Temperature acquisition circuit

Abstract

The utility model relates to the technical field of temperature acquisition, in particular to a temperature acquisition circuit, which comprises a control module, a thermistor, a first constant current circuit, a second constant current circuit and a voltage acquisition circuit, the other end of the thermistor is connected with the output end of the second constant current circuit, so that the influence of current floating at the two ends of the thermistor on the precision of the voltage difference at the two ends of the thermistor output by the voltage acquisition circuit is avoided; therefore, the control module can obtain the temperature result represented by the thermistor according to the voltage difference output by the voltage acquisition circuit, the current value output by the first constant current circuit and the current value output by the second constant current circuit, and the acquisition precision of the temperature acquisition circuit is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of temperature acquisition, in particular to a temperature acquisition circuit and equipment. Background Art

[0002] Temperature acquisition circuits are widely used in medical devices. Temperature acquisition circuits are divided into digital temperature acquisition circuits and analog temperature acquisition circuits. Existing digital temperature acquisition circuits have high system resource occupancy and low precision, and are generally used in situations where system control is simple and precision requirements are not high; while analog temperature acquisition circuits conventionally use NTC or PTC thermistors, which are sampled by ADC after voltage division with sampling resistors, calibrated data, and the temperature value is calculated based on the collected voltage and resistance values, but its precision is low. Summary of the invention

[0003] The embodiments of the utility model provide a temperature acquisition circuit and a device to solve the problem of low acquisition accuracy of the temperature acquisition circuit in the prior art.

[0004] In a first aspect, the utility model provides a temperature acquisition circuit, comprising: a control module, a thermistor, a first constant current circuit, a second constant current circuit and a voltage acquisition circuit; wherein,

[0005] One end of the thermistor is connected to the output end of the first constant current circuit and the first acquisition end of the voltage acquisition circuit respectively, the other end of the thermistor is connected to the output end of the second constant current circuit and the second acquisition end of the voltage acquisition circuit respectively, and the output end of the voltage acquisition circuit is connected to the input end of the control module;

[0006] The control module is used to obtain a temperature result represented by the thermistor according to the voltage difference across the thermistor output by the voltage acquisition circuit, the current value output by the first constant current circuit, and the current value output by the second constant current circuit.

[0007] In one embodiment, the voltage acquisition circuit includes: a first adjustable gain amplifier circuit and a first differential-to-single-ended amplifier filter circuit;

[0008] The first input end of the first adjustable gain amplifier circuit is connected to one end of the thermistor, the second input end of the first adjustable gain amplifier circuit is connected to the other end of the thermistor, the first output end of the first adjustable gain amplifier circuit is connected to the first input end of the first differential-to-single-ended amplifier and filter circuit, the second output end of the first adjustable gain amplifier circuit is connected to the second input end of the first differential-to-single-ended amplifier and filter circuit, and the output end of the first differential-to-single-ended amplifier and filter circuit is connected to the input end of the control module.

[0009] In one implementation, the voltage acquisition circuit further includes: a first filtering circuit;

[0010] The first input end of the first filter circuit is connected to one end of the thermistor, the second input end of the first filter circuit is connected to the other end of the thermistor, the first output end of the first filter circuit is connected to the first input end of the first adjustable gain amplifier circuit, and the second output end of the first filter circuit is connected to the second input end of the first adjustable gain amplifier circuit.

[0011] In one embodiment, the voltage acquisition circuit further includes: a first radio frequency interference filter;

[0012] The first input end of the first RFI filter is connected to the first output end of the first adjustable gain amplifier circuit, the second input end of the first RFI filter is connected to the second output end of the first adjustable gain amplifier circuit, the first output end of the first RFI filter is connected to the first input end of the first differential-to-single-ended amplifier and filter circuit, and the second output end of the first RFI filter is connected to the second input end of the first differential-to-single-ended amplifier and filter circuit.

[0013] In one embodiment, the temperature acquisition circuit further includes: a current acquisition resistor and a current acquisition circuit;

[0014] One end of the current collection resistor is connected to the other end of the thermistor, and the other end of the current collection resistor is grounded. The first current collection signal input end of the current collection circuit is connected to one end of the current collection resistor, the second current collection signal input end of the current collection circuit is connected to the other end of the current collection resistor, and the output end of the current collection circuit is connected to the current collection signal input end of the control module.

[0015] In one embodiment, the current acquisition circuit includes: a second filtering circuit, a second adjustable gain amplifier circuit, a second radio frequency interference filter, and a second differential-to-single-ended amplifier and filter circuit;

[0016] The first input end of the second filtering circuit is connected to one end of the current collection resistor, the second input end of the second filtering circuit is connected to the other end of the current collection resistor, the first output end of the second filtering circuit is connected to the first input end of the second adjustable gain amplifier circuit, the second output end of the second filtering circuit is connected to the second input end of the second adjustable gain amplifier circuit, the first output end of the second adjustable gain amplifier circuit is connected to the first input end of the second radio frequency interference filter, the second output end of the second adjustable gain amplifier circuit is connected to the second input end of the second radio frequency interference filter, the first output end of the second radio frequency interference filter is connected to the first input end of the second differential-to-single-ended amplifier and filter circuit, the second output end of the second radio frequency interference filter is connected to the second input end of the second differential-to-single-ended amplifier and filter circuit, and the output end of the second differential-to-single-ended amplifier and filter circuit is connected to the current collection signal input end of the control module.

[0017] In one embodiment, the temperature acquisition circuit further includes: a first wire, a second wire and a third wire;

[0018] One end of the thermistor is connected to the first collection end of the thermistor through the first wire, the other end of the thermistor is connected to the second collection end of the thermistor through the second wire, and the other end of the thermistor is grounded and connected to one end of the current collection resistor through the third wire.

[0019] In one embodiment, the first constant current circuit includes: a first operational amplifier, a second operational amplifier, a first voltage divider circuit, a first negative feedback gain adjustment circuit, a first current limiting resistor, a first filter capacitor and a first current adjustment resistor;

[0020] The non-inverting end of the first operational amplifier is connected to the first output end of the first voltage divider circuit, the inverting end of the first operational amplifier is connected to the output end of the first negative feedback gain adjustment circuit, the output end of the first operational amplifier is connected to the input end of the first current limiting resistor, the output end of the first current limiting resistor is connected to the input end of the first negative feedback gain adjustment circuit, and the output end of the first current limiting resistor is connected to the input end of the first current regulating resistor, the output end of the first current regulating resistor is connected to one end of the thermistor, and the output end of the first current regulating resistor is connected to the non-inverting end of the second operational amplifier, the first input end of the first voltage divider circuit is connected to the first constant current control signal output end of the control module, the second input end of the first voltage divider circuit is connected to the inverting end of the second operational amplifier, and the second input end of the first voltage divider circuit is connected to the output end of the second operational amplifier, the power supply end of the second operational amplifier is connected to the input end of the first filter capacitor, and the power supply end of the second operational amplifier is used to receive the power supply voltage, and the output end of the first filter capacitor is grounded.

[0021] In one embodiment, the second constant current circuit includes: a third operational amplifier, a fourth operational amplifier, a second voltage divider circuit, a second negative feedback gain adjustment circuit, a second current limiting resistor, a second filter capacitor and a second current adjustment resistor;

[0022] The non-inverting end of the third operational amplifier is connected to the first output end of the second voltage divider circuit, the inverting end of the third operational amplifier is connected to the output end of the second negative feedback gain adjustment circuit, the output end of the third operational amplifier is connected to the input end of the second current limiting resistor, the output end of the second current limiting resistor is connected to the input end of the second negative feedback gain adjustment circuit, and the output end of the second current limiting resistor is connected to the input end of the second current regulating resistor, the output end of the second current regulating resistor is connected to the other end of the thermistor, and the output end of the second current regulating resistor is connected to the non-inverting end of the fourth operational amplifier, the first input end of the second voltage divider circuit is connected to the second constant current control signal output end of the control module, the second input end of the second voltage divider circuit is connected to the inverting end of the fourth operational amplifier, and the second input end of the second voltage divider circuit is connected to the output end of the fourth operational amplifier, the power supply end of the fourth operational amplifier is connected to the input end of the second filter capacitor, and the power supply end of the fourth operational amplifier is used to receive the power supply voltage, and the output end of the second filter capacitor is grounded.

[0023] In a second aspect, the present invention provides a temperature acquisition device, comprising a temperature acquisition circuit as described in any one of the first aspects above.

[0024] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0025] The temperature acquisition circuit of the utility model comprises: a control module, a thermistor, a first constant current circuit, a second constant current circuit and a voltage acquisition circuit, wherein one end of the thermistor is connected to the output end of the first constant current circuit, and the other end of the thermistor is connected to the output end of the second constant current circuit, so as to avoid the current floating at both ends of the thermistor affecting the accuracy of the voltage difference at both ends of the thermistor output by the voltage acquisition circuit, thereby enabling the control module to obtain a temperature result represented by the thermistor according to the voltage difference output by the voltage acquisition circuit, the current value output by the first constant current circuit and the current value output by the first constant current circuit, thereby improving the acquisition accuracy of the temperature acquisition circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the utility model, the drawings required for use in the description of the embodiments of the utility model will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 It is a structural schematic diagram of a temperature acquisition circuit provided by an embodiment of the utility model;

[0028] Figure 2 It is a circuit diagram of a temperature acquisition circuit provided by an embodiment of the utility model;

[0029] Figure 3 1 is a circuit diagram of a first constant current circuit provided in one embodiment of the utility model;

[0030] Figure 4 It is a circuit diagram of a second constant current circuit provided in one embodiment of the utility model. DETAILED DESCRIPTION

[0031] In order to make the technical problems, technical solutions and beneficial effects solved by the utility model more clear, the utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model and are not used to limit the utility model.

[0032] In the description of the present invention, it should be understood that the terms "longitudinal", "radial", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0033] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] In order to thoroughly understand the present invention, detailed structures and steps will be presented in the following description to illustrate the technical solution proposed by the present invention. The preferred embodiments of the present invention are described in detail below, but in addition to these detailed descriptions, the present invention may also have other implementations.

[0035] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure belongs. It will be further understood that the terms used herein should be interpreted as having a meaning consistent with their meaning in the context of this specification and the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined as such herein.

[0036] In one embodiment, if Figure 1 As shown, a schematic diagram of the structure of a temperature acquisition circuit is provided, including: a control module 10, a thermistor Rrtd, a first constant current circuit 20, a second constant current circuit 30 and a voltage acquisition circuit 40; wherein:

[0037] One end of the thermistor Rrtd is respectively connected to the output end of the first constant current circuit 20 and the first collection end of the voltage collection circuit 40, and the other end of the thermistor Rrtd is respectively connected to the output end of the second constant current circuit 30 and the second collection end of the voltage collection circuit 40, and the output end of the voltage collection circuit 40 is connected to the input end of the control module 10.

[0038] In practical applications, the control module 10 is used to obtain the temperature result represented by the thermistor Rrtd according to the voltage difference across the thermistor Rrtd output by the voltage acquisition circuit 40, the current value output by the first constant current circuit 20, and the current value output by the first constant current circuit 20.

[0039] The working process of the above-mentioned temperature acquisition circuit is as follows: when the temperature acquisition circuit is working, the first constant current circuit 20 provides a constant current to one end of the thermistor Rrtd, and the second constant current circuit 30 provides a constant current to the other end of the thermistor Rrtd, so that the voltage acquisition circuit 40 can accurately acquire the voltage difference between the two ends of the thermistor Rrtd and output it to the control module 10, so that the control module 10 can obtain the resistance value of the thermistor Rrtd according to the voltage difference output by the voltage acquisition circuit 40, the current value output by the first constant current circuit 20, the current value output by the second constant current circuit 30 and Ohm's theorem, and then the control module 10 can query the temperature value corresponding to the resistance according to the resistance value of the thermistor Rrtd and the specification of the thermistor Rrtd.

[0040] The temperature acquisition circuit of this embodiment includes: a control module 10, a thermistor Rrtd, a first constant current circuit 20, a second constant current circuit 30 and a voltage acquisition circuit 40, wherein one end of the thermistor Rrtd is connected to the output end of the first constant current circuit 20, and the other end of the thermistor Rrtd is connected to the output end of the second constant current circuit 30, so as to avoid the current floating across the thermistor Rrtd affecting the accuracy of the voltage difference output by the voltage acquisition circuit 40, thereby enabling the control module 10 to obtain the temperature result represented by the thermistor Rrtd according to the voltage difference output by the voltage acquisition circuit 40, the current value output by the first constant current circuit 20 and the current value output by the second constant current circuit 30, thereby improving the acquisition accuracy of the temperature acquisition circuit.

[0041] In one embodiment, the voltage acquisition circuit 40 can be as follows: Figure 2 As shown, it includes: a first adjustable gain amplifier circuit 42 and a first differential to single-ended amplifier filter circuit 44; wherein:

[0042] The first input end of the first adjustable gain amplifier circuit 42 is connected to one end of the thermistor Rrtd, the second input end of the first adjustable gain amplifier circuit 42 is connected to the other end of the thermistor Rrtd, the first output end of the first adjustable gain amplifier circuit 42 is connected to the first input end of the first differential to single-ended amplifier and filter circuit 44, the second output end of the first adjustable gain amplifier circuit 42 is connected to the second input end of the first differential to single-ended amplifier and filter circuit 44, and the output end of the first differential to single-ended amplifier and filter circuit 44 is connected to the input end of the control module 10.

[0043] Optionally, the first adjustable gain amplifier circuit 42 can be as follows Figure 2 As shown, it is composed of resistors RF1, RF2, RG1 and operational amplifiers U2A, U2B, and capacitor C7. In practical applications, the resistance value of resistor RF1 can be set equal to the resistance value of resistor RF2, and the gain multiple S1 of the first adjustable gain amplifier circuit 42 is S1 = (RF1*2 / RG1) + 1, wherein RF1 is the resistance value of resistor RF1, and RG1 is the resistance value of resistor RG1; and its first differential to single-ended amplifier filter circuit 44 can also be as shown Figure 2 As shown, it is composed of resistors R10, R11, R7, operational amplifier U5A, capacitors C15, C18. In practical applications, resistor R7 and capacitor C15 together form a low-pass filter circuit to filter out differential interference signals. In practical applications, the resistance value of resistor R10 can also be set equal to the resistance value of resistor R11, and the gain multiple of the first differential to single-ended amplification filter circuit 44 is S2=R11 / R12, where R21 is the resistance value of resistor R11, and R12 is the resistance value of resistor R12. In practical applications, it is not limited to this, and it depends on the specific application environment, which is within the protection scope of this application.

[0044] The working process of the above-mentioned temperature acquisition circuit is as follows: when the temperature acquisition circuit is working, the first constant current circuit 20 provides a constant current for one end of the thermistor Rrtd, and the second constant current circuit 30 provides a constant current for the other end of the thermistor Rrtd, so that the first adjustable gain amplifier circuit 42 can gain amplify the voltage output from both ends of the thermistor Rrtd and output it to the first differential to single-ended amplifier filter circuit 44, and then the first differential to single-ended amplifier filter circuit 44 can obtain the voltage difference between both ends of the thermistor Rrtd according to the voltage after gain amplification, and output it to the control module 10, and the control module 10 can obtain the resistance value of the thermistor Rrtd according to the voltage difference output by the voltage acquisition circuit 40, the current value output by the first constant current circuit 20, the current value output by the second constant current circuit 30 and Ohm's theorem, and then the control module 10 can query the temperature value corresponding to the resistance according to the resistance value of the thermistor Rrtd and the specification of the thermistor Rrtd.

[0045] The temperature acquisition circuit of this embodiment uses a first adjustable gain amplifier circuit 42 and a first differential to single-ended amplifier filter circuit 44 to form a voltage acquisition circuit 40, so as to improve the acquisition accuracy of the voltage acquisition circuit 40, thereby improving the acquisition accuracy of the temperature acquisition circuit.

[0046] In one embodiment, if Figure 2 As shown, the voltage acquisition circuit 40 further includes: a first filtering circuit 41; wherein:

[0047] The first input end of the first filter circuit 41 is connected to one end of the thermistor Rrtd, the second input end of the first filter circuit 41 is connected to the other end of the thermistor Rrtd, the first output end of the first filter circuit 41 is connected to the first input end of the first adjustable gain amplifier circuit 42, and the second output end of the first filter circuit 41 is connected to the second input end of the first adjustable gain amplifier circuit 42.

[0048] Optionally, the first filter circuit 41 may be a low-pass filter circuit, specifically, Figure 2 As shown, it is composed of resistors R2, R13 and capacitors C1, C5 to filter out single-ended differential mode interference signals. In practical applications, the resistance value of resistor R2 can be set equal to the resistance value of resistor R13, and the capacitance of capacitor C1 can be equal to the capacitance of capacitor C5. The practical application is not limited to this and depends on the specific application environment, which is within the protection scope of this application.

[0049] The working process of the above-mentioned temperature acquisition circuit is as follows: when the temperature acquisition circuit is working, the first constant current circuit 20 provides a constant current for one end of the thermistor Rrtd, and the second constant current circuit 30 provides a constant current for the other end of the thermistor Rrtd, and the voltage outputted from both ends of the thermistor Rrtd is filtered by the first filter circuit 41 and then outputted to the first adjustable gain amplifier circuit 42, so as to gain-amplify the voltage outputted from both ends of the thermistor Rrtd and then output it to the first differential-to-single-ended amplifier filter circuit 44, and then the first differential-to-single-ended amplifier filter circuit 44 can obtain the voltage difference between both ends of the thermistor Rrtd according to the voltage after gain amplification, and output it to the control module 10, and the control module 10 can obtain the resistance value of the thermistor Rrtd according to the voltage difference outputted by the voltage acquisition circuit 40, the current value outputted by the first constant current circuit 20, the current value outputted by the second constant current circuit 30 and Ohm's theorem, and then the control module 10 can query the temperature value corresponding to the resistance according to the resistance value of the thermistor Rrtd and the specification of the thermistor Rrtd.

[0050] The temperature acquisition circuit of this embodiment uses a first filter circuit 41 to filter the voltage output across the thermistor Rrtd and then outputs it to a first adjustable gain amplifier circuit 42, so as to reduce the influence of noise on the voltage output across the thermistor Rrtd, thereby improving the acquisition accuracy of the voltage acquisition circuit 40, and further improving the acquisition accuracy of the temperature acquisition circuit.

[0051] In one embodiment, if Figure 2 As shown, the voltage acquisition circuit 40 further includes: a first radio frequency interference filter 43; wherein:

[0052] The first input end of the first RFI filter 43 is connected to the first output end of the first adjustable gain amplifier circuit 42, the second input end of the first RFI filter 43 is connected to the second output end of the first adjustable gain amplifier circuit 42, the first output end of the first RFI filter 43 is connected to the first input end of the first differential-to-single-ended amplifier and filter circuit 44, and the second output end of the first RFI filter 43 is connected to the second input end of the first differential-to-single-ended amplifier and filter circuit 44.

[0053] Optional, such as Figure 2 As shown, resistors R8, R12, capacitors C2, C3, and C4 can be used to form a first radio frequency interference filter 43 to achieve the corresponding filtering function, and in actual applications, the resistance of resistor R8 can be set equal to the resistance of resistor R12, and the capacitance of capacitor C2 can be set equal to the capacitance of capacitor C4. The actual application is not limited to this, and it depends on the specific application environment, which is within the protection scope of this application.

[0054] The working process of the above-mentioned temperature acquisition circuit is as follows: when the temperature acquisition circuit is working, the first constant current circuit 20 provides a constant current for one end of the thermistor Rrtd, and the second constant current circuit 30 provides a constant current for the other end of the thermistor Rrtd, so that the first adjustable gain amplifier circuit 42 can gain amplify the voltage output from both ends of the thermistor Rrtd and output it to the first radio frequency interference filter 43 for filtering, and then output it to the first differential to single-ended amplifier filter circuit 44, and then the first differential to single-ended amplifier filter circuit 44 can obtain the voltage difference between both ends of the thermistor Rrtd according to the voltage after gain amplification and filtering, and output it to the control module 10, and the control module 10 can obtain the resistance value of the thermistor Rrtd according to the voltage difference output by the voltage acquisition circuit 40, the current value output by the first constant current circuit 20 and the current value output by the second constant current circuit 30 and Ohm's theorem, and then the control module 10 can query the temperature value corresponding to the resistance according to the resistance value of the thermistor Rrtd and the specification of the thermistor Rrtd.

[0055] The temperature acquisition circuit of this embodiment uses the first RFI filter 43 to filter the voltage output from both ends of the thermistor Rrtd after gain amplification to reduce the influence of noise on the voltage acquisition circuit 40, thereby improving the acquisition accuracy of the temperature acquisition circuit.

[0056] In one embodiment, if Figure 2 As shown, the temperature acquisition circuit also includes: a current acquisition resistor Rref and a current acquisition circuit 50; wherein:

[0057] One end of the current acquisition resistor Rref is connected to the other end of the thermistor Rrtd, the other end of the current acquisition resistor Rref is grounded, the first current acquisition signal input end of the current acquisition circuit 50 is connected to one end of the current acquisition resistor Rref, the second current acquisition signal input end of the current acquisition circuit 50 is connected to the other end of the current acquisition resistor Rref, and the output end of the current acquisition circuit 50 is connected to the current acquisition signal input end of the control module 10.

[0058] The working process of the above-mentioned temperature acquisition circuit is as follows: when the temperature acquisition circuit is working, the current acquisition resistor Rref acquires the current value output by the first constant current circuit 20 and the second constant current circuit 30, and outputs the corresponding current acquisition signal to the control module 10 through the current acquisition circuit 50, so that the control module 10 can obtain the resistance value of the thermistor Rrtd according to the voltage difference output by the voltage acquisition circuit 40, the current acquisition signal output by the current acquisition circuit 50 and Ohm's theorem, and then the control module 10 can query the temperature value corresponding to the resistance according to the resistance value of the thermistor Rrtd and the specification of the thermistor Rrtd.

[0059] The temperature acquisition circuit of this embodiment acquires the current value output by the first constant current circuit 20 and the second constant current circuit 30 by using the current acquisition resistor Rref and the current acquisition circuit 50, so as to monitor the current value output by the first constant current circuit 20 and the second constant current circuit 30 through the control module 10, and then the resistance value of the thermistor Rrtd can be obtained according to the current value output by the first constant current circuit 20 and the second constant current circuit 30, the voltage difference output by the voltage acquisition circuit 40 and Ohm's theorem.

[0060] In one embodiment, if Figure 2 As shown, the current acquisition circuit 50 includes: a second filtering circuit 51, a second adjustable gain amplifier circuit 52, a second radio frequency interference filter 53 and a second differential to single-ended amplifier filter circuit 54; wherein:

[0061] The first input end of the second filter circuit 51 is connected to one end of the current collection resistor Rref, the second input end of the second filter circuit 51 is connected to the other end of the current collection resistor Rref, the first output end of the second filter circuit 51 is connected to the first input end of the second adjustable gain amplifier circuit 52, the second output end of the second filter circuit 51 is connected to the second input end of the second adjustable gain amplifier circuit 52, the first output end of the second adjustable gain amplifier circuit 52 is connected to the first input end of the second radio frequency interference filter 53, the second output end of the second adjustable gain amplifier circuit 52 is connected to the second input end of the second radio frequency interference filter 53, the first output end of the second radio frequency interference filter 53 is connected to the first input end of the second differential to single-ended amplifier filter circuit 54, the second output end of the second radio frequency interference filter 53 is connected to the second input end of the second differential to single-ended amplifier filter circuit 54, and the output end of the second differential to single-ended amplifier filter circuit 54 is connected to the current collection signal input end of the control module 10.

[0062] Optionally, the second adjustable gain amplifier circuit 52 can be as follows Figure 2 As shown, it is composed of resistors RF3, RF4, RG2 and operational amplifiers U3A, U3B, and capacitor C13. In actual applications, the resistance value of resistor RF3 can be set equal to the resistance value of resistor RF4, and the gain multiple S3 of the second adjustable gain amplifier circuit 51 is S3 = (RF3*2 / RG2) + 1, where RF3 is the resistance value of resistor RF3, and RG2 is the resistance value of resistor RG2; and its second differential to single-ended amplifier filter circuit 54 can also be as shown Figure 2 As shown, it is composed of resistors R21, R22, R17 and operational amplifier U6A, capacitors C16, C18. In practical applications, resistor R17 and capacitor C16 together form a low-pass filter circuit to filter out differential mode interference signals. In practical applications, the resistance value of resistor R21 can also be set equal to the resistance value of resistor R22, and the gain multiple of the second differential to single-ended amplification filter circuit 54 is S4=R22 / R23, wherein R22 is the resistance value of resistor R22, and R23 is the resistance value of resistor R23; optionally, as Figure 2 As shown, resistors R18, R23, capacitors C9, C10, and C11 can be used to form a second RFI filter 53 to achieve the corresponding filtering function, and in practical applications, the resistance of resistor R18 can be set equal to the resistance of resistor R23, and the capacitance of capacitor C9 can be set equal to the capacitance of capacitor C11. The practical application is not limited to this, and it depends on the specific application environment, which is within the protection scope of this application.

[0063] Optionally, the second filter circuit 51 may be a low-pass filter circuit, specifically, Figure 2As shown, it is composed of resistors R14, R26 and capacitors C8, C12 to filter out single-ended differential mode interference signals. In practical applications, the resistance of resistor R14 can be set equal to the resistance of resistor R26, and the capacitance of capacitor C8 can be equal to the capacitance of capacitor C12. The practical application is not limited to this and depends on the specific application environment, which is within the protection scope of this application.

[0064] The working process of the above-mentioned temperature acquisition circuit is as follows: when the temperature acquisition circuit is working, the current acquisition resistor Rref acquires the current value output by the first constant current circuit 20 and the second constant current circuit 30, and after filtering the acquired current acquisition signal through the second filter circuit 51, the filtered current acquisition signal is output to the second adjustable gain amplifier circuit 52, so that after gain amplification through the second adjustable gain amplifier circuit 52, the gain-amplified current acquisition signal is output to the second radio frequency interference filter 53 for filtering, and then output to the second differential to single-ended amplifier filter circuit 54, so that the corresponding current acquisition signal is output to the control module 10 through the second differential to single-ended amplifier filter circuit 54, and the control module 10 can obtain the resistance value of the thermistor Rrtd according to the voltage difference output by the voltage acquisition circuit 40, the current acquisition signal output by the current acquisition circuit 50 and Ohm's theorem, and then the control module 10 can query the temperature value corresponding to the resistance according to the resistance value of the thermistor Rrtd and the specification of the thermistor Rrtd.

[0065] The temperature acquisition circuit of this embodiment adopts a second filtering circuit 51, a second adjustable gain amplifier circuit 52, a second radio frequency interference filter 53 and a second differential to single-ended amplifier filter circuit 54 to form a current acquisition circuit 50, so as to collect the current value output by the first constant current circuit 20 and the second constant current circuit 30, and then obtain the resistance value of the thermistor Rrtd through the control module 10 according to the current value output by the first constant current circuit 20 and the second constant current circuit 30, the voltage difference output by the voltage acquisition circuit 40 and Ohm's theorem.

[0066] In one embodiment, if Figure 2 As shown, the temperature acquisition circuit further includes: a first wire, a second wire and a third wire; wherein:

[0067] One end of the thermistor Rrtd is connected to the first collection end of the thermistor Rrtd through a first wire, the other end of the thermistor Rrtd is connected to the second collection end of the thermistor Rrtd through a second wire, and the other end of the thermistor Rrtd is grounded and connected to one end of the current collection resistor Rref through a third wire.

[0068] In practical applications, such as Figure 2As shown, the line resistance Rlead1 of the first wire, the line resistance Rlead2 of the second wire and the line resistance Rlead3 of the third wire are all equal. The line resistance of each wire is not limited here, and it can be determined according to its actual application environment, which is within the protection scope of this application.

[0069] The temperature acquisition circuit of this embodiment uses a first wire, a second wire and a third wire of equal wire groups to achieve a three-wire connection method, thereby reducing the acquisition error of the temperature acquisition circuit and improving the acquisition accuracy of the temperature acquisition circuit.

[0070] In one embodiment, the first constant current circuit 20 can be as follows Figure 3 As shown, it includes: a first operational amplifier U1A, a second operational amplifier U1B, a first voltage divider circuit 21, a first negative feedback gain adjustment circuit 22, a first current limiting resistor R5, a first filter capacitor C6 and a first current adjustment resistor R9; wherein:

[0071] The in-phase terminal of the first operational amplifier U1A is connected to the first output terminal of the first voltage divider circuit 21, the inverting terminal of the first operational amplifier U1A is connected to the output terminal of the first negative feedback gain adjustment circuit 22, the output terminal of the first operational amplifier U1A is connected to the input terminal of the first current limiting resistor R5, the output terminal of the first current limiting resistor R5 is connected to the input terminal of the first negative feedback gain adjustment circuit 22, and the output terminal of the first current limiting resistor R5 is connected to the input terminal of the first current regulating resistor R9, the output terminal of the first current regulating resistor R9 is connected to one end of the thermistor Rrtd, and the first current regulating resistor R9 is connected to the input terminal of the first current regulating resistor R9. The output end of the resistor R9 is connected to the in-phase end of the second operational amplifier U1B, the first input end of the first voltage divider circuit 21 is connected to the first constant current control signal output end of the control module 10, the second input end of the first voltage divider circuit 21 is connected to the inverting end of the second operational amplifier U1B, and the second input end of the first voltage divider circuit 21 is connected to the output end of the second operational amplifier U1B, the power supply end of the second operational amplifier U1B is connected to the input end of the first filter capacitor C6, and the power supply end of the second operational amplifier U1B is used to receive the power supply voltage, and the output end of the first filter capacitor C6 is grounded.

[0072] Optionally, the first voltage divider circuit 21 may be as follows: Figure 3 As shown, it is composed of resistors R4 and R6 to realize the corresponding voltage division function, and the resistance value of resistor R4 can be set equal to the resistance value of resistor R6. At this time, U1A_Up=(U_DAC1+U1B_OUT) / 2, wherein U1A_Up is the input voltage value received by the in-phase terminal of the first operational amplifier U1A, U_DAC1 is the voltage value output by the first constant current control signal output terminal of the control module 10, and U1B_OUT is the voltage value output by the output terminal of the second operational amplifier U1B; and the first negative feedback gain adjustment circuit 22 can also be as shown Figure 3As shown, it is composed of resistors R3 and R1 to achieve the gain adjustment function. In practical applications, the resistance value of resistor R3 can be set equal to the resistance value of resistor R1, and equal to the resistance value of the first current limiting resistor R5. Specifically, the current value flowing through the resistor R3 is I_R3=U1A_Un / R3, and the current value flowing through the resistor R1 is I_R1=(U1A_Un-U1A_OUT) / R1. From I_R3=I_R1, it can be obtained that U1A_Un / R3=(U1A_OUT-U1A_Un) / R1, and at this time, from R1=R3=R5, it can be obtained that U1A_Un=(U1A_OUT-U1A_Un), that is, U1A_OUT=2*U1A_Un. According to the virtual short of the first operational amplifier U1A, U1A_Up=U1A_Un, that is, U1A_OUT=2*U1A_Up=U_DA C1-U1B_Un, and according to the virtual short of the second operational amplifier U1B, U1B_Up=U1B_Un, the current flowing through the resistor R9 is equal to I_R9=(U1A_OUT+U1B_Up) / R9=(U_DAC1+U1B_Un-U1B_Up) / R9=U_DAC1 / R9, in practical applications, when the resistance of resistor R9 remains constant, the current value of IDAC1 can be adjusted by adjusting the voltage value of U_DAC1; and U1A_Un is the input voltage value received by the inverting end of the first operational amplifier U1A, U1A_OUT is the voltage value output by the output end of the first operational amplifier U1A, U1B_Un is the input voltage value received by the inverting end of the second operational amplifier U1B, and U1B_OUT is the voltage value output by the output end of the second operational amplifier U1B. In practical applications, it is not limited to this, and it can be determined according to its specific application environment, which is within the protection scope of this application.

[0073] The working process of the above-mentioned temperature acquisition circuit is as follows: when the temperature acquisition circuit is working, the first voltage divider circuit 21 outputs the corresponding voltage signal to the in-phase terminal of the first operational amplifier U1A according to the first constant current control signal output by the control module 10 and the output signal of the output terminal of the second operational amplifier U1B, so that the first operational amplifier U1A can output the corresponding current signal to the first current regulating resistor R9 through the first current limiting resistor R5, so that the first current regulating resistor R9 can provide a constant current to one end of the thermistor Rrtd after receiving the current signal, and the second operational amplifier U1B can adjust the voltage signal output by the first voltage divider circuit 21 according to the constant current output by the first current regulating resistor R9.

[0074] The temperature acquisition circuit of this embodiment adopts a first operational amplifier U1A, a second operational amplifier U1B, a first voltage divider circuit 21, a first negative feedback gain adjustment circuit 22, a first current limiting resistor R5, a first filter capacitor C6 and a first current regulating resistor R9 to form a first constant current circuit 20, so as to provide a constant current to one end of the thermistor Rrtd, thereby avoiding the current floating at both ends of the thermistor Rrtd from affecting the voltage difference accuracy output by the voltage acquisition circuit 40, reducing the acquisition error of the temperature acquisition circuit, and improving the acquisition accuracy of the temperature acquisition circuit.

[0075] In one embodiment, the second constant current circuit 30 can be as follows Figure 4 As shown, it includes: a third operational amplifier U4A, a fourth operational amplifier U4B, a second voltage divider circuit 31, a second negative feedback gain adjustment circuit 32, a second current limiting resistor R20, a second filter capacitor C14 and a second current adjustment resistor R25; wherein:

[0076] The in-phase terminal of the third operational amplifier U4A is connected to the first output terminal of the second voltage divider circuit 31, the inverting terminal of the third operational amplifier U4A is connected to the output terminal of the second negative feedback gain adjustment circuit 32, the output terminal of the third operational amplifier U4A is connected to the input terminal of the second current limiting resistor R20, the output terminal of the second current limiting resistor R20 is connected to the input terminal of the second negative feedback gain adjustment circuit 32, and the output terminal of the second current limiting resistor R20 is connected to the input terminal of the second current regulating resistor R25, the output terminal of the second current regulating resistor R25 is connected to the other terminal of the thermistor Rrtd, and the second current limiting resistor R20 is connected to the input terminal of the second current regulating resistor R25. The output end of the regulating resistor R25 is connected to the in-phase end of the fourth operational amplifier U4B, the first input end of the second voltage divider circuit 31 is connected to the second constant current control signal output end of the control module 10, the second input end of the second voltage divider circuit 31 is connected to the inverting end of the fourth operational amplifier U4B, and the second input end of the second voltage divider circuit 31 is connected to the output end of the fourth operational amplifier U4B, the power supply end of the fourth operational amplifier U4B is connected to the input end of the second filter capacitor C14, and the power supply end of the fourth operational amplifier U4B is used to receive the power supply voltage, and the output end of the second filter capacitor C14 is grounded.

[0077] Optionally, the second voltage divider circuit 31 can be as follows Figure 4 As shown, it is composed of resistors R19 and R24 to realize the corresponding voltage division function, and the resistance value of resistor R19 can be set equal to the resistance value of resistor R24. At this time, U4A_Up=(U_DAC2+U4B_OUT) / 2, wherein U4A_Up is the input voltage value received by the in-phase terminal of the third operational amplifier U4A, U_DAC2 is the voltage value output by the first constant current control signal output terminal of the control module 10, and U4B_OUT is the voltage value output by the output terminal of the fourth operational amplifier U4B; and the second negative feedback gain adjustment circuit 32 can also be as shown Figure 4 As shown, it is composed of resistors R15 and R16 to achieve a gain adjustment function. In practical applications, the resistance value of resistor R15 can be set equal to the resistance value of resistor R16, and equal to the resistance value of the second current limiting resistor R20. Specifically, the current value flowing through resistor R15 is I_R15=U4A_Un / R15, and the current value flowing through resistor R16 is I_R16=(U4A_Un-U4A_OUT) / R16. From I_R15=I_R16, it can be obtained that U4A_Un / R15=(U4A_OUT-U4A_Un) / R16, and at this time, from R16=R15=R20, it can be obtained that U4A_Un=(U4A_OUT-U4A_Un), that is, U4A_OUT=2*U4A_Un. According to the virtual short of the third operational amplifier U4A, U4A_Up=U4A_Un, that is, U4A_OUT=2*U4A_U p=U_DAC2-U4B_Un, and according to the virtual short of the fourth operational amplifier U4B, U4B_Up=U4B_Un, the current flowing through the resistor R25 is equal to I_R25=(U4A_OUT+U4B_Up) / R25=(U_DAC2+U4B_Un-U4B_Up) / R25=U_DAC2 / R25. In practical applications, when the resistance of the resistor R25 remains constant, the current value of IDAC2 can be adjusted by adjusting the voltage value of U_DAC2; and U4A_Un is the input voltage value received by the inverting end of the third operational amplifier U4A, U4A_OUT is the voltage value output by the output end of the third operational amplifier U4A, U4B_Un is the input voltage value received by the inverting end of the fourth operational amplifier U4B, and U4B_OUT is the voltage value output by the output end of the fourth operational amplifier U4B. In practical applications, it is not limited to this, and it can be determined according to its specific application environment, which is within the protection scope of this application.

[0078] The working process of the above-mentioned temperature acquisition circuit is as follows: when the temperature acquisition circuit is working, the second voltage divider circuit 31 outputs a corresponding voltage signal to the in-phase terminal of the third operational amplifier U4A according to the second constant current control signal output by the control module 10 and the output signal of the output terminal of the fourth operational amplifier U4B, so that the third operational amplifier U4A can output a corresponding current signal to the second current regulating resistor R25 through the second current limiting resistor R20, so that the second current regulating resistor R25 can provide a constant current to the other end of the thermistor Rrtd after receiving the current signal, and the fourth operational amplifier U4B can adjust the voltage signal output by the second voltage divider circuit 31 according to the constant current output by the second current regulating resistor R25.

[0079] The temperature acquisition circuit of this embodiment adopts a third operational amplifier U4A, a fourth operational amplifier U4B, a second voltage divider circuit 31, a second negative feedback gain adjustment circuit 32, a second current limiting resistor R20, a second filter capacitor C14 and a second current adjustment resistor R25 to form a second constant current circuit 30 to provide a constant current to the other end of the thermistor Rrtd, thereby avoiding the current floating at both ends of the thermistor Rrtd from affecting the voltage difference accuracy output by the voltage acquisition circuit 40, reducing the acquisition error of the temperature acquisition circuit, and improving the acquisition accuracy of the temperature acquisition circuit.

[0080] In a second embodiment, a temperature acquisition device is provided, in which a temperature acquisition circuit as described in any one of the above-mentioned first embodiments is provided.

[0081] The temperature acquisition device of this embodiment adopts the temperature acquisition circuit as described in any one of the first embodiments above, so as to improve the acquisition accuracy of the temperature acquisition device by improving the acquisition accuracy of the temperature acquisition circuit.

[0082] In practical applications, Figure 2 For example, the first differential input voltage U (R_AINP) of the voltage acquisition circuit 40 is UR_AINP) = I_DAC1*Rrtd+(I_DAC1+I_DAC2)*(Rlead3+Rref)+I_DAC1*Rlead1, and the second differential input voltage U (R_AINN) of the voltage acquisition circuit 40 is

[0083] U(R_AINN)=(I_DAC1+I_DAC2)*(Rlead3+Rref)+I_DAC2*Rlead2, where I_DAC1=I_DAC2, Rlead1=Rlead2, U(R_AINP)-U(R_AINN)=I_DAC1*Rrtd, and similarly, U(R_EFP)-U(R_EFN)=(I_DAC1+I_DAC2)*Rref. It can be seen that the voltage value output by the voltage acquisition circuit 40 is only related to the resistance value of the thermistor Rrtd and the current value output by the first constant current circuit 20 and the second constant current circuit 30, thereby completely eliminating the influence of the line impedance and improving the acquisition accuracy of the temperature acquisition circuit. Among them, I_DAC1 is the current value output by the first constant current circuit 20, I_DAC2 is the current value output by the second constant current circuit 30, Rlead1 is the line resistance of the first wire, Rlead2 is the line resistance of the second wire, Rlead3 is the line resistance of the third wire, U (R_AINN) is the voltage value input to the non-inverting input terminal of the operational amplifier U2B, U (R_AINP) is the voltage value input to the non-inverting input terminal of the operational amplifier U2A, U (R_EFP) is the voltage value input to the non-inverting input terminal of the operational amplifier U3A, U (R_EFN) is the voltage value input to the non-inverting input terminal of the operational amplifier U3B, Rrtd is the resistance value of the thermistor Rrtd, and Rref is the resistance value of the current collection resistor Rref.

[0084] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention.

Claims

1. A temperature acquisition circuit, characterized in that: include: control module, thermistor, first constant current circuit, second constant current circuit and voltage acquisition circuit; wherein, One end of the thermistor is connected to the output end of the first constant current circuit and the first acquisition end of the voltage acquisition circuit respectively, the other end of the thermistor is connected to the output end of the second constant current circuit and the second acquisition end of the voltage acquisition circuit respectively, and the output end of the voltage acquisition circuit is connected to the input end of the control module; The control module is used to obtain a temperature result represented by the thermistor according to the voltage difference across the thermistor output by the voltage acquisition circuit, the current value output by the first constant current circuit, and the current value output by the second constant current circuit.

2. The temperature acquisition circuit according to claim 1, characterized in that: The voltage acquisition circuit comprises: a first adjustable gain amplifier circuit and a first differential to single-ended amplifier filter circuit; The first input end of the first adjustable gain amplifier circuit is connected to one end of the thermistor, the second input end of the first adjustable gain amplifier circuit is connected to the other end of the thermistor, the first output end of the first adjustable gain amplifier circuit is connected to the first input end of the first differential-to-single-ended amplifier and filter circuit, the second output end of the first adjustable gain amplifier circuit is connected to the second input end of the first differential-to-single-ended amplifier and filter circuit, and the output end of the first differential-to-single-ended amplifier and filter circuit is connected to the input end of the control module.

3. The temperature acquisition circuit according to claim 2, characterized in that: The voltage acquisition circuit further includes: a first filtering circuit; The first input end of the first filter circuit is connected to one end of the thermistor, the second input end of the first filter circuit is connected to the other end of the thermistor, the first output end of the first filter circuit is connected to the first input end of the first adjustable gain amplifier circuit, and the second output end of the first filter circuit is connected to the second input end of the first adjustable gain amplifier circuit.

4. The temperature acquisition circuit according to claim 2, characterized in that: The voltage acquisition circuit also includes: a first radio frequency interference filter; The first input end of the first RFI filter is connected to the first output end of the first adjustable gain amplifier circuit, the second input end of the first RFI filter is connected to the second output end of the first adjustable gain amplifier circuit, the first output end of the first RFI filter is connected to the first input end of the first differential-to-single-ended amplifier and filter circuit, and the second output end of the first RFI filter is connected to the second input end of the first differential-to-single-ended amplifier and filter circuit.

5. The temperature acquisition circuit according to claim 1, characterized in that: The temperature acquisition circuit also includes: a current acquisition resistor and a current acquisition circuit; One end of the current collection resistor is connected to the other end of the thermistor, and the other end of the current collection resistor is grounded. The first current collection signal input end of the current collection circuit is connected to one end of the current collection resistor, the second current collection signal input end of the current collection circuit is connected to the other end of the current collection resistor, and the output end of the current collection circuit is connected to the current collection signal input end of the control module.

6. The temperature acquisition circuit according to claim 5, characterized in that: The current acquisition circuit includes: a second filtering circuit, a second adjustable gain amplifier circuit, a second radio frequency interference filter and a second differential to single-ended amplifier and filter circuit; The first input end of the second filtering circuit is connected to one end of the current collection resistor, the second input end of the second filtering circuit is connected to the other end of the current collection resistor, the first output end of the second filtering circuit is connected to the first input end of the second adjustable gain amplifier circuit, the second output end of the second filtering circuit is connected to the second input end of the second adjustable gain amplifier circuit, the first output end of the second adjustable gain amplifier circuit is connected to the first input end of the second radio frequency interference filter, the second output end of the second adjustable gain amplifier circuit is connected to the second input end of the second radio frequency interference filter, the first output end of the second radio frequency interference filter is connected to the first input end of the second differential-to-single-ended amplifier and filter circuit, the second output end of the second radio frequency interference filter is connected to the second input end of the second differential-to-single-ended amplifier and filter circuit, and the output end of the second differential-to-single-ended amplifier and filter circuit is connected to the current collection signal input end of the control module.

7. The temperature acquisition circuit according to claim 5, characterized in that: The temperature acquisition circuit also includes: a first wire, a second wire and a third wire; One end of the thermistor is connected to the first collection end of the thermistor through the first wire, the other end of the thermistor is connected to the second collection end of the thermistor through the second wire, and the other end of the thermistor is grounded and connected to one end of the current collection resistor through the third wire.

8. The temperature acquisition circuit according to claim 1, characterized in that: The first constant current circuit comprises: a first operational amplifier, a second operational amplifier, a first voltage divider circuit, a first negative feedback gain adjustment circuit, a first current limiting resistor, a first filter capacitor and a first current adjustment resistor; The non-inverting end of the first operational amplifier is connected to the first output end of the first voltage divider circuit, the inverting end of the first operational amplifier is connected to the output end of the first negative feedback gain adjustment circuit, the output end of the first operational amplifier is connected to the input end of the first current limiting resistor, the output end of the first current limiting resistor is connected to the input end of the first negative feedback gain adjustment circuit, and the output end of the first current limiting resistor is connected to the input end of the first current regulating resistor, the output end of the first current regulating resistor is connected to one end of the thermistor, and the output end of the first current regulating resistor is connected to the non-inverting end of the second operational amplifier, the first input end of the first voltage divider circuit is connected to the first constant current control signal output end of the control module, the second input end of the first voltage divider circuit is connected to the inverting end of the second operational amplifier, and the second input end of the first voltage divider circuit is connected to the output end of the second operational amplifier, the power supply end of the second operational amplifier is connected to the input end of the first filter capacitor, and the power supply end of the second operational amplifier is used to receive the power supply voltage, and the output end of the first filter capacitor is grounded.

9. The temperature acquisition circuit according to claim 1, characterized in that: The second constant current circuit comprises: the second constant current circuit comprises: a third operational amplifier, a fourth operational amplifier, a second voltage divider circuit, a second negative feedback gain adjustment circuit, a second current limiting resistor, a second filter capacitor and a second current adjustment resistor; The non-inverting end of the third operational amplifier is connected to the first output end of the second voltage divider circuit, the inverting end of the third operational amplifier is connected to the output end of the second negative feedback gain adjustment circuit, the output end of the third operational amplifier is connected to the input end of the second current limiting resistor, the output end of the second current limiting resistor is connected to the input end of the second negative feedback gain adjustment circuit, and the output end of the second current limiting resistor is connected to the input end of the second current regulating resistor, the output end of the second current regulating resistor is connected to the other end of the thermistor, and the output end of the second current regulating resistor is connected to the non-inverting end of the fourth operational amplifier, the first input end of the second voltage divider circuit is connected to the second constant current control signal output end of the control module, the second input end of the second voltage divider circuit is connected to the inverting end of the fourth operational amplifier, and the second input end of the second voltage divider circuit is connected to the output end of the fourth operational amplifier, the power supply end of the fourth operational amplifier is connected to the input end of the second filter capacitor, and the power supply end of the fourth operational amplifier is used to receive the power supply voltage, and the output end of the second filter capacitor is grounded.

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