Non-inverting amplifier circuit

Abstract

To make it possible to raise the voltage output from a reference voltage circuit to a target voltage more reliably than in a conventional circuit.SOLUTION: A non-inverting amplifier circuit 1 includes a first circuit 51 that detects a current value of a drawing current IAMP generated in the direction of drawing into a first operational amplifier AMP1, and outputs a first current having the current value corresponding to the detected current value, a second circuit 52 that outputs a second current having a current value corresponding to the upper limit of the current value that the second operational amplifier can output on the basis of information indicating the upper limit of the current value that the second operational amplifier AMP2 can output, and a comparison circuit 53 that compares the current value of the first current and the current value of the second current, and performs feedback control to reduce the current value of the current drawn into the first operational amplifier to be equal to or less than the upper limit of the current value that the second operational amplifier can output when the current value of the first current is greater than the current value of the second current.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This disclosure relates to a non-inverting amplifier circuit.

Background Art

[0002] A non-inverting amplifier circuit is a circuit that amplifies and outputs an input signal input from a non-inverting input terminal (+) according to a predetermined amplification factor. This non-inverting amplifier circuit may be configured to include a reference voltage circuit that supplies a reference voltage to the input signal. This reference voltage is supplied as a voltage for vibrating the input signal input from the non-inverting input terminal of the non-inverting amplifier circuit around the reference voltage.

[0003] A configuration example of a non-inverting amplifier circuit including a reference voltage circuit is shown in FIG. 2. The non-inverting amplifier circuit shown in FIG. 2 (hereinafter also referred to as "the first conventional circuit") includes an amplifier unit 100 and a reference voltage circuit 150.

[0004] The amplifier unit 100 includes a first operational amplifier AMP1 having a negative feedback unit, a first input resistor R1, a feedback resistor R2, and a second input resistor R3.

[0005] One end of the first input resistor R1 is connected at connection point a to the inverting input terminal (-) of the first operational amplifier AMP1 and the other end of the feedback resistor R2, and the other end is connected at connection point b to one end of the second input resistor R3 and the output terminal of a second operational amplifier AMP2 described later.

[0006] The feedback resistor R2 is connected to the negative feedback unit of the first operational amplifier AMP1. Specifically, one end of the feedback resistor R2 is connected to the output terminal of the first operational amplifier AMP1, and the other end is connected at connection point a to the inverting input terminal of the first operational amplifier AMP1 and one end of the first input resistor R1.

[0007] The second input resistor R3 has one end connected at connection point b to the other end of the first input resistor R1 and the output terminal of the second operational amplifier AMP2, and the other end connected at connection point c to the non-inverting input terminal (+) of the first operational amplifier AMP1 and the output terminal SENS of a sensor (e.g., a piezoelectric element) that outputs the input signal input to the non-inverting input terminal.

[0008] The first operational amplifier AMP1 has a non-inverting input terminal, an inverting input terminal, and an output terminal. The non-inverting input terminal of the first operational amplifier AMP1 is connected at connection point c to the sensor's output terminal SENS and the other end of the second input resistor R3. The output terminal of the first operational amplifier AMP1 is connected to one end of the feedback resistor R2. The inverting input terminal of the first operational amplifier AMP1 is connected at connection point b to one end of the first input resistor R1 and the other end of the feedback resistor R2.

[0009] The reference voltage circuit 150 includes a second operational amplifier AMP2 having a negative feedback section. The output terminal of diode D, which acts as a voltage source, is connected to the non-inverting input terminal of the second operational amplifier AMP2. The output terminal of the second operational amplifier AMP2 is connected to the other end of the first input resistor R1 and to one end of the second input resistor R3.

[0010] The first conventional circuit configured in this way operates as follows under normal circumstances when the power is turned on by the user. For example, when the power to the first conventional circuit is turned on by the user, the reference voltage circuit 150 functions as a voltage follower circuit. Specifically, first a predetermined voltage signal is input from the output terminal of diode D to the non-inverting input terminal of the second operational amplifier AMP2. Then, a voltage VR due to this voltage signal is applied to the non-inverting input terminal of the second operational amplifier AMP2. A reference voltage VB, which has approximately the same voltage value as voltage VR, is then generated at the output terminal of the second operational amplifier AMP2.

[0011] The reference voltage VB generated at the output terminal of the second operational amplifier AMP2 is passed through the second input resistor R3 and applied to the input signal input from the sensor's output terminal SENS to the non-inverting input terminal of the first operational amplifier AMP1. The first operational amplifier AMP1 amplifies the input signal to which the reference voltage VB has been applied according to a predetermined amplification factor and outputs the voltage resulting from the amplified signal as the output voltage VOUT. In Figure 2, the symbol VOFS represents the input offset voltage input to the non-inverting input terminal of the first operational amplifier AMP1.

[0012] On the other hand, in the first conventional circuit described above, even if the power is turned on by the user, it may not start operating normally for the following reasons.

[0013] For example, in the first conventional circuit described above, the voltage at the output terminal of the first operational amplifier AMP1 is 0V when the power is started. Therefore, in the first conventional circuit described above, when the power is started, a current IAMP (hereinafter also referred to as "pull-in current") is generated that flows from the output terminal of the first operational amplifier AMP1 into the interior of the first operational amplifier AMP1.

[0014] Here, if the current value of this pull-in current IAMP exceeds the current value IB corresponding to the upper limit of the current value that the second operational amplifier AMP2 of the reference voltage circuit 150 can output (hereinafter also referred to as the "drive current value"), depending on the magnitude of the input offset voltage VOFS input to the non-inverting input terminal of the first operational amplifier AMP1, the voltage generated at the output terminal of the second operational amplifier AMP2 may not rise to the predetermined reference voltage VB.

[0015] For example, if the voltage E1 applied to the non-inverting input terminal of the first operational amplifier AMP1 is smaller than the voltage E2 applied to the inverting input terminal of the first operational amplifier AMP1, the voltage generated at the output terminal of the second operational amplifier AMP2 may not rise to a predetermined reference voltage VB. Here, if we let the resistance value of the first input resistor R1 be R1 and the resistance value of the feedback resistor R2 be R2, and the second operational amplifier AMP2 outputs a current with a drive current value IB (hereinafter also referred to as the "drive current") IB, then the voltages generated at connection point b and connection point c will be IB × (R1 + R2), and the voltage generated at connection point a will be IB × R2.

[0016] At this time, the voltage E1 applied to the non-inverting input terminal of the first operational amplifier AMP1 is the voltage obtained by subtracting the input offset voltage VOFS mentioned above from the voltage generated at connection point c. Also, the voltage E2 applied to the inverting input terminal of the first operational amplifier AMP1 is the voltage generated at connection point a. Therefore, voltages E1 and E2 can be expressed by the following equations, respectively. E1 = IB × (R1 + R2) - VOFS (1) E2 = IB × R2 (2) Therefore, when E1 ≤ E2, that is, VOFS ≥ IB × R1, the voltage generated at the output terminal of the second operational amplifier AMP2 may not rise to the predetermined reference voltage VB. Hereafter, this condition VOFS ≥ IB × R1 will also be referred to as the "input offset voltage condition".

[0017] One possible solution to this problem is to increase the drive current value IB mentioned above. However, this solution is limited from a design perspective, as the goal is to keep the overall circuit power consumption low.

[0018] Another possible solution is to increase the resistance values ​​of the first input resistor R1 and the feedback resistor R2 to reduce the pull-in current IAMP. However, this solution is also limited in terms of the driving capability of the amplifier section 100 and the low-noise design. Yet another possible solution is to reduce the input offset voltage VOFS. However, this solution is also limited in terms of the complexity of the circuit configuration and the circuit area (chip area for integration).

[0019] Next, Figure 3 shows an example of the configuration of a conventional non-inverting amplifier circuit having a configuration similar to the first conventional circuit described above. The non-inverting amplifier circuit shown in Figure 3 (hereinafter also referred to as the "second conventional circuit") is composed of an amplifier section 300 and a voltage follower section 400 (for example, Patent Document 1).

[0020] The amplifier section 300 includes a first operational amplifier 301 having a negative feedback section, a feedback resistor 302 connected to the negative feedback section, and an input resistor 303 with one end connected to the inverting input terminal of the first operational amplifier 301. The amplifier section amplifies and outputs the signal input to the non-inverting input terminal of the first operational amplifier 301.

[0021] The voltage follower section 400 includes a second operational amplifier 401 having a negative feedback section. The second operational amplifier 401 has its non-inverting input terminal grounded, and its output terminal connected to the other end of the input resistor 303 of the amplifier section 300. In the second conventional circuit, the first operational amplifier 301 and the second operational amplifier 401 are operational amplifiers in the same package.

[0022] According to such a configuration, the second operational amplifier 401 has a negative feedback section and its non-inverting input terminal is grounded, thus forming a voltage follower circuit and outputting the input offset voltage VinDC2 in the second operational amplifier 401. Also, since the output terminal of the second operational amplifier 401 is connected to the other end of the input resistor 303, the input offset voltage VinDC2 in the second operational amplifier 401 is applied to the other end of the input resistor 303. And since the first operational amplifier 301 and the second operational amplifier 401 are operational amplifiers within the same package, the input offset voltages of each operational amplifier are substantially the same. As a result, the second conventional circuit can achieve effects such as being able to prevent the input offset voltage from being amplified according to the gain without previously knowing the input offset voltage.

Prior Art Documents

Patent Documents

[0023]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0024] However, even in the above second conventional circuit, there exists an input offset voltage VinDC1 input to the non-inverting input terminal of the first operational amplifier 301. Therefore, even in the above second conventional circuit, similar to the first conventional circuit described above, when the current value of the drawing-in current IAMP generated at power-on exceeds the current value (drive current value) IB corresponding to the upper limit of the current value that the second operational amplifier AMP2 in the voltage follower section 400 can output, depending on the magnitude of the input offset voltage VinDC1 input to the non-inverting input terminal of the first operational amplifier AMP1, the voltage generated at the output terminal of the second operational amplifier AMP2 may not rise (increase) up to the input offset voltage VinDC2.

[0025] Note that the above problem can occur not only when the power supply is started in the first conventional circuit and the second conventional circuit (hereinafter, these are also collectively referred to as "conventional circuits"), but also when the supply of the power current to the conventional circuit is stopped and then restarted.

[0026] The present disclosure has been made to solve the above problems, and an object thereof is to provide a non-inverting amplifier circuit that can more reliably raise the voltage output from a reference voltage circuit to a target voltage than a conventional circuit.

Means for Solving the Problems

[0027] The non-inverting amplifier circuit according to the present disclosure includes a first operational amplifier whose non-inverting input terminal is connected to an output terminal of a sensor, a feedback resistor R2 having one end connected to the output terminal of the first operational amplifier and the other end connected to the inverting input terminal of the first operational amplifier, a first input resistor R1 having one end connected to the inverting input terminal of the first operational amplifier and the other end of the feedback resistor R2, a second input resistor R3 having one end connected to the non-inverting input terminal of the first operational amplifier and the output terminal of the sensor and the other end connected to the other end of the first input resistor R1, a second operational amplifier whose non-inverting input terminal is connected to a predetermined voltage source and whose output terminal is connected to the other end of the first input resistor R1, one end of the second input resistor R3, and the inverting input terminal, a first circuit that detects a current value of a drawing current generated in a direction of drawing into the first operational amplifier and outputs a first current having a current value corresponding to the detected current value, a second circuit that holds in advance information indicating an upper limit of a current value that the second operational amplifier can output and outputs a second current having a current value corresponding to the upper limit of the current value that the second operational amplifier can output based on the held information, and a third circuit that compares the current value of the first current with the current value of the second current and performs feedback control to suppress the current value of the drawing current to be equal to or less than a current value corresponding to the upper limit of the current value that the second operational amplifier can output when the current value of the first current is greater than the current value of the second current.

Effects of the Invention

[0028] According to this disclosure, with the configuration described above, it becomes possible to raise the voltage output from the reference voltage circuit to the target voltage more reliably than with conventional circuits. [Brief explanation of the drawing]

[0029] [Figure 1] This figure shows an example configuration of a non-inverting amplifier circuit according to Embodiment 1. [Figure 2] This figure shows an example of the configuration of the first conventional circuit. [Figure 3] This figure shows a second example of a conventional circuit configuration. [Modes for carrying out the invention]

[0030] The embodiments of this disclosure will be described in detail below with reference to the drawings. Embodiment 1. Figure 1 shows an example of the configuration of a non-inverting amplifier circuit 1 according to Embodiment 1. As shown in Figure 1, the non-inverting amplifier circuit 1 is composed of an amplifier section 2 and a reference voltage circuit 3.

[0031] The amplifier section 2 comprises a first operational amplifier AMP1 having a negative feedback section, a first input resistor R1, a feedback resistor R2, and a second input resistor R3.

[0032] The first input resistor R1 has one end connected at connection point a to the inverting input terminal (-) of the first operational amplifier AMP1 and the other end of the feedback resistor R2, and the other end connected at connection point b to one end of the second input resistor R3 and the output terminal of the second operational amplifier AMP2, which will be described later.

[0033] The feedback resistor R2 is connected to the negative feedback section of the first operational amplifier AMP1. Specifically, one end of the feedback resistor R2 is connected to the output terminal of the first operational amplifier AMP1, and the other end is connected at connection point a to the inverting input terminal of the first operational amplifier AMP1 and to one end of the first input resistor R1.

[0034] The second input resistor R3 has one end connected at connection point b to the other end of the first input resistor R1 and the output terminal of the second operational amplifier AMP2, and the other end connected at connection point c to the non-inverting input terminal of the first operational amplifier AMP1 and the output terminal SENS of a sensor that outputs the input signal input to the non-inverting input terminal. The sensor is, for example, a piezoelectric element.

[0035] The first operational amplifier AMP1 has a non-inverting input terminal (+), an inverting input terminal (-), and an output terminal. The non-inverting input terminal of the first operational amplifier AMP1 is connected at connection point c to the sensor's output terminal SENS and the other end of the second input resistor R3. The output terminal of the first operational amplifier AMP1 is connected to one end of the feedback resistor R2. The inverting input terminal of the first operational amplifier AMP1 is connected at connection point a to one end of the first input resistor R1 and the other end of the feedback resistor R2.

[0036] The first operational amplifier AMP1 consists of a first stage AMP11 and an output stage AMP12, and a current limiting circuit 5 is provided between the first stage AMP11 and the output stage AMP12. The current limiting circuit 5 will be described later. In Figure 1, the symbol VOFS represents the input offset voltage input to the non-inverting input terminal of the first operational amplifier AMP1.

[0037] The reference voltage circuit 3 includes a second operational amplifier AMP2 having a negative feedback section. The output terminal of diode D, which acts as a voltage source, is connected to the non-inverting input terminal (+) of the second operational amplifier AMP2. Furthermore, the output terminal of the second operational amplifier AMP2 is connected at connection point b to the other end of the first input resistor R1 and to one end of the second input resistor R3.

[0038] Next, the current limiting circuit 5 will be described. The current limiting circuit 5 is a circuit that suppresses the current value of the current (draw-in current) IAMP generated in the direction of drawing current from the output terminal side of the first operational amplifier AMP1 into the interior of the first operational amplifier AMP1 when the power supply of the non-inverting amplifier circuit 1 is started up, or when the supply of power supply current to the non-inverting amplifier circuit 1 is stopped and then restarted, to a current value equivalent to the upper limit of the current value that the second operational amplifier AMP2 (reference voltage circuit 3) can output. The current limiting circuit 5 is provided, for example, between the first stage AMP11 and the output stage AMP12 of the first operational amplifier AMP1, as described above.

[0039] The current limiting circuit 5 is configured to include, for example, an output current monitoring circuit (first circuit) 51, a limiting current reference circuit (second circuit) 52, and a comparison circuit (third circuit) 53, as shown in Figure 1.

[0040] The output current monitor circuit 51 monitors the pull-in current IAMP generated at the output terminal of the first operational amplifier AMP1 and detects its current value. The output current monitor circuit 51 then generates a current (hereinafter also referred to as the "first current") with a current value corresponding to the detected current value and outputs it to the comparison circuit 53.

[0041] The current limiting reference circuit 52 stores information indicating the upper limit of the current value that the second operational amplifier AMP2 can output in its internal memory or the like. Based on the information stored in the memory or the like, the current limiting reference circuit 52 generates a current (hereinafter also referred to as the "second current") having a current value corresponding to the upper limit of the current value that the second operational amplifier AMP2 can output, and outputs it to the comparison circuit 53. The upper limit of the current value that the second operational amplifier AMP2 can output can be determined in advance from the specifications of the second operational amplifier AMP2, etc.

[0042] The comparison circuit 53 compares the first current output from the output current monitor circuit 51 with the second current output from the limiting current reference circuit 52. If, as a result of this comparison, the current value of the first current is greater than the current value of the second current, the comparison circuit 53 performs feedback control to the output stage AMP12 of the first operational amplifier AMP1 to suppress the current value of the pull-in current IAMP to a current value equivalent to the upper limit of the current value that the second operational amplifier AMP2 can output.

[0043] For example, the comparator circuit 53 controls the voltage applied to the base terminal of a transistor that carries the pull-in current IAMP, which is located in the output stage AMP12 of the first operational amplifier AMP1, thereby making it difficult for the pull-in current IAMP to flow through the transistor. As a result, the comparator circuit 53 can control the current value of the pull-in current IAMP to be less than or equal to the upper limit of the current value that the second operational amplifier AMP2 can output, using a simple configuration. However, this is merely an example, and the method of control by the comparator circuit 53 is not particularly limited.

[0044] As a result, the non-inverting amplifier circuit 1 can more reliably raise the voltage output from the reference voltage circuit 3 to the target voltage than the conventional circuit. In particular, the non-inverting amplifier circuit 1 can more reliably raise the voltage output from the reference voltage circuit 3 to the target voltage than the conventional circuit when the power supply to the non-inverting amplifier circuit 1 is started up, or when the supply of power current to the non-inverting amplifier circuit 1 is stopped and then restarted. Furthermore, since this effect is achieved regardless of whether the above-mentioned input offset voltage conditions are met, there is no need to reduce the input offset voltage VOFS input to the non-inverting input terminal of the non-inverting amplifier circuit 1.

[0045] Furthermore, once the voltage output from the reference voltage circuit 3 rises to the target voltage (for example, the reference voltage VB), the non-inverting amplifier circuit 1 operates as usual. For example, the reference voltage VB generated at the output terminal of the reference voltage circuit 3 is applied to the input signal input from the sensor's output terminal SENS to the non-inverting input terminal of the first operational amplifier AMP1, via the second input resistor R3. The first operational amplifier AMP1 amplifies the input signal to which the reference voltage VB has been applied according to a predetermined amplification factor and outputs the voltage of the amplified signal as the output voltage VOUT.

[0046] The output current monitor circuit 51 may monitor the incoming current IAMP, divide the detected current value by a predetermined value, and output the resulting current value as the first current. In that case, the limiting current reference circuit 52 may divide the upper limit of the current value held in the memory, etc., by the same value as the predetermined value, and output the resulting current value as the second current.

[0047] For example, the output current monitor circuit 51 monitors the inducting current IAMP, and if the detected current value is 15 μA, it generates and outputs a first current with a value of 1.5 μA, obtained by dividing this current value by a predetermined value of 10. Similarly, the limiting current reference circuit 52, if the upper limit of the current value held in the memory is 10 μA, generates and outputs a second current with a value of 1.0 μA, obtained by dividing this current value by a predetermined value of 10. In this case, the comparison circuit 53 performs the feedback control described above because the current value of the first current (1.5 μA) is greater than the current value of the second current (1.0 μA).

[0048] In other words, since the comparison circuit 53 only needs to be able to compare the current values ​​of the two currents, the output current monitor circuit 51 and the limiting current reference circuit 52 may reduce the current values ​​that are the basis for generating the first current and the second current by the same ratio, and generate currents with the resulting current values ​​as the first current and the second current, respectively. This allows the non-inverting amplifier circuit 1 to reduce the current value of the output current, leading to a reduction in power consumption.

[0049] In the above explanation, an example was described in which the current limiting circuit 5 is provided between the first stage AMP11 and the output stage AMP12 of the first operational amplifier AMP1. However, the current limiting circuit 5 does not necessarily have to be provided between the first stage AMP11 and the output stage AMP12 of the first operational amplifier AMP1. However, when the current limiting circuit 5 is provided between the first stage AMP11 and the output stage AMP12 of the first operational amplifier AMP1 as described above, the current limiting circuit 5 can be included inside the first operational amplifier AMP1, thereby enabling miniaturization of the non-inverting amplifier circuit 1.

[0050] As described above, according to Embodiment 1, the non-inverting amplifier circuit 1 includes a first operational amplifier AMP1 whose non-inverting input terminal is connected to the output terminal of a sensor, a feedback resistor R2 whose one end is connected to the output terminal of the first operational amplifier AMP1 and whose other end is connected to the inverting input terminal of the first operational amplifier AMP1, a first input resistor R1 whose one end is connected to the inverting input terminal of the first operational amplifier AMP1 and the other end of the feedback resistor R2, a second input resistor R3 whose one end is connected to the non-inverting input terminal of the first operational amplifier AMP1 and the output terminal SENS of the sensor and whose other end is connected to the other end of the first input resistor R1, a second operational amplifier AMP2 whose non-inverting input terminal is connected to a predetermined voltage source and whose output terminal is connected to the other end of the first input resistor R1, one end of the second input resistor R3, and the inverting input terminal, and a method for drawing into the interior of the first operational amplifier AMP1 The non-inverting amplifier circuit 1 includes an output current monitor circuit (first circuit) 51 that detects the current value of the incoming current IAMP generated in the direction and outputs a first current having a current value corresponding to the detected current value; a limiting current reference circuit (second circuit) 52 that holds information indicating the upper limit of the current value that the second operational amplifier AMP2 can output and outputs a second current having a current value corresponding to the upper limit of the current value that the second operational amplifier AMP2 can output based on the held information; and a comparison circuit (third circuit) 53 that compares the current value of the first current with the current value of the second current and, if the current value of the first current is greater than the current value of the second current, performs feedback control to the first operational amplifier AMP1 to suppress the current value of the incoming current IAMP to a current value corresponding to the upper limit of the current value that the second operational amplifier AMP2 can output. As a result, the non-inverting amplifier circuit 1 can raise the voltage output from the reference voltage circuit (second operational amplifier AMP2) to the target voltage more reliably than conventional circuits.

[0051] Furthermore, the output current monitor circuit 51 outputs a current with a value obtained by dividing the detected current value by a predetermined value as the first current, and the limiting current reference circuit 52 outputs a current with a value obtained by dividing the upper limit of the held current value by the same value as the predetermined value as the second current. As a result, the non-inverting amplifier circuit 1 can reduce the current value of the output current, leading to a reduction in power consumption.

[0052] Furthermore, the output current monitor circuit 51, the limiting current reference circuit 52, and the comparison circuit 53 are provided between the first stage AMP11 and the output stage AMP12 of the first operational amplifier AMP1. This allows the non-inverting amplifier circuit 1 to be made more compact.

[0053] Furthermore, the comparison circuit 53 performs feedback control by controlling the voltage applied to the base terminal of the transistor that carries the pull-in current IAMP, which is provided in the output stage AMP12 of the first operational amplifier AMP1, when the current value of the first current is greater than the current value of the second current. As a result, the non-inverting amplifier circuit 1 can perform feedback control with a simple configuration.

[0054] Within the scope of this disclosure, any component of the embodiment may be modified, or any component may be omitted in the embodiment. [Explanation of Symbols]

[0055] 1. Non-inverting amplifier circuit 2. Amplifier section 3. Reference voltage circuit 5. Current limiting circuit 51 Output current monitoring circuit (first circuit) 52. Current-limiting reference circuit (second circuit) 53. Comparison Circuit (Third Circuit) 100 Amplifier section 150 Reference Voltage Circuit 300 Amplifier Section 301 First operational amplifier 302 Feedback resistor 303 Input Resistor 400 Voltage Follower Section 401 Second operational amplifier a connection point AMP1 First operational amplifier AMP11 1st Dan AMP12 output stage AMP2 Second operational amplifier b Connection point c connection point D diode IAMP current draw-in IB drive current value R1 is the first input resistance. R2 Feedback resistor R3 is the second input resistance. SENS output terminal VB Reference Voltage VinDC1 Input Offset Voltage VinDC2 Input Offset Voltage VOFS Input Offset Voltage VOUT output voltage VR voltage

Claims

1. A first operational amplifier whose non-inverting input terminal is connected to the sensor's output terminal, A feedback resistor, with one end connected to the output terminal of the first operational amplifier and the other end connected to the inverting input terminal of the first operational amplifier, A first input resistor, one end of which is connected to the inverting input terminal of the first operational amplifier and the other end of the feedback resistor, A second input resistor, one end of which is connected to the non-inverting input terminal of the first operational amplifier and the output terminal of the sensor, and the other end of which is connected to the other end of the first input resistor, The non-inverting input terminal is connected to a predetermined voltage source, and the output terminal is connected to the other end of the first input resistor, one end of the second input resistor, and a second operational amplifier connected to the inverting input terminal. A first circuit that detects the current value of the pull-in current generated in the direction of drawing it into the first operational amplifier and outputs a first current having a current value corresponding to the detected current value, A second circuit that pre-stores information indicating the upper limit of the current value that the second operational amplifier can output, and outputs a second current having a current value corresponding to the upper limit of the current value that the second operational amplifier can output, A third circuit compares the current value of the first current with the current value of the second current, and if the current value of the first current is greater than the current value of the second current, it performs feedback control on the first operational amplifier to suppress the current value of the pull-in current to a current value equivalent to the upper limit of the current value that the second operational amplifier can output, A non-inverting amplifier circuit equipped with [a specific feature].

2. The first circuit outputs a current having a current value obtained by dividing the detected current value by a predetermined value as the first current. The second circuit outputs a current having a current value obtained by dividing the upper limit of the held current value by the same value as the predetermined value, as the second current. The non-inverting amplifier circuit according to feature 1.

3. The first circuit, the second circuit, and the third circuit are provided between the first stage and the output stage of the first operational amplifier. A non-inverting amplifier circuit according to claim 1 or 2.

4. The third circuit is, If the current value of the first current is greater than the current value of the second current, the feedback control is performed by controlling the voltage applied to the base terminal of the transistor that carries the pull-in current, which is provided in the output stage of the first operational amplifier. The non-inverting amplifier circuit according to claim 3, characterized in that it is as described above.

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