An ion detection amplifier and ion detection method

Abstract

The application provides an ion detection amplifier and an ion detection method, and belongs to the field of mass spectrometers. The ion detection amplifier provided by the application comprises: a primary amplification circuit configured to receive a current signal output by an ion detector; a load module connected in parallel with the primary amplification circuit, wherein the load module comprises a plurality of feedback branches; a secondary amplification circuit connected with an output end of the primary amplification circuit and configured to amplify an output signal of the primary amplification circuit, wherein the secondary amplification circuit is provided with a plurality of secondary gain gears; a gain switching control circuit connected with the load module and the secondary amplification circuit respectively; and a signal processing circuit configured to receive an output signal of the secondary amplification circuit. The ion detection amplifier and the ion detection method provided by the application can accurately and efficiently complete the collection, amplification, switching and digital output of ion signals in a complex scene.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mass spectrometers, and particularly relates to an ion detection amplifier and an ion detection method. BACKGROUND

[0002] In the field of mass spectrometers and ion detection, the ion detection amplifier is a core device for realizing accurate analysis of ion signals. The original signal output by the ion detector after interacting with the ions to be detected is usually a very weak micro-current signal (usually in the range of femtoampere to picoampere), and the signal strength fluctuates greatly due to the influence of ion concentration, energy and detection scene, from weak continuous signals to strong pulse signals. Therefore, the ion detection amplifier needs to have high sensitivity, wide dynamic range and accurate signal processing capability to complete the collection, amplification and quantitative analysis of ion signals, and to provide reliable support for the subsequent output of detection results.

[0003] The current mainstream ion detection amplifier technology scheme is based on an operational amplifier circuit, which includes a signal amplification module, a gain adjustment module and a signal processing module. The signal amplification module converts the micro-current signal into a voltage signal and preliminarily amplifies it through a single-stage or two-stage operational amplifier; the gain adjustment module mainly relies on fixed feedback resistors or a limited number of feedback branch switches, and some schemes use relays to control the on-off of the branch to adapt to different signal strengths; the signal processing module digitizes the analog signal through voltage-to-frequency conversion or analog-to-digital conversion, and outputs the result through counting or calculation. These schemes can realize basic ion signal detection in conventional scenes, but still have obvious limitations in complex scenarios.

[0004] There are four key problems in the prior art: first, the micro-current detection precision is insufficient, the input bias current of the conventional operational amplifier is large, and the feedback network is easy to introduce noise and interference, which causes distortion or drowning of the weak signal; second, the dynamic range is limited, fixed or limited gain steps cannot cover a wide range of signals, and the secondary amplification circuit has insufficient voltage resistance, which further compresses the dynamic range, and strong signal saturation or weak signal amplification deficiency may occur; third, the gain switching and range adaptation are not flexible, the ordinary relay has poor isolation, which causes cross talk, the residual charge of the capacitor branch affects the switching stability, and there is a lack of real-time linkage with the signal strength; fourth, the signal processing link is incomplete, the voltage-to-frequency conversion has low precision for low-level signals, and the counting result is not converted with the gain parameter, which causes deviation of the final result, and it is difficult to meet the high-precision detection requirements in complex scenarios. SUMMARY

[0005] Therefore, the present application provides an ion detection amplifier and an ion detection method to solve the problems of insufficient micro-current detection precision, limited dynamic range, inflexible gain switching and range adaptation, and incomplete signal processing link of the existing ion detection amplifier.

[0006] Specifically, the application is realized by the following technical solutions:

[0007] The first aspect of the application provides an ion detection amplifier, which comprises:

[0008] A primary amplification circuit for receiving a current signal output by an ion detector, the primary amplification circuit comprising a primary operational amplifier and a secondary operational amplifier connected in cascade;

[0009] A load module connected in parallel with the primary amplification circuit, the load module comprising a plurality of feedback branches, the feedback elements in each feedback branch being different in type, and different feedback branches corresponding to different primary gain positions;

[0010] A secondary amplification circuit connected to the output end of the primary amplification circuit, for amplifying the output signal of the primary amplification circuit, the secondary amplification circuit being provided with a plurality of secondary gain positions;

[0011] A gain switching control circuit connected to the load module and the secondary amplification circuit respectively, for controlling the amplification gain of the primary amplification circuit and the secondary amplification circuit;

[0012] A signal processing circuit for receiving the output signal of the secondary amplification circuit, realizing data processing of the output signal and outputting the detection result.

[0013] The second aspect of the application provides an ion detection method, which comprises:

[0014] Receiving a current signal output by an ion detector and inputting the current signal to the primary amplification circuit;

[0015] After being sequentially amplified by the primary amplification circuit and the secondary amplification circuit, the signal is processed by the signal processing circuit to obtain an ion detection result.

[0016] The ion detection amplifier and the ion detection method provided by the application significantly improve the adaptability, amplification flexibility and processing integrity of the ion detection amplifier to a wide range of ion signals through a modular structure design and a multi-stage gain adjustment mechanism, and provide reliable hardware support for ion signal detection in complex scenarios. Specifically, through the structure of the first-stage amplification circuit including the cascaded primary operational amplifier and secondary operational amplifier, the hierarchical amplification of the weak current signal output by the ion detector is realized. The load module is connected in parallel with the first-stage amplification circuit and includes multiple feedback branches, and different feedback branches correspond to the design of different first-stage gain positions, which gives the first-stage amplification circuit flexible gain adjustment capability. By switching different feedback branches, different intensity ion signals can be adapted, solving the problem that a single gain cannot cover a wide range of signals and improving the adaptability of the amplifier to diversified ion signals. The multi-position design of the two-stage amplification circuit significantly widens the dynamic range of the overall amplifier, which can not only meet the full amplification demand of weak signals, but also avoid distortion caused by excessive amplification of strong signals, ensuring that different intensity signals can be effectively processed. The gain switching control circuit is connected with the load module and the second-stage amplification circuit respectively, realizing the overall control of the gain of the first-stage and second-stage amplification circuits, ensuring the coordination and accuracy of the two-stage gain adjustment; and the signal processing circuit receives the output signal of the second-stage amplification circuit and realizes data processing and detection result output, which completes the complete link from signal amplification to result output, ensuring the effective output of the ion detection result. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The structural diagram of the ion detection amplifier provided by the application is shown in the figure.

[0018] Figure 2 The connection structure diagram of the primary operational amplifier shown in the application is shown in the figure.

[0019] Figure 3 The connection structure diagram of the secondary operational amplifier shown in the application is shown in the figure.

[0020] Figure 4 The structural diagram of the load module provided by the application is shown in the figure.

[0021] Figure 5 The structural diagram of the second-stage amplification circuit provided by the application is shown in the figure.

[0022] Figure 6 The structural diagram of the gain switching control circuit shown in the application is shown in the figure.

[0023] Figure 7 The structural diagram of the voltage-to-frequency conversion module provided by the application is shown in the figure.

[0024] Figure 8 The structural diagram of the pulse signal analysis module provided by the application is shown in the figure.

[0025] Figure 9 A structure diagram of a digital-to-analog conversion circuit provided in the present application is shown in FIG. 1.

[0026] Figure 10 A flow chart of an ion detection method provided in the present application is shown in FIG. 2. DETAILED DESCRIPTION

[0027] The exemplary embodiments will be described in detail herein with reference to the attached drawings. In the following description, unless otherwise indicated, like numbers in the attached drawings refer to the same or similar elements. The following detailed description includes specific details for the purpose of providing a thorough understanding of the exemplary embodiments. However, it will be apparent to those skilled in the art that the exemplary embodiments can be practiced without these specific details.

[0028] The terminology used in the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used in the description of the embodiments of the application and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It also will be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0029] It is to be understood that the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. It is to be understood that the term "comprising" as used herein is intended to mean "including but not limited to." It is further noted that the claims can be drafted to exclude any or all of the features that can be considered to be conventional or known in the art. Therefore, the terms "comprising", "including", "containing", "consisting" and "consisting essentially of" are not intended to be limiting.

[0030] The following detailed description is presented to understand and appreciate the teachings of the present application. The detailed description is presented primarily for the purpose of enabling others to make and use the application.

[0031] Embodiment One

[0032] Figure 1 A structure diagram of an ion detection amplifier provided in the present application is shown in FIG. 3. Please refer to Figure 1 The method provided in the present embodiment can include:

[0033] A primary amplification circuit for receiving a current signal output by an ion detector, the primary amplification circuit including a primary operational amplifier and a secondary operational amplifier connected in cascade;

[0034] A load module connected in parallel to the primary amplification circuit, the load module including a plurality of feedback branches, each feedback branch having a different type of feedback element, and different feedback branches corresponding to different primary gain levels;

[0035] A second-stage amplification circuit is connected to an output end of the first-stage amplification circuit, and is configured to amplify an output signal of the first-stage amplification circuit, and the second-stage amplification circuit is provided with a plurality of second-stage gain gears;

[0036] A gain switching control circuit is connected to the load module and the second-stage amplification circuit, and is configured to control amplification gains of the first-stage amplification circuit and the second-stage amplification circuit.

[0037] A signal processing circuit is configured to receive an output signal of the second-stage amplification circuit, and to implement data processing of the output signal and output of a detection result.

[0038] It should be noted that the first-stage amplification circuit is a front-end core unit of the ion detection amplifier, and is configured to convert and amplify an extremely weak current signal (usually in the range of femtoampere to picoampere) output by an ion detector into a voltage signal suitable for subsequent processing. The first-stage amplification circuit adopts a cascade structure (simply put, one after another, the output of the former is used as the input of the latter), and is composed of a primary operational amplifier and a secondary operational amplifier connected in sequence.

[0039] The primary operational amplifier is directly connected to a signal output end of the ion detector, and is mainly configured to convert an input micro-current signal into a voltage signal and perform preliminary amplification. The primary operational amplifier is selected to be an ultra-low input bias current type device, and is matched with a high-resistance feedback element, so as to effectively suppress the measurement error introduced by the input bias current, and reduce the input noise, thereby ensuring the detection sensitivity at an extremely low current level.

[0040] The input end of the secondary operational amplifier is connected to the output end of the primary operational amplifier, and is configured to further amplify the voltage amplitude while retaining the signal waveform, and to improve the output driving capability. The secondary operational amplifier adopts a high-voltage design, so that the supply voltage is higher than the rated value of a conventional operational amplifier, thereby widening the output dynamic range of the first-stage amplification circuit, and providing a higher signal-to-noise ratio input signal for the subsequent second-stage amplification circuit.

[0041] Through the cascade mode of the primary and secondary operational amplifiers, the first-stage amplification circuit can realize a large total gain while maintaining low noise characteristics. Specifically, the primary operational amplifier converts the micro-current signal output by the ion detector into a voltage signal through a non-inverting amplification topology, and adapts to the signal polarity requirement by using the reverse amplification characteristic; the secondary operational amplifier further improves the signal amplitude and enhances the output driving capability. The cooperation of the two stages makes the first-stage amplification circuit have both the conversion capability from the micro-current in the range of femtoampere to picoampere to the processable voltage signal, and a wide input dynamic range, so as to adapt to the application scenarios in which the signal amplitude changes greatly in the ion detection process.

[0042] Specifically, Figure 2For the connection structure diagram of the primary operational amplifier shown in the present application, please refer to Figure 2 The inverting input end (pin 2) of the primary operational amplifier is connected to the current signal output end of the ion detector; the non-inverting input end (pin 3) is connected to the first bias voltage VB1 through the first resistor R1 and the second resistor R2; the feedback capacitor C1 (100pF) is connected in parallel between the output end (pin 6) and the inverting input end (pin 3); the positive power supply end (pin 8) is connected to the positive power supply VCC, and the negative power supply end (pin 4) is connected to the negative power supply VEE.

[0043] It should be noted that the inverting input end (pin 2) is connected to the current signal output end of the ion detector, which outputs a current signal with extremely small amplitude when working. Through the connection of the inverting input end (pin 2) and the input end of the load module, the current signal enters the feedback element in the load module for signal amplification, and the obtained voltage signal is output through the output end of the secondary amplifier. The non-inverting input end (pin 2) is connected to the first bias voltage VB1 through the first resistor R1 to set the working reference potential of the operational amplifier, and is connected to the ground through the second resistor R2 to realize voltage division, thereby forming a stable input bias network to suppress zero drift and external interference. The output end (pin 6) and the inverting input end (pin 3) are connected in parallel with the feedback capacitor C1 (100pF), which constitutes a direct negative feedback path from input to output, used to suppress high-frequency noise, improve the stability of the amplifier, and reduce the influence of parasitic capacitance in weak current signal measurement. In the power supply part, the positive power supply end (pin 8) is connected to the positive power supply VCC, and the negative power supply end (pin 4) is connected to the negative power supply VEE, which provides bipolar power supply for the operational amplifier to support bidirectional signal swing and widen the dynamic range.

[0044] Through the above connection mode, the primary operational amplifier can stably convert the current signal output by the ion detector from the femtoampere to the picoampere level to a voltage signal under the premise of ensuring extremely low input bias current, while reducing input noise and bias error, laying a foundation for high signal-to-noise ratio for subsequent secondary amplification and signal processing.

[0045] In addition, Figure 2 The pins 1 and 5 in the above formula are zeroing pins for offset voltage compensation of the operational amplifier.

[0046] Figure 3 For the connection structure diagram of the secondary operational amplifier shown in the present application, please refer to Figure 3 The secondary operational amplifier is a high-voltage amplification unit realized by discrete devices, including:

[0047] The differential input stage is composed of two first NPN transistors (Q2, Q3), the bases of which are respectively connected to the output terminal of the primary operational amplifier and the reference potential terminal, the emitters of which are commonly connected to the same node, and then connected to the common collector terminal of a current mirror composed of two second PNP transistors (Q6, Q7), and the emitters of the current mirror are connected to the positive power supply terminal (VCC), for providing a constant tail current to the differential input stage;

[0048] The intermediate amplification stage includes a third NPN transistor (Q5) and a compensation capacitor (C2), the base of the third NPN transistor is connected to the output terminal of the differential input stage, the collector is connected to the positive power supply terminal, and the emitter is connected to the ground through a second resistor (R2), the input terminal of the compensation capacitor (C2) is connected to the output terminal of the differential input stage, and the output terminal is connected to the input terminal of the push-pull output stage, for introducing Miller compensation (local negative feedback), suppressing high-frequency oscillation, improving the phase margin of the amplifier, and ensuring stable operation within a wide frequency band;

[0049] The push-pull output stage includes two diodes (D1, D2), a fourth transistor (Q8), and two fifth transistors (Q1, Q4), the fourth transistor (Q8) is connected to the intermediate amplification stage, and the collector is connected to the diode (D2) to transmit the intermediate stage signal to the output terminal, realize large current output, and drive the subsequent circuit, the collectors and emitters of the two fifth transistors (Q1, Q4) are respectively connected to the positive power supply terminal (VCC) and the negative power supply terminal (VEE), the diodes (D1, D2) are connected in series and are connected across the base-emitter path of the fifth transistors (Q1, Q4) to provide a stable bias voltage for the two transistors, and at the same time, the diode forward voltage drop is used to realize high-voltage design;

[0050] The negative power supply terminal (VEE) of the secondary operational amplifier is connected to the negative power supply node of the entire circuit.

[0051] It should be noted that the secondary operational amplifier is a high-voltage amplification unit based on discrete devices (i.e. independent transistors, diodes, resistors, capacitors, and other discrete components), and its core function is to accept the signal output by the primary operational amplifier, and to realize stable amplification, noise suppression, and driving capacity enhancement of the signal through multi-stage circuit cooperation, to provide adaptive signal input for the subsequent secondary amplification circuit. Compared with integrated operational amplifiers, discrete device design can flexibly optimize the voltage withstand performance and amplification characteristics, and is more suitable for the signal processing requirements of wide dynamic range in ion detection.

[0052] Specifically, the differential input stage is the signal input end of the secondary operational amplifier, and is composed of two first NPN transistors (Q2, Q3) in a differential pair structure. The differential pair here refers to a circuit unit that compares and amplifies the input signal with the reference potential through two symmetric transistors, which can effectively suppress common-mode noise (such as environmental electromagnetic interference, power supply fluctuations, etc. affecting both transistors). The bases of the two transistors are respectively connected to the output end of the primary operational amplifier (receiving the pre-stage amplified signal) and the reference potential end (providing a reference level), forming a differential signal input path; the emitters are commonly connected to the same node and then connected to the current mirror composed of two second PNP transistors (Q6, Q7), where the current mirror is a circuit that can output a constant current, and its emitter is connected to the positive power supply end (VCC), providing stable tail current for the differential input stage. This connection ensures that the differential pair can work stably under different signal strengths, avoiding signal distortion caused by current fluctuations, and providing accurate original signals for subsequent amplification.

[0053] The intermediate amplification stage is a relay unit for signal amplification, composed of a third NPN transistor (Q5), a second resistor (R2), and a compensation capacitor (C2). The base of Q5 is connected to the output end of the differential input stage, receiving the preliminary amplified signal; the collector is connected to the positive power supply end to obtain energy, and the emitter is connected to the ground through the second resistor to form a current path. To avoid circuit oscillation under high-frequency signals (signal instability caused by phase shift during amplification), the output end of the push-pull output stage is connected to the output end of the differential input stage through the compensation capacitor (C2), forming a Miller compensation. This connection uses the phase compensation effect of the capacitor to suppress the phase lag of high-frequency signals, improves the frequency response characteristics of the circuit, and ensures the stability of signal amplification in a wide frequency range. Through the current amplification characteristics of the transistor, the intermediate amplification stage can further enhance the signal amplitude output by the differential input stage, providing sufficient signal driving capability for the subsequent output stage.

[0054] The push-pull output stage is the signal output end of the secondary operational amplifier, composed of two diodes (D1, D2), a fourth transistor (Q8), and two fifth transistors (Q1, Q4). It realizes large current output through the push-pull working mode of the fifth transistors (Q1, Q4), adapts to the load requirements of the subsequent stage, and the diode bias network ensures stable operation of the output stage under high voltage; its core function is to enhance the driving capability of the circuit to effectively drive the secondary amplification circuit of the subsequent stage.

[0055] In the power supply design, the positive power supply end (VCC) of the secondary operational amplifier provides energy for the current mirror, intermediate amplification stage, etc., and the negative power supply end (VEE) is connected to the negative power supply node of the entire circuit, forming a wide voltage supply range. This design, combined with the high voltage resistance characteristics of discrete devices, significantly widens the output dynamic range of the secondary operational amplifier, making it adaptable to a variety of ion signal amplification needs from weak to strong.

[0056] In summary, the secondary operational amplifier realizes the signal amplification function of low noise, high linearity, high voltage resistance and wide frequency stability through the accurate reception of the differential input stage, the stable working point of the load circuit, the signal enhancement of the intermediate amplification stage, the driving and compensation of the push-pull output stage and the wide voltage power supply design.

[0057] It should be noted that the load module is used to realize flexible adjustment of the first-stage gain, and the connection mode and internal structure design of the load module and the first-stage amplification circuit directly determine the adaptability of the first-stage amplification circuit to different intensity ion signals. Among them, the parallel connection of the load module and the first-stage amplification circuit means that the input end and the output end of the load module are connected to the output end and the input end of the first-stage amplification circuit respectively, forming a closed feedback loop. In the operational amplifier circuit, parallel feedback is a classic topology structure for realizing signal amplification. After the first-stage amplification circuit converts the current signal output by the ion detector into a voltage signal, part of the signal will flow back to the input end of the first-stage amplification circuit through the feedback branch of the load module. The intensity and characteristics of the feedback signal directly affect the overall gain (amplification factor) of the first-stage amplification circuit. This parallel connection mode ensures that the feedback signal can participate in the signal amplification process in real time.

[0058] It should also be noted that the load module includes a plurality of feedback branches, and the different types of feedback elements in each feedback branch clearly define the internal structure characteristics of the load module. The feedback branch refers to a sub-circuit in the load module that can be independently switched, and the core difference between each branch is that the type of feedback element used is different. In addition, each feedback branch usually also includes a high-isolation relay and other switching elements for realizing the rapid switching on and off of the branch, ensuring that there is no signal crosstalk when switching between different branches.

[0059] The load module realizes flexible adjustment of the gain of the first-stage amplification circuit through a plurality of feedback branches of different types, and the internal structure design directly determines the adaptability to different ion signals. Specifically, the load module includes a plurality of resistance feedback branches and a plurality of capacitance feedback branches, and the two types of branches are arranged in parallel, each branch is connected in series with a high-isolation relay to realize independent switching, and signal crosstalk is ensured when the branch is turned on and off.

[0060] Among them, a plurality of resistance feedback branches are provided, and the core element of each branch is a high-precision resistor with different resistance values, and the resistance values present significant order differences. According to the gain formula of the operational amplifier circuit, the feedback resistance value is proportional to the amplification gain, so different orders of resistance correspond to proportional incremental first-stage gain positions, which can adapt to medium-strength, weak and extremely weak direct current or low-frequency ion signals.

[0061] The capacitor feedback branch is provided with multiple branches, and the core element of each branch is a pF-level vacuum capacitor with different values. The capacitor feedback characteristic has frequency selectivity, and the feedback effect on high-frequency signals is significant, and the feedback effect on low-frequency signals is weak, so the branches with different capacitor values can adapt to high-frequency pulse signals of different frequency ranges (low capacitor value adapts to higher frequency signals, and high capacitor value adapts to slightly lower frequency pulse signals), which can effectively filter out low-frequency noise and avoid distortion caused by excessive amplification of high-frequency signals; at the same time, the capacitor feedback avoids the inherent thermal noise problem of high-resistance resistors, and for occasions where the current intensity is equal to or less than the thermal noise current of the resistor, the capacitor feedback can more accurately realize signal amplification

[0062] It should be noted that the core difference between resistance feedback and capacitor feedback is the type of signal adaptation. Resistance feedback is suitable for continuous and stable direct current or low-frequency signals, and the gain adjustment depends on the resistance value, and the high-frequency noise suppression capability is weak. Capacitor feedback is suitable for rapidly changing high-frequency pulse signals, and relies on frequency selectivity to achieve precise amplification, or in situations where the current intensity is lower than the thermal noise current of a high-resistance resistor, the low-loss characteristic of the vacuum capacitor ensures the accuracy of high-frequency signal transmission and the low noise and high stability characteristics of extremely weak current measurement. In addition, each capacitor branch is parallelly connected with a protection resistor branch, which can limit the charging and discharging current during switching to avoid component damage and provide a discharge path for residual charge to ensure switching stability. Through the above design, the load module realizes dual adaptation of wide gain range and multiple signal types, providing a reliable gain adjustment basis for the first-stage amplification circuit.

[0063] Specifically, Figure 4 The structure diagram of the load module provided in the present application is shown in Figure 4 The load module comprises: a plurality of resistance feedback branches, each of the resistance feedback branches comprising a resistor with different resistance and a high-isolation relay; a plurality of capacitor feedback branches parallelly connected with the resistance feedback branches, each of the capacitor feedback branches comprising a pF-level vacuum capacitor with a high-isolation relay connected in series at both ends of the capacitor; and a protection resistor branch parallelly connected with the resistance feedback and capacitor feedback branches, comprising a low-resistance (10k) protection resistor.

[0064] It should be noted that the resistance feedback branch is the basic unit for adjusting the gain of the first-stage amplification circuit in the load module, and the core components of each branch include resistors with different resistance and high-isolation relays. Among them, the resistance element is the key parameter that determines the feedback strength, and the resistance values of the resistance feedback branches in this module are significantly different. According to the gain formula of the operational amplifier circuit, the resistance value of the feedback resistor is proportional to the amplification gain (when the input resistance is fixed, the larger the resistance, the higher the gain). Therefore, resistors with different resistance values correspond to different first-stage gain positions, which can adapt to weak (high gain required) and medium-intensity (medium gain required) ion current signals.

[0065] The high-isolation relay connected in series in each resistance branch is the core element for branch switching. Its high-isolation characteristic ensures that when a certain branch is disconnected, the resistance of the branch will not interfere with the signals of other branches or the primary amplification circuit (avoiding the influence of leakage current, parasitic capacitance, etc.), while ensuring the accuracy of signal transmission when the branch is connected. Through the on-off control of the relay by the gain switching control circuit, the target resistance branch can be quickly selected to achieve precise adjustment of the primary gain.

[0066] It should also be noted that the capacitor feedback branch and the resistance feedback branch are connected in parallel to form a complementary gain adjustment mechanism, which consists of pF-level vacuum capacitors and high-isolation relays. Among them, the feedback characteristic of the pF-level vacuum capacitor is related to the signal frequency (the feedback effect on high-frequency signals is stronger), and the use of pF-level (pico-farad) vacuum capacitors can adapt to the rapidly changing pulse signals in ion detection (such as ion flow bursts in a short period of time). Compared with resistance feedback, capacitor feedback can effectively suppress low-frequency noise, while avoiding distortion of high-frequency signals due to excessive amplification, and is particularly suitable for capturing transient ion signals; in addition, capacitors do not have thermal noise characteristics, so they have lower detection limits and higher stability and signal-to-noise ratio, and can detect signal regions that resistance feedback cannot achieve high-precision measurement (such as below 10 4 cps). The high-isolation relay here is similar to the resistance branch, and the high-isolation relay connected in series across the capacitor is used to achieve independent switching of the capacitor branch, ensuring isolation from other branches and avoiding the influence of parasitic parameters of the capacitor on circuit stability.

[0067] In addition, the protection resistance branch (usually a low-resistance resistor such as 10kΩ) is a key auxiliary design. When the capacitor or resistance branch is switched in, the protection resistor can limit the instantaneous charging and discharging current to avoid damaging the feedback elements or core elements of the primary amplification circuit; when the capacitor branch is disconnected, the protection resistor can also provide a discharge path for residual charge to ensure the accuracy of the signal next time.

[0068] Through the parallel design of the resistance feedback branch and the capacitor feedback branch, the load module has the dual advantages of wide gain range and multiple signal type adaptation. For stable direct current or low-frequency ion signals, the appropriate gain is selected by switching the resistance feedback branch to achieve precise amplification of the signal; for rapidly changing high-frequency pulse signals, switch to the capacitor feedback branch to utilize its frequency characteristics to achieve noise suppression and transient signal capture; the design of high-isolation relays and protection resistors ensures the reliability of branch switching and the safety of the circuit. This structure enables the primary amplification circuit to flexibly adjust the gain mode according to the intensity and frequency characteristics of the ion signal, providing high-quality input signals for subsequent secondary amplification and signal processing.

[0069] In addition, it needs to be explained that in order to realize the accurate adaptation of the first-stage amplification circuit to ion signals of different intensities and types, firstly, according to the ion current signals output by each detection point at the front end of the mass spectrometer, the intensity range of the input signal of the amplifier is preliminarily determined, if the signal intensity is in the nanoampere (nA) level or the picoampere (pA) level, the resistance feedback branch in the load module is preferentially selected; if the signal intensity is in the femtoampere (fA) level and below, the capacitance feedback branch is preferentially selected, and the basis for this selection is that the extremely weak signal in the fA level and below is easy to be covered by the inherent thermal noise current of the resistance element, and the capacitance feedback has no thermal noise characteristic, so that the noise can be avoided to interfere with the signal.

[0070] Meanwhile, the type of the branch is further verified in combination with the dynamic characteristics of the signal, if the ion signal is a low-frequency, continuously stable and approximately direct-current signal (such as a conventional ion concentration detection scene), the selection of the resistance feedback branch is maintained; if the detection object is a narrow peak signal such as an isotope spectrum peak (the intensity change rate is fast and the high-frequency characteristic is significant), the capacitance feedback branch is switched to adapt to the transient capture requirement of the high-frequency pulse signal.

[0071] It also needs to be explained that the feedback branch type switching and gain level adjustment of the first-stage amplification circuit are as follows: the host computer control software generates a selection instruction of the feedback branch type (resistance / capacitance) and the corresponding gain level of the first-stage amplification circuit according to the aforementioned signal determination result; the selection instruction is transmitted to the microprocessor (MCU) in the gain switching control circuit in the form of a digital control signal; after receiving the instruction, the MCU configures the level of the pins corresponding to the 5-way control signal, and outputs a driving level matched with the target feedback branch; the above driving level is input into the input end of the dual-channel voltage comparator, and compared with the preset reference level (1.2V); the dual-channel voltage comparator outputs a front-end control signal and a rear-end control signal according to the comparison result, and transmits them to the high-isolation relay of the corresponding feedback branch in the load module; the high-isolation relay performs the opening or closing action according to the level state of the control signal: if the control signal is a valid level, the relay is closed, the corresponding feedback loop is turned on, and the first-stage amplification circuit is switched to the gain level corresponding to the branch; if the control signal is an invalid level, the relay is opened, and the corresponding feedback loop is closed.

[0072] It should be noted that the connection position of the secondary amplification circuit and the gain adjustment capability directly affect the amplification effect and dynamic range coverage of the overall amplifier on the weak ion signal. Specifically, the connection of the secondary amplification circuit with the output end of the primary amplification circuit determines its position in the signal link. After the primary amplification circuit converts the weak current signal output by the ion detector into a voltage signal and completes the preliminary amplification, the output signal will be directly transmitted to the input end of the secondary amplification circuit. This series connection forms a relay type signal processing link from primary amplification to secondary amplification, ensuring that the weak signal reaches the intensity range that can be recognized by the subsequent signal processing circuit after being amplified by two stages. In specific implementation, the original signal output by the ion detector is usually at the level of micro-current (such as pA to nA), and after being converted into a voltage signal by the primary amplification circuit, its amplitude may still not meet the input requirements of the signal processing circuit (for example, the voltage value of part of the weak signal after primary amplification is still lower than 1 mV). The secondary amplification circuit further amplifies the primary output signal (for example, by 10 times, 100 times, etc.) through the amplification of the internal operational amplifier, so that the signal amplitude is raised to a range suitable for subsequent processing (such as 10 mV to 1 V). In addition, the amplification process of the secondary amplification circuit can also optimize the signal characteristics, such as reducing signal noise and adjusting signal polarity through circuit design (to adapt to the detection needs of different ion polarities), to ensure that the signal output to the signal processing circuit has a high signal-to-noise ratio and stability.

[0073] In addition, the secondary amplification circuit is provided with multiple secondary gain positions, and the ion signal intensity in different scenarios differs greatly (for example, the signal is weak in a low-concentration ion environment, and the signal is strong in a high-concentration environment). If the secondary amplification circuit uses a fixed gain, it may result in insufficient amplification of weak signals (which cannot be effectively detected) or excessive amplification of strong signals (signal saturation distortion). To solve this problem, the secondary amplification circuit is pre-set with multiple gain positions (such as 1 times, 10 times, 100 times, 1000 times, etc.) through internal hardware design. Each position corresponds to a different amplification factor, which can be flexibly selected by the gain switching control circuit according to the signal intensity. For example, when the output signal of the primary amplification circuit is weak, a high gain position (such as 100 times) is selected to ensure that the signal is sufficiently amplified; when the output signal of the primary amplification circuit is strong, a low gain position (such as 1 times) is selected to avoid signal distortion.

[0074] Figure 5 For the secondary amplification circuit structure provided in this application, please refer to Figure 5 , which includes two cascaded operational amplifiers, wherein the input end of the first amplifier is connected to the output end of the primary amplification circuit through a multi-way analog switch, for switching the signal input direction according to the polarity of the ion signal; a T-shaped adjustable resistance network is provided in the feedback loop of the second amplifier, and different resistance combinations are selected by the control signal output by the gain switching control circuit.

[0075] It should be noted that, in order to realize the precise adaptation of the two-stage amplification circuit gain and the feedback element, and to ensure that the output signal meets the subsequent voltage-frequency conversion and signal processing requirements, it is necessary to select and calculate based on the intensity and dynamic characteristics of the input ion signal through the processes of signal judgment, element selection, gear testing and parameter optimization. Specifically, first, the input signal intensity range is preliminarily judged. The signal acquisition unit of the mass spectrometer front-end detection point acquires the current signal output by the ion detector in real time, and the signal amplitude is recorded by the host computer data processing module and divided into intensity ranges. If the signal amplitude is in the nanoampere (nA, 10 -9 A) to picoampere (pA, 10 -12 A) level, it is determined to be a medium-strong signal range; if the signal amplitude is in the femtoampere (fA, 10 -15 A) level and below, it is determined to be an extremely weak signal range. This judgment result can provide a basis for subsequent feedback element type selection, avoiding noise interference or signal distortion caused by mismatch between element type and signal intensity.

[0076] Secondly, the feedback element type selection of the first-stage amplification circuit is completed. The element type is determined in combination with the signal intensity range and dynamic characteristics. If the input signal is in the medium-strong signal range, or the signal presents low-frequency, continuous and stable direct current characteristics (such as isotopic conventional concentration detection scenarios), the resistance feedback branch in the load module is preferentially selected. This selection is because the intensity signal is not easily covered by the inherent thermal noise of the resistance, and the linear amplification characteristics of the resistance feedback can guarantee the amplification accuracy of the stable signal; if the input signal is in the extremely weak signal range, or the signal is an isotopic narrow peak signal (narrow peak width, high intensity change rate, and significant high-frequency characteristics), the capacitance feedback branch is preferentially selected. The thermal noise-free characteristic of the capacitance can avoid the fA-level signal being submerged by noise, and the integral amplification characteristic can accurately capture the transient changes of high-frequency pulse signals, adapting to the detection requirements of narrow peak signals.

[0077] Subsequently, the gain gear selection and test verification of the first-stage amplification circuit are performed. The gain of the first-stage amplification circuit is determined by the feedback element parameters (the gain is proportional to the resistance value when the resistance feedback is used, and the gain is inversely proportional to the capacitance value when the capacitance feedback is used), and needs to be tested step by step from the low gain gear. Taking the medium-strong signal range (pA-nA level) as an example, the low resistance value resistance gear (such as 10 10 Ω) in the resistance feedback branch is selected first, and the second amplifier of the second-stage amplification circuit is adjusted to the lowest gain gear at the same time; the second-stage ion spectrum peak scanning is started, and the scanning results are monitored through the signal processing circuit, focusing on verifying the baseline stability (the baseline amplitude is required to be ≤1‰ of the signal intensity), the spectrum peak intensity (initially ≥5 mV) and the signal-to-noise ratio (≥10:1); if the spectrum peak intensity is insufficient or the signal-to-noise ratio is not up to standard, the medium resistance value resistance gear (such as 10 11Ω), repeat the peak scanning and parameter monitoring until the baseline, peak intensity and signal-to-noise ratio meet the requirements, and lock the current primary feedback element parameters and the corresponding gain position.

[0078] Finally, the gain position selection and optimization of the secondary amplification circuit are carried out. After the gain position of the primary amplification circuit is locked, the T-shaped adjustable resistance network of the second amplifier of the secondary amplification circuit is adjusted to switch the gain position to optimize the signal output. The primary feedback element and the gain are kept unchanged, and the secondary gain position is switched in turn. Peak scanning is carried out after each position switching. Key parameters such as the peak amplitude, the baseline fluctuation value and the signal-to-noise ratio are calculated. The peak amplitude is required to be in the range of 10 mV to 1 V (adapted to the input range of the voltage-frequency conversion circuit), the baseline fluctuation value is required to be less than or equal to 5 mV, and the signal-to-noise ratio is required to be greater than or equal to 20:1. The position with the peak amplitude in the target range, the minimum baseline fluctuation and the highest signal-to-noise ratio is selected as the optimal gain position of the secondary.

[0079] Through the above steps, the precise matching of the type of the feedback element of the primary amplification circuit, the gain position and the gain position of the secondary amplification circuit can be realized, the total gain of the two-stage amplification circuit is adapted to the characteristics of the input ion signal, and high signal-to-noise ratio and high stability voltage signals are provided for subsequent voltage-frequency conversion and ion counting rate conversion.

[0080] Among them, the first amplifier focuses on signal polarity adaptation, and the second amplifier focuses on gain position adjustment. Both of them work together to meet the amplification needs of different ion signals.

[0081] Specifically, the first amplifier is the signal input end of the secondary amplification circuit. Its core feature is that the input end is connected to the output end of the primary amplification circuit through a multi-channel analog switch. The multi-channel analog switch is an electronic switch that can be controlled by an electrical signal. It can selectively connect the input signal to different input terminals (non-inverting input terminal or inverting input terminal) of the operational amplifier to realize the switching of the signal input path. In the ion detection scene, the polarity of the ion signal may differ (positive voltage signal or negative voltage signal) due to the detection object (such as positive ions or negative ions) or the detector working mode. If the signal polarity does not match the input direction of the amplifier, the signal may be amplified in the opposite direction or distorted. The first amplifier is designed with a multi-channel analog switch connection, which can switch the input direction according to the actual polarity of the ion signal: when a positive signal is detected, the switch connects the signal to the non-inverting input terminal of the amplifier to realize positive amplification; when a negative signal is detected, the switch is switched to the inverting input terminal to ensure that the signal polarity matches the amplification circuit. The core effect of this connection method is to eliminate signal distortion caused by polarity differences, ensuring that ion signals of different polarities can be correctly amplified, and improving the adaptability of the circuit to complex ion environments.

[0082] The second amplifier is the gain adjustment core of the two-stage amplification circuit, and a T-shaped adjustable resistance network is arranged in the feedback loop, and precise adjustment is realized through a gain switching control circuit. The T-shaped adjustable resistance network is a feedback circuit formed by connecting three resistors in a T-shaped structure (for example, usually including one series resistor and two parallel ground resistors), and by changing the resistance combination connected to the feedback loop, the feedback amount of the operational amplifier can be flexibly adjusted, and then the amplification factor (gain) is changed. Specifically, the gain switching control circuit will output a control signal (such as a high or low level signal) to the switching switch (usually a relay or an analog switch) of the T-shaped network according to the output signal strength of the first-stage amplification circuit or the upper computer instruction, and select different resistance combinations to connect to the feedback loop. For example, when a large resistance combination is selected, the feedback amount is small, and the amplifier gain is high (suitable for weak signals); when a small resistance combination is selected, the feedback amount is large, and the amplifier gain is low (suitable for strong signals).

[0083] In combination with the above description, the first amplifier ensures correct signal polarity input through the multi-channel analog switch, ensuring that the input voltage of the voltage-frequency conversion circuit is always a positive signal; the second amplifier realizes flexible gain adjustment through the T-shaped adjustable resistance network, and amplifies the signal to an intensity suitable for the subsequent signal processing circuit. The combination of the two makes the two-stage amplification circuit have both polarity adaptation capability and wide-range gain adjustment function, providing support for the high adaptability and high precision characteristics of the entire ion detection amplifier.

[0084] Specifically, the first-stage amplification circuit is the core module of the amplifier that undertakes the main signal amplification task, and is responsible for converting the input ultra-low ion current into a recognizable voltage signal through high-value resistors or high-precision capacitors for subsequent signal processing; the first operational amplifier of the second-stage amplification circuit is responsible for polarity conversion, because the voltage-frequency conversion circuit requires the input voltage to be a positive voltage, and the first-stage amplification circuit is a negative amplifier, when the input is a positive current, the output is a negative voltage, at this time the voltage-frequency converter has no output, therefore, to ensure that the VF conversion input is always a positive voltage, polarity conversion is needed, and the basis for conversion is the polarity of the primary ion. When the primary ion is a positive ion and the secondary ion current is a negative ion, the output voltage of the first-stage amplification circuit is a positive voltage, and the first operational amplifier in the second-stage amplification circuit is a voltage follower. When the primary ion is a negative ion and the secondary ion is a positive ion, the output of the first-stage amplification circuit is a negative voltage, and the first operational amplifier in the second-stage amplification circuit is a reverse amplifier with a gain of 1, which converts the negative voltage to a positive voltage. The second operational amplifier of the second-stage amplification circuit is to further ensure the intensity of the VF conversion input signal. For some very small currents, such as fA level, the output of the first-stage amplification circuit can only reach mV level, at this time the voltage-frequency conversion will have the problem of insufficient stability and excessive noise due to the too small input signal, therefore, secondary amplification is needed to ensure the precision and accuracy of the VF conversion. 12 The amplifier, the output of the first-stage amplification circuit can only reach mV level, at this time the voltage-frequency conversion will have the problem of insufficient stability and excessive noise due to the too small input signal, therefore, secondary amplification is needed to ensure the precision and accuracy of the VF conversion.

[0085] It should be noted that the gain switching control circuit is connected with the load module and the secondary amplification circuit through the control signal line. Among them, the high-isolation relay connected to each feedback branch in the load module through the control signal line realizes the on-off control of the resistance feedback branch and the capacitance feedback branch; the T-shaped adjustable resistance network switching switch connected to the second amplifier in the secondary amplification circuit through the control signal line realizes the selection of the secondary gain position. This connection mode enables the gain switching control circuit to simultaneously control the gain adjustment nodes of the primary and secondary amplification circuits.

[0086] Specifically, the gain of the primary amplification circuit is determined by the selection of the feedback branch in the load module, and the gain switching control circuit drives the high-isolation relay of the target feedback branch in the load module to act by outputting a control signal (such as high-level conduction and low-level disconnection), thereby realizing the switching of different branches; the gain of the secondary amplification circuit is determined by the resistance combination of the T-shaped adjustable resistance network in the feedback loop of the second amplifier, and the gain switching control circuit selects a specific resistance combination in the network to access the feedback loop by outputting a control signal, thereby realizing the switching of the secondary gain position.

[0087] Among them, the gain switching control circuit does not independently control the two-stage amplification circuit, but realizes the coordinated adjustment of the primary and secondary gains according to the overall characteristics (such as intensity, frequency, and polarity) of the ion signal. When a weak ion signal is detected, the load module is controlled to access the high-gain resistance branch (primary high gain), and at the same time, the secondary amplification circuit is controlled to select the high-gain position (secondary high gain), thereby ensuring that the signal is fully amplified; when a strong signal is detected, the low-gain resistance branch (primary low gain) and the secondary low-gain position are switched to, thereby avoiding signal overload.

[0088] Figure 6 For the structure diagram of the gain switching control circuit shown in the present application, please refer to Figure 6 The gain switching control circuit mainly includes a microprocessor and a plurality of voltage comparators, wherein the dual-channel control signal 1 is responsible for controlling the multi-way switch 1 of the secondary amplification circuit to realize signal polarity switching; the dual-channel control signal 2 is sent to the multi-way switch 2 of the secondary amplification circuit to realize the adjustment of four kinds of gains; after the five-way control signal is output from the microprocessor, each way enters the input end of a dual-channel voltage comparator, the supply voltage of each dual-channel voltage comparator is +5V and 0V respectively, the reference voltage is set to 1.2V, and each output pin of the voltage comparator is connected with a TVS tube to limit the maximum output voltage to +5V, thereby preventing high voltage pulses from damaging the front-end and rear-end relays of the load module; the outputs of the five dual-channel voltage comparators are five front-end control signals and five rear-end control signals, which are used to control the selection of the feedback elements of the load module of the primary amplification circuit, so as to switch the amplification multiple of the primary amplification circuit.

[0089] To clarify the two-stage amplification circuit for input ion current signal amplification law, the input current signal to the two-stage amplification circuit output voltage calculation method is described, wherein the input ion current signal strength is denoted as I (unit: A, including nA, pA, fA level), when the first stage amplification circuit adopts resistance element as feedback, assuming that the resistance value is R at this time, the output of the first stage amplification circuit is V=-I*R, and when the capacitor element is used as feedback, assuming that the capacitance value is C at this time, the output is V=∫I / Cdt. The first amplifier of the second amplification circuit selects the polarity, assuming that it is a positive signal, it remains unchanged, and assuming that it is a negative signal-V, it is converted into a positive signal V. The second amplifier of the second amplification circuit has four gain positions of 1, 10, 100 and 1000, assuming that they are G1, G2, G3 and G4 respectively, then the output of the second amplification circuit V2=I*R*G (second-stage gain) or V2=G / C*∫Idt. Please continue to refer to Figure 6 The host computer control signal is input to the MCU, and the MCU program controls the reading of the control signal and outputs the level at the corresponding pin to control the signal 1. For example, when the host computer control feedback loop 1 is selected, the corresponding control signal pin outputs a high level (5V), which is compared with the reference level 1.2V through the voltage comparator U1AU1B. If the voltage is higher than 1.2V, the positive terminal of U1AB outputs the supply voltage VCC (5V). At this time, the front-end and rear-end control signals are high, which are input to the relay to drive it to close. For example, the double control signal 2 is output to the MCU, and the corresponding pin outputs the control level. According to the high and low levels, the double control signal 2 can realize four combinations (HH, HL, LH, LL), which correspond to four positions of 1, 10, 100 and 1000 respectively.

[0090] It should be noted that after the ion signal is amplified to a voltage signal suitable for processing by the two-stage amplification circuit, the signal is directly transmitted to the input end of the signal processing circuit. At this time, the input signal is an analog voltage signal, the amplitude of which is proportional to the current signal strength output by the ion detector, but it has not been converted into a digital quantity or a physical parameter that can be directly analyzed. The primary task of the signal processing circuit is to receive this analog signal as the original input for subsequent data processing.

[0091] Specifically, the signal processing circuit comprises:

[0092] A voltage-to-frequency conversion module is configured to convert the output voltage signal of the two-stage amplification circuit into a pulse frequency signal.

[0093] A pulse signal analysis module comprising an FPGA chip is configured to count the pulse frequency signal and convert it into an ion current value or a counting rate according to the current gain position.

[0094] A communication interface module is configured to upload the converted detection result to the host computer.

[0095] Figure 7 The structural diagram of the voltage-frequency conversion module provided in the application is shown in Figure 7 The voltage-frequency conversion module mainly comprises a secondary bias adjustment unit and a VF conversion unit, wherein the secondary bias adjustment unit is a reverse addition circuit composed of an operational amplifier and a peripheral circuit, and the voltage V input to the voltage-frequency converter is obtained based on the formula , wherein V is the output voltage of the reverse addition circuit, that is, the input voltage of the AD652; RF, R1 and R2 are feedback resistors of U1; V2 is the output voltage of the secondary amplification circuit; and VB2 is the secondary bias voltage output by the MCU through the DAC. By adjusting the value of VB2, the input end voltage adjustment of the VF conversion chip AD652 is realized, and the zero output of the frequency under the condition of zero input is ensured. The VF conversion unit is the voltage-frequency conversion chip AD652 and the peripheral circuit. By inputting the clock signal frequency and the maximum input voltage , the frequency signal output proportional to the input voltage signal is obtained.

[0096] Figure 8 The structural diagram of the pulse signal analysis module provided in the application is shown in Figure 8 The pulse signal analysis module mainly comprises an FPGA, an optical fiber communication chip and a peripheral circuit, is responsible for counting the output frequency of the voltage-frequency conversion circuit, and obtains the counting value of the input end of the amplifier according to the counting result and the gain amplification multiple. The optical fiber communication is realized through the COM20020 and uploaded to the upper computer.

[0097] In addition, the ion detection amplifier provided in the application can further comprise a digital-to-analog conversion circuit, Figure 9 The structural diagram of the digital-to-analog conversion circuit provided in the application is shown in Figure 9 The digital-to-analog conversion circuit receives the hexadecimal bias adjustment instruction transmitted by the upper computer to the microprocessor, transmits to the double-channel DAC chip, converts into an analog bias voltage, and is input to the primary amplification circuit and the voltage-frequency conversion circuit respectively, so as to adjust the output voltage value of the primary amplification circuit and the output frequency value of the voltage-frequency conversion circuit.

[0098] The ion detection amplifier provided by the embodiment realizes multiple key beneficial effects through modular structure design and fine circuit optimization. The primary amplification circuit adopts a cascade of a primary operational amplifier and a secondary operational amplifier. The primary operational amplifier adopts an ultra-low input bias current device and cooperates with a high-resistance feedback element to effectively suppress noise and bias error and improve weak signal detection sensitivity. The secondary operational amplifier builds a high-voltage amplification unit with discrete devices, cooperates with a current mirror, a stable design of a load circuit, and a Miller compensation to optimize frequency response, widens an output dynamic range, and provides a high signal-to-noise ratio signal for subsequent amplification. The load module is designed in parallel through a resistance feedback branch and a capacitance feedback branch, cooperates with a high-isolation relay to realize non-crosstalk switching, the resistance branch is adapted to low-frequency / direct-current signals of different intensities, the capacitance branch is adapted to high-frequency pulse signals, and the protection resistance branch guarantees switching safety, thereby significantly improving flexibility of primary gain adjustment and signal adaptation capability. The secondary amplification circuit is cascaded through two operational amplifiers. The first stage realizes signal polarity adaptive switching through a multi-path analog switch, and the second stage precisely adjusts gain through a T-shaped adjustable resistance network, cooperates with the primary amplification to widen the overall dynamic range, and avoids signal distortion. The gain switching control circuit coordinates gain adjustment of the load module and the secondary amplification circuit, realizes cooperative linkage of two-stage gain, and ensures rapid adaptation to optimal gain when signal intensity fluctuates. The signal processing circuit eliminates bias error through a reverse addition circuit, realizes analog signal digitization through voltage-to-frequency conversion, combines high-precision counting of an FPGA and gain parameter conversion, and finally outputs accurate ion count rate through a communication interface, thereby forming a complete and reliable link of signal acquisition-amplification-adjustment-processing-output. In summary, the amplifier effectively improves micro-current detection precision, widens dynamic range, optimizes gain switching flexibility, and provides high-performance hardware support for ion detection in complex scenarios.

[0099] Embodiment Two

[0100] Corresponding to the foregoing embodiment of the ion detection amplifier, the application further provides an embodiment of an ion detection method.

[0101] Figure 10 A flowchart of the ion detection method provided by the application is shown in FIG. 1. Figure 10 The method provided by the embodiment includes the following steps.

[0102] S101, receiving a current signal output by an ion detector and inputting the current signal to the primary amplification circuit.

[0103] It should be noted that the ion detector is a component that directly interacts with the ions to be detected. When ions (such as radioactive ions, gas ions, etc.) enter the sensitive area of the detector, they will generate weak current signals through ionization, charge collection and other physical processes. Such signals are extremely weak, usually in the order of picoampere (pA) or even femtoampere (fA), but their intensity is directly related to the number and energy of the ions. Since the current signal output by the ion detector is too weak to be directly processed by the subsequent circuit, it must be preliminarily amplified by a first-stage amplification circuit. Therefore, the current signal output by the detector is accurately introduced into the input end of the first-stage amplification circuit.

[0104] S102, after being sequentially amplified by the first-stage amplification circuit and the second-stage amplification circuit, the signal processing circuit processes the signal to obtain an ion detection result.

[0105] It should be noted that after receiving the weak current signal introduced in step S101, the first-stage amplification circuit converts the current signal to a voltage signal and completes preliminary amplification through the cascade of the primary operational amplifier (ultra-low input bias current characteristic) and the secondary operational amplifier (high voltage resistance and wide dynamic range design). At this time, the amplification gain is determined by the selected feedback branch in the load module (such as a high resistance resistance branch for weak signals and a capacitance branch for high frequency pulse signals), ensuring that the signal strength is converted from pA / fA current to mV voltage, providing a basis for subsequent processing.

[0106] Specifically, the first-stage amplification circuit works with the cascade of the primary operational amplifier and the secondary operational amplifier to sequentially complete the functions of current-voltage conversion, reverse amplification and signal enhancement. Specifically, the primary operational amplifier directly receives the pA / fA weak current signal introduced in step S101, and realizes core conversion and preliminary amplification based on the inverting amplification topology. Its inverting input is connected to the current output of the ion detector through a first resistor, and a closed loop is formed between its output and inverting input through the feedback branch of the load module. According to the virtual short and virtual open characteristics of the operational amplifier, the input current signal flows through the feedback branch, and the current-voltage conversion formula V out1 =-I in ×R f (I in is the output current of the ion detector, R f is the impedance of the feedback branch) is used to convert the current signal to a voltage signal.

[0107] The secondary operational amplifier receives the output signal of the primary operational amplifier, and realizes further amplification and driving capacity enhancement with high voltage resistance design: the differential input stage receives the mV level voltage signal of the primary output, the working point is stabilized by the constant tail current provided by the current mirror, the signal amplitude is improved through the intermediate amplification stage, and finally the push-pull output stage is output. The high voltage resistance characteristic of the secondary operational amplifier widens the output swing, avoids distortion in the process of amplifying weak signals, and enhances the output driving capacity, ensuring that the signal can be effectively transmitted to the secondary amplification circuit.

[0108] At this time, the total gain of the primary amplification circuit is determined by the selected feedback branch in the load module: if it is a weak DC / low frequency signal, select a high resistance feedback branch, increase R f to increase the gain (such as 10 12 Ω resistance corresponds to high gain); if it is a high frequency pulse signal, select a pF level capacitor feedback branch, and use the low impedance characteristic of the capacitor to high frequency signal to realize targeted amplification. Finally, the primary amplification circuit converts and amplifies the pA / fA level current signal into the mV level and above reverse voltage signal, providing a stable input basis for the subsequent secondary amplification circuit. The voltage signal after the primary amplification is transmitted to the secondary amplification circuit, and the secondary amplification is completed through the synergistic effect of two cascaded operational amplifiers. The first amplifier adapts the signal polarity through the multi-path analog switch, avoiding the polarity difference leading to the polarity input error of the voltage-frequency circuit; the second amplifier selects the target gain gear (such as 10 times, 100 times) through the T-type adjustable resistance network, and further amplifies the signal to the V level, ensuring that the signal strength meets the input requirements of the subsequent signal processing circuit, while avoiding strong signal saturation.

[0109] In combination with the above description, the selection of the type and specific value of the feedback element of the first-stage amplification circuit includes: judging the signal type to determine the type of feedback element; selecting the specific feedback element value according to the signal strength or frequency range; and performing branch switching and adaptation verification. Specifically, first, the signal type is judged. The gain switching control circuit identifies the frequency characteristics of the ion signal through signal preprocessing or preset parameters of the upper computer, and determines that the signal type is suitable for resistance feedback if the signal is a continuous and stable direct current signal or a low-frequency signal (frequency ≤ 1 kHz); and determines that the signal type is suitable for capacitance feedback if the signal is a rapidly changing pulse signal or a high-frequency signal (frequency > 1 kHz). Second, the type of feedback element is selected according to the signal type. For direct current or low-frequency signals, the resistance feedback branch is selected because the resistance feedback has stable amplification characteristics for low-frequency signals and has no frequency-selective attenuation, so that linear amplification can be achieved; for high-frequency pulse signals, the capacitance feedback branch is selected to utilize the low-impedance characteristics of capacitance for high-frequency signals (the capacitive reactance decreases with the increase of frequency), so that the transient signal can be accurately captured and low-frequency noise can be suppressed. Then, the specific parameters are selected according to the signal strength or frequency range. The resistance feedback branch includes high-precision resistors with different resistance values (e.g., 10 10 Ω, 10 11 Ω, 10 12 Ω): for extremely weak signals (femto-ampere level), a high-resistance resistor branch (e.g., 10 12 Ω) is selected to improve the gain, for weak signals (pico-ampere level), a medium-resistance branch (e.g., 10 11 Ω) is selected, and for medium-intensity signals (nano-ampere level), a low-resistance branch (e.g., 10 10 Ω) is selected. The capacitance feedback branch includes pF-level vacuum capacitors (e.g., 10 pF, 50 pF, 100 pF). For example, a high-frequency signal with a frequency > 10 kHz is adapted to a 10 pF low-capacitance branch, a medium-high frequency signal with a frequency of 1 kHz to 10 kHz is adapted to a 100 pF high-capacitance branch, and the feedback strength is balanced with the signal integrity.

[0110] Finally, the branch switching and adaptation verification are performed. The gain switching control circuit drives the high-isolation relay of the target branch to conduct, switches the capacitance branch, and turns on the side protection resistance branch to limit the charging and discharging current. After switching is completed, the side protection resistance branch is turned off, the input signal is amplified, and the signal processing circuit monitors the output signal amplitude. If the output signal amplitude is within the preset range of 10 mV to 1 V, it is confirmed that the adaptation is successful; if not, the above steps are repeated to reselect, so as to ensure that the output signal of the first-stage amplification circuit meets the subsequent processing requirements.

[0111] Specifically, in the process of obtaining the ion detection result, the following steps are included:

[0112] (1) The signal processing circuit monitors the frequency value of the current output signal in real time.

[0113] It should be noted that the voltage-frequency conversion module of the signal processing circuit has converted the voltage signal output by the secondary amplification circuit into a pulse frequency signal (the higher the voltage, the higher the frequency), and the frequency value directly reflects the intensity of the current ion signal (the higher the frequency, the stronger the corresponding ion signal).

[0114] The signal processing circuit continuously tracks the dynamic changes in signal intensity by real-time sampling and counting the pulse frequency through the pulse signal analysis module.

[0115] (2) When the frequency value exceeds the preset threshold range, send a switching instruction to the gain switching control circuit.

[0116] It should be noted that the preset threshold range is a frequency interval set according to the requirements of the ion detection scene (for example, a low threshold corresponds to a signal that is too weak and needs to increase the gain, and a high threshold corresponds to a signal that is too strong and needs to reduce the gain). If the frequency is lower than the low threshold, it means that the current signal is still weak after amplification, and the subsequent processing may not be able to recognize it due to insufficient gain; if the frequency is higher than the high threshold, it means that the signal is too strong and may have reached the saturation limit of the amplification circuit, and further amplification may cause signal distortion.

[0117] Specifically, when the signal processing circuit detects that the frequency exceeds the above threshold, it will immediately generate a switching instruction (such as a specific binary coded electrical signal) and send it to the gain switching control circuit through the control line, and the instruction contains information about the target gain level (such as increasing the primary gain + increasing the secondary gain or reducing the primary gain + reducing the secondary gain), triggering subsequent hardware adjustment actions.

[0118] (3) The gain switching control circuit responds to the switching instruction, disconnects the current feedback branch, and switches to the feedback branch and secondary gain level that adapts to the range, and then continues signal processing.

[0119] Specifically, the high-isolation relay in the driving load module that is currently connected to the feedback branch is disconnected, and a new branch that adapts to the range (such as a higher resistance feedback branch when the signal is too weak, or a low resistance or capacitance branch when the signal is too strong) is turned on, completing the primary gain adjustment. Simultaneously control the switching switch of the T-shaped adjustable resistance network in the secondary amplification circuit to select the secondary gain level that matches the primary gain (such as high primary gain corresponding to high secondary gain to ensure sufficient signal amplification), completing the secondary gain adjustment.

[0120] After switching is completed, the gain switching control circuit feeds back a regulation completion signal to the signal processing circuit, and the signal processing circuit resumes monitoring and processing the signal frequency under the new gain level, so that the ion signal returns to the preset threshold range, ensuring the accuracy of subsequent detection results.

[0121] In this way, by monitoring the sensing signal state in real time, triggering adjustment decisions through abnormal responses, and achieving gain adaptation through hardware switching, the signal is finally ensured to be clear and distortion-free regardless of changes in ion signal strength, providing a guarantee for the signal processing circuit to output accurate ion detection results.

[0122] It should be noted that obtaining the ion detection result also includes:

[0123] (1) receiving the voltage signal output by the secondary amplification circuit, and superimposing a bias compensation voltage through a reverse addition circuit.

[0124] It should be noted that although the voltage signal output by the secondary amplification circuit meets the strength requirement, it may introduce a fixed bias error due to the hardware characteristics of the circuit (such as the input offset voltage of the operational amplifier, the baseline shift caused by temperature drift), for example, the output voltage is not 0 when there is no ion signal, but there is a small DC offset.

[0125] The reverse addition circuit is a circuit that can perform algebraic operations on input signals and compensation signals. Its function is to offset the fixed bias in the original signal by superimposing a pre-set bias compensation voltage (equal in size and opposite in polarity to the error voltage). For example, if the circuit has a +5mV error due to inherent offset, the reverse addition circuit superimposes a -5mV compensation voltage to make the compensated signal baseline return to around 0. This can eliminate the inherent error of the system and ensure that subsequent conversion and counting only reflect the true ion signal, not the offset of the circuit itself.

[0126] (2) converting the compensated voltage signal into a pulse frequency signal through the voltage-to-frequency conversion module.

[0127] It should be noted that the voltage signal after bias compensation is still a continuously changing analog quantity and cannot be directly counted and analyzed by digital circuits. The voltage-to-frequency conversion module linearly maps the amplitude of the voltage signal to the frequency of the pulse signal through a precision oscillator circuit or a dedicated chip: the higher the voltage, the higher the frequency of the output pulse. In this way, even if there is small noise in the signal, it will not significantly affect the statistical results of the pulse frequency; at the same time, the frequency signal is easy to transmit over long distances and process by digital circuits, providing a stable digital input format for subsequent counting analysis.

[0128] (3) counting the pulse frequency signal within a pre-designed number of time lengths to obtain the cumulative number of pulses.

[0129] The pulse signal analysis module (FPGA chip) pre-designs a time length (such as 1 second, 100 milliseconds) according to detection requirements, and counts the pulse signal output by the voltage-frequency conversion module in the time length to obtain a total number of accumulated pulses (for example, 5000 pulses are counted in 1 second, corresponding to a frequency of 5000 Hz).

[0130] It should be noted that the selection of the counting time length needs to take into account the detection accuracy and response speed, wherein a long counting time length (such as 1 second) can reduce statistical error and is suitable for stable signal detection; and a short counting time length (such as 10 milliseconds) can improve the response speed and is suitable for rapidly changing pulse signals. This step converts the dynamic frequency signal into quantifiable digital quantity through time dimension statistics, thereby providing basic data for subsequent parameter conversion.

[0131] (4) According to the total number of accumulated pulses, the counting time length, and the current first-stage and second-stage gain positions, the current value output by the ion detector and the corresponding ion counting rate are converted and obtained, and the counting rate is output as the final detection result.

[0132] It should be noted that, first, the output voltage of the second-stage amplification circuit is calculated from the pulse frequency. According to the preset linear relationship of the voltage-frequency conversion module, the actual frequency of the pulse signal (the total number of accumulated pulses divided by the counting time length) is multiplied by the conversion coefficient to obtain the output voltage value of the second-stage amplification circuit. For example, if the total number of accumulated pulses in 1 second is 5000, the corresponding frequency is 5000 Hz (i.e., 5 kHz), and according to the relationship that 1 kHz corresponds to 1 mV, the output voltage of the second stage is calculated to be 5 mV.

[0133] Secondly, the output voltage of the first-stage amplification circuit is inversely calculated in combination with the second-stage gain position. The gain position (such as 100 times) of the second-stage amplification circuit is determined by the currently selected T-type resistance network combination, and the output voltage of the first-stage amplification circuit is the output voltage of the second-stage amplification circuit divided by the gain value. In the above example, the output voltage of the first stage is 0.05 mV (i.e., 5 x 10 -5 V) obtained by dividing the second-stage output voltage (5 mV) by the 100 times gain.

[0134] Then, the original current value is calculated based on the parameters of the first feedback branch. The output voltage of the first-stage amplification circuit is generated by the current-voltage conversion of the primary operational amplifier, and the relationship is first-stage output voltage = original current x feedback element impedance (ignoring the polarity influence of reverse amplification). If the resistance value of the currently selected first feedback branch resistor is 10 12 Ω, then the original current value is the first-stage output voltage (5 x 10 -5 V) divided by the feedback resistor resistance value (10 12 Ω), and the calculation result is 5 x 10 -17 A (i.e., 50 fA).

[0135] Finally, the count rate is converted according to the ion charge amount. The physical nature of the current is the amount of charge passing through per unit time, and the amount of charge carried by a single ion is a elementary charge (about 1.602 x 10 -19 C). The number of ions passing per unit time (count rate) can be obtained by dividing the original current value by the elementary charge. For example, a current of 5 x 10 -17 A corresponds to an amount of charge passing per second of 5 x 10 - 17 C, divided by 1.602 x 10 -19 C / ion, and the count rate is calculated to be about 312 cps. The result is uploaded to the host computer through the communication interface module to complete the output of the detection result.

[0136] In this step, the system error is eliminated by bias compensation, the signal is digitized by V / F conversion, and the digital quantity is converted into a physical parameter by counting and conversion. The ion count rate output can be directly used for ion concentration analysis, environmental monitoring and other practical scenarios, and the ion detection method can realize the closed loop from signal acquisition to result application.

[0137] The method provided in the embodiment realizes the full-link optimization of ion signals from acquisition, amplification, adjustment to quantization output through structured process design and dynamic adjustment logic, effectively improves the dynamic range, precision and reliability of detection, and perfectly adapts to the precise detection requirements of wide-range ion signals in complex scenarios.

[0138] The above only describes the preferred embodiments of the present application and does not limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An ion detection amplifier characterized by, The ion detection amplifier comprises: A primary amplification circuit for receiving a current signal output by an ion detector, the primary amplification circuit comprising a primary operational amplifier and a secondary operational amplifier connected in cascade; the secondary operational amplifier comprising: a differential input stage composed of two first NPN transistors, the bases of the two first NPN transistors being respectively connected to an output terminal of the primary operational amplifier and a reference potential terminal, the emitters being commonly connected to the same node and then connected to a common collector terminal of a current mirror composed of two second PNP transistors, the emitters of the current mirror being connected to a positive power supply terminal; an intermediate amplification stage comprising a third NPN transistor and a compensation capacitor, the base of the third NPN transistor being connected to an output terminal of the differential input stage, the collector being connected to the positive power supply terminal, and the emitter being connected to ground through a second resistor, the input terminal of the compensation capacitor being connected to an output terminal of the differential input stage, and the output terminal being connected to an input terminal of a push-pull output stage; the push-pull output stage comprising two diodes, a fourth transistor and two fifth transistors, the fourth transistor being connected to the intermediate amplification stage, the collector of the fourth transistor being connected to a diode for transmitting the intermediate stage signal to an output terminal for driving a subsequent stage circuit, the collectors and emitters of the two fifth transistors being respectively connected to a positive power supply terminal and a negative power supply terminal, and the diodes being connected in series and then connected across the base-emitter path of the fifth transistors; and a negative power supply terminal of the secondary operational amplifier being connected to a negative power supply node of the whole circuit; A load module connected in parallel with the primary amplification circuit, the load module comprising a plurality of feedback branches, the feedback elements in each feedback branch being different in type, and different feedback branches corresponding to different primary gain positions; A secondary amplification circuit connected to an output terminal of the primary amplification circuit, for amplifying an output signal of the primary amplification circuit, the secondary amplification circuit being provided with a plurality of secondary gain positions; A gain switching control circuit connected to the load module and the secondary amplification circuit respectively, for controlling the amplification gain of the primary amplification circuit and the secondary amplification circuit; A signal processing circuit for receiving an output signal of the secondary amplification circuit, for realizing data processing of the output signal and outputting a detection result.

2. The ion detection amplifier of claim 1, wherein, The structure of the primary operational amplifier comprises: The inverting input terminal of the primary operational amplifier is connected to a current signal output terminal of an ion detector; the non-inverting input terminal is connected to a primary bias voltage through a first resistor and a second resistor; a feedback capacitor is connected in parallel between the output terminal and the inverting input terminal; the positive power supply terminal is connected to a positive power supply, and the negative power supply terminal is connected to a negative power supply.

3. The ion detection amplifier of claim 1, wherein, The load module comprises: A plurality of resistance feedback branches, each of the resistance feedback branches comprising resistors of different resistance values and high-isolation relays; A plurality of capacitance feedback branches connected in parallel with the resistance feedback branches, each of the capacitance feedback branches comprising a pF-level vacuum capacitor and high-isolation relays connected in series across the capacitor; A protection resistance branch connected in parallel with the resistance feedback branches and the capacitance feedback branches, comprising a protection resistor.

4. The ion detection amplifier of claim 1, wherein, The secondary amplification circuit comprises two cascaded operational amplifiers, wherein the input end of the first amplifier is connected to the output end of the primary amplification circuit through a multi-path analog switch for switching the input direction according to the polarity of the ion signal; a T-shaped adjustable resistance network is arranged in the feedback loop of the second amplifier, and different resistance combinations are selected by the control signal output by the gain switching control circuit.

5. The ion detection amplifier of claim 1, wherein, The signal processing circuit comprises: a voltage-to-frequency conversion module for converting the output voltage signal of the secondary amplification circuit into a pulse frequency signal; a pulse signal analysis module comprising an FPGA chip for counting the pulse frequency signal and converting it into an ion current value or a counting rate according to the current gain level; a communication interface module for uploading the converted detection result to an upper computer.

6. A method of ion detection, characterized by, The method is applied to the ion detection amplifier according to any one of claims 1-5, and the method comprises: receiving the current signal output by the ion detector and inputting the current signal into the primary amplification circuit; after being sequentially amplified by the primary amplification circuit and the secondary amplification circuit, processing the signal by the signal processing circuit to obtain the ion detection result.

7. The method of claim 6, wherein, Before the receiving of the current signal output by the ion detector and the inputting of the current signal into the primary amplification circuit, the method comprises: the upper computer sends a level selection instruction to the gain switching control circuit according to the type of the ion to be detected and the expected signal strength; the gain switching control circuit selects the target feedback branch in the load module according to the instruction, determines the gain level of the primary amplification circuit, and selects the target gain level of the secondary amplification circuit.

8. The method of claim 6, wherein, During the obtaining of the ion detection result, the method comprises: the signal processing circuit monitors the frequency value of the current output signal in real time; when the frequency value exceeds the preset threshold range, the gain switching control circuit sends a switching instruction; the gain switching control circuit responds to the switching instruction, disconnects the current feedback branch, and switches to the feedback branch and the secondary gain level that are suitable for the range, and continues the signal processing after completion.

9. The method of claim 6, wherein, The obtaining of the ion detection result further comprises: receiving the voltage signal output by the secondary amplification circuit, superimposing a bias compensation voltage through a reverse addition circuit; converting the compensated voltage signal into a pulse frequency signal through a voltage-to-frequency conversion module; counting the pulse frequency signal within a preset counting time to obtain the cumulative pulse number; according to the cumulative pulse number, the counting time, and the current primary and secondary gain levels, converting the ion detector output current value and the corresponding ion counting rate, and outputting the counting rate as the final detection result.

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