Micro-current detection device and gas chromatograph

Abstract

The invention provides a micro-current detection device and a gas chromatograph, the micro-current detection device comprises a transimpedance amplification circuit, the transimpedance amplification circuit comprises a current amplification circuit and a feedback resistor, the resistance value of the feedback resistor is greater than 100G omega, and the transimpedance amplification circuit is used for receiving a micro-current signal and generating a first voltage signal based on the micro-current signal; the analog-to-digital conversion circuit is connected with the voltage signal output end of the transimpedance amplification circuit and is used for receiving the first voltage signal and converting the first voltage signal into a first digital signal; the main control circuit is connected with the digital signal output end of the analog-to-digital conversion circuit and is used for receiving the first digital signal and filtering the first digital signal to obtain a second digital signal; the low-ripple power supply circuit is connected with the transimpedance amplification circuit, the analog-to-digital conversion circuit and the master control circuit and is used for providing low-ripple power supply voltage; and the upper computer is connected with the serial port output end of the main control circuit and is used for receiving the second digital signal and determining the current magnitude of the micro-current signal according to the second digital signal.

Description

Technical Field

[0001] This application relates to the field of electronic measurement technology, and in particular to a microcurrent detection device and a gas chromatograph. Background Technology

[0002] In fields such as environmental monitoring, gas analysis, and biomedicine, the requirements for detecting trace gases and ultrafine particulate matter are increasing, making microcurrent detection technology a key means to achieve high-precision ion signal measurement. Microcurrent detection typically involves the acquisition of current signals at the fA (femtoampere) level or even smaller, which places extremely high demands on the sensitivity, noise suppression capability, and dynamic range of the detection system.

[0003] Traditional microammeters employ multi-range microammeters, which require constant switching between multiple ranges when measuring different organic concentrations. They also have high detection limits and are not effective at detecting microcurrents generated by trace amounts of organic matter at the ppb level. They suffer from low measurement sensitivity and small dynamic range. In practical use, the concentration and current signal of the sample to be tested need to be estimated in advance, making them unsuitable for accurate measurement of mixtures containing numerous organic compounds of different concentrations. Summary of the Invention

[0004] This application provides a microcurrent detection device and a gas chromatograph.

[0005] In a first aspect, a microcurrent detection device is provided, comprising: a transimpedance amplifier circuit, including a current amplifier circuit and a feedback resistor, wherein the resistance value of the feedback resistor is greater than 100G. The transimpedance amplifier circuit receives a micro-current signal and generates a first voltage signal based on the micro-current signal; the analog-to-digital converter circuit is connected to the voltage signal output terminal of the transimpedance amplifier circuit, receives the first voltage signal, and converts the first voltage signal into a first digital signal; the main control circuit is connected to the digital signal output terminal of the analog-to-digital converter circuit, receives the first digital signal, and filters the first digital signal to obtain a second digital signal; the low-ripple power supply circuit is connected to the transimpedance amplifier circuit, the analog-to-digital converter circuit, and the main control circuit, and provides a low-ripple power supply voltage; the host computer is connected to the serial port output terminal of the main control circuit, receives the second digital signal, and determines the current magnitude of the micro-current signal based on the second digital signal.

[0006] Based on the above technical means, by using high resistance values ​​greater than 100G The transimpedance amplifier circuit with feedback resistor, combined with an ultra-low bias current operational amplifier, enables I / V conversion of micro-currents in the fA range, significantly improving detection sensitivity. Simultaneously, the low-ripple power supply circuit effectively reduces power supply noise, improves the signal-to-noise ratio, and thus enhances the detection accuracy of micro-current signals.

[0007] In some embodiments, the low-ripple power supply circuit includes a switching power supply circuit and a linear power supply circuit connected in series; the switching power supply circuit is used to convert the input voltage into an intermediate voltage; and the linear power supply circuit is used to convert the intermediate voltage into the low-ripple power supply voltage.

[0008] Based on the above technical means, by using a combination of switching power supply and linear power supply, it is possible to achieve efficient voltage reduction, avoid the overheating problem of the first-stage linear power supply, and maintain extremely low output voltage ripple, thereby reducing interference to micro-current measurement and improving system stability and measurement accuracy.

[0009] In some embodiments, the transimpedance amplifier circuit, the analog-to-digital converter circuit, the main control circuit, and the low-ripple power supply circuit are all mounted on a printed circuit board. The printed circuit board is made of FR-4 epoxy glass cloth laminate material, and the sheet resistance of the FR-4 epoxy glass cloth laminate material is greater than... .

[0010] Based on the above technical means, using FR-4 material with high sheet resistance can effectively reduce surface leakage current and avoid its interference with weak current signals, thereby improving the measurement accuracy and reliability of the overall system.

[0011] In some embodiments, a protective ring is provided on the printed circuit board. The protective ring is disposed at the micro-current input terminal of the transimpedance amplifier circuit and is used to guide the leakage current between the micro-current input terminal and the voltage output terminal of the low-ripple power supply circuit into the low-impedance loop.

[0012] Based on the above technical means, setting up a protection ring can effectively collect and conduct the leakage current between the micro-current input terminal and the power supply terminal, preventing it from entering the signal channel and causing interference, thereby improving the measurement accuracy of the micro-current signal.

[0013] In some embodiments, the protection ring is a multi-turn protection ring, which is disposed between the transimpedance amplifier circuit and the analog-to-digital converter circuit, the main control circuit, and the low-ripple power supply circuit.

[0014] Based on the above technical means, by setting up multiple protection rings, signal interference between different functional modules can be isolated more effectively, especially suppressing noise from power supply and digital circuits, thereby improving the electromagnetic compatibility and measurement accuracy of the entire system.

[0015] In some embodiments, the printed circuit board further includes a cutout area, which is disposed between the power input terminal of the transimpedance amplifier circuit and the microcurrent input terminal of the transimpedance amplifier circuit.

[0016] Based on the above technical means, by utilizing the high resistivity of air, setting a hollow area on the printed circuit board can significantly increase the insulation resistance between the input terminal and the power supply terminal, thereby significantly reducing leakage current and avoiding interference with fA-level micro-current signals.

[0017] In some embodiments, the microcurrent detection device further includes: a shielding housing covering the outside of the printed circuit board, the shielding housing including a first shielding housing and a second shielding housing stacked together, the first shielding housing being made of a high magnetic material for absorbing low-frequency magnetic noise, and the second shielding housing being made of a diamagnetic material for reflecting high-frequency magnetic noise.

[0018] Based on the above technical means, the double-layer shielding structure effectively suppresses low-frequency and high-frequency electromagnetic interference, thereby improving the system's immunity to external electromagnetic environments and ensuring the accuracy and stability of measurement results.

[0019] In some embodiments, the printed circuit board is provided with a multi-turn windowed ground wire, and the grounding terminals of the transimpedance amplifier circuit, the analog-to-digital conversion circuit, the main control circuit, and the low ripple power supply circuit are all connected to the multi-turn windowed ground wire.

[0020] Based on the above technical means, a multi-turn windowed ground wire is set up to optimize the grounding path, reduce parasitic inductance and impedance in the grounding loop, and improve the overall stability and anti-interference capability of the system.

[0021] In some embodiments, the analog-to-digital converter circuit is configured to operate in bipolar conversion mode to process positive and negative bidirectional voltage signals, and the voltage range that the analog-to-digital converter circuit can acquire is greater than the voltage range of the first voltage signal.

[0022] Based on the above technical means, the analog-to-digital conversion circuit adopts a bipolar conversion mode to expand the voltage acquisition range, enabling the system to adapt to a wider range of input signal changes and improving the flexibility and applicability of measurement.

[0023] In a second aspect, a gas chromatograph is provided, including the microcurrent detection device as described in the first aspect. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a microcurrent detection device provided in an embodiment of this application; Figure 2 This is a schematic diagram of the low-ripple power supply circuit in the microcurrent detection device provided in this application embodiment; Figure 3 This is a schematic diagram of the structure of a microcurrent detection device provided in another embodiment of this application; Figure 4This is a schematic diagram of the structure of a microcurrent detection device provided in another embodiment of this application; Figure 5 This is a schematic diagram of a technical solution that uses a protective ring on a printed circuit board to suppress leakage current. Figure 6 This is a schematic diagram of a technical solution that uses slots on a printed circuit board to suppress leakage current. Figure 7 This is a schematic diagram of the analog-to-digital conversion circuit in the microcurrent detection device provided in the embodiments of this application; Figure 8 This is a schematic diagram of the main control circuit in the microcurrent detection device provided in the embodiments of this application; Figure 9 This is a schematic diagram of the transimpedance amplifier circuit in the microcurrent detection device provided in the embodiments of this application; Figure 10 This is a schematic diagram of the low-ripple power supply circuit in the microcurrent detection device provided in the embodiments of this application. Detailed Implementation

[0025] The embodiments of this application will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be understood that the preferred embodiments are only for illustrating this application and are not intended to limit the scope of protection of this application.

[0026] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. Therefore, the drawings only show the components related to this application and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0027] In recent years, due to stricter emission standards for motor vehicles and increased requirements for monitoring toxic gases in the environment, trace analysis of atmospheric gases and emitted particulate matter has become more demanding. To achieve monitoring of ultra-trace toxic gases and particulate matter, high-precision ion detection technologies such as gas chromatography and mass spectrometry are needed. A prerequisite for using these ion detection technologies is the development of highly sensitive microammeters, especially fA-level microammeters. Currently, research on fA-level weak current acquisition and measurement technologies is limited, particularly in areas essential for microcurrent measurement such as ultra-low noise LDO power supplies, ultra-low noise I / V preamplifiers, and range-free, large dynamic range measurements. These areas still present critical scientific and technical challenges that urgently need to be addressed.

[0028] In related technologies, traditional GC-FID microammeters suffer from low sensitivity, small dynamic range, and the need for frequent range switching, making them unsuitable for the detection of trace organic compounds. Particularly when detecting gas samples with concentrations at the ppb level, their detection limits are high, failing to accurately capture microcurrent signals at the fA level. Furthermore, the lack of effective leakage current suppression and electromagnetic interference shielding measures makes the input signal susceptible to interference, affecting the accuracy of the final measurement results.

[0029] To address the aforementioned problems, this application provides a microcurrent detection device and a gas chromatograph. The technical solution of this application will be described in detail below with reference to the accompanying drawings.

[0030] Figure 1 This is a schematic structural diagram of the microcurrent detection device provided in the embodiments of this application. Figure 1 The microcurrent detection device 100 includes a transimpedance amplifier circuit 110, an analog-to-digital converter circuit 120, a main control circuit 130, a low-ripple power supply circuit 140, and a host computer 150.

[0031] The transimpedance amplifier circuit 110 includes a current amplifier circuit 111 and a feedback resistor 112. The transimpedance amplifier circuit 110 can convert the input micro-current signal into a first voltage signal and output it. The core principle of the transimpedance amplifier circuit 110 is based on Ohm's law U=IR. In the transimpedance amplifier circuit 110, the larger the resistance value of the feedback resistor, the higher the sensitivity for detecting micro-current signals.

[0032] In this embodiment, the transimpedance amplifier circuit 110 uses a power greater than 100G. The feedback resistor has an ultra-large resistance value to achieve high-gain amplification of fA-level micro-current signals.

[0033] In some embodiments, the feedback resistor 112 is a resistor with a low temperature drift coefficient to ensure that its resistance changes significantly with temperature, thereby maintaining a stable gain.

[0034] In some embodiments, the current amplification circuit 111 includes an operational amplifier chip, such as an ADA4530 operational amplifier chip, which has ultra-low bias current and ultra-low voltage noise, and is suitable for detecting extremely weak micro-current signals.

[0035] The analog-to-digital converter circuit 120 is connected to the voltage signal output terminal of the transimpedance amplifier circuit 110 to receive the first voltage signal and convert the first voltage signal into a first digital signal for further processing by the main control circuit 130.

[0036] For example, in the solution of this application, the analog-to-digital converter circuit 120 is a 24-bit analog-to-digital converter circuit, such as the AD7124 chip, which has high resolution and high precision and can accurately convert the first voltage signal generated by the transimpedance amplifier circuit 110 into a first digital signal.

[0037] In some embodiments, the analog-to-digital converter 120 employs a bipolar conversion mode, meaning that the analog-to-digital converter 120 can process both positive and negative voltage signals. For example, the voltage signal range that the analog-to-digital converter 120 can process is ±5.4V, which covers the range of voltage signals generated by the transimpedance amplifier circuit 110.

[0038] The main control circuit 130 is connected to the digital signal output terminal of the analog-to-digital converter circuit 120, reads the first digital signal generated by the analog-to-digital converter circuit 120, and performs filtering processing on the first digital signal to remove noise and extract the useful signal (i.e., the second digital signal).

[0039] For example, the main control circuit 130 employs an embedded processor to run specific filtering algorithms, such as moving average filtering or low-pass filtering, to remove high-frequency noise and improve signal stability and accuracy. After filtering, the main control circuit 130 generates a second digital signal that is smoother and closer to the actual microcurrent signal.

[0040] In the above embodiments, the main control circuit 130 can effectively reduce signal noise through filtering. The main control circuit 130 can also improve the accuracy and reliability of the measurement results through filtering. Finally, the output second digital signal can more realistically reflect the microcurrent situation.

[0041] The low-ripple power supply circuit 140 is connected to the transimpedance amplifier circuit 110, the analog-to-digital converter circuit 120, and the main control circuit 130 to provide a low-ripple power supply voltage. The low-ripple power supply circuit 140 is a DC power supply module with extremely small output voltage fluctuations. It is often used in noise-sensitive electronic measurement equipment to reduce signal noise caused by power supply fluctuations and improve the system's signal-to-noise ratio and detection accuracy.

[0042] In some embodiments of this application, see Figure 2 The low-ripple power supply circuit 140 includes a switching power supply circuit 141 and a linear power supply circuit 142 connected in series. The switching power supply circuit 141 converts the input voltage to an intermediate voltage, and the linear power supply circuit 142 converts the intermediate voltage to a low-ripple power supply voltage. This circuit structure avoids the heat generation phenomenon during voltage conversion by a single-stage linear unit, and also avoids the complexity of designing multi-stage linear power supplies. Through this two-stage conversion method, the output ripple of the power supply circuit is extremely small, and it will not interfere with the input micro-current signal of the transimpedance amplifier circuit.

[0043] Based on the above technical means, by using a combination of switching power supply and linear power supply, it is possible to achieve efficient voltage reduction, avoid the overheating problem of the first-stage linear power supply, and maintain extremely low output voltage ripple, thereby reducing interference to micro-current measurement and improving system stability and measurement accuracy.

[0044] Revisit Figure 1 The host computer 150 receives the second digital signal through serial communication and determines the magnitude of the microcurrent signal based on the signal.

[0045] In this embodiment, the host computer 150 refers to an external computing device connected to the main control circuit 130, such as a personal computer or an industrial control computer. The host computer 150 is connected to the main control circuit 130 through a serial communication interface, receives the second digital signal sent by the main control circuit 130, and calculates the current magnitude of the corresponding micro-current signal based on the second digital signal.

[0046] Based on the above technical means, by using high resistance >100G The transimpedance amplifier circuit with feedback resistor, combined with an ultra-low bias current operational amplifier, enables I / V conversion of micro-currents in the fA range, significantly improving detection sensitivity. Simultaneously, the low-ripple power supply circuit effectively reduces power supply noise, improves the signal-to-noise ratio, and thus enhances the detection accuracy of micro-current signals.

[0047] In some embodiments, see Figure 3 The transimpedance amplifier circuit 110, the analog-to-digital converter circuit 120, the main control circuit 130, and the low-ripple power supply circuit 140 are all mounted on the printed circuit board 160.

[0048] In this embodiment, the printed circuit board is made of FR-4 epoxy glass cloth laminate material, which has a sheet resistance greater than [missing information]. .

[0049] Based on the above technical means, using FR-4 material with high sheet resistance can effectively reduce surface leakage current and avoid its interference with weak current signals, thereby improving the measurement accuracy and reliability of the overall system.

[0050] In some embodiments, see Figure 4 A protective ring 161 is provided on the printed circuit board. The protective ring is located at the micro-current input terminal of the transimpedance amplifier circuit 110 and is used to guide the leakage current between the micro-current input terminal and the voltage output terminal of the low ripple power supply circuit 140 into the low impedance loop.

[0051] Figure 5The diagram illustrates the principle of a technical solution that uses a protective ring on a printed circuit board to suppress leakage current. When the current input terminal and the power supply voltage are simultaneously on the same dielectric, a certain leakage resistance Rx exists between the current input terminal and the power supply voltage due to the surface resistance of the dielectric. The resulting leakage current is: I = Uin / Rx. When the leakage resistance of the dielectric is not large enough, a significant leakage current disturbance will occur.

[0052] Taking the aforementioned FR-4 material circuit board as an example, a leakage current of several pA will be generated under a ±5V power supply. This level of leakage current will overwhelm the fA-level current signal at the input terminal. However, by setting up a protection ring, a low-impedance loop with an open window is set at the current input signal terminal, and the leakage current flowing to the signal input terminal is diverted into the low-impedance loop, thereby reducing the leakage current.

[0053] Based on the above technical means, setting up a protection ring can effectively collect and conduct the leakage current between the micro-current input terminal and the power supply terminal, preventing it from entering the signal channel and causing interference, thereby improving the measurement accuracy of the micro-current signal.

[0054] In some embodiments, the protection ring is a multi-turn protection ring, which is disposed between the transimpedance amplifier circuit 110 and the analog-to-digital converter circuit 120, the main control circuit 130 and the low ripple power supply circuit 140.

[0055] Because single-loop protection rings may have shielding gaps (such as PCB edges or wiring interference), multi-loop concentric rings form a "gradient shield," further compressing the leakage current path space. The inner ring is close to the micro-current input terminal and is at the same potential as the sensitive node; the outer ring can be connected to ground or power supply reference points, blocking interference in different areas layer by layer.

[0056] Based on the above technical means, by setting up multiple protection rings, signal interference between different functional modules can be isolated more effectively, especially suppressing noise from power supply and digital circuits, thereby improving the electromagnetic compatibility and measurement accuracy of the entire system.

[0057] In some embodiments, the printed circuit board also includes a cutout area, which is disposed between the power input terminal of the transimpedance amplifier circuit 110 and the microcurrent input terminal of the transimpedance amplifier circuit 110.

[0058] Figure 6This diagram illustrates a schematic of a technique for suppressing leakage current by creating a cutout area on a printed circuit board. Part of the printed circuit board is hollowed out (removing the printed circuit board substrate and copper foil), cutting off the physical conductive path between them. Utilizing the high resistivity of air, the leakage resistance Rx between the current input terminal and the power supply voltage is increased, simultaneously increasing the path length of the leakage current and thus reducing its magnitude. In the circuit of this application, the distance between the power supply pin and the signal input pin of the transimpedance amplifier circuit 110 is short, requiring a cutout process by creating a trench approximately 2mm wide between them.

[0059] Based on the above technical means, by utilizing the high resistivity of air, setting a hollow area on the printed circuit board can significantly increase the insulation resistance between the input terminal and the power supply terminal, thereby significantly reducing leakage current and avoiding interference with fA-level micro-current signals.

[0060] In some embodiments, the microcurrent detection device further includes a shielding housing covering the outside of the printed circuit board, the shielding housing including a first shielding housing and a second shielding housing stacked together.

[0061] The first shielding shell is made of a high-magnetic material to absorb low-frequency magnetic noise. This high-magnetic material can be, for example, permalloy or ferrite, and its high permeability absorbs low-frequency magnetic fields (low-frequency magnetic fields have strong penetrating power and need to be absorbed and attenuated) to reduce low-frequency interference such as power frequency.

[0062] The second shielding shell is made of antimagnetic materials such as copper or aluminum: it uses the eddy current effect of good conductors to reflect high-frequency electromagnetic fields (high-frequency interference can be shielded by metal reflection) and block high-frequency magnetic noise.

[0063] Based on the above technical means, the double-layer shielding structure effectively suppresses low-frequency and high-frequency electromagnetic interference, thereby improving the system's immunity to external electromagnetic environments and ensuring the accuracy and stability of measurement results.

[0064] In some embodiments, a multi-turn windowed ground wire is provided on the printed circuit board, and the ground terminals of the transimpedance amplifier circuit 110, analog-to-digital converter circuit 120, main control circuit 130 and low ripple power supply circuit 140 are all connected to the multi-turn windowed ground wire.

[0065] In this design, the ground copper foil is exposed on the surface of the printed circuit board (without being covered by solder mask), forming a multi-turn ground loop around the circuit. This multi-turn ground loop achieves near-single-point grounding, as the grounding current from each circuit is collected through the loop, reducing ground loops. Simultaneously, the exposed copper foil acts as an additional shielding layer, absorbing static electricity or stray charges on the printed circuit board surface. The multi-turn structure increases the redundancy of the grounding path, ensuring low-impedance grounding and preventing ground potential fluctuations from affecting signals. Based on the above technical means, a multi-turn windowed ground wire is set up to optimize the grounding path, reduce parasitic inductance and impedance in the grounding loop, and improve the overall stability and anti-interference capability of the system.

[0066] The technical solution of this application will be further explained below with reference to a usage scenario.

[0067] In recent years, due to stricter emission standards for motor vehicles and increased requirements for monitoring toxic gases in the environment, trace analysis of atmospheric gases and emitted particulate matter has become more demanding. To monitor ultra-trace toxic gases and particulate matter, high-precision ion detection technologies such as gas chromatography and mass spectrometry are needed. The use of these technologies necessitates the development of highly sensitive microammeters, especially fA-level microammeters. Currently, China is almost entirely lacking in fA-level weak current acquisition and measurement technology, particularly in areas essential for microcurrent measurement such as ultra-low noise LDO power supplies, ultra-low noise I / V preamplifiers, and range-free, large dynamic range measurements. These areas still present critical scientific and technical challenges that urgently need to be addressed.

[0068] Traditional GC-FID microammeters employ multi-range microammeters, requiring frequent range switching when measuring different organic concentrations. They also have high detection limits and are ineffective at detecting microcurrents generated by trace amounts of organic matter at the ppb level. Traditional GC-FID microammeters suffer from low sensitivity and small dynamic range, necessitating prior estimation of the sample concentration and current signal in practical applications, making them unsuitable for accurate measurements of mixtures containing numerous organic compounds of varying concentrations. To address these issues, this application proposes a microcurrent acquisition system based on a transimpedance amplifier circuit, supplemented by various leakage current suppression and ultra-low noise control technologies, to achieve real-time and accurate fA-level microcurrent detection.

[0069] To address the aforementioned issues, this application employs a transimpedance amplifier circuit as its core, utilizing Guard rings, cutouts, and double-layer shielding to reduce extreme noise, and employing a 24-bit high-order analog-to-digital converter chip to improve the accuracy of the acquired signal, ultimately achieving precise measurement of fA-level microcurrents.

[0070] To address the issues of insufficient acquisition sensitivity and low detection limit in existing microammeters, this application proposes a microcurrent acquisition system based on a transimpedance amplifier circuit, supplemented by various leakage current suppression and ultra-low noise control technologies, to achieve real-time and accurate fA-level microcurrent detection.

[0071] The transimpedance amplifier circuit adopts Ohm's law: U=I*R, uses the ADA4530 chip with ultra-low bias current and ultra-low voltage noise, and builds a feedback loop with a 10G ultra-large resistance resistor to amplify the fA-level current to a voltage level that can be detected by the subsequent analog-to-digital conversion circuit.

[0072] 1) Leakage current suppression technology In the technical solution of this application, the leakage current suppression technology includes guard ring technology and hollowing technology.

[0073] When the current input terminal and the power supply voltage are simultaneously on the same medium, a certain leakage resistance Rx exists between the current input terminal and the power supply voltage due to the surface resistance of the medium. The resulting leakage current is: I = Uin / Rx. When the leakage resistance of the medium is insufficient, a significant leakage current disturbance will occur. This application uses FR-4 sheet metal, composed of fiberglass cloth, epoxy resin, and other materials. The sheet resistance is... Around ±5V, a leakage current of several pA will be generated. This level of leakage current will overwhelm the fA-level current signal at the input terminal. Therefore, Guard ring technology and cutout technology are needed to reduce leakage current.

[0074] See Figure 4 and Figure 5 Guard loop technology refers to setting a low-impedance loop with an open window at the current input signal terminal to guide the leakage current flowing to the signal input terminal into the low-impedance loop. The technical solution of this application can adopt a multi-turn Guard loop mode to isolate the current input terminal, the transimpedance amplifier circuit and other circuits.

[0075] See Figure 6 The cutout technique involves hollowing out a portion of the printed circuit board material. By utilizing the high resistivity of air, the leakage resistance Rx between the current input terminal and the power supply voltage is increased, thereby reducing the leakage current.

[0076] In the technical solution of this application, the distance between the power supply pin and the signal input pin of the operational amplifier chip is short, and it is necessary to perform a hollowing process, that is, to carve out a groove about 2mm wide between the two.

[0077] 2) Low noise control technology First, a double-layer electromagnetic shielding technology is employed. The electromagnetic waves present in the air cover the entire frequency band, and a single-material metal shielding shell cannot simultaneously shield both high- and low-frequency electromagnetic waves. Therefore, two metals with different properties are used as the shielding shell: a high-magnetic material and a diamagnetic material. The high-magnetic material absorbs low-frequency magnetic noise, while the diamagnetic material reflects high-frequency magnetic noise and provides electrostatic shielding.

[0078] Secondly, an LDO (Low Ripple Discharge) power supply is used to reduce the noise impact caused by voltage disturbances in the power supply. A low ripple power supply voltage is crucial for the accuracy of the transimpedance amplifier circuit in detecting fA-level micro-currents. Reducing power supply ripple decreases the noise ultimately superimposed on the output voltage signal, improving the system's signal-to-noise ratio. This application employs a two-stage conversion for the negative power supply: first, a switching power supply converts the 12V voltage to -5.8V, and then a linear power supply boosts it to -5V. This avoids the heat generated during voltage conversion in a single linear unit and eliminates the need for a multi-stage linear power supply, resulting in low power consumption and low ripple.

[0079] Finally, a 24-bit analog-to-digital converter (ADC) circuit is used. To more accurately read the generated voltage signal, a 24-bit AD7124 chip is used to build the ADC circuit. Furthermore, taking advantage of the transimpedance amplifier circuit's ability to detect positive and negative current signals, this circuit employs a bipolar conversion mode, capable of acquiring ±5.4V voltage, thus covering the signal generated by the transimpedance amplifier circuit.

[0080] Figures 7-10 These are the circuit schematics of the analog-to-digital conversion circuit, the main control circuit, the transimpedance amplifier circuit, and the low-ripple power supply circuit in the technical solution of this application.

[0081] The analog-to-digital converter (ADC) circuit converts the analog voltage signal obtained from the I / V conversion of the transimpedance amplifier circuit into a digital signal that the main control circuit can read. The main control circuit reads the digital signal generated by the ADC, performs simple filtering, and then sends this data to the computer via serial communication. The transimpedance amplifier circuit converts the fA-level micro-current into a detectable voltage signal. The low-ripple power supply circuit provides a low-ripple power supply voltage for the entire micro-current acquisition system.

[0082] In the technical solution of this application, the feedback resistor is 10 with a low temperature coefficient. 10 With high resistance, the detectable current value is lower, down to the fA level.

[0083] By utilizing guard ring technology and cutout technology, leakage current interference caused by power supply voltage and voltage from other components is reduced at the current input terminal. Multiple turns of windowed ground lines are placed on the printed circuit board, serving a similar function to the guard rings around signal lines, separating different circuit modules as much as possible and reducing signal interference between them.

[0084] The system employs a double-layer electromagnetic shielding technology, utilizing two metal materials with different magnetic impedances as the shielding shell for the micro-current acquisition system. This significantly reduces external electromagnetic interference and ensures the accuracy of the final read electrical signal.

[0085] Employing the ADA4530 with ultra-low bias current and a low temperature drift coefficient of 100G A feedback loop is constructed using resistors to achieve I / V conversion of the fA-level current signal generated by the detection of trace organic gases.

[0086] This application uses the ADA4530-1 operational amplifier chip with ultra-low leakage current, in conjunction with... Large resistance can generate The gain effect allows for the detection of micro-currents at the fA level, amplifying them to the uV level. A 24-bit analog-to-digital converter is also designed to improve voltage reading accuracy, enabling the detection of micro-currents at the uV level.

[0087] Double-layer shielding is used to solve external high and low frequency electromagnetic interference, and multi-turn guard rings and printed circuit board cutout technology are used to suppress the effective signal from being overwhelmed.

[0088] Compared to the microammeter carried by traditional GC-FID, the final resolution / noise of this application can reach 8.1 fA, which can meet the requirements of gas chromatograph for the detection of trace ppb-level volatile organic gases.

[0089] This application also provides a gas chromatograph, including a microcurrent detection device as described in any of the preceding embodiments.

[0090] It should be understood that in the embodiments of this application, "B corresponding to A" means that B is associated with A, and B can be determined based on A. However, it should also be understood that determining B based on A does not mean that B is determined solely based on A; B can also be determined based on A and / or other information.

[0091] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0092] In the embodiments provided in this application, it should be understood that the disclosed systems and devices can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0093] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0094] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0095] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can read or a data storage device such as a server or data center that integrates one or more available media. The available media may be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., digital video discs (DVDs)), or semiconductor media (e.g., solid-state disks (SSDs)).

[0096] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A micro-current detection device, characterized by, include: A transimpedance amplification circuit, comprising a current amplification circuit and a feedback resistor, the feedback resistor having a resistance greater than 100G The transimpedance amplification circuit is configured to receive a micro-current signal and generate a first voltage signal based on the micro-current signal. An analog-to-digital converter circuit is connected to the voltage signal output terminal of the transimpedance amplifier circuit, and is used to receive the first voltage signal and convert the first voltage signal into a first digital signal. The main control circuit is connected to the digital signal output terminal of the analog-to-digital converter circuit, and is used to receive the first digital signal and filter the first digital signal to obtain the second digital signal. A low-ripple power supply circuit is connected to the transimpedance amplifier circuit, the analog-to-digital converter circuit, and the main controller to provide a low-ripple power supply voltage. The host computer is connected to the serial port output of the main control circuit and is used to receive the second digital signal and determine the current magnitude of the micro-current signal based on the second digital signal.

2. The micro-current detection device of claim 1, wherein, The low-ripple power supply circuit includes a switching power supply circuit and a linear power supply circuit connected in series. The switching power supply circuit is used to convert the input voltage into an intermediate voltage, and the linear power supply circuit is used to convert the intermediate voltage into the low-ripple power supply voltage.

3. The micro-current detection device according to claim 1 or 2, characterized in that, The transimpedance amplification circuit, the analog-to-digital conversion circuit, the main control circuit and the low-ripple power supply circuit are arranged on a printed circuit board, the printed circuit board is made of FR-4 epoxy glass cloth laminated plate material, the square resistance of the FR-4 epoxy glass cloth laminated plate material is greater than .

4. The micro-current detection device of claim 3, wherein, A protective ring is provided on the printed circuit board. The protective ring is located at the micro-current input terminal of the transimpedance amplifier circuit and is used to guide the leakage current between the micro-current input terminal and the voltage output terminal of the low-ripple power supply circuit into the low-impedance loop.

5. The microcurrent detection device according to claim 4, characterized in that, The protection ring is a multi-turn protection ring, which is disposed between the transimpedance amplifier circuit, the analog-to-digital converter circuit, the main control circuit, and the low-ripple power supply circuit.

6. The micro-current detection device of claim 3, wherein, The printed circuit board also includes a cutout area, which is located between the power input terminal of the transimpedance amplifier circuit and the microcurrent input terminal of the transimpedance amplifier circuit.

7. The micro-current detection device of claim 3, wherein, Also includes: A shielding housing covers the outside of the printed circuit board; The shielding shell includes a first shielding shell and a second shielding shell stacked together. The first shielding shell is made of a high magnetic material to absorb low-frequency magnetic noise, and the second shielding shell is made of a diamagnetic material to reflect high-frequency magnetic noise.

8. The micro-current detection device of claim 3, wherein, The printed circuit board has multiple turns of open-window ground wire, and the grounding terminals of the transimpedance amplifier circuit, the analog-to-digital converter circuit, the main control circuit, and the low-ripple power supply circuit are all connected to the multiple turns of open-window ground wire.

9. The micro-current detection device of claim 1 or 2, wherein, The analog-to-digital converter circuit is configured to operate in bipolar conversion mode to process positive and negative bidirectional voltage signals. The voltage range that the analog-to-digital converter circuit can acquire is greater than the voltage range of the first voltage signal.

10. A gas chromatograph characterized by, Includes the microcurrent detection device as described in any one of claims 1-9.

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