Signal processing circuit for pulmonary function instrument and pulmonary function instrument

Abstract

The utility model provides a signal processing circuit for a pulmonary function instrument and the pulmonary function instrument, and a signal input module receives an initial signal from an infrared receiving module and sends the initial signal to a peak tracking module and a differential amplification module respectively. The peak value tracking module adapts to the change of ambient light intensity, performs peak value tracking on the initial signal, ensures that the peak value of the output peak value tracking signal is consistent with the peak value of the initial signal, and meanwhile, the peak value tracking signal is a constant direct current signal. And the differential amplification module performs differential amplification processing on the initial signal and the peak tracking signal to generate a differential amplification signal in a pulse direct current signal form. And finally, the signal output module outputs a differential amplification signal. The signal processing circuit for the pulmonary function instrument can effectively extract pulse direct current signals and can adapt to the change of ambient light intensity, so that the reliability and the practicability of the pulmonary function instrument are enhanced.

Description

Technical Field

[0001] This utility model relates to the field of circuit technology, and in particular to a signal processing circuit for a pulmonary function instrument and a pulmonary function instrument. Background Technology

[0002] A pulmonary function testing device is a widely used medical device in hospitals, clinics, and homes, used to accurately measure various parameters of lung function. During the test, the air exhaled by the subject is converted into rotating airflow by a turbine in the instrument, which in turn drives the blades to rotate. The pulmonary function testing device is equipped with infrared emitting and receiving modules, which are aimed at the rotating blades. As the blades rotate, the intensity of the infrared light received by the receiving module changes due to the change in its angle, thus forming a signal in the receiving module that changes synchronously with the rotation of the blades. The signals output by the infrared receiving module include pulsating DC signals and constant DC signals. Changes in the pulsating DC signal directly reflect the rotation of the blades; by analyzing these signals, the subject's pulmonary function parameters can be calculated. However, the voltage of the constant DC signal is usually higher than that of the pulsating DC signal, and its voltage value is easily affected by changes in ambient light. When the voltage of the constant DC signal exceeds a certain threshold, it may interfere with the accurate detection of pulmonary function. Utility Model Content

[0003] This invention provides a signal processing circuit and a pulmonary function instrument for use in pulmonary function testing. It can effectively extract pulsed DC signals and adapt to changes in ambient light intensity, thereby enhancing the reliability and practicality of the pulmonary function instrument.

[0004] This invention provides a signal processing circuit for a pulmonary function instrument, comprising: a signal input module for receiving an initial signal output from an infrared receiving module and outputting the initial signal to a peak tracking module and a differential amplification module respectively; the peak tracking module for adaptively tracking the initial signal according to changes in ambient light intensity and outputting a peak tracking signal to the differential amplification module; the peak value of the peak tracking signal is the same as the peak value of the initial signal, and the peak tracking signal is a constant DC signal; the differential amplification module for differentially amplifying the initial signal and the peak tracking signal and outputting a differential amplified signal to a signal output module; the differential amplified signal is a pulsed DC signal; and the signal output module for outputting the differential amplified signal.

[0005] According to the present invention, a signal processing circuit for a pulmonary function instrument further includes a voltage follower module, which is used to follow the initial signal and output a follower signal to the peak tracking module so that the peak tracking module performs peak tracking on the follower signal; the voltage of the follower signal is equal to the voltage of the initial signal.

[0006] According to the present invention, a signal processing circuit for a pulmonary function instrument further includes a square wave generation module, which is used to convert the differential amplified signal into a square wave signal and output the square wave signal to the signal output module so that the signal output module outputs the square wave signal.

[0007] According to the present invention, a signal processing circuit for a pulmonary function instrument is provided, wherein the voltage follower module includes a first operational amplifier and a first capacitor; the positive input terminal of the first operational amplifier serves as the input terminal of the voltage follower module, the negative input terminal of the first operational amplifier is connected to the output terminal of the first operational amplifier, the output terminal of the first operational amplifier serves as the output terminal of the voltage follower module, the positive power supply terminal of the first operational amplifier is connected to the first terminal of the first capacitor and the power supply, and the second terminal of the first capacitor and the negative power supply terminal of the first operational amplifier are both grounded.

[0008] According to the present invention, a signal processing circuit for a pulmonary function instrument includes a peak tracking module comprising a second operational amplifier, a first diode, a second diode, a first resistor, and a second capacitor. The positive input terminal of the second operational amplifier serves as the input terminal of the peak tracking module. The negative input terminal of the second operational amplifier is connected to the anode of the first diode and the first terminal of the first resistor, respectively. The output terminal of the second operational amplifier is connected to the cathode of the first diode and the anode of the second diode, respectively. The common terminal of the cathode of the second diode connected to the second terminal of the first resistor and the first terminal of the second capacitor serves as the output terminal of the peak tracking module. The second terminal of the second capacitor is grounded.

[0009] According to the present invention, a signal processing circuit for a pulmonary function instrument is provided, wherein the differential amplifier module includes a third operational amplifier, a second resistor, a third resistor, a fourth resistor, and a fifth resistor; the first end of the second resistor serves as the first input terminal of the differential amplifier module, the first end of the third resistor serves as the second input terminal of the differential amplifier module, the second end of the second resistor is connected to the negative input terminal of the third operational amplifier and the first end of the fifth resistor, the second end of the third resistor is connected to the positive input terminal of the third operational amplifier and the first end of the fourth resistor, the second end of the fourth resistor is grounded, and the common terminal of the second end of the fifth resistor and the output terminal of the third operational amplifier serves as the output terminal of the differential amplifier module.

[0010] According to the present invention, a signal processing circuit for a pulmonary function instrument is provided, wherein the square wave generation module includes a sixth resistor, a seventh resistor, and a fourth operational amplifier; the positive input terminal of the fourth operational amplifier serves as the input terminal of the square wave generation module; the first terminal of the sixth resistor is connected to a power supply; the common terminal connecting the second terminal of the sixth resistor and the first terminal of the seventh resistor is connected to the negative input terminal of the fourth operational amplifier; the second terminal of the seventh resistor is grounded; and the output terminal of the fourth operational amplifier serves as the output terminal of the square wave generation module.

[0011] This utility model also provides a pulmonary function instrument, including the above-described signal processing circuit for the pulmonary function instrument.

[0012] According to the present invention, a pulmonary function instrument further includes an infrared emitting module, a turbine assembly, an infrared receiving module, and a microprocessor; the infrared emitting module and the infrared receiving module are respectively disposed on both sides of the turbine assembly; the infrared emitting module is used to emit infrared light; the turbine assembly is used to rotate under the action of the subject's exhaled air; the infrared receiving module is used to receive infrared light and convert the infrared light into an initial signal output to the signal processing circuit; the microprocessor is used to process the output signal of the signal processing circuit to obtain the pulmonary function test result.

[0013] According to the present invention, a pulmonary function instrument is provided, wherein the turbine assembly includes a turbine and turbine blades.

[0014] This invention provides a signal processing circuit and a pulmonary function instrument for use in a pulmonary function testing device. The signal input module receives an initial signal from an infrared receiving module and sends the initial signal to a peak tracking module and a differential amplification module. The peak tracking module adapts to changes in ambient light intensity by tracking the peak of the initial signal, ensuring that the peak value of the output peak tracking signal matches the peak value of the initial signal. This peak tracking signal is a constant DC signal. The differential amplification module differentially amplifies the initial signal and the peak tracking signal to generate a differential amplified signal in the form of a pulsed DC signal. Finally, the signal output module outputs the differential amplified signal. This signal processing circuit for a pulmonary function testing device can effectively extract pulsed DC signals and adapt to changes in ambient light intensity, thereby enhancing the reliability and practicality of the pulmonary function testing device. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the signal processing circuit for a pulmonary function instrument provided by this utility model.

[0017] Figure 2 This is a schematic diagram of a signal processing circuit for a pulmonary function instrument provided by this utility model.

[0018] Figure 3 This is a waveform diagram of the input and output signals of the voltage follower module provided by this utility model.

[0019] Figure 4 This is a waveform diagram of the input and output signals of the peak tracking module provided by this utility model.

[0020] Figure 5 This is a waveform diagram of the output signal of the differential amplifier module provided by this utility model.

[0021] Figure 6 This is a waveform diagram of the input and output signals of the square wave generation module provided by this utility model.

[0022] Figure 7 This is a schematic diagram of the pulmonary function instrument provided by this utility model. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this utility model clearer, the technical solutions of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0024] Pulmonary function tests are an important means of diagnosing respiratory diseases. By measuring lung function, abnormalities in the respiratory system can be detected. This is of great guiding significance for the early detection of lung and respiratory tract lesions, such as chronic bronchitis, emphysema, bronchial asthma, and intermittent lung disease.

[0025] A pulmonary function analyzer is a device used in hospitals, clinics, and homes to examine various parameters of lung function. Current pulmonary function analyzers combine a turbine with infrared light acquisition. The air exhaled by the test subject is converted into rotating airflow by the turbine, which drives the blades to rotate. The infrared emitting and receiving modules within the pulmonary function analyzer are aligned with the blades. The infrared emitting module generates infrared light, and as the blades rotate, the intensity of the light received by the receiving module varies depending on the blade angle, thus forming a signal that changes synchronously with the blade rotation. However, the output signal of the infrared receiving module consists of a pulsating DC component and a constant DC component; that is, the signal does not pulsate from zero. For the pulmonary function analyzer, only the pulsating DC component is useful; the constant DC component is useless. The voltage of this constant DC component is higher than that of the pulsating DC component, and the voltage value of this constant DC component varies with the ambient light level. The stronger the ambient light, the higher the voltage value of the constant DC component. When it exceeds a certain level, the signal will be ineffective, and the pulmonary function analyzer will not function properly.

[0026] Please refer to Figure 1 , Figure 1 This invention provides a schematic diagram of a signal processing circuit for a pulmonary function instrument.

[0027] To address the technical problems existing in the prior art, this utility model provides a signal processing circuit for a pulmonary function instrument, comprising: a signal input module for receiving an initial signal output from an infrared receiving module and outputting the initial signal to a peak tracking module and a differential amplification module respectively; a peak tracking module for adaptively tracking the peak of the initial signal according to changes in ambient light intensity and outputting a peak tracking signal to the differential amplification module; the peak value of the peak tracking signal is the same as the peak value of the initial signal, and the peak tracking signal is a constant DC signal; a differential amplification module for differentially amplifying the initial signal and the peak tracking signal and outputting a differential amplified signal to a signal output module; the differential amplified signal is a pulsed DC signal; and a signal output module for outputting the differential amplified signal.

[0028] In this embodiment, the signal processing circuit for the pulmonary function analyzer includes a signal input module, a peak tracking module, a differential amplification module, and a signal output module. Specifically, the signal input module receives the initial signal output from the infrared receiving module and maintains consistency between the output and input signals to enhance signal driving capability. This initial signal is sent to both the peak tracking module and the differential amplification module. The peak tracking module adapts to changes in ambient light intensity, performs peak tracking on the initial signal, and outputs a peak tracking signal to the differential amplification module. The peak value of the peak tracking signal is the same as the peak value of the initial signal, and the peak tracking signal is a constant DC signal, ensuring that even with changes in ambient light intensity, the peak tracking signal accurately reflects the peak value of the initial signal. The differential amplification module differentially amplifies the initial signal and the peak tracking signal and outputs a differential amplified signal to the signal output module; the differential amplified signal is a pulsed DC signal. The signal output module outputs the differential amplified signal, which is a pulsed DC signal, suitable for further digital and logical operations by the microcontroller to obtain the relevant results of the pulmonary function test.

[0029] Through the above design, the signal processing circuit of this embodiment can effectively extract useful information from the signal output by the infrared receiving module and convert it into a signal that the microcontroller can recognize. At the same time, it can automatically adapt to changes in ambient light intensity, thereby improving the reliability and practicality of the pulmonary function instrument.

[0030] In a preferred embodiment, the system further includes a voltage follower module, which follows the initial signal and outputs the follower signal to the peak tracking module so that the peak tracking module performs peak tracking on the follower signal; the voltage of the follower signal is equal to the voltage of the initial signal.

[0031] To improve the stability and accuracy of signal processing, and to ensure that the peak tracking module can accurately capture the peak value of the initial signal, the signal processing circuit for the pulmonary function instrument in this embodiment also includes a voltage follower module. The voltage follower module performs voltage tracking on the initial signal output from the infrared receiving module, ensuring that the voltage of the output follower signal is equal to that of the initial signal. This configuration does not change the amplitude or phase of the signal, but provides stronger driving capability, avoiding operational instability caused by insufficient driving capability of the infrared receiving module's output signal. It does not amplify or invert the input signal; that is, the output voltage (the voltage of the follower signal) is equal to the input voltage (the voltage of the initial signal).

[0032] In a preferred embodiment, the system further includes a square wave generation module, which converts the differential amplified signal into a square wave signal and outputs the square wave signal to the signal output module so that the signal output module outputs the square wave signal.

[0033] Considering that the microcontroller can recognize square wave signals, in this embodiment, the signal processing circuit for the pulmonary function instrument also includes a square wave generation module. The square wave generation module converts the pulsed DC signal (divider amplification signal) into a square wave signal and outputs it to the microcontroller through the signal output module. The microcontroller performs digital and logical operations on the pulsed DC signal to obtain the relevant results of the pulmonary function test.

[0034] In a preferred embodiment, the voltage follower module includes a first operational amplifier and a first capacitor; the positive input terminal of the first operational amplifier serves as the input terminal of the voltage follower module, the negative input terminal of the first operational amplifier is connected to the output terminal of the first operational amplifier, the output terminal of the first operational amplifier serves as the output terminal of the voltage follower module, the positive power supply terminal of the first operational amplifier is connected to the first terminal of the first capacitor and the power supply, and the second terminal of the first capacitor and the negative power supply terminal of the first operational amplifier are both grounded.

[0035] Please refer to Figure 2 , Figure 2 This is a schematic diagram of a signal processing circuit for a pulmonary function instrument provided by this utility model.

[0036] Please refer to Figure 3 , Figure 3 Waveforms of the input and output signals of the voltage follower module provided by this utility model.

[0037] In this embodiment, the voltage follower module includes a first operational amplifier U1A and a first capacitor (C-OP1). The initial signal NET IRM is input from the positive input terminal of the first operational amplifier U1A, and the follower signal is output from the output terminal of the first operational amplifier U1A, thereby improving the signal driving capability and avoiding instability caused by insufficient driving capability of the infrared receiver module's output signal. It will not amplify or invert the input signal, that is, the voltage of the follower signal is equal to the voltage of the initial signal.

[0038] In a preferred embodiment, the peak tracking module includes a second operational amplifier, a first diode, a second diode, a first resistor, and a second capacitor. The positive input terminal of the second operational amplifier serves as the input terminal of the peak tracking module. The negative input terminal of the second operational amplifier is connected to the anode of the first diode and the first terminal of the first resistor, respectively. The output terminal of the second operational amplifier is connected to the cathode of the first diode and the anode of the second diode, respectively. The common terminal connecting the cathode of the second diode, the second terminal of the first resistor, and the first terminal of the second capacitor serves as the output terminal of the peak tracking module. The second terminal of the second capacitor is grounded.

[0039] Please refer to Figure 4 , Figure 4The waveforms of the input and output signals of the peak tracking module provided by this utility model are shown. The solid line represents the output signal, and the dashed line represents the input signal.

[0040] In this embodiment, the peak tracking module includes a second operational amplifier U1B, a first diode D-OP1, a second diode D-OP2, a first resistor R-OP1, and a second capacitor C-OP2. The follower signal is input from the positive input terminal of the second operational amplifier U1B, and the peak tracking signal is output from the cathode of the second diode D-OP2. The output of the peak tracking module has the same peak value as the follower signal and is a constant DC signal. It also has an automatic tracking function, automatically adapting to changes in ambient light intensity. The signal peak value is high when the ambient light intensity is high and low when the ambient light intensity is low. Through the cooperation of the four components—first diode D-OP1, second diode D-OP2, first resistor R-OP1, and second capacitor C-OP2—the module automatically tracks the peak value, ensuring that the magnitude of the output constant DC signal is always consistent with the peak value of the follower signal.

[0041] In a preferred embodiment, the differential amplifier module includes a third operational amplifier, a second resistor, a third resistor, a fourth resistor, and a fifth resistor. The first end of the second resistor serves as the first input terminal of the differential amplifier module, the first end of the third resistor serves as the second input terminal of the differential amplifier module, the second end of the second resistor is connected to the negative input terminal of the third operational amplifier and the first end of the fifth resistor, the second end of the third resistor is connected to the positive input terminal of the third operational amplifier and the first end of the fourth resistor, the second end of the fourth resistor is grounded, and the common terminal of the second end of the fifth resistor and the output terminal of the third operational amplifier serves as the output terminal of the differential amplifier module.

[0042] Please refer to Figure 5 , Figure 5 The waveform of the output signal of the differential amplifier module provided by this utility model.

[0043] In this embodiment, the differential amplifier module includes a third operational amplifier U1C, a second resistor R-OP2, a third resistor R-OP3, a fourth resistor R-OP4, and a fifth resistor R-OP5. The follower signal is input from the negative input terminal of the third operational amplifier U1C, the peak tracking signal is input from the positive input terminal of the third operational amplifier U1C, and the differential amplified signal is output from the output terminal of the third operational amplifier U1C. By differentially amplifying the follower signal output from the voltage follower module and the peak tracking signal (constant DC signal) output from the peak tracking module, the constant current signal is eliminated, and the pulse portion of the follower signal is out of phase. The amplitude is also amplified, with the amplification factor determined by resistors (R-OP2~R-OP5), thus obtaining the useful pulsating DC portion (differential amplified signal).

[0044] In a preferred embodiment, the square wave generation module includes a sixth resistor, a seventh resistor, and a fourth operational amplifier; the positive input terminal of the fourth operational amplifier serves as the input terminal of the square wave generation module, the first terminal of the sixth resistor is connected to the power supply, the common terminal connecting the second terminal of the sixth resistor and the first terminal of the seventh resistor is connected to the negative input terminal of the fourth operational amplifier, the second terminal of the seventh resistor is grounded, and the output terminal of the fourth operational amplifier serves as the output terminal of the square wave generation module.

[0045] Please refer to Figure 6 , Figure 6 The diagram shows the waveforms of the input and output signals of the square wave generation module provided by this invention. The solid line represents the output signal, and the dashed line represents the input signal.

[0046] In this embodiment, the square wave generation module includes a sixth resistor R-OP6, a seventh resistor R-OP7, and a fourth operational amplifier U1D. The differential amplified signal is input from the positive input terminal of the fourth operational amplifier U1D, and the square wave signal is output from the output terminal of the fourth operational amplifier U1D. The square wave generation module converts the useful pulsating DC signal (differential amplified signal) into a square wave signal NET OPA, which is supplied to the microcontroller for digital and logic operations to obtain lung function test results. A comparator composed of the fourth operational amplifier U1D, the sixth resistor R-OP6, and the seventh resistor R-OP7 compares the differential amplified signal with a fixed voltage. The comparison voltage is determined by the sixth resistor R-OP6 and the seventh resistor R-OP7; a high level is output when the voltage is higher than the comparison voltage, and a low level is output when the voltage is lower than the comparison voltage, thus obtaining the square wave signal.

[0047] In summary, the signal processing circuit of this invention can enhance signal driving capability, extract pulsed DC signals from the initial signal, convert pulsed DC signals into square wave signals that can be recognized by the microcontroller, and adapt to fluctuations in ambient light intensity.

[0048] The pulmonary function instrument provided by this utility model is described below. The pulmonary function instrument described below can be referred to in correspondence with the signal processing circuit for the pulmonary function instrument described above.

[0049] Please refer to Figure 7 , Figure 7 A schematic diagram of the pulmonary function instrument provided by this utility model.

[0050] This utility model also provides a pulmonary function instrument, including the above-described signal processing circuit for the pulmonary function instrument.

[0051] In a preferred embodiment, the system further includes an infrared emitting module, a turbine assembly, an infrared receiving module, and a microprocessor; the infrared emitting module and the infrared receiving module are respectively disposed on both sides of the turbine assembly; the infrared emitting module is used to emit infrared light; the turbine assembly is used to rotate under the action of the subject's exhaled air; the infrared receiving module is used to receive infrared light and convert it into an initial signal output to the signal processing circuit; the microprocessor is used to process the output signal of the signal processing circuit to obtain the lung function test results.

[0052] In a preferred embodiment, the turbine assembly includes a turbine and turbine blades.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and not to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A signal processing circuit for a pulmonary function instrument, characterized in that, include: The signal input module is used to receive the initial signal output by the infrared receiving module and output the initial signal to the peak tracking module and the differential amplification module respectively; The peak tracking module is used to adapt to changes in ambient light intensity, perform peak tracking on the initial signal, and output the peak tracking signal to the differential amplification module. The peak value of the peak tracking signal is the same as the peak value of the initial signal, and the peak tracking signal is a constant DC signal; The differential amplifier module is used to differentially amplify the initial signal and the peak tracking signal, and output the differential amplified signal to the signal output module; the differential amplified signal is a pulsed DC signal. The signal output module is used to output the differential amplified signal.

2. The signal processing circuit for a pulmonary function instrument according to claim 1, characterized in that, It also includes a voltage follower module, which is used to follow the initial signal and output a follower signal to the peak tracking module so that the peak tracking module performs peak tracking on the follower signal; the voltage of the follower signal is equal to the voltage of the initial signal.

3. The signal processing circuit for a pulmonary function instrument according to claim 1, characterized in that, It also includes a square wave generation module, which is used to convert the differential amplified signal into a square wave signal and output the square wave signal to the signal output module so that the signal output module outputs the square wave signal.

4. The signal processing circuit for a pulmonary function instrument according to claim 2, characterized in that, The voltage follower module includes a first operational amplifier and a first capacitor; The positive input terminal of the first operational amplifier serves as the input terminal of the voltage follower module. The negative input terminal of the first operational amplifier is connected to the output terminal of the first operational amplifier. The output terminal of the first operational amplifier serves as the output terminal of the voltage follower module. The positive power supply terminal of the first operational amplifier is connected to the first terminal of the first capacitor and the power supply, respectively. The second terminal of the first capacitor and the negative power supply terminal of the first operational amplifier are both grounded.

5. The signal processing circuit for a pulmonary function instrument according to claim 1, characterized in that, The peak tracking module includes a second operational amplifier, a first diode, a second diode, a first resistor, and a second capacitor; The positive input terminal of the second operational amplifier serves as the input terminal of the peak tracking module. The negative input terminal of the second operational amplifier is connected to the anode of the first diode and the first end of the first resistor, respectively. The output terminal of the second operational amplifier is connected to the cathode of the first diode and the anode of the second diode, respectively. The common terminal of the cathode of the second diode, the second end of the first resistor, and the first end of the second capacitor serves as the output terminal of the peak tracking module. The second end of the second capacitor is grounded.

6. The signal processing circuit for a pulmonary function instrument according to claim 1, characterized in that, The differential amplifier module includes a third operational amplifier, a second resistor, a third resistor, a fourth resistor, and a fifth resistor; The first end of the second resistor serves as the first input terminal of the differential amplifier module, the first end of the third resistor serves as the second input terminal of the differential amplifier module, the second end of the second resistor is connected to the negative input terminal of the third operational amplifier and the first end of the fifth resistor, the second end of the third resistor is connected to the positive input terminal of the third operational amplifier and the first end of the fourth resistor, the second end of the fourth resistor is grounded, and the common terminal of the second end of the fifth resistor and the output terminal of the third operational amplifier serves as the output terminal of the differential amplifier module.

7. The signal processing circuit for a pulmonary function instrument according to claim 3, characterized in that, The square wave generation module includes a sixth resistor, a seventh resistor, and a fourth operational amplifier; The positive input terminal of the fourth operational amplifier serves as the input terminal of the square wave generation module. The first terminal of the sixth resistor is connected to the power supply. The common terminal of the connection between the second terminal of the sixth resistor and the first terminal of the seventh resistor is connected to the negative input terminal of the fourth operational amplifier. The second terminal of the seventh resistor is grounded. The output terminal of the fourth operational amplifier serves as the output terminal of the square wave generation module.

8. A pulmonary function instrument, characterized in that, Includes the signal processing circuit for a pulmonary function instrument as described in any one of claims 1 to 7.

9. The pulmonary function instrument according to claim 8, characterized in that, It also includes an infrared emitting module, a turbine assembly, an infrared receiving module, and a microprocessor; the infrared emitting module and the infrared receiving module are respectively disposed on both sides of the turbine assembly; The infrared emitting module is used to emit infrared light; The turbine assembly is designed to rotate under the action of the subject's exhaled air; The infrared receiving module is used to receive infrared light and convert the infrared light into an initial signal, which is then output to the signal processing circuit. The microprocessor is used to process the output signal of the signal processing circuit to obtain the lung function test results.

10. The pulmonary function instrument according to claim 9, characterized in that, The turbine assembly includes a turbine and turbine blades.

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