Ion detection amplifier and ion detection method

Abstract

The invention 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 invention comprises a primary amplification circuit used for receiving a current signal output by an ion detector; the load module is connected with the primary amplification circuit in parallel, and the load module comprises a plurality of feedback branches; the secondary amplification circuit is connected with the output end of the primary amplification circuit, is used for amplifying an output signal of the primary amplification circuit, and is provided with a plurality of secondary gain gears; the gain switching control circuit is respectively connected with the load module and the secondary amplification circuit; and the signal processing circuit is used for receiving an output signal of the secondary amplification circuit. According to the ion detection amplifier and the ion detection method provided by the invention, collection, amplification, switching and digital output of ion signals can be accurately and efficiently completed in a complex scene.

Description

Technical Field

[0001] This application relates to the field of mass spectrometry technology, and in particular to an ion detection amplifier and an ion detection method. Background Technology

[0002] In the fields of mass spectrometry and ion detection, ion detection amplifiers are core devices for achieving accurate ion signal analysis. The raw signal output by the ion detector after interacting with the analyte ion is typically an extremely weak microcurrent signal (mostly in the femtoampere to picoampere range), and its intensity fluctuates greatly depending on ion concentration, energy, and the detection environment, ranging from weak, continuous signals to strong pulse signals. Therefore, ion detection amplifiers must possess high sensitivity, wide dynamic range, and precise signal processing capabilities to complete the acquisition, amplification, and quantitative analysis of ion signals, providing reliable support for subsequent detection result output.

[0003] Current mainstream ion detection amplifier technologies are based on operational amplifier circuits, including signal amplification, gain adjustment, and signal processing modules. The signal amplification stage uses a single or two-stage operational amplifier to convert the micro-current signal into a voltage signal and amplify it initially. Gain adjustment often relies on fixed feedback resistors or limited-range feedback branch switching; some solutions use relays to control the branch's on / off state to adapt to different signal strengths. Signal processing digitizes the analog signal through voltage-to-frequency conversion or analog-to-digital conversion, and outputs the result through counting or calculation. These solutions can achieve basic ion signal detection in conventional scenarios, but they still have significant limitations under complex requirements.

[0004] Existing technologies suffer from four key problems: First, insufficient accuracy in micro-current detection. Conventional operational amplifiers have large input bias currents, and feedback networks are prone to introducing noise and interference, leading to distortion or submersion of weak signals. Second, limited dynamic range. Fixed or limited gain levels cannot cover a wide range of signals, and insufficient voltage withstand of secondary amplifier circuits further compresses the dynamic range, easily resulting in saturation of strong signals or insufficient amplification of weak signals. Third, inflexible gain switching and range adaptation. Poor isolation of ordinary relays leads to crosstalk, residual charge in capacitor branches affects switching stability, and there is a lack of real-time linkage with signal strength. Fourth, incomplete signal processing links. Voltage-frequency conversion has low accuracy for low-level signals, and the counting results are not coordinated with gain parameters, resulting in deviations in the final results and making it difficult to meet the high-precision detection requirements in complex scenarios. Summary of the Invention

[0005] In view of this, this application provides an ion detection amplifier and an ion detection method to solve the problems of insufficient microcurrent detection accuracy, limited dynamic range, inflexible gain switching and range adaptation, and lack of signal processing link integrity in existing ion detection amplifiers.

[0006] Specifically, this application is implemented through the following technical solution:

[0007] A first aspect of this application provides an ion detection amplifier, the ion detection amplifier comprising:

[0008] A first-stage amplifier circuit is used to receive the current signal output by the ion detector. The first-stage amplifier circuit includes a cascaded primary operational amplifier and a secondary operational amplifier.

[0009] A load module is connected in parallel with the first-stage amplifier circuit. The load module includes multiple feedback branches, each with a different type of feedback element, and different feedback branches correspond to different first-stage gain levels.

[0010] A secondary amplifier circuit is connected to the output terminal of the primary amplifier circuit and is used to amplify the output signal of the primary amplifier circuit. The secondary amplifier circuit has multiple secondary gain levels.

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

[0012] The signal processing circuit is used to receive the output signal of the secondary amplifier circuit and realize the data processing and detection result output of the output signal.

[0013] A second aspect of this application provides an ion detection method, the method comprising:

[0014] Receive the current signal output by the ion detector and input the current signal to the first-stage amplifier circuit;

[0015] After being amplified sequentially by the first-stage amplifier circuit and the second-stage amplifier circuit, the signal is processed by the signal processing circuit to obtain the ion detection result.

[0016] The ion detection amplifier and ion detection method provided in this application significantly improve the adaptability, amplification flexibility, and processing integrity of the ion detection amplifier to a wide range of ion signals through modular structural design and multi-stage gain adjustment mechanism, providing reliable hardware support for ion signal detection in complex scenarios. Specifically, the structure of the first-stage amplifier circuit, including cascaded primary and secondary operational amplifiers, achieves graded amplification of the weak current signal output by the ion detector. The load module is connected in parallel with the first-stage amplifier circuit and contains multiple feedback branches. The design of different feedback branches corresponding to different first-stage gain levels gives the first-stage amplifier circuit flexible gain adjustment capability. By switching different feedback branches, it can adapt to ion signals of different intensities, solving the problem that a single gain cannot cover a wide range of signals and improving the amplifier's adaptability to diverse ion signals. The multi-level design of the two-stage amplifier circuit significantly broadens the dynamic range of the overall amplifier, which can meet the amplification requirements of weak signals while avoiding distortion caused by over-amplification of strong signals, ensuring that signals of different intensities can be effectively processed. The gain switching control circuit is connected to the load module and the second-stage amplifier circuit respectively, realizing the overall control of the gain of the first-stage and second-stage amplifier circuits, ensuring the coordination and accuracy of the two-stage gain adjustment; while the signal processing circuit receives the output signal of the second-stage amplifier circuit and realizes data processing and detection result output, thus completing the complete link from signal amplification to result output, ensuring the effective output of ion detection results. Attached Figure Description

[0017] Figure 1 This is a structural diagram of the ion detection amplifier provided in this application;

[0018] Figure 2 This is a connection diagram of the primary operational amplifier shown in this application;

[0019] Figure 3 This is a connection diagram of the secondary operational amplifier shown in this application;

[0020] Figure 4 This is a schematic diagram of the load module provided in this application;

[0021] Figure 5 The structure diagram of the two-stage amplifier circuit provided in this application;

[0022] Figure 6 This is a structural diagram of the gain switching control circuit shown in this application;

[0023] Figure 7 This is a structural diagram of the voltage-to-frequency conversion module provided in this application;

[0024] Figure 8 A structural diagram of the pulse signal analysis module provided in this application;

[0025] Figure 9 The circuit diagram for the digital-to-analog converter provided in this application;

[0026] Figure 10 A flowchart of the ion detection method provided in this application. Detailed Implementation

[0027] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0028] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used herein are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0029] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0030] The following specific embodiments are given to illustrate the technical solution of this application in detail.

[0031] Example 1

[0032] Figure 1 This is a structural diagram of the ion detection amplifier provided in this application. Please refer to... Figure 1 The method provided in this embodiment may include:

[0033] A first-stage amplifier circuit is used to receive the current signal output by the ion detector. The first-stage amplifier circuit includes a cascaded primary operational amplifier and a secondary operational amplifier.

[0034] A load module is connected in parallel with the first-stage amplifier circuit. The load module includes multiple feedback branches, each with a different type of feedback element, and different feedback branches correspond to different first-stage gain levels.

[0035] A secondary amplifier circuit is connected to the output terminal of the primary amplifier circuit and is used to amplify the output signal of the primary amplifier circuit. The secondary amplifier circuit has multiple secondary gain levels.

[0036] A gain switching control circuit is connected to the load module and the secondary amplifier circuit respectively, and is used to control the amplification gain of the primary amplifier circuit and the secondary amplifier circuit;

[0037] The signal processing circuit is used to receive the output signal of the secondary amplifier circuit and realize the data processing and detection result output of the output signal.

[0038] It should be noted that the first-stage amplifier circuit is the core front-end unit of the ion detection amplifier, used to convert and amplify the extremely weak current signal (typically in the femtoampere to picoampere range) output by the ion detector into a voltage signal suitable for subsequent processing. This first-stage amplifier circuit adopts a cascaded structure (simply put, it is connected one after another, with the output of the previous one serving as the input of the next), 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 the signal output of the ion detector. Its main function is to convert the input micro-current signal into a voltage signal and perform preliminary amplification. This primary operational amplifier uses an ultra-low input bias current type device and is equipped with a high-resistance feedback element to effectively suppress the measurement error introduced by the input bias current, while reducing input noise, thereby ensuring detection sensitivity at extremely low current levels.

[0040] The input of the secondary operational amplifier is connected to the output of the primary operational amplifier. It is used to further amplify the voltage amplitude while preserving the signal waveform and to improve the output drive capability. This secondary operational amplifier adopts a high-voltage design, making its supply voltage higher than the rated value of conventional operational amplifiers. This widens the output dynamic range of the first-stage amplifier circuit and provides a higher signal-to-noise ratio input signal for the subsequent second-stage amplifier circuit.

[0041] By cascading primary and secondary operational amplifiers, the first-stage amplifier circuit can achieve a large overall gain while maintaining low noise characteristics. Specifically, the primary operational amplifier converts the micro-current signal output from the ion detector into a voltage signal through an inverting amplification topology and adapts to the signal polarity requirements using its inverting amplification characteristics. The secondary operational amplifier further enhances the signal amplitude and strengthens the output drive capability. The synergy of the two stages enables the first-stage amplifier circuit to have both the ability to convert micro-currents from femtoamperes to picoamperes into processable voltage signals and a wide input dynamic range, adapting to application scenarios where the signal amplitude changes significantly during ion detection.

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

[0043] It should be noted that the inverting input terminal (pin 2) is connected to the current signal output terminal of the ion detector. During operation, the ion detector outputs a very small current signal, which is connected to the input terminal of the load module via the inverting input terminal (pin 2). This current signal enters the feedback element in the load module for signal amplification, and the resulting voltage signal is output through the secondary amplifier. The non-inverting input terminal (pin 2) is connected to the first-stage bias voltage VB1 through the first resistor R1 to set the operating reference potential of the operational amplifier. It is then grounded through the second resistor R2 to achieve voltage division, thus forming a stable input bias network and suppressing zero-point drift and external interference. A feedback capacitor C1 (100pF) is connected in parallel between the output terminal (pin 6) and the inverting input terminal (pin 3). This capacitor forms a direct negative feedback path from input to output, used to suppress high-frequency noise, improve amplifier stability, and reduce the influence of parasitic capacitance in weak current signal measurements. In the power supply section, the positive power supply terminal (pin 8) is connected to the positive power supply VCC, and the negative power supply terminal (pin 4) is connected to the negative power supply VEE, providing bipolar power supply for the operational amplifier to support bidirectional signal swing and widen the dynamic range.

[0044] Through the above connection method, the primary operational amplifier can stably convert the femtoampere to picoampere level current signal output by the ion detector into a voltage signal while ensuring extremely low input bias current. At the same time, it reduces input noise and bias error, laying a high signal-to-noise ratio foundation for subsequent secondary amplification and signal processing.

[0045] also, Figure 2 Labels 1 and 5 are zero-adjustment pins used for offset voltage compensation of operational amplifiers.

[0046] Figure 3 For a connection diagram of the secondary operational amplifier shown in this application, please refer to... Figure 3 The secondary operational amplifier is a high-voltage amplifier unit implemented with discrete devices, comprising:

[0047] The differential input stage consists of two first NPN transistors (Q2, Q3). The bases of the two first NPN transistors are connected to the output terminal and the reference potential terminal of the primary operational amplifier, respectively. Their emitters are connected to the same node and then to the common collector terminal of a current mirror consisting of two second PNP transistors (Q6, Q7). The emitter of the current mirror is connected to the positive power supply terminal (VCC) to provide 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 of the differential input stage, the collector is connected to the positive power supply, and the emitter is grounded through a second resistor (R2). The input of the compensation capacitor (C2) is connected to the output of the differential input stage, and the output is connected to the input of the push-pull output stage. This is used to introduce Miller compensation (local negative feedback), suppress high-frequency oscillations, improve the phase margin of the amplifier, and ensure stable operation over a wide bandwidth.

[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 its collector is connected to the diode (D2) to transmit the intermediate stage signal to the output terminal, realizing high current output and driving the subsequent circuit. The collectors and emitters of the two fifth transistors (Q1, Q4) are connected to the positive power supply terminal (VCC) and the negative power supply terminal (VEE) respectively. The diodes (D1, D2) are connected in series and then connected across the base-emitter path of the fifth transistors (Q1, Q4) to provide a stable bias voltage for the two transistors. At the same time, the forward voltage drop of the diodes is used to achieve a high withstand 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 built based on discrete components (i.e., independent transistors, diodes, resistors, capacitors, etc.). Its core function is to receive the signal output from the primary operational amplifier and, through multi-stage circuitry, achieve stable signal amplification, noise suppression, and enhanced driving capability, providing a suitable signal input for subsequent secondary amplification circuits. Compared to integrated operational amplifiers, discrete component design allows for flexible optimization of voltage withstand performance and amplification characteristics, making it more suitable for the wide dynamic range signal processing requirements in ion detection.

[0052] Specifically, the differential input stage is the signal input terminal of the secondary operational amplifier, consisting of a differential pair structure formed by two first NPN transistors (Q2, Q3). Here, a differential pair refers to a circuit unit that uses two symmetrically characterized transistors to compare and amplify the input signal against a reference potential, effectively suppressing common-mode noise (such as the combined effects of environmental electromagnetic interference and power supply fluctuations on the two transistors). The bases of the two transistors are connected to the output terminal of the primary operational amplifier (receiving the amplified signal from the previous stage) and the reference potential terminal (providing a reference level), respectively, forming a differential signal input path. Their emitters are connected to the same node and then to a current mirror formed by two second PNP transistors (Q6, Q7). The current mirror is a circuit that outputs a constant current; its emitter is connected to the positive power supply terminal (VCC), providing a stable tail current for the differential input stage. This connection method ensures that the differential pair can operate stably under different signal strengths, avoiding signal distortion caused by current fluctuations and providing an accurate original signal for subsequent amplification.

[0053] The intermediate amplification stage, acting as a relay unit for signal amplification, consists of a third NPN transistor (Q5), a second resistor (R2), and a compensation capacitor (C2). The base of Q5 is connected to the output of the differential input stage, receiving the initially amplified signal; its collector is connected to the positive power supply to obtain energy, and its emitter is grounded through the second resistor, forming a current path. To avoid circuit oscillations at high frequencies (instability caused by phase shift during signal amplification), the output of the push-pull output stage is connected to the output of the differential input stage via the compensation capacitor (C2), forming Miller compensation. This connection utilizes the phase compensation effect of the capacitor to suppress phase lag in high-frequency signals, improve the frequency response characteristics of the circuit, and ensure the stability of signal amplification over a wide frequency range. Through the current amplification characteristics of the transistor, the intermediate amplification stage can further increase the signal amplitude output from the differential input stage, providing sufficient signal driving capability for subsequent output stages.

[0054] The push-pull output stage is the signal output terminal of the secondary operational amplifier. It consists of two diodes (D1, D2), a fourth transistor (Q8), and two fifth transistors (Q1, Q4). The push-pull operation mode of the fifth transistors (Q1, Q4) enables high current output to meet the load requirements of the subsequent stage. The diode bias network ensures that the output stage operates stably under high voltage. Its core function is to enhance the driving capability of the circuit to effectively drive the secondary amplifier circuit.

[0055] In terms of power supply design, the positive power supply terminal (VCC) of the secondary operational amplifier provides power to the current mirror, intermediate amplification stages, etc., while the negative power supply terminal (VEE) connects to the negative power supply node of the entire circuit, forming a wide voltage supply range. This design, combined with the high voltage withstand characteristics of discrete components, significantly widens the output dynamic range of the secondary operational amplifier, making it suitable for amplifying various ion signals from weak to strong.

[0056] In summary, the secondary operational amplifier achieves low-noise, high-linearity, high-voltage withstand, and wide-band stable signal amplification through precise reception of the differential input stage, stable operating point of the load circuit, signal enhancement of the intermediate amplification stage, drive and compensation of the push-pull output stage, and wide-voltage power supply design.

[0057] It should be noted that the load module is used to achieve flexible gain adjustment of the first-stage amplifier circuit. Its connection method with the first-stage amplifier circuit and its internal structural design directly determine the first-stage amplifier circuit's adaptability to ion signals of different intensities. Specifically, the load module is connected in parallel with the first-stage amplifier circuit, meaning that the input and output terminals of the load module are respectively connected to the output and input terminals of the first-stage amplifier circuit, forming a closed feedback loop. In operational amplifier circuits, parallel feedback is a classic topology for signal amplification. After the first-stage amplifier circuit converts the current signal output from the ion detector into a voltage signal, a portion of the signal flows back to the input terminal of the first-stage amplifier circuit through the feedback branch of the load module. The strength and characteristics of the feedback signal directly affect the overall gain (amplification factor) of the first-stage amplifier circuit. This parallel connection method 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 multiple feedback branches, and the different types of feedback elements in each branch clearly define the internal structural characteristics of the load module. A feedback branch is an independently switchable sub-circuit within the load module, and the core difference between each branch lies in the type of feedback element used. Furthermore, each feedback branch typically includes switching elements such as high-isolation relays to enable rapid connection and disconnection of the branch, ensuring no signal crosstalk during switching between different branches.

[0059] The load module achieves flexible gain adjustment of the first-stage amplifier circuit through multiple feedback branches of different types, and its internal structure design directly determines its adaptability to different ion signals. Specifically, the load module includes multiple resistive feedback branches and multiple capacitive feedback branches, which are set in parallel. Each branch is connected in series with a high-isolation relay to achieve independent switching, ensuring no signal crosstalk when the branch is switched on or off.

[0060] The circuit includes multiple resistor feedback branches, each with a core component consisting of high-precision resistors of varying resistance values, exhibiting significant differences in magnitude. According to the operational amplifier gain formula, the feedback resistor value is proportional to the amplification gain. Therefore, different resistance levels correspond to proportionally increasing gain levels, suitable for medium, weak, and extremely weak DC or low-frequency ion signals.

[0061] The capacitor feedback circuit has multiple branches, each with a pF-level vacuum capacitor as its core component, and the capacitance values ​​vary. Capacitive feedback exhibits frequency selectivity, showing significant effect on high-frequency signals but weak effect on low-frequency signals. Therefore, branches with different capacitance values ​​can adapt to different frequency ranges of high-frequency pulse signals (lower capacitance values ​​adapt to higher frequency signals, and higher capacitance values ​​adapt to slightly lower frequency pulse signals), effectively filtering out low-frequency noise and avoiding distortion caused by excessive amplification of high-frequency signals. Simultaneously, capacitive feedback avoids the thermal noise problem inherent in high-resistance resistors. In situations where the current intensity is equal to or less than the resistor's thermal noise current, capacitive feedback can achieve more precise signal amplification.

[0062] It's important to note that the core difference between resistive and capacitive feedback lies in the signal adaptation type. Resistive feedback is suitable for continuous, stable DC or low-frequency signals, with gain adjustment depending on the resistor value, and it has weaker high-frequency noise suppression capabilities. Capacitive feedback, on the other hand, is suitable for rapidly changing high-frequency pulse signals, achieving precise amplification through frequency selectivity, or in situations where the current intensity is lower than the thermal noise current of high-resistance resistors. The low-loss characteristics of vacuum capacitors ensure accurate high-frequency signal transmission and low-noise, high-stability characteristics for extremely weak current measurements. Furthermore, each capacitor branch is connected in parallel with a protection resistor branch to limit the charging and discharging current during switching, preventing component damage and providing a discharge path for residual charge, ensuring switching stability. Through this design, the load module achieves dual adaptation for a wide gain range and multiple signal types, providing a reliable foundation for gain adjustment in the first-stage amplifier circuit.

[0063] Specifically, Figure 4 Please refer to the structural diagram of the load module provided in this application. Figure 4 The load module includes: multiple resistive feedback branches, each of which contains a resistor of different resistance value and a high-isolation relay; multiple capacitive feedback branches connected in parallel with the resistive feedback branches, each of which contains a pF-level vacuum capacitor with a high-isolation relay connected in series across the capacitor; and a protection resistor branch connected in parallel with the resistive and capacitive feedback branches, which contains a low-resistance (10k) protection resistor.

[0064] It should be noted that the resistive feedback branch is the fundamental unit in the load module used to adjust the gain of the first-stage amplifier circuit. The core components of each branch include resistors of varying values ​​and high-isolation relays. The resistor is the key parameter determining the feedback strength, and the resistance values ​​of the different feedback branches in this module vary significantly. According to the gain formula for operational amplifier circuits, the value of the feedback resistor is directly proportional to the amplification gain (with a fixed input resistance, the higher the resistance, the higher the gain). Therefore, different resistor values ​​correspond to different first-stage gain levels, which can be adapted to weak (requiring high gain) and medium-intensity (requiring medium gain) ion current signals, respectively.

[0065] The high-isolation relay connected in series in each resistor branch is the core component for branch switching. Its high isolation ensures that when a branch is disconnected, the resistance of that branch will not interfere with the signals of other branches or the first-stage amplifier circuit (avoiding the effects of leakage current, parasitic capacitance, etc.), while also guaranteeing the accuracy of signal transmission when the branch is connected. By controlling the on / off state of the relay through the gain switching control circuit, the target resistor branch can be quickly selected, achieving precise adjustment of the first-stage gain.

[0066] It should also be noted that the capacitive feedback branch and the resistive feedback branch are connected in parallel to form a complementary gain adjustment mechanism, which consists of a pF-level vacuum capacitor and a high-isolation relay. The feedback characteristics of the pF-level vacuum capacitor are frequency-dependent (with a stronger feedback effect on high-frequency signals). Using a pF-level (picofarad-level) vacuum capacitor is suitable for rapidly changing pulsed signals in ion detection (such as short-term ion bursts). Compared to resistive feedback, capacitive feedback effectively suppresses low-frequency noise while avoiding distortion of high-frequency signals due to excessive amplification, making it particularly suitable for capturing transient ion signals. Furthermore, because capacitors do not have thermal noise characteristics, they have a lower detection limit and higher stability and signal-to-noise ratio, enabling the detection of signal regions where resistive feedback cannot achieve high-precision measurements (such as below 10). 4 (cps). The high-isolation relay here is similar to the resistor branch. 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 preventing the parasitic parameters of the capacitor from affecting circuit stability.

[0067] In addition, the protection resistor branch (usually a low-resistance resistor, such as 10kΩ) is a crucial auxiliary design. When the capacitor or resistor branch is switched on, the protection resistor can limit the instantaneous charging and discharging current, preventing large current surges from damaging the feedback components or the core components of the first-stage amplifier circuit; when the capacitor branch is disconnected, the protection resistor can also provide a discharge path for residual charge, ensuring signal accuracy during the next switch.

[0068] By using a parallel design of resistive and capacitive feedback branches, the load module possesses the dual advantages of a wide gain range and adaptability to multiple signal types. For stable DC or low-frequency ion signals, the appropriate gain is selected by switching the resistive feedback branch to achieve precise signal amplification. For rapidly changing high-frequency pulse signals, the circuit switches to the capacitive feedback branch, utilizing its frequency characteristics to achieve noise suppression and transient signal capture. The design of high-isolation relays and protective resistors ensures the reliability of branch switching and circuit safety. This structure allows the first-stage amplifier circuit to flexibly adjust the gain mode according to the intensity and frequency characteristics of the ion signal, providing a high-quality input signal for subsequent second-stage amplification and signal processing.

[0069] Furthermore, it should be noted that in order to achieve accurate adaptation of the first-stage amplifier circuit to ion signals of different intensities and types, the intensity range of the amplifier input signal is initially determined based on the ion current signals output from each detection point at the front end of the mass spectrometer. If the signal intensity is in the nanoampere (nA) or picoampere (pA) level, the resistive feedback branch in the load module is preferred; if the signal intensity is in the femtoampere (fA) level or below, the capacitive feedback branch is preferred. This selection is based on the fact that for extremely weak signals in the fA level and below, their amplitude is easily covered by the inherent thermal noise current of the resistive element, while the capacitive feedback has no thermal noise characteristics, which can avoid noise interference to the signal.

[0070] Meanwhile, the branch type is further verified by combining the dynamic characteristics of the signal. If the ion signal is a low-frequency, stable and approximately DC signal (such as in conventional ion concentration detection scenarios), the selection of the resistance feedback branch is maintained. If the detection object is a narrow peak signal such as isotope spectrum peaks (with fast intensity change rate and significant high-frequency characteristics), the capacitor feedback branch is switched to adapt to the transient capture requirements of high-frequency pulse signals.

[0071] It should also be noted that the switching of the feedback branch type and the adjustment of the gain level in the first-stage amplifier circuit are as follows: the host computer control software generates a selection instruction for the feedback branch type (resistor / capacitor) and the corresponding gain level of the first-stage amplifier circuit based on the aforementioned signal determination results. This 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 five control signals and outputs a drive level that matches the target feedback branch. The above drive level is input to the input of the dual-channel voltage comparator and compared with the preset reference level (1.2V). The dual-channel voltage comparator outputs the front-end control signal and the back-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 an open or closed action according to the level state of the control signal: if the control signal is an effective level, the relay is closed, the corresponding feedback loop is turned on, and the first-stage amplifier circuit switches to the gain level corresponding to that 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 and gain adjustment capability of the secondary amplifier circuit directly affect the overall amplifier's amplification effect and dynamic range coverage of weak ion signals. Specifically, the connection between the secondary amplifier circuit and the output terminal of the primary amplifier circuit clearly defines its position in the signal chain. After the primary amplifier circuit converts the weak current signal output by the ion detector into a voltage signal and performs preliminary amplification, the output signal is directly transmitted to the input terminal of the secondary amplifier circuit. This series connection forms a relay-style signal processing chain from primary to secondary amplification, ensuring that the weak signal reaches the intensity range that subsequent signal processing circuits can recognize after two stages of amplification. In practice, the original signal output by the ion detector is usually at the micro-current level (e.g., pA to nA). After being converted into a voltage signal by the primary amplifier circuit, its amplitude may still not meet the input requirements of the signal processing circuit (e.g., some weak signals still have a voltage value below 1mV after primary amplification). The secondary amplifier circuit further amplifies the primary output signal (e.g., amplified by 10 times, 100 times, etc.) through the amplification effect of its internal operational amplifier, increasing the signal amplitude to a range suitable for subsequent processing (e.g., 10mV to 1V). In addition, the amplification process of the secondary amplifier circuit can also optimize signal characteristics, such as reducing signal noise and adjusting signal polarity through circuit design (to adapt to the detection requirements 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] Furthermore, the secondary amplifier circuit has multiple gain levels. Ion signal strength varies greatly under different scenarios (e.g., weak signal in low-concentration ion environments, strong signal in high-concentration environments). If the secondary amplifier circuit uses a fixed gain, it may result in insufficient amplification of weak signals (making them undetectable) or excessive amplification of strong signals (signal saturation distortion). To address this issue, the secondary amplifier circuit uses internal hardware design to preset multiple gain levels (e.g., 1x, 10x, 100x, 1000x, etc.). Each level corresponds to a different amplification factor, which can be flexibly selected according to signal strength via a gain switching control circuit. For example, when the primary amplifier circuit output signal is weak, a high gain level (e.g., 100x) is selected to ensure the signal is sufficiently amplified; when the primary amplifier circuit output signal is strong, a low gain level (e.g., 1x) is selected to avoid signal distortion.

[0074] Figure 5 Please refer to the schematic diagram of the two-stage amplifier circuit provided in this application. Figure 5 The secondary amplifier circuit includes two cascaded operational amplifiers. The input terminal of the first amplifier is connected to the output terminal of the primary amplifier circuit through a multiplexer analog switch to switch the signal input direction according to the polarity of the ion signal. The feedback loop of the second amplifier is provided with a T-type adjustable resistor network, and different resistor combinations are selected by the control signal output by the gain switching control circuit.

[0075] It should be noted that, in order to achieve precise matching of the gain and feedback components of the two-stage amplifier circuit, and to ensure that the output signal meets the requirements of subsequent voltage-to-frequency conversion and signal processing, the selection calculation must be completed based on the intensity and dynamic characteristics of the input ion signal, through a process of signal determination, component selection, range testing, and parameter optimization. Specifically, the initial determination of the input signal intensity range is performed first. The current signal output by the ion detector is acquired in real time by the signal acquisition unit at the front-end detection point of the mass spectrometer. The upper computer data processing module records the signal amplitude and divides the intensity range. If the signal amplitude is within the nanoampere (nA, 10) range... -9 A) to Pian (pA, 10) -12 Level A) is determined to be a medium-strong signal range; if the signal amplitude is within the flight range (fA, 10... -15 Level A and below are classified as extremely weak signals. This classification can provide a basis for the selection of subsequent feedback element types, avoiding noise interference or signal distortion caused by mismatch between element type and signal strength.

[0076] Next, the selection of the feedback element type for the first-stage amplifier circuit is completed. The element type is determined based on the signal strength range and dynamic characteristics. If the input signal is in the medium-to-strong range, or exhibits low-frequency, continuously stable, near-DC characteristics (as in isotope concentration detection scenarios), the resistive feedback branch in the load module is preferred. This choice is made because the signal strength is not easily masked by the inherent thermal noise of the resistor, and the linear amplification characteristics of the resistive feedback ensure the amplification accuracy of the stable signal. If the input signal is in the extremely weak range, or is an isotope narrow-peak signal (narrow peak width, fast intensity change rate, and significant high-frequency characteristics), the capacitive feedback branch is preferred. The capacitor's lack of thermal noise prevents the fA-level signal from being submerged by noise, and its integral amplification characteristics can accurately capture the transient changes of high-frequency pulse signals, adapting to the requirements of narrow-peak signal detection.

[0077] Next, the gain selection and testing of the first-stage amplifier circuit are performed. The gain of the first-stage amplifier circuit is determined by the parameters of the feedback components (the gain is directly proportional to the resistance value in resistive feedback, and inversely proportional to the capacitance value in capacitive feedback). Testing must begin with a low gain setting and proceed step by step. Taking a medium-to-strong signal range (pA-nA level) as an example, first select a low resistance setting in the resistive feedback branch (e.g., 10). 10 Ω), and simultaneously adjust the second amplifier of the secondary amplifier circuit to the lowest gain setting; start the secondary ion peak scan, and monitor the scan results through the signal processing circuit, focusing on verifying baseline stability (baseline amplitude ≤ 1‰ of signal strength), peak intensity (initial ≥ 5mV), and signal-to-noise ratio (≥ 10:1); if the peak intensity is insufficient or the signal-to-noise ratio is not up to standard, switch to the medium resistance setting (e.g., 10Ω). 11Repeat 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 corresponding gain level.

[0078] Finally, the gain level selection and optimization of the secondary amplifier circuit were carried out. After the gain level of the primary amplifier circuit was locked, the gain level was switched to optimize the signal output by adjusting the T-type adjustable resistor network of the second amplifier in the secondary amplifier circuit. The primary feedback element and gain were kept unchanged, and the secondary gain level was switched sequentially. After each level switch, a spectral peak scan was performed. Key parameters were calculated from the scan results. For example, the spectral peak amplitude should be within 10mV~1V (adapted to the input range of the voltage-frequency conversion circuit), the baseline fluctuation value should be ≤5mV, and the signal-to-noise ratio should be ≥20:1. The level with the spectral peak amplitude in the target range, the smallest baseline fluctuation, and the highest signal-to-noise ratio was selected as the optimal secondary gain level.

[0079] Through the above steps, the feedback element type and gain level of the first-stage amplifier circuit can be accurately matched with the gain level of the second-stage amplifier circuit, ensuring that the total gain of the two-stage amplifier circuit is adapted to the characteristics of the input ion signal, and providing a high signal-to-noise ratio and high stability voltage signal for subsequent voltage-to-frequency conversion and ion count rate conversion.

[0080] The first amplifier focuses on signal polarity adaptation, while the second amplifier focuses on gain level adjustment. Together, they meet the amplification requirements of different ion signals.

[0081] Specifically, the first amplifier is the signal input terminal of the second-stage amplifier circuit. Its core feature is that its input terminal is connected to the output terminal of the first-stage amplifier circuit via a multiplexer analog switch. This multiplexer analog switch is an electronic switch that can be controlled by electrical signals, selectively connecting the input signal to different input terminals (non-inverting or inverting) of the operational amplifier, thus switching the signal input path. In ion detection scenarios, the polarity of the ion signal may differ due to the detected object (e.g., positive or negative ions) or the detector's operating mode (positive or negative voltage signal). If the signal polarity does not match the amplifier's input direction, it may lead to reverse amplification or distortion of the signal. The first amplifier, through its multiplexer analog switch connection design, 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 amplifier's non-inverting input terminal for positive amplification; when a reverse signal is detected, the switch switches to the inverting input terminal, ensuring that the signal polarity matches the amplifier 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 circuit's adaptability to complex ion environments.

[0082] The second amplifier is the core of gain adjustment in the two-stage amplifier circuit. Its feedback loop incorporates a T-type adjustable resistor network, which is precisely adjusted via a gain switching control circuit. The T-type adjustable resistor network is a feedback circuit formed by three resistors connected in a T-shape (e.g., typically including one series resistor and two parallel resistors connected to ground). By changing the combination of resistors connected to the feedback loop, the feedback quantity of the operational amplifier can be flexibly adjusted, thereby changing the amplification factor (gain). Specifically, the gain switching control circuit outputs a control signal (such as a high / low level signal) to the switching switch (usually a relay or analog switch) of the T-type network based on the output signal strength of the first-stage amplifier circuit or instructions from the host computer, selecting different resistor combinations for the feedback loop. For example, selecting a large resistor combination results in a small feedback quantity and a high amplifier gain (suitable for weak signals); selecting a small resistor combination results in a large feedback quantity and a low amplifier gain (suitable for strong signals).

[0083] Based on the above description, the first amplifier ensures correct signal polarity input through a multiplexed analog switch, guaranteeing that the input voltage to the voltage-to-frequency conversion circuit is always a positive signal. The second amplifier achieves flexible gain adjustment through a T-type adjustable resistor network, amplifying the signal to a strength suitable for subsequent signal processing circuits. The combination of these two amplifiers gives the two-stage amplifier circuit both polarity self-adaptation capability and wide-range gain adjustment functionality, supporting the high adaptability and high precision characteristics of the entire ion detection amplifier.

[0084] Specifically, the first-stage amplifier circuit is the core module of the amplifier, responsible for amplifying the main signal. It converts the input ultra-low ion current into a identifiable voltage signal using high-resistance resistors or high-precision capacitors for subsequent signal processing. The first operational amplifier in the second-stage amplifier circuit is responsible for polarity switching. Because the voltage-to-frequency conversion circuit requires a positive input voltage, and the first-stage amplifier circuit is an inverting amplifier, when the input is positive current, the output is negative voltage, and the voltage-to-frequency converter has no output. Therefore, to ensure that the VF conversion input is always positive, polarity switching is necessary. The switching is based on the polarity of the primary ions. When the primary ions are positive and the secondary ion current is negative, the output voltage of the first-stage amplifier circuit is positive. The first operational amplifier in the second-stage amplifier circuit is a voltage follower. When the primary ions are negative and the secondary ions are positive, the output voltage of the first-stage amplifier circuit is negative. The first operational amplifier in the second-stage amplifier circuit is an inverting amplifier with a gain of 1, converting the negative voltage to a positive voltage. The second operational amplifier in the second-stage amplifier circuit further ensures the strength of the VF conversion input signal. For very small currents, such as those in the fA level, a 10-gain operational amplifier is used. 12 The output of the amplifier's first-stage amplifier circuit can only reach the mV level. At this level, the voltage-to-frequency conversion will suffer from insufficient stability and excessive noise due to the small input signal. Therefore, a second amplification is required to ensure the accuracy and precision of the VF conversion.

[0085] It should be noted that the gain switching control circuit is connected to the load module and the second-stage amplifier circuit via control signal lines. Specifically, it connects to the high-isolation relays of each feedback branch in the load module via control signal lines to control the on / off state of the resistive and capacitive feedback branches; and it connects to the T-type adjustable resistor network switch of the second amplifier in the second-stage amplifier circuit via control signal lines to select the gain level of the second stage. This connection method allows the gain switching control circuit to simultaneously control the gain adjustment nodes of both the first and second-stage amplifier circuits.

[0086] Specifically, the gain of the first-stage amplifier circuit is determined by the selection of the feedback branch in the load module. The gain switching control circuit drives the high-isolation relay of the target feedback branch in the load module to operate by outputting a control signal (such as high level to turn on, low level to turn off), thereby realizing the switching of different branches. The gain of the second-stage amplifier circuit is determined by the resistance combination of the T-type adjustable resistor network in the feedback loop of the second amplifier. The gain switching control circuit selects a specific resistance combination in the network to be connected to the feedback loop by outputting a control signal, thereby realizing the switching of the second-stage gain level.

[0087] The gain switching control circuit does not independently control the two-stage amplifier circuit. Instead, it coordinates the gain of the first and second stages based on the overall characteristics of the ion signal (such as intensity, frequency, and polarity). When a weak ion signal is detected, the load module is connected to the high-gain resistor branch (high gain of the first stage), and the second-stage amplifier circuit is simultaneously controlled to select a high-gain setting (high gain of the second stage) to ensure that the signal is fully amplified. When a strong signal is detected, it switches to the low-gain resistor branch (low gain of the first stage) and the low-gain setting of the second stage to avoid signal overload.

[0088] Figure 6 For a schematic diagram of the gain switching control circuit shown in this application, please refer to... Figure 6 The gain switching control circuit mainly includes a microprocessor and a multi-channel voltage comparator. Dual-channel control signal 1 controls the multi-channel switch 1 of the secondary amplifier circuit to achieve signal polarity switching. Dual-channel control signal 2 is sent to the multi-channel switch 2 of the secondary amplifier circuit to achieve four gain adjustments. After being output from the microprocessor, each of the five control signals enters the input terminal of a dual-channel voltage comparator. The power supply voltages of each dual-channel voltage comparator are +5V and 0V, respectively, with a reference voltage set to 1.2V. Each output pin of the voltage comparator is connected to a TVS diode to limit the maximum output voltage to +5V, preventing excessive voltage pulses from damaging the front-end and back-end relays of the load module. The five dual-channel voltage comparators output five front-end control signals and five back-end control signals to control the selection of the feedback element of the load module in the primary amplifier circuit, thereby switching the amplification factor of the primary amplifier circuit.

[0089] To clarify the amplification law of the input ion current signal in the two-stage amplifier circuit, the calculation method of the voltage at the output of the two-stage amplifier circuit is explained below. The intensity of the input ion current signal is denoted as I (unit: A, including nA, pA, fA levels). When the first-stage amplifier circuit uses a resistor as feedback, assuming the resistance value is R, the output of the first-stage amplifier circuit is V = -I*R. When using a capacitor as feedback, assuming the capacitance value is C, the output is V = ∫I / Cdt. The first amplifier in the second-stage amplifier circuit undergoes polarity selection. Assuming a positive signal, it remains unchanged; assuming a negative signal -V, it is converted to a positive signal V. The second amplifier in the second-stage amplifier circuit has four gain levels: 1, 10, 100, and 1000, assuming they are G1, G2, G3, and G4 respectively. Then the output of the second-stage amplifier circuit is V2 = I*R*G (second-stage gain) or V2 = G / C*∫Idt. Please continue to refer to... Figure 6 The host computer inputs control signals to the MCU. The MCU program reads the control signals and outputs levels at the corresponding pins. Taking control signal 1 as an example, when the host computer control feedback loop 1 is selected, the corresponding control signal pin outputs a high level (5V). This is compared with the reference level of 1.2V through voltage comparator U1AU1B. If the level is higher than 1.2V, the positive terminal supply voltage VCC (5V) of U1AB is output. At this time, the front-end and back-end control signals are both high, which are input to the relay to drive it to close. Taking dual-channel control signal 2 as an example, the host computer outputs control signals to the MCU, and the corresponding pins output control levels. Dual-channel control signal 2 can achieve four combinations (HH, HL, LH, LL) based on the high and low levels, corresponding to four levels: 1, 10, 100, and 1000, respectively.

[0090] It should be noted that after the secondary amplifier circuit amplifies the ion signal to a voltage signal suitable for processing, it is directly transmitted to the input terminal of the signal processing circuit. At this time, the input signal is an analog voltage signal, the amplitude of which is proportional to the strength of the current signal output by the ion detector. However, it has not yet been converted into a digital quantity or physical parameter that can be directly analyzed. The primary task of the signal processing circuit is to receive this analog signal and provide the raw input for subsequent data processing.

[0091] Specifically, the signal processing circuit includes:

[0092] A voltage-to-frequency conversion module is used to convert the output voltage signal of the secondary amplifier circuit into a pulse frequency signal;

[0093] The pulse signal analysis module, which includes an FPGA chip, is used to count the pulse frequency signal and convert it into an ion current value or count rate based on the current gain level.

[0094] The communication interface module is used to upload the converted detection results to the host computer.

[0095] Figure 7 For a structural diagram of the voltage-to-frequency conversion module provided in this application, please refer to... Figure 7 The voltage-to-frequency conversion module mainly includes a two-stage bias adjustment unit and a VF conversion unit. The two-stage bias adjustment unit is an inverting adder circuit composed of an operational amplifier and peripheral circuits, based on the formula... The voltage V input to the voltage-to-frequency converter is obtained, where V is the output voltage of the inverting adder circuit, i.e., the input voltage of AD652; RF, R1, and R2 are the feedback resistors of U1; V2 is the output voltage of the second-stage amplifier circuit; and VB2 is the second-stage bias voltage output by the MCU through the DAC. By adjusting the value of VB2, the input voltage of the AD652 VF converter chip is adjusted to ensure zero frequency output under zero input conditions. The VF conversion unit consists of the AD652 voltage-to-frequency converter chip and its peripheral circuitry, and is controlled by the input clock signal frequency. With maximum input voltage The output frequency signal is proportional to the input voltage signal. .

[0096] Figure 8 For a structural diagram of the pulse signal analysis module provided in this application, please refer to... Figure 8 The pulse signal analysis module mainly includes an FPGA, an optical fiber communication chip, and peripheral circuits. It is responsible for counting the output frequency of the voltage-frequency conversion circuit, converting the count result and gain amplification factor to obtain the count value at the amplifier input, and uploading it to the host computer through optical fiber communication via COM20020.

[0097] Furthermore, the ion detection amplifier provided in this application may also include a digital-to-analog converter circuit. Figure 9 For the digital-to-analog converter circuit structure diagram provided in this application, please refer to... Figure 9 The digital-to-analog converter circuit receives the hexadecimal bias adjustment command transmitted from the host computer to the microprocessor, transmits it to the dual-channel DAC chip, converts it into an analog bias voltage, and inputs it to the first-stage amplifier circuit and the voltage-to-frequency converter circuit respectively to adjust the output voltage value of the first-stage amplifier circuit and the output frequency value of the voltage-to-frequency converter circuit.

[0098] The ion detection amplifier provided in this embodiment achieves several key beneficial effects through modular structural design and refined circuit optimization. The first-stage amplifier circuit employs cascaded primary and secondary operational amplifiers. The primary stage uses ultra-low input bias current devices and high-resistance feedback components to effectively suppress noise and bias errors, improving the sensitivity of weak signal detection. The secondary stage uses discrete components to build a high-voltage amplification unit. Combined with the stable design of the current mirror and load circuit, and Miller compensation to optimize the frequency response, it widens the output dynamic range, providing a high signal-to-noise ratio signal for subsequent amplification. The load module uses a parallel design of resistive and capacitive feedback branches, paired with a high-isolation relay to achieve crosstalk-free switching. The resistive branch adapts to low-frequency / DC signals of different intensities, while the capacitive branch adapts to high-frequency pulse signals. The protection resistor branch ensures switching safety, significantly improving the flexibility of first-stage gain adjustment and signal adaptability. The second-stage amplifier circuit uses two cascaded operational amplifiers. The first stage uses a multi-channel analog switch to achieve adaptive signal polarity switching, while the second stage uses a T-type adjustable resistor network to precisely adjust the gain, working in conjunction with the first-stage amplification to widen the overall dynamic range and avoid signal distortion. The gain switching control circuit coordinates the gain adjustment of the load module and the secondary amplifier circuit, achieving synergistic linkage between the two stages to ensure rapid adaptation to the optimal gain when signal strength fluctuates. The signal processing circuit eliminates bias errors through an inverting adder circuit, digitizes the analog signal via voltage-to-frequency conversion, and combines this with FPGA high-precision counting and gain parameter conversion to finally output a precise ion count rate through the communication interface, forming a complete and reliable link from signal acquisition to amplification, adjustment, processing, and output. In summary, this amplifier effectively improves the accuracy of micro-current detection, widens the dynamic range, and optimizes gain switching flexibility, providing high-performance hardware support for ion detection in complex scenarios.

[0099] Example 2

[0100] Corresponding to the aforementioned embodiment of an ion detection amplifier, this application also provides an embodiment of an ion detection method.

[0101] Figure 10 A flowchart of the ion detection method provided in this application. Please refer to... Figure 10 The method provided in this embodiment includes:

[0102] S101. Receive the current signal output by the ion detector and input the current signal to the first-stage amplifier circuit.

[0103] It should be noted that the ion detector is the component that directly interacts with the ions to be measured. When ions (such as radioactive ions, gaseous ions, etc.) enter the sensitive area of ​​the detector, they generate a weak current signal through physical processes such as ionization and charge collection. This signal is extremely weak, typically in the picoampere (pA) or even femtoampere (fA) range, but its intensity is directly related to key parameters such as the number and energy of the ions. Because the current signal output by the ion detector is too weak to be directly processed by subsequent circuits, it must be pre-amplified by a first-stage amplifier circuit. Therefore, the current signal output by the detector is precisely fed into the input of the first-stage amplifier circuit.

[0104] S102. After being amplified sequentially by the first-stage amplifier circuit and the second-stage amplifier circuit, the signal is processed by the signal processing circuit to obtain the ion detection result.

[0105] It should be noted that after receiving the weak current signal introduced in step S101, the first-stage amplifier circuit converts the current signal into a voltage signal and completes the initial amplification through a cascaded primary operational amplifier (with ultra-low input bias current characteristics) and a secondary operational amplifier (with high withstand voltage and wide dynamic range design). The amplification gain at this point is determined by the selected feedback branch in the load module (e.g., a high-resistance resistor branch is suitable for weak signals, and a capacitor branch is suitable for high-frequency pulse signals), ensuring that the signal strength is converted from pA / fA level current to mV level voltage, providing a foundation for subsequent processing.

[0106] Specifically, the first-stage amplifier circuit, through the coordinated operation of cascaded primary and secondary operational amplifiers, sequentially performs current-to-voltage conversion, inverting amplification, and signal enhancement. Specifically, the primary operational amplifier directly receives the weak pA / fA level current signal introduced in step S101, achieving core conversion and preliminary amplification based on an inverting amplification topology. Its inverting input is connected to the current output of the ion detector via a first resistor, and a closed loop is formed between the output and the inverting input through the feedback branch of the load module. Based on the virtual short and virtual open characteristics of the operational amplifier, the entire input current signal flows through the feedback branch, and is converted to voltage using the current-to-voltage conversion formula V... out1 =-I in ×R f (I) in R is the output current of the ion detector. f (For the impedance of the feedback branch element) converts the current signal into a voltage signal.

[0107] The secondary operational amplifier receives the output signal from the primary operational amplifier and employs a high-voltage design to further amplify the signal and enhance its driving capability. Its differential input stage receives the mV-level voltage signal from the primary output, stabilizes the operating point with a constant tail current provided by a current mirror, increases the signal amplitude through intermediate amplification stages, and finally outputs the signal through a push-pull output stage. The high voltage withstand characteristic of the secondary operational amplifier widens the output swing, avoids distortion during weak signal amplification, and enhances the output driving capability, ensuring that the signal can be effectively transmitted to the secondary amplifier circuit.

[0108] At this point, the overall gain of the first-stage amplifier circuit is determined by the selected feedback branch in the load module: for weak DC / low-frequency signals, a high-resistance feedback branch is selected, and the gain is increased by increasing R. f Increase the gain (e.g., 10) 12 (Ω resistor corresponds to high gain); for high-frequency pulse signals, a pF-level capacitor feedback branch is selected, utilizing the low impedance characteristic of the capacitor for high-frequency signals to achieve targeted amplification. Finally, the first-stage amplifier circuit converts and amplifies the pA / fA-level current signal into a reverse voltage signal at the mV level or higher, providing a stable input foundation for the subsequent second-stage amplifier circuit. The voltage signal amplified by the first stage is input to the second-stage amplifier circuit, where secondary amplification is completed through the synergistic action of two cascaded operational amplifiers. The first amplifier adapts the signal polarity through a multiplexed analog switch to avoid polarity input errors in the voltage-frequency circuit caused by polarity differences; the second amplifier selects the target gain level (e.g., 10x, 100x) through a T-type adjustable resistor network, further amplifying the signal to the V-level level to ensure the signal strength meets the input requirements of subsequent signal processing circuits, while avoiding strong signal saturation.

[0109] Based on the above description, the selection of the feedback element type and specific value for the first-stage amplifier circuit includes: determining the signal type and thus the feedback element type; selecting the specific feedback element value based on the signal strength or frequency range; and performing branch switching and adaptation verification. Specifically, the signal type is first determined. The gain switching control circuit identifies the frequency characteristics of the ion signal through signal preprocessing or preset parameters from the host computer. If the signal is a continuous and stable DC signal or a low-frequency signal (frequency ≤ 1kHz), it is determined to be a signal type suitable for resistive feedback; if the signal is a rapidly changing pulse signal or a high-frequency signal (frequency > 1kHz), it is determined to be a signal type suitable for capacitive feedback. Next, the feedback element type is selected based on the signal type. For DC or low-frequency signals, a resistive feedback branch is selected because resistive feedback provides stable amplification characteristics for low-frequency signals, has no frequency-selective attenuation, and can achieve linear amplification. For high-frequency pulse signals, a capacitive feedback branch is selected, utilizing the low impedance characteristics of capacitors for high-frequency signals (capacitive reactance decreases as frequency increases) to accurately capture transient signals and suppress low-frequency noise. Finally, specific parameters are selected based on the signal strength or frequency range. The resistive feedback branch contains high-precision resistors with varying resistance values, ranging from 10 to 1000 ohms. 10 Ω, 10 11 Ω, 10 12 Ω): For extremely weak signals (fly-safety level), select a high-resistance branch (e.g., 10Ω). 12 To increase gain, for weaker signals (picoamperes), choose a medium-resistance branch (e.g., 10Ω). 11 For medium-strength signals (nanoamperes), select a low-resistance branch (e.g., 10Ω). 10 (Ω). The capacitive feedback branch includes pF-level vacuum capacitors (such as 10pF, 50pF, 100pF). For example, high-frequency signals >10kHz are adapted to a 10pF low-capacitance branch, and mid-to-high frequency signals from 1kHz to 10kHz are adapted to a 100pF high-capacitance branch, balancing feedback strength and signal integrity.

[0110] Finally, branch switching and adaptation verification are performed. The gain switching control circuit drives the high-isolation relay of the target branch to conduct, switching the capacitor branch and turning on the bypass protection resistor branch to limit the charging and discharging current. After switching, the bypass protection resistor branch is turned off, and the input signal is amplified. The signal processing circuit monitors the output signal amplitude. If it is within the preset range of 10mV to 1V, adaptation is confirmed; if it does not meet the standard, the above steps are repeated to reselect, ensuring that the output signal of the first-stage amplifier circuit meets the requirements of subsequent processing.

[0111] Specifically, the process of obtaining ion detection results includes:

[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-to-frequency conversion module of the signal processing circuit has converted the voltage signal output by the secondary amplifier circuit into a pulse frequency signal (the higher the voltage, the higher the frequency), and the frequency value directly reflects the strength of the current ion signal (the higher the frequency, the stronger the corresponding ion signal).

[0114] The signal processing circuit uses a pulse signal analysis module to sample and count the pulse frequency in real time, continuously tracking the dynamic changes in signal strength.

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

[0116] It should be noted that the preset threshold range is a frequency range set according to the requirements of the ion detection scenario (for example, a low threshold corresponds to a weak signal that requires increased gain, while a high threshold corresponds to a strong signal that requires decreased gain). If the frequency is lower than the low threshold, it means that the current signal is still weak after amplification, and may not be able to be identified in subsequent processing due to insufficient gain; if the frequency is higher than the high threshold, it means that the signal is too strong and may have approached the saturation limit of the amplification circuit, and further amplification may easily lead to signal distortion.

[0117] Specifically, when the signal processing circuit detects that the frequency exceeds the above threshold, it will immediately generate a switching command (such as an electrical signal with a specific binary code) and send it to the gain switching control circuit through the control line. The command contains information about the target gain level (such as increasing the first level gain + increasing the second level gain or decreasing the first level gain + decreasing the second level gain), triggering subsequent hardware adjustment actions.

[0118] (3) The gain switching control circuit responds to the switching command, disconnects the current feedback branch, and switches to the feedback branch and the second-level gain level that are suitable for the range. After completion, it continues signal processing.

[0119] Specifically, the high-isolation relay of the current feedback branch in the drive load module is disconnected, while a new branch adapted to the range is simultaneously activated (e.g., switching to a higher resistance feedback branch when the signal is too weak, and switching to a lower resistance or capacitor branch when the signal is too strong), completing the first-stage gain adjustment. Simultaneously, the switching switch of the T-type adjustable resistor network in the second-stage amplifier circuit is controlled to select the second-stage gain level that matches the first-stage gain (e.g., high gain in the first stage corresponds to high gain in the second stage, ensuring sufficient signal amplification), completing the second-stage gain adjustment.

[0120] After the switching is completed, the gain switching control circuit feeds back the adjustment completion signal to the signal processing circuit. The signal processing circuit then 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 state of the sensing signal in real time, triggering adjustment decisions through abnormal responses, and achieving gain adaptation through hardware switching, it is ultimately ensured that no matter how the strength of the ion signal changes, a clear and distortion-free signal can be obtained by dynamically adjusting the amplification gain, thus providing a guarantee for the signal processing circuit to output accurate ion detection results.

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

[0123] (1) Receive the voltage signal output by the second-stage amplifier circuit and superimpose the bias compensation voltage through the inverting adder circuit.

[0124] It should be noted that although the voltage signal output by the secondary amplifier circuit meets the strength requirements, a fixed bias error may be introduced due to the characteristics of the circuit hardware (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 slight DC offset.

[0125] An inverting adder circuit is a circuit that performs algebraic operations on the input signal and the compensation signal. Its function is to cancel out a fixed bias in the original signal by superimposing a preset bias compensation voltage (equal in magnitude but opposite in polarity to the error voltage). For example, if the inherent offset of the circuit causes a +5mV error to be added to the signal, the inverting adder circuit will add a -5mV compensation voltage, bringing the baseline of the compensated signal back to near zero. This eliminates the inherent error of the system, ensuring that subsequent conversions and counting only reflect the true ion signal, rather than the offset of the circuit itself.

[0126] (2) The compensated voltage signal is converted into a pulse frequency signal through the voltage-frequency conversion module.

[0127] It should be noted that the bias-compensated voltage signal is still a continuously changing analog quantity and cannot be directly counted and analyzed by digital circuits. The voltage-to-frequency conversion module uses a precise oscillation circuit or dedicated chip to linearly map the amplitude of the voltage signal to the frequency of a pulse signal: the higher the voltage, the higher the frequency of the output pulse. In this way, even if there is small amount of 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) Count the pulse frequency signal within a preset counting time to obtain the cumulative number of pulses.

[0129] The pulse signal analysis module (FPGA chip) presets the counting duration (such as 1 second or 100 milliseconds) according to the detection requirements. Within this duration, it performs high-precision counting of the pulse signal output by the voltage-frequency conversion module to obtain the total number of cumulative pulses (for example, counting 5000 pulses in 1 second, corresponding to a frequency of 5000Hz).

[0130] It should be noted that the choice of counting duration must balance detection accuracy and response speed. A longer counting duration (e.g., 1 second) can reduce statistical error and is suitable for detecting stable signals; a shorter counting duration (e.g., 10 milliseconds) can improve response speed and is suitable for rapidly changing pulse signals. This step converts the dynamic frequency signal into a quantifiable digital quantity through statistical analysis over time, providing the foundational data for subsequent parameter conversion.

[0131] (4) Based on the cumulative number of pulses, the counting duration and the current first-level and second-level gain levels, the current value output by the ion detector and the corresponding ion count rate are calculated, and the count rate is output as the final detection result.

[0132] It should be noted that, firstly, the output voltage of the secondary amplifier circuit is calculated from the pulse frequency. Based on the preset linear relationship of the voltage-frequency conversion module, the actual frequency of the pulse signal (the cumulative number of pulses divided by the counting duration) is multiplied by the conversion coefficient to obtain the output voltage value of the secondary amplifier circuit. For example, if the cumulative number of pulses in 1 second is 5000, the corresponding frequency is 5000Hz (i.e., 5kHz). According to the relationship that 1kHz corresponds to 1mV, the secondary output voltage can be calculated to be 5mV.

[0133] Secondly, the output voltage of the first-stage amplifier circuit is calculated by reverse engineering the gain level of the second-stage amplifier circuit. The gain level of the second-stage amplifier circuit (e.g., 100x) is determined by the currently selected T-type resistor network combination. The output voltage of the second stage divided by this gain value is the output voltage of the first-stage amplifier circuit. In the example above, 5mV divided by a gain of 100x yields a first-stage output voltage of 0.05mV (i.e., 5 × 10⁻⁶ mV). -5 V).

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

[0135] Finally, the count rate is calculated based on the ion charge. The physical essence of electric current is the amount of charge passing through per unit time; the charge carried by a single ion is the elementary charge (approximately 1.602 × 10⁻⁶). -19 C). Dividing the original current value by the elementary charge yields the number of ions per unit time (count rate). For example, 5 × 10⁻⁶. -17 The current A corresponds to a charge passing through it of 5 × 10⁻⁶ per second. - 17 C, divided by 1.602 × 10 -19 The C / ion count was calculated to be approximately 312 cps. This result was uploaded to the host computer via the communication interface module, completing the output of the detection results.

[0136] In this step, bias compensation is used to eliminate system errors, V / F conversion is used to digitize the signal, and counting and conversion are used to convert digital quantities into physical parameters. The final output ion count rate can be directly used in practical scenarios such as ion concentration analysis and environmental monitoring, thus realizing a closed loop from signal acquisition to result application in ion detection methods.

[0137] The method provided in this embodiment achieves end-to-end optimization of ion signals from acquisition, amplification, adjustment to quantization output through structured process design and dynamic adjustment logic, effectively improving the dynamic range, accuracy and reliability of detection, and perfectly adapting to the precise detection needs of wide-range ion signals in complex scenarios.

[0138] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An ion detection amplifier, characterized in that, The ion detection amplifier includes: A first-stage amplifier circuit is used to receive the current signal output by the ion detector. The first-stage amplifier circuit includes a cascaded primary operational amplifier and a secondary operational amplifier. A load module is connected in parallel with the first-stage amplifier circuit. The load module includes multiple feedback branches, each with a different type of feedback element, and different feedback branches correspond to different first-stage gain levels. A secondary amplifier circuit is connected to the output terminal of the primary amplifier circuit and is used to amplify the output signal of the primary amplifier circuit. The secondary amplifier circuit has multiple secondary gain levels. A gain switching control circuit is connected to the load module and the secondary amplifier circuit respectively, and is used to control the amplification gain of the primary amplifier circuit and the secondary amplifier circuit; The signal processing circuit is used to receive the output signal of the secondary amplifier circuit and realize the data processing and detection result output of the output signal.

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

3. The ion detection amplifier according to claim 1, characterized in that, The secondary operational amplifier includes: The differential input stage consists of two first NPN transistors. The bases of the two first NPN transistors are respectively connected to the output terminal and the reference potential terminal of the primary operational amplifier. Their emitters are connected to the same node and then connected to the common collector terminal of a current mirror consisting of two second PNP transistors. The emitter of the current mirror is connected to the positive power supply terminal. The intermediate amplification stage includes a third NPN transistor and a compensation capacitor. The base of the third NPN transistor is connected to the output of the differential input stage, the collector is connected to the positive power supply, and the emitter is grounded through a second resistor. The input of the compensation capacitor is connected to the output of the differential input stage, and the output is connected to the input of the push-pull output stage. The push-pull output stage includes two diodes, a fourth transistor, and two fifth transistors. The fourth transistor is connected to the intermediate amplification stage. The collector of the fourth transistor is connected to the diode, which transmits the intermediate stage signal to the output terminal to drive the subsequent circuit. The collectors and emitters of the two fifth transistors are connected to the positive and negative power supply terminals, respectively. The diodes are connected in series and then connected across the base-emitter path of the fifth transistor. The negative power supply terminal of the secondary operational amplifier is connected to the negative power supply node of the entire circuit.

4. The ion detection amplifier according to claim 1, characterized in that, The load module includes: Multiple resistance feedback branches, each of which includes resistors with different resistance values ​​and high-isolation relays; Multiple capacitive feedback branches are connected in parallel with the resistive feedback branch. Each capacitive feedback branch includes a pF-level vacuum capacitor, with a high-isolation relay connected in series across the capacitor. The protection resistor branch, connected in parallel with the resistor feedback and capacitor feedback branches, includes a protection resistor.

5. The ion detection amplifier according to claim 1, characterized in that, The secondary amplifier circuit includes two cascaded operational amplifiers. The input terminal of the first amplifier is connected to the output terminal of the primary amplifier circuit through a multiplexer analog switch to switch the signal input direction according to the polarity of the ion signal. The feedback loop of the second amplifier is provided with a T-type adjustable resistor network, and different resistor combinations are selected by the control signal output by the gain switching control circuit.

6. The ion detection amplifier according to claim 1, characterized in that, The signal processing circuit includes: A voltage-to-frequency conversion module is used to convert the output voltage signal of the secondary amplifier circuit into a pulse frequency signal; The pulse signal analysis module, which includes an FPGA chip, is used to count the pulse frequency signal and convert it into an ion current value or count rate based on the current gain level. The communication interface module is used to upload the converted detection results to the host computer.

7. An ion detection method, characterized in that, The method is applied to the ion detection amplifier as described in any one of claims 1-6, and the method comprises: Receive the current signal output by the ion detector and input the current signal to the first-stage amplifier circuit; After being amplified sequentially by the first-stage amplifier circuit and the second-stage amplifier circuit, the signal is processed by the signal processing circuit to obtain the ion detection result.

8. The method according to claim 7, characterized in that, Before receiving the current signal output from the ion detector and inputting the current signal to the first-stage amplifier circuit, the process includes: The host computer sends a gear selection command to the gain switching control circuit based on the type of 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 first-stage amplifier circuit, and selects the target gain level of the second-stage amplifier circuit.

9. The method according to claim 7, characterized in that, The process of obtaining ion detection results includes: 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, a switching command is sent to the gain switching control circuit; The gain switching control circuit responds to the switching command by disconnecting the current feedback branch and switching to the feedback branch and secondary gain level that are compatible with the range. After completion, it continues signal processing.

10. The method according to claim 7, characterized in that, The method for obtaining ion detection results also includes: The voltage signal output from the second-stage amplifier circuit is received and superimposed with a bias compensation voltage via an inverting adder circuit; The compensated voltage signal is converted into a pulse frequency signal through a voltage-to-frequency conversion module. The pulse frequency signal is counted within a preset counting time to obtain the cumulative number of pulses; Based on the cumulative pulse count, counting duration, and the current first and second level gain settings, the current value output by the ion detector and the corresponding ion count rate are calculated, and the count rate is output as the final detection result.

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