WO2005045367A1

WO2005045367A1 - Noise filter and sensor circuit

Info

Publication number: WO2005045367A1
Application number: PCT/JP2004/014609
Authority: WO
Inventors: Makoto Matsubara; Toru Tominaga; Yukichi Sakurai; Takaaki Ooi
Original assignee: Murata Manufacturing Co., Ltd.
Priority date: 2003-11-10
Filing date: 2004-10-04
Publication date: 2005-05-19
Also published as: TW200516845A; JPWO2005045367A1

Abstract

A noise filter capable of realizing an electromagnetic interference tolerance in a desired frequency range in a high frequency band. A noise filter (4) and a sensor circuit (1) using the noise filter. The noise filter (4) is inserted in a path electrically connecting output terminals (2a,2b) of a sensor (2) to a detector circuit (5) that detects an output signal of the sensor (2). The noise filter (4) comprises first and second inductance elements (7,8) located, as at least one impedance element, on the sensor side; and at least one capacitance element (9) connected between the impedance element and the detector circuit (5).

Description

Description Technical field

The present invention relates to a noise filter that is connected between a sensor such as a gyro sensor and a detection circuit, or connected to an operational amplifier that forms the detection circuit, and a sensor circuit including the noise filter. The present invention relates to a noise filter capable of effectively removing noise in a desired frequency range and a sensor circuit including the noise filter.

Background art

[0002] Conventionally, in a sensor circuit having various sensors such as a gyro sensor and a temperature detection sensor, it has been strongly required to prevent a malfunction and a decrease in measurement accuracy due to an electromagnetic interference wave. An example of such a sensor circuit is disclosed in Patent Document 1 below.

FIG. 10 is a circuit diagram showing a sensor circuit described in Patent Document 1. Here, a noise filter composed of inductance elements 102 and 103, a capacitance element 104, and a color filter is connected to an output terminal of the temperature detection sensor 101. Further, an operational amplifier 105 constituting a detection circuit is connected downstream of the inductance elements 102 and 103.

[0004] More specifically, the first inductance element 102 is connected between the hot-side output terminal of the temperature detection sensor 101 and the hot-side input terminal of the operational amplifier 105. The second inductance element 103 is connected between the output terminal on the reference potential side of the temperature detection sensor 101 and the input terminal on the reference potential side of the operational amplifier 105. A capacitance is connected between a connection point 106 between the temperature detection sensor 101 and the first inductance element 102 and a connection point 107 between the temperature detection sensor 102 and the second inductance element 103. The element 104 is connected.

[0005] In the sensor circuit shown in FIG. 10, it is stated that the resistance to electromagnetic interference waves is improved by inserting a noise filter including the first and second inductance elements 102 and 103 and the capacitance element 104.

Patent Document 1: JP-A-2002-164509

Disclosure of the invention [0006] In the sensor circuit shown in FIG. 10, an LC low-pass filter including the above-described inductance elements 102 and 103 and the capacitance element 104 is configured, and thereby it is described that the resistance to electromagnetic interference is increased. However, in practice, there has been a problem that the malfunction of the temperature detecting sensor 101 cannot be reliably prevented, the effect of resistance to electromagnetic interference is small, and there is a frequency range. In particular, in the low frequency region, the effect of immunity to electromagnetic interference was not sufficient. This is because the input impedance of the detection circuit connected downstream of the noise filter is relatively high. In the high-frequency region, since the capacitance Ca exists at the input end of the detection circuit as schematically shown in FIG. 11, the input impedance is low in the high-frequency region, and the immunity to electromagnetic interference is low in the high-frequency region. However, due to the parasitic inductance in the IC that composes the operational amplifier 105, the difference in input capacitance, etc., even at high frequencies, it is possible to increase the resistance to electromagnetic interference. There is a possibility that the power may not be improved or the effect may not be produced.

[0007] An object of the present invention is to solve the above-mentioned disadvantages of the prior art, and to provide a noise filter connected to a detection circuit between a sensor and a detection circuit, or in a detection circuit, the electromagnetic filter having a specific frequency range. An object of the present invention is to provide a noise filter and a sensor circuit including the noise filter, which can suppress a decrease in wave resistance and have improved resistance to electromagnetic interference waves over a wider frequency range.

[0008] A noise filter according to the present invention is a noise filter inserted into a path that electrically connects an output terminal of a sensor and a detection circuit that detects an output signal of the sensor, and is disposed on the sensor side. At least one impedance element, and at least one capacitance element connected between the impedance element and the detection circuit.

In a specific aspect of the noise filter according to the present invention, the output terminal of the sensor has a hot-side output terminal and a reference potential-side output terminal, and the input terminal of the detection circuit has a hot-side input terminal. A first inductance element inserted between a hot-side output terminal of the sensor and a hot-side input terminal of the detection circuit as the at least one impedance element. A second inductance element connected between a reference potential side output terminal of the sensor and a reference potential side input terminal of the detection circuit; Wherein the capacitance element comprises: a connection point between the first inductance element and a hot-side input terminal of the detection circuit; a second inductance element and a reference potential-side input terminal of the detection circuit. It is inserted so as to connect the connection point between.

In another specific aspect of the noise filter according to the present invention, the at least one impedance element and the at least one capacitance element are selected such that an insertion loss at a frequency of 800 MHz or more of a circuit constant power is 20 dB or more. .

[0009] In a further specific aspect of the noise filter according to the present invention, the sensor is a gyro sensor, and a gyro sensor noise filter is configured.

[0010] A sensor circuit according to the present invention includes a sensor, a detection circuit for detecting an output signal of the sensor, and a noise filter connected between an output terminal of the sensor and the detection circuit. Noise Filter Power A noise filter configured according to the present invention.

[0011] In a specific aspect of the sensor circuit according to the present invention, the sensor is configured by a piezoelectric gyro sensor.

According to another broad aspect of the present invention, in a detection circuit including an operational amplifier having a pair of input terminals, a noise filter connected to each input terminal of the operational amplifier, wherein the noise filter is a first filter. And a second inductance element, and a capacitance element, wherein the capacitance element is connected to each input terminal side of the operational amplifier more than the first and second inductance elements. A noise filter is provided.

[0012] In the noise filter according to the present invention, at least one impedance element is arranged on the sensor side between the hot output terminal of the sensor and the detection circuit, and between the impedance element and the detection circuit. Since at least one capacitance element is connected, even if high-frequency noise is superimposed on the path connecting the hot-side output terminal and the detection circuit, the noise is reliably prevented without being greatly affected by the input impedance of the detection circuit. Can be attenuated. Therefore, it is possible to enhance the resistance to electromagnetic interference over a wide frequency range.

[0013] In the present invention, at least one impedance element is provided at the hot side of the sensor. A first inductance element inserted between the input terminal and the hot input terminal of the detection circuit, and a first inductance element connected between the reference potential output terminal of the sensor and the reference potential input terminal of the detection circuit. A first inductance element and a connection point between the hot side input terminal of the detection circuit, a second inductance element and a reference potential side input terminal of the detection circuit. When the connection is made so as to connect the connection points between the two, the capacitance element is connected to the detection circuit side more than the first and second inductance elements, and thus is greatly affected by the input impedance of the detection circuit. Nothing. Therefore, the resistance to electromagnetic interference can be increased.

[0014] If the circuit constant of at least one impedance element and at least one capacitance element is selected so that the insertion loss at a frequency of 800 MHz or more is 20 dB or more, a high-frequency Equipment used in equipment can also have the effect of improving resistance to electromagnetic interference.

[0015] In the present invention, when the sensor is a gyro sensor, according to the present invention, sufficient immunity to electromagnetic interference is realized in a desired frequency range that is not significantly affected by the input impedance of the detection circuit. Thus, a gyro sensor noise filter can be provided.

[0016] A sensor circuit according to the present invention includes a sensor, a detection circuit, and a noise filter configured according to the present invention. Therefore, it is possible to provide a sensor circuit in which the immunity to electromagnetic interference is effectively improved in a desired frequency range that is not significantly affected by the input impedance of the detection circuit.

[0017] In the sensor circuit according to the present invention, when the sensor is a gyro sensor, according to the present invention, in a desired frequency range, a sufficient electromagnetic interference wave without being significantly affected by the input impedance of the detection circuit. A sensor circuit for a gyro sensor having resistance can be provided.

A noise filter according to the present invention, in a detection circuit having an operational amplifier, a noise filter connected to an input terminal of the operational amplifier, the first filter having first and second inductance elements and a capacitance element; When the capacitance element is a noise filter connected to the input terminal side of the operational amplifier rather than the first and second inductance elements, Since the capacitance element is connected to the input terminal side of the operational amplifier rather than the first and second inductance elements, the influence of the capacitance Ca generated between the pair of input terminals inside the operational amplifier in the low frequency region is reduced. Suffering,.

Brief Description of Drawings

FIG. 1 is a circuit diagram of a sensor circuit including a noise filter according to an embodiment of the present invention.

[FIG. 2] FIG. 2 is a graph showing the frequency of an applied electromagnetic wave, the strength of a malfunction electric field, and the horizontal polarized wave before and after the noise filter is connected to the camera shake correction sensor circuit of the digital video camera and after the noise filter is inserted. FIG.

[FIG. 3] FIG. 3 is a graph showing a relationship between an applied electromagnetic wave frequency and a malfunction electric field strength of a vertically polarized wave before connecting a noise filter and after inserting a noise filter in a camera shake correction sensor circuit of a digital video camera. It is a figure showing a relation.

[Figure 4] Figure 4 shows various changes in the capacitance of the capacitance element of the noise filter before and after connecting the noise filter in the camera shake correction sensor circuit of the digital video camera. FIG. 9 is a diagram illustrating a relationship between an applied frequency and a malfunction electric field strength for horizontal polarization in the case where the above-described operation is performed.

[Fig. 5] Fig. 5 shows various changes in the capacitance of the capacitance element of the noise filter before and after the noise filter is connected in the camera shake correction sensor circuit of the digital video camera. FIG. 9 is a diagram showing a relationship between an applied frequency and a malfunction electric field strength for the water-polarized wave in the case of having been made to operate.

[FIG. 6] FIG. 6 is a diagram showing Z frequency characteristics of insertion loss loss of a capacitance element used for a noise filter.

[Fig. 7] Fig. 7 shows the horizontal polarization when the noise filter is connected before the noise filter is connected and the inductance of the inductance element in the noise filter is changed in the camera shake correction sensor circuit of the digital video camera. FIG. 4 is a diagram illustrating a relationship between a frequency of an applied electromagnetic wave and a malfunction electric field intensity.

[FIG. 8] FIG. 8 is a circuit diagram of a camera shake correction sensor circuit of a digital video camera before connecting a noise filter and connecting a noise filter to the inductance element in the noise filter. FIG. 5 is a diagram showing the relationship between the frequency of an applied electromagnetic wave and the strength of a malfunctioning electric field for vertically polarized waves when the inductance of FIG.

FIG. 9 is a diagram showing frequency dependence of insertion loss of an inductance element used as an impedance element used in a noise filter according to one embodiment of the present invention.

FIG. 10 is a circuit diagram showing a sensor circuit to which a conventional noise filter is connected.

FIG. 11 is a diagram for explaining a problem in the sensor circuit shown in FIG. 10

12 (a) and (b) are diagrams showing impedance frequency characteristics of the inductance elements L1, L2 and L3 shown in FIG. 7;

[FIG. 13] FIG. 13 shows an initial state before connecting a noise filter in a camera shake correction sensor circuit of a digital video camera, a case where a noise filter is connected according to a conventional example shown in FIG. FIG. 7 is a diagram illustrating a relationship between the frequency of an applied electromagnetic wave and the strength of a malfunction electric field for a horizontally polarized wave in a case where a noise filter is configured according to the embodiment illustrated in FIG.

FIG. 14 shows an initial state before a noise filter is connected in a camera shake correction sensor circuit of a digital video camera, a case where a noise filter is connected according to a conventional example shown in FIG. 10, and FIG. FIG. 7 is a diagram showing a relationship between the frequency of an applied electromagnetic wave and the strength of a malfunction electric field for vertically polarized waves in a case where a noise filter is configured according to the embodiment shown in FIG.

[FIG. 15] FIGS. 15 (a) and (b) show the mounting structure near the noise filter when the noise filter is configured according to the conventional example shown in FIG. 10 and the embodiment shown in FIG. 1, respectively. It is a schematic plan view.

Explanation of symbols

1… Sensor circuit

2Gyro sensor

2a… Hot side output terminal

2b… Reference potential side output terminal 3 ... Detection circuit

4 Noise filter

5… Operational amplifier

5a… Hot side input terminal

5b… Ground side input terminal

7… First inductance element

8… Second inductance element

9 ... Capacitance element

10a, 10b… Connection point

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

FIG. 1 is a circuit diagram of a sensor circuit including a noise filter according to one embodiment of the present invention.

In the sensor circuit 1, the noise filter 4 of the present embodiment is connected between the gyro sensor 2 and the detection circuit 3. The gyro sensor 2 is a piezoelectric gyro sensor and has a hot side output terminal 2a and a reference potential side output terminal 2b.

The detection circuit 3 has an operational amplifier 5 for amplifying an output signal output from the gyro sensor 2, and the operational amplifier 5 has a hot side input terminal 5a and a reference potential side input terminal 5b. .

The noise filter 4 has first and second inductance elements 7 and 8 as impedance elements and a capacitance element 9. The first inductance element 7 is connected between the hot-side output terminal 2a of the gyro sensor 2 and the hot-side input terminal 5a of the operational amplifier 5 constituting the detection circuit 5. On the other hand, the second inductance element 8 is electrically connected to the reference potential side output terminal 2 b of the gyro sensor 2 and the reference potential side input terminal 5 b which is the other input terminal of the operational amplifier 5.

The capacitance element 9 is connected on the detection circuit 5 side of the first and second inductance elements 7 and 8. That is, one end of the capacitance element 5 is connected to the first The connection point 10a is connected between the inductance element 7 and the hot-side input terminal 5a of the operational amplifier 5, and the other end of the capacitance element 9 is connected to the second inductance element 8 and the reference of the operational amplifier 5. It is connected to a connection point 10b between it and the potential side input terminal 5b.

Therefore, in the low-frequency region where the input impedance of the detection circuit 3 is high, and in the high-frequency region where the influence of the input capacitance Ca of the detection circuit shown in FIG. By being connected to the detection circuit 3 side rather than the inductance elements 7 and 8, it functions as a noise filter in a low frequency region and acts as a noise filter without being affected by the capacitance Ca in a high frequency region.

Therefore, when the noise filter 4 of the present embodiment is used, it is possible to operate as a noise filter that is not significantly affected by the impedance on the input side of the detection circuit. Therefore, for example, even if a high frequency as an electromagnetic interference wave is superimposed on the path between the sensor 2 and the detection circuit 3, the high frequency noise is surely attenuated in the noise filter 4 and this attenuation operation is performed. Is not so affected by the magnitude of the input impedance of the detection circuit 3.

Therefore, by appropriately setting the circuit constants such as the inductance of the inductance elements 7 and 8 of the noise filter 4 and the inductance of the capacitance element 9 ゃ the capacitance, it is possible to ensure the immunity to electromagnetic interference in a desired frequency range. And it becomes possible to increase effectively.

This will be described with reference to FIGS.

FIG. 2 shows a horizontal deviation when a gyro sensor 2 for digital camera shake correction is used as the gyro sensor 2 in FIG. 1, and a noise filter 4 and a detection circuit 3 are connected in the circuit configuration shown in FIG. It is a figure showing change of electromagnetic interference wave tolerance to a wave.

In FIG. 2, the horizontal axis indicates the frequency of the applied electromagnetic wave as the electromagnetic interference wave, and the vertical axis indicates the malfunction electric field intensity. The malfunction electric field strength means the lowest electric field strength at which a malfunction occurs when an electromagnetic wave having a frequency on the horizontal axis is applied.

[0032] Except that the linear force noise filter 4 connecting the points indicated by the triangles in Fig. 2 is connected, the results in the sensor circuit of the comparative example configured in the same manner as the above embodiment are obtained. , And the line connecting the points indicated by □ indicates the result of the sensor circuit of the above embodiment in which the noise filter 4 was connected. FIG. 2 shows the force as a result of the horizontal polarization. FIG. 3 shows the result as to the vertical polarization. In FIG. 3 as well, the seal indicates the result of the embodiment, and the triangle indicates the result of the comparative example in which the noise filter 4 is connected.

[0034] As is clear from Figs. 2 and 3, compared to a sensor circuit to which the noise filter 4 is not connected, a malfunction occurs even when an electromagnetic wave of a high frequency region, particularly 800 MHz, is superimposed by connecting the noise filter 4. It can be seen that the electric field strength can be effectively increased. In other words, it can be seen that the insertion of the noise filter 4 dramatically improves the immunity to electromagnetic interference.

When the mobile phone is actually brought closer to the digital video camera, if the noise filter 4 is not connected, even if the distance between the mobile phone and the digital video camera is more than lm, the image is not affected. A malfunction occurred during the detection of blur. On the other hand, by inserting the noise filter 4, no malfunction occurred even if the distance between the two was set to 30 cm.

[0036] In the noise filter 4 of the above embodiment, by changing the circuit constants of the first and second inductance elements 7, 8 and the capacitance element 9 in various ways, the resistance to electromagnetic interference in various frequency ranges is improved. Can be increased. This will be described with reference to FIGS.

[0037] Figs. 4 and 5 show the frequency of the applied electromagnetic wave for the horizontal polarization and the vertical polarization when the capacitance of the capacitance element 9 is changed to 330pF, 180pF, 33pF, 10pF and 2pF, and the malfunction electric field strength. FIG. In FIGS. 4 and 5, the inductance L1 of the first and second inductance elements 7, 8 has an impedance characteristic as shown in FIG. 12 in which the capacitance of the capacitance element 9 is changed. Ferrite beads.

As is clear from FIGS. 4 and 5, it is understood that the electromagnetic interference immunity of the digital video camera changes by variously changing the capacitance of the capacitance element 9. Therefore, it is important to appropriately select the capacitance of the capacitance element 9 in order to realize sufficient electromagnetic interference wave resistance in a desired frequency range.

FIG. 6 shows the insertion loss frequency characteristics of the capacitance element. FIG. 6 shows the insertion loss versus frequency characteristics of the five types of capacitance elements used in FIGS. 4 and 5.

[0040] As is apparent from a comparison of Fig. 6 with Figs. 4 and 5, the electromagnetic interference in Figs. It can be seen that there is a correlation between the frequency region where the wave resistance is enhanced and the frequency position where the insertion loss is maximum in FIG. That is, it can be seen that the malfunction electric field strength in the noise filter 4 can be effectively increased in the frequency range where the insertion loss of the capacitance element is the maximum. Therefore, a capacitance element having a large insertion loss in a frequency region to be improved should be selected.

Note that the results in FIGS. 4 and 5 do not always match the results in FIG. In other words, the frequency at which the malfunction electric field intensity is the highest and the frequency at which the insertion loss is the maximum do not completely match, and there is a slight shift. This is considered to be slightly affected by the wiring pattern of the sensor circuit and the input impedance of the detection circuit. However, if the capacitance of the capacitance element is slightly changed while taking such an effect into consideration, the strength of the malfunction electric field in the frequency region to be improved can be effectively increased according to the above embodiment.

FIGS. 7 and 8 are diagrams showing changes in the electromagnetic interference immunity of the digital camera when the circuit constants of the first and second inductance elements 7 and 8 are changed. 7 and 8, similarly to FIGS. 4 and 5, the relationship between the frequency of the applied electromagnetic wave and the malfunction electric field strength in horizontal polarization and vertical polarization is shown. Note that the inductance elements LI, L2, and L3 in FIGS. 7 and 8 have the impedance-frequency characteristics shown in FIG. 12, respectively, and the capacitance of the capacitance element is 10 pF.

As is clear from FIG. 7 and FIG. 8, the malfunction electric field intensity changes by changing the inductance of the first and second inductance elements 7 and 8 in both horizontal polarization and vertical polarization. You can see that. 7 and 8, it can be seen that the malfunction electric field strength is effectively increased in the high frequency range in the characteristics indicated by the one-dot chain line, the broken line Y and the two-dot chain line corresponding to the example.

FIG. 9 is a diagram showing the insertion loss Z frequency characteristics of the inductance elements L1 and L3. As is evident from FIG. 9, the frequency position at which the insertion loss of the inductance element becomes maximum changes depending on the inductance value. It can also be seen that the results in FIG. 9 correlate with the results shown in FIGS. 7 and 8. Therefore, it is understood that V, the magnitude of the insertion loss, and the inductance element should be set in the frequency range to be improved. As is apparent from the results shown in FIGS. 4 and 9, in the noise filter 4, by appropriately selecting the circuit constants of the inductance elements 7, 8 and the capacitance element 9, the electromagnetic interference wave in a desired frequency range is obtained. It is important to be able to increase resistance effectively.

The sensor circuit of the conventional example shown in FIG. 10 is compared with the sensor circuit of the present embodiment shown in FIG. FIGS. 13 and 14 show the initial state before connecting the noise filter in the camera shake correction sensor circuit of the digital video camera, the case where the noise filter is connected according to the conventional sensor circuit shown in FIG. 10, and FIG. FIG. 14 is a diagram showing the relationship between the frequency of an applied electromagnetic wave and the intensity of a malfunctioning electric field for horizontal polarization when a noise filter is connected according to the embodiment shown in FIG. 1. FIG. 14 shows a sensor circuit for camera shake correction of a digital video camera. In the initial state before connecting the noise filter, when the noise filter is connected according to the conventional sensor circuit shown in Fig. 10, and when the noise filter is connected according to the embodiment shown in Fig. 1. FIG. 4 is a diagram showing the relationship between the frequency of an applied electromagnetic wave and the strength of a malfunction electric field in the case of FIG. As is clear from FIGS. 13 and 14, according to the present embodiment, the malfunction electric field strength is about three times as large as that of the conventional example shown in FIG.

The mounting structure of the sensor circuit of the conventional example shown in FIG. 10 and the mounting structure of the sensor circuit of the embodiment shown in FIG. 1 will be compared. FIGS. 15 (a) and (b) show a mounting structure of a sensor circuit having a noise filter configured according to the conventional example shown in FIG. 10 and a sensor circuit configured with a noise filter according to the embodiment shown in FIG. 1, respectively. 3 is a plan view schematically showing main parts of FIG. The noise filter can be further improved by bringing the noise filter close to the detection circuit side. As shown in FIG. The arrangement allows the noise filter to be provided close to the detection circuit 3. For example, as shown in the figure, the capacitance element 9 can be directly connected so as to straddle between a pair of lead terminals of the detection circuit 3. Therefore, since the capacitance element 9 straddles between the lead terminals, it can be mounted stably. Therefore, there is an advantage that the mounting area of the noise filter is reduced and the noise removing effect is further improved.

On the other hand, as shown in FIG. 15A, in the conventional example, inductance elements 102 and 103 are arranged on the detection circuit side. When the inductance elements 102 and 103 are mounted on the lead terminals, There is a possibility of rattling between the wiring pattern of the board and the lead terminal, and the flow of noise current without passing through the inductance element. Therefore, it is difficult to bring the inductance element close to the IC.

Claims

The scope of the claims

[1] A noise filter inserted into a path for electrically connecting an output terminal of the sensor and a detection circuit for detecting an output signal of the sensor, wherein the noise filter includes at least one impedance element arranged on the sensor side. A noise filter, comprising: at least one capacitance element connected between the impedance element and the detection circuit.

[2] The output terminal of the sensor has a hot side output terminal and a reference potential side output terminal, and the input terminal of the detection circuit has a hot side input terminal and a reference potential side input terminal. A first inductance element inserted between the hot output terminal of the sensor and the hot input terminal of the detection circuit as the at least one impedance element; a reference potential output terminal of the sensor; A second inductance element connected between the input terminal and the reference potential side input terminal of the circuit;

The capacitance element includes a connection point between the first inductance element and a hot-side input terminal of the detection circuit, and a connection point between the second inductance element and a reference potential-side input terminal of the detection circuit. The noise filter according to claim 1, wherein the noise filter is inserted so as to connect the same.

[3] The circuit constant of the at least one impedance element and the at least one capacitance element is selected such that an insertion loss at a frequency of 800 MHz or more is 20 dB or more. The noise filter according to 1.

[4] The noise filter according to claim 1 or 2, wherein the sensor is a gyro sensor, and is a gyro sensor noise filter.

[5] The sensor according to claim 1 or 2, comprising a sensor, a detection circuit for detecting an output signal of the sensor, and a noise filter connected between an output terminal of the sensor and the detection circuit. A sensor circuit, which is the noise filter according to any one of the preceding claims.

6. The sensor circuit according to claim 5, wherein the sensor is a gyro sensor.

[7] In a detection circuit including an operational amplifier having a pair of input terminals, a noise filter connected to each input terminal of the operational amplifier, wherein the noise filter includes first and second inductance elements and a capacitance And the capacitance element is connected to the input terminal side of the operational amplifier with respect to the first and second inductance elements. A noise filter, characterized in that: