by changing the resistance value of the second resistor while keeping the resistance value of the first resistor constant, voltage-current conversion is performed. If the transconductance of the converter is the reciprocal of the resistance of the first resistor, sufficient noise removal can be performed without changing the transconductance of the voltage-current converter even if the resistance of the second resistor is changed. be able to.

  Further, the voltage-current converter may adapt a transconductance of the voltage-current converter to a reciprocal of a resistance value of the first resistor. Further, the transconductance of the voltage-current converter does not depend on the resistance value of the second resistor, and the voltage-current converter changes the predetermined value by changing the resistance value of the second resistor. May be changed so that the transconductance of the voltage-current converter is adapted only to the reciprocal of the resistance value of the first resistor.

  In this way, the voltage-current converter can adapt the transconductance to the reciprocal of the resistance of the first resistor.

  Further, the voltage-current converter may be constituted by a circuit that does not require a negative voltage power supply to the reference voltage terminal.

  According to this, common mode noise can be effectively removed with a simpler circuit configuration.

  Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Each of the embodiments described below shows a specific example of the present disclosure. Numerical values, shapes, materials, constituent elements, arrangement positions and connection forms of constituent elements, drive timings, and the like shown in the following embodiments are merely examples, and do not limit the present disclosure. In addition, among the components in the following embodiments, components that are not described in independent claims indicating the highest concept of the present disclosure are described as arbitrary components. In addition, each drawing is not necessarily strictly illustrated. In each of the drawings, duplicate descriptions of substantially the same configuration will be omitted or simplified.

(Embodiment)
FIG. 1 is a circuit configuration diagram of the noise removal circuit 100 according to the embodiment. FIG. 1 shows the input signal 8, the first ground point 11, and the second ground point 10 connected to the noise elimination circuit 100, in addition to the noise elimination circuit 100. The positive side of the input signal 8 is connected to the first input signal terminal 1 of the noise elimination circuit 100, and the negative side is connected to the second input signal terminal 2 of the noise elimination circuit 100. The negative side of the input signal 8 is connected to the first ground point 11.

  The noise elimination circuit 100 attenuates the difference voltage signal between the first input signal terminal 1 and the second input signal terminal 2 at a predetermined ratio to generate a voltage signal based on the voltage of the reference voltage terminal 3. It has the function of an attenuator for converting and outputting to the output signal terminal 4. Generally, at the input stage of an electronic device, when using such an attenuator to convert the amplitude of the input signal into an appropriate amplitude that can be processed by the electronic circuit of the electronic device, the ground potential of the input signal, Noise generated between the ground potentials of the voltage signal detection circuit constituting the attenuator may cause the voltage signal detection circuit to be superimposed on both the positive and negative input signal terminals with the same phase and the same amplitude. This superimposed signal is called common mode noise, and is a signal that hinders correct detection, and therefore needs to be removed. On the other hand, the noise removing circuit 100 is a circuit having a function of removing common mode noise superimposed on the positive and negative input signal terminals with the same phase and the same amplitude in an attenuator used in an electronic device. Specifically, the noise elimination circuit 100 outputs noise input in-phase between the first input signal terminal 1 and the second input signal terminal 2 and the reference voltage terminal 3 from the output signal terminal 4. This is a circuit for removing from the output signal. The noise elimination circuit 100 includes a first resistor 5, a second resistor 6, and a voltage-current converter 7 to realize the function.

  The first resistor 5 has one end connected to the first input signal terminal 1 and the other end connected to the output signal terminal 4. One end of the first resistor 5 is the left end of the first resistor 5 in FIG. 1, and the other end of the first resistor 5 is the right end of the first resistor 5 in FIG. One end of the first resistor is connected to the positive side of the input signal 8 via the first input signal terminal 1.

  The second resistor 6 has one end connected to a path connecting the output signal terminal 4 and the other end of the first resistor 5, and the other end connected to the reference voltage terminal 3. One end of the second resistor 6 is the upper end of the second resistor 6 in FIG. 1, and the other end of the second resistor 6 is the lower end of the second resistor 6 in FIG. The other end of the second resistor 6 is connected to the second ground point 10 via the reference voltage terminal 3. The second resistor 6 is, for example, a variable resistor.

The voltage-current converter 7 converts a difference voltage between the reference voltage terminal 3 and the second input signal terminal 2 into a current and outputs a current signal to the output signal terminal 4. The ground potential V _g1 of the first ground point 11 is applied to the second input signal terminal 2, and the ground potential V _g2 of the second ground point 10 is applied to the reference voltage terminal 3. The voltage-current converter 7 is connected to the second input signal terminal 2, and is connected to the negative input signal terminal to which the ground potential V _g1 of the first ground point 11 is applied and the reference voltage terminal 3. Thus, a positive input signal terminal to which the ground potential _Vg2 of the second ground point 10 is applied is provided.

Further, as shown in Figure 1, the ground potential _{V g1} of the input signal 8, the potential difference _{V cmn} with respect to the ground potential _{V g2} represents the amplitude of the noise signal generated between the ground potential _{V g2} and the ground potential _{V g1} When viewed from the second ground point 10 (ground potential V _g2 ), common mode noise superimposed on the positive and negative input signal terminals of the input signal 8 with the same phase and the same amplitude hinders detection of a correct input signal. The noise is removed by the noise removing circuit 100.

  Here, in order to facilitate understanding of the present embodiment, a general circuit will be described below with reference to the drawings.

  FIG. 2 is a circuit configuration diagram showing an example of a general noise removal circuit. FIG. 2 shows a general circuit (noise elimination circuit 100a). Specifically, the noise elimination circuit 100a is a differential amplifier circuit using a general operational amplifier (op-amp), Used for mode noise removal.

  The noise elimination circuit 100a outputs a difference voltage between the first input signal terminal 1 and the second input signal terminal 2 to the output signal terminal 4 as a voltage signal for the reference voltage terminal 3. The positive side of the input signal 8 is connected to one end of the first resistor 5 via the first input signal terminal 1, and the other end of the first resistor 5 is connected to one end of the second resistor 6 and the positive input of the operational amplifier 33. The other end of the second resistor 6 is connected to the second ground point 10 via the reference voltage terminal 3. The negative side of the input signal 8 is connected to one end of the third resistor 31 via the second input signal terminal 2, and the other end of the third resistor 31 is connected to one end of the fourth resistor 32 and the negative input of the operational amplifier 33. The other end of the fourth resistor 32 is connected to the output signal terminal 4 of the operational amplifier 33.

As in FIG. 1, in the noise removing circuit 100a, the potential difference V _cmn of the ground potential of the input signal 8 (the ground potential V _{g1 of} the first ground point 11) with respect to the ground potential V _g2 of the second ground point 10 is _equal to the ground potential. The amplitude of the noise signal generated between the potential V _g1 and the ground potential V _g2 is shown.

In the noise removal circuit 100a, the first resistor 5, the second resistor 6, a third resistor 31, the fourth resistor 32 to the resistance values and _{R 1,} R _{2, R} 3, _{R 4,} an input signal The voltage gain G _Vin of the output signal with respect to 8 can be expressed by the following equation (1) when the voltage gain of the operational amplifier 33 is sufficiently high.

G _Vin = (1 + R ₄ / R ₃ ) / (1 + R ₁ / R ₂ ) Equation (1)

_Therefore, it is possible to change the voltage gain By changing the value of R 1 / _{R 2} or _R 4 / _{R 3.}

On the other hand, the voltage gain G _Vcm of the output signal with respect to the amplitude V _cmn of the noise signal can be expressed by the following equation (2).

_{G Vcm = (R 2 / R} 1 -R 4 / R 3) / (1 + R 2 / R 1) (2)

The noise component can be removed from the output by setting G _Vcm to zero. The condition can be expressed by the following equation (3).

_{R 2 / R 1 = R 4} / R 3 formula (3)

That is, it is possible to remove the common mode noise component by making the values of the resistance ratios R ₂ / R ₁ and R ₄ / R ₃ equal.

In the noise removal circuit 100a, the voltage gain _{G Vin} of Formula (1) When switching by changing the values of _{R 2,} so that the voltage gain _{G Vcm} is zero for the noise signal, namely, the formula (3) It is necessary to change the value of R ₃ or R ₄ so that In this case, a method of changing the value of R _{4 according to} the value of R ₂ is generally used. Therefore, when changing the voltage gain by changing the value of R _2, in proportion to the value of R ₂ is required to change the value of R _4.

In this case, the circuit becomes complicated and the scale becomes large, and it becomes difficult to make the relative ratios of R ₂ / R ₁ and R ₄ / R ₃ exactly equal by changing R ₂ and R ₄ . When the relative ratios do not match, there is a problem that noise cannot be sufficiently removed.

  The noise elimination circuit 100a uses the operational amplifier 33 to apply negative feedback from the output to the input. However, applying negative feedback always involves the risk of oscillation, so the noise elimination circuit 100a is designed with attention to oscillation stability. There is a need. In general, it is necessary to take measures such as adding a phase compensation circuit inside the operational amplifier 33 so as not to oscillate, so that the circuit becomes complicated and the chip area increases when a semiconductor integrated circuit is used. Problems arise.

  Further, the operational amplifier has a characteristic that the frequency band is limited in order to avoid the risk of oscillation. This characteristic causes a problem that common mode noise cannot be sufficiently removed due to a decrease in gain and a phase shift in a high frequency band.

  FIG. 3 is a circuit configuration diagram showing another example of a general noise removal circuit. FIG. 3 shows a general circuit (noise elimination circuit 100b). Specifically, the noise elimination circuit 100b is a general differential amplifier circuit different from the circuit shown in FIG.

  The noise elimination circuit 100b outputs a difference voltage between the first input signal terminal 1 and the second input signal terminal 2 to the output signal terminal 4 as a voltage signal with respect to the reference voltage terminal 3, similarly to the noise elimination circuit 100a.

  The noise elimination circuit 100b has a configuration in which, as shown in FIG. 3, in addition to the differential amplifier circuit shown in FIG. 2, the input stage includes a balanced input / differential output amplifier circuit. .

  The positive side of the input signal 8 is connected to the positive input terminal of the operational amplifier 34 via the first input signal terminal 1, and the negative side of the input signal 8 is connected to the positive input terminal of the operational amplifier 35 via the second input terminal 2. Connected to signal terminal. A fifth resistor 36 is connected between the negative input signal terminal of the operational amplifier 34 and the negative input signal terminal of the operational amplifier 35, and a sixth resistor 36 is connected between the negative input signal terminal of the operational amplifier 34 and the output signal terminal of the operational amplifier 34. , And a seventh resistor 38 is connected between the negative input signal terminal of the operational amplifier 35 and the output signal terminal of the operational amplifier 35. The output signal terminal of the operational amplifier 34 is connected to the first resistor 5 described in FIG. 2, and the output signal terminal of the operational amplifier 35 is connected to the third resistor 31 described in FIG.

2 Similarly noise removal circuit 100b, the potential difference _{V cmn} with respect to the ground potential _{V g2} of the ground potential _{V g1} of the input signal 8, represents the amplitude of the noise signal generated between the ground potential _{V g2} and the ground potential _{V g1} I have.

Since the voltage gains of the output of the operational amplifier 34 and the output of the operational amplifier 35 with respect to the amplitude V _{cmn of the} noise signal are both 1, the voltage gain G _Vcm of the output signal of the operational amplifier 33 with respect to the amplitude V _cmn of the noise signal is Equivalent to equation (2). Therefore, the condition for removing the noise component from the output is also equal to the equation (3).

  When changing the voltage gain for the input signal 8 in the noise removing circuit 100b, the voltage gain can be changed only by the value of the fifth resistor 36, and the influence on the common-mode signal rejection ratio is small even if the values of the other resistors are not changed at the same time.

  However, since the noise removing circuit 100b is a circuit using three operational amplifiers and seven resistors, there is a problem that the noise removing circuit 100b is complicated and large in scale.

  In addition, since the noise removal circuit 100b applies negative feedback to each of the three operational amplifiers, there is a danger of oscillation, and a problem arises in that a phase compensation circuit must be added to deal with the risk.

  Further, as described above, the operational amplifier has a characteristic that the frequency band is limited in order to avoid the risk of oscillation, and the noise reduction circuit 100b has a characteristic such that the gain reduction or the phase shift in the high frequency band is caused by the characteristic. This causes a problem that common mode noise cannot be sufficiently removed.

  On the other hand, the noise removal circuit 100 according to the present embodiment can solve the above-described problem. Hereinafter, the details will be described with reference to FIG.

First, in the noise removing circuit 100, the voltage - the transconductance of the current converter 7 and g _m, when the first resistor 5 and the resistance values the second resistor 6 and R _1, R _2, with respect to the input signal 8 The voltage gain G _Vin of the output signal can be expressed by the following equation (4).

G _Vin = 1 / (1 + R ₁ / R ₂ ) Equation (4)

Therefore, the noise removal circuit 100 can change the voltage gain by changing the value of R ₁ / R ₂ .

On the other hand, the voltage gain G _Vcm of the output signal with respect to the amplitude V _cmn of the noise signal can be expressed by the following equation (5).

_{G Vcm = (1-R 1} g m) / (1 + R 1 / R 2) (5)

The noise component can be removed from the output by setting G _Vcm to zero.

  The condition can be expressed by the following equation (6).

g _m = 1 / R ₁ Equation (6)

As shown in equation (6), the voltage - transconductance g _m of the current converter 7 is not dependent on the resistance of the second resistor 6, is the reciprocal of the resistance value of the first resistor 5 . That noise removal circuit 100 includes a voltage - the common mode noise component by the transconductance g _m of the current converter 7 to 1 / R ₁ is the inverse of the resistance of the first resistor 5 most effectively Can be removed. For example, the voltage-current converter 7 adapts the transconductance g _m of the voltage-current converter 7 to the reciprocal of the resistance value of the first resistor 5.

Further, in the noise elimination circuit 100, R ₂ is not included in Expression (6) of the condition for removing the noise component, but the input / output voltage gain G _Vin represented by Expression (4) is R ₁ / R ₂ Can be changed.

Therefore, the noise elimination circuit 100 changes the input / output voltage gain of the input / output signal, that is, the attenuation ratio, by changing the resistance value R2 of the _second resistor 6 while keeping the resistance value R1 of the _first resistor 5 constant. when the voltage - if the transconductance g _m of the current converter 7 is adapted to the reciprocal of the resistance value R ₁ of the first resistor 5, without changing the mutual conductance g _m be changed resistance value R ₂ , Sufficient noise removal can be performed. For example, a voltage - current converter 7, changing the predetermined proportions (damping ratio) by varying the resistance value of the second resistor 6, the voltage - current converter 7 transconductance g _m first resistor in the resistance of the Fit only the reciprocal of the value 5.

  In addition, the noise elimination circuit 100 of the present embodiment does not have a risk of oscillation because there is no negative feedback loop in which the output signal returns to the input signal terminal. This eliminates the need for a phase compensation circuit or the like that needs to be added inside the operational amplifier, simplifies the circuit, and reduces the chip area for a semiconductor integrated circuit.

  Further, since the voltage-current converter 7 is used without using the operational amplifier, a decrease in gain and a phase shift hardly occur in the high frequency band, and the common mode noise can be sufficiently removed up to the high frequency band. Further, in order to obtain the same noise removing effect, three operational amplifiers and seven resistors were used in the noise removing circuit 100b. However, in the noise removing circuit 100, one voltage-current converter 7 and two resistors were used. And a simple circuit configuration.

  Next, the details of the voltage-current converter 7 provided in the noise removal circuit 100 of the present embodiment will be described.

  FIG. 4A is a circuit configuration diagram illustrating an example of the voltage-current converter 7 according to the present embodiment.

  In the voltage-current converter 7 shown in FIG. 4A, a terminal 12 is a positive input signal terminal of the voltage-current converter 7, a terminal 13 is a negative input signal terminal of the voltage-current converter 7, and a terminal 14 is a voltage-current converter. 7 is an output signal terminal.

  In the voltage-current converter 7, a constant current source 18 and one end of a resistor 19 are connected to an emitter of a PNP transistor 16 whose base is connected to a terminal 12, and an emitter of a PNP transistor 15 whose base is connected to a terminal 13. Is connected to the other end of the constant current source 17 and the resistor 19.

  Assuming that the current of the constant current source 18 and the current of the constant current source 17 are equal at Iref, and that the base-emitter voltage of the PNP transistor 16 and the base-emitter voltage of the PNP transistor 15 are equal at a constant value, the resistor 19 has A current having a value obtained by dividing the voltage between the positive and negative input signal terminals by the resistance value flows. A current obtained by subtracting a current flowing from the constant current source 18 to the resistor 19 flows through the emitter of the PNP transistor 16. A constant current flows through the emitter of the PNP transistor 15. A current flows, which is obtained by adding the current flowing from the current source 17 to the resistor 19.

  The collector current of the PNP transistor 16 supplies a negative current to the terminal 14 via the current mirror including the NPN transistor 20 and the NPN transistor 21, and the collector current of the PNP transistor 15 corresponds to the current of the NPN transistor 22 and the NPN transistor 23. A positive current is supplied to the terminal 14 via a mirror and further via a current mirror including a PNP transistor 24 and a PNP transistor 25.

From the terminal 14, a current having a difference between the collector current of the PNP transistor 15 and the collector current of the PNP transistor 16 is output. When the resistance value of the resistor 19 and _{R 8,} the voltage - transconductance _{g m} of the current converter 7 _will g m = 2 / _{R 8.}

  When the circuit shown in FIG. 4A is used as the voltage-current converter 7 provided in the noise elimination circuit 100 of the present embodiment, there is no danger of oscillation because no negative feedback is applied, and the gain is high in a high frequency band. Common mode noise up to high frequencies can be sufficiently removed while preventing the drop and the phase shift.

  FIG. 4B is a circuit configuration diagram illustrating another example of the voltage-current converter 7 according to the present embodiment.

  In the voltage-current converter 7 shown in FIG. 4B, a terminal 12 is a positive input signal terminal of the voltage-current converter 7, a terminal 13 is a negative input signal terminal of the voltage-current converter 7, and a terminal 14 is a voltage-current converter. 7 is an output signal terminal.

  The terminal 12 is connected to one end of the resistor 40, the other end of the resistor 40 is connected to the source of the NchMOSFET 29, the terminal 13 is connected to one end of the resistor 39, and the other end of the resistor 39 is connected to the source of the NchMOSFET 28. I have. The gate and the drain of the NchMOSFET 28 are connected to the constant current source 17 and the gate of the NchMOSFET 29, and the drain of the NchMOSFET 29 is connected to the constant current source 18 and the terminal 14.

Assuming that the current values of the constant current source 17 and the constant current source 18 are equal at Iref, the gate-source voltage of the NchMOSFET 28 and the gate-source voltage of the NchMOSFET 29 are constant and equal, and the resistance values of the resistors 39 and 40 are equal. , from the terminal 14 is output current of the voltage divided by the resistance value R ₁₀ of the resistor 40 between the positive input signal terminal and the negative input signal terminal. Than this, the voltage - transconductance _{g m} of the current converter 7 _will g m = 1 _{/ R 10.}

The voltage-current converter 7 shown in FIG. 4B has a drawback that a current of Iref flows through the negative input signal terminal and a current of Iref ± V _cmn / R ₁₀ flows through the positive input signal terminal, but the connection destination is the first connection in FIG. These are the point 11 and the second grounding point 10, both of which have low impedance and do not cause potential fluctuation even when current flows therein, so that there is no influence on the voltage gain characteristics.

  Also, as shown in FIG. 1, when each input signal terminal of the voltage-current converter 7 is connected to the ground point and the potential is zero, in the voltage-current converter 7 shown in FIG. 4B is required to supply a negative voltage power to the terminal 27 and the terminal 27, whereas the voltage-current converter 7 shown in FIG. The advantage is that it can be operated just by doing. As described above, the voltage-current converter 7 illustrated in FIG. 4B is configured by a circuit that does not need to supply a negative voltage power to the reference voltage terminal 3.

  Also, in the case where the circuit of FIG. 4B is used as the voltage-current converter 7 provided in the noise elimination circuit 100 of the present embodiment, similarly to the case of FIG. In addition, common mode noise can be sufficiently removed up to the high frequency band by preventing gain reduction and phase shift in the high frequency band.

Above, the voltage shown in FIGS. 4A and 4B - one of the current converter 7, by using the noise eliminating circuit 100 of the present embodiment shown in FIG. 1, the transconductance g _m Equation (6) Can be set according to the resistance value of the first resistor 5 so that an optimum common-mode signal rejection ratio can be obtained up to a high frequency band. Further, since no negative feedback is applied, there is no danger of oscillation, and it is possible to prevent a decrease in gain and a phase shift in a high frequency band.

  As described above with reference to the drawings, the noise elimination circuit according to the present embodiment can be configured by a simple circuit including only a resistor and a voltage-current converter, and depends on a change in a voltage gain set as an attenuator. It is always optimal and can remove common mode noise over a wide frequency band.

REFERENCE SIGNS LIST 1 first input signal terminal 2 second input signal terminal 3 reference voltage terminal 4 output signal terminal 5 first resistor 6 second resistor 7 voltage-current converter 8 input signal 10 second ground point 11 first Ground points 12 to 14, 26, 27 Terminals 15, 16, 24, 25 PNP transistors 17, 18 Constant current sources 19, 39, 40 Resistors 20 to 23 NPN transistors 28, 29 Nch MOSFET
31 third resistor 32 fourth resistor 33-35 operational amplifier 36 fifth resistor 37 sixth resistor 38 seventh resistor 100, 100a, 100b noise removal circuit

Claims (6)

A differential voltage signal between the first input signal terminal and the second input signal terminal is attenuated at a predetermined ratio, converted to a voltage signal based on the voltage of the reference voltage terminal, and output to the output signal terminal. It has the function of an attenuator, and converts noise input in phase between the first input signal terminal and the second input signal terminal and the reference voltage terminal from an output signal output from the output signal terminal. A noise removing circuit for removing,
A first resistor having one end connected to the first input signal terminal and the other end connected to the output signal terminal;
A second resistor having one end connected to a path connecting the output signal terminal and the other end of the first resistor, and the other end connected to the reference voltage terminal;
A voltage-current converter that converts a difference voltage between the reference voltage terminal and the second input signal terminal into a current and outputs a current signal to the output signal terminal;
A noise elimination circuit comprising:   2. The noise removal circuit according to claim 1, wherein the voltage-current converter has no negative feedback loop in which an output signal returns to an input signal terminal. A ground potential of a first ground point is applied to the second input signal terminal, a ground potential of a second ground point is applied to the reference voltage terminal,
The voltage-current converter is connected to the second input signal terminal, and is connected to the negative input signal terminal to which the ground potential of the first ground point is applied, and to the reference voltage terminal. The noise elimination circuit according to claim 1, further comprising a positive input signal terminal to which a ground potential of the second ground point is applied.   4. The noise according to claim 1, wherein the voltage-current converter adapts a transconductance of the voltage-current converter to a reciprocal of a resistance value of the first resistor. 5. Elimination circuit. The transconductance of the voltage-current converter does not depend on the resistance of the second resistor,
The voltage-current converter changes the predetermined ratio by changing the resistance value of the second resistor, and adapts the transconductance of the voltage-current converter to only the reciprocal of the resistance value of the first resistor. The noise elimination circuit according to claim 1, wherein the noise is eliminated.   The noise removal circuit according to claim 1, wherein the voltage-current converter is configured by a circuit that does not need to supply a power supply of a negative voltage to the reference voltage terminal.

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