FA-level tiny signal amplifier for four-level mass spectrometer
By designing a femtoampere-level micro-signal amplifier for a quadrupole mass spectrometer, the problem of difficulty in amplifying and collecting positive ion and electron signals in a quadrupole mass spectrometer is solved, achieving high-precision signal measurement and anti-interference capabilities, which is suitable for aerospace, semiconductor manufacturing and other fields.
Patent Information
- Application Number
- CN202510825939.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-19
- Publication Date
- 2025-10-10
AI Technical Summary
The weak ion flow signals in a quadrupole mass spectrometer are difficult to measure simultaneously, especially the amplification and collection of positive ion and electron signals are difficult and susceptible to interference.
A femtoampere-class small signal amplifier for a four-stage mass spectrometer was designed. It includes a positive ion signal processing system, an electronic signal processing system, a signal acquisition module, and an isolation module. Through components such as a multiplexer, a follower, and a single-ended to differential chip, it achieves amplification, conversion, and acquisition of positive ion and electronic signals. A high-precision analog-to-digital converter and digital isolator are used to improve anti-interference capability.
It achieves effective amplification and acquisition of signals in the range of 1×10-14A to 1×10-8A for positive ions and 1×10-12A to 1×10-6A for electrons, spanning a total of 8 ranges, with excellent amplification gain and acquisition accuracy, and strong anti-interference ability.
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Figure CN120768274A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of vacuum measuring instruments, and in particular to a femtoampere-class micro-signal amplifier for a four-stage mass spectrometer. Background Art
[0002] As a typical product among mass spectrometers, the quadrupole mass spectrometer is a dynamic mass spectrometer that uses a quadrupole electric field for mass separation. Due to its advantages such as small size, light weight, high sensitivity and fast scanning speed, it is widely used in vacuum residual gas analysis in aerospace, semiconductor manufacturing, large scientific projects, etc. It is an indispensable high-end measuring instrument for aerospace environment detection, vacuum and surface physics research, residual gas analysis of special vacuum devices, gas monitoring of thin film manufacturing processes and space technology research.
[0003] The ion current signal passing through the quadrupole mass filter is usually collected after being amplified by a Faraday cup or an electron multiplier. However, the ion current is a weak current signal with an extremely low amplitude, usually in the range of nA (10 -9 A), pA(10 -12 A) or even fA(10 -15 A) magnitude, which is very susceptible to interference. Furthermore, the Faraday cage collects positively charged ions, while the electron multiplier produces electrons. Therefore, simultaneous measurement of tiny positive ions and electrons is quite difficult. Summary of the Invention
[0004] The present application provides an fA-class micro-signal amplifier for a quadrupole mass spectrometer, which can amplify, convert and collect the positive ion signals collected by the Faraday cup of the quadrupole mass spectrometer and the electronic signals collected by the electron multiplier.
[0005] In order to achieve the above-mentioned purpose, the present application provides an fA-class small signal amplifier for a four-stage mass spectrometer, including a positive ion signal processing system, an electronic signal processing system, a signal acquisition module and an isolation module, wherein: the positive ion signal processing system includes a positive ion IV conversion module and a positive ion signal conditioning module, and the positive ion IV conversion module is connected to the positive ion signal conditioning module; the electronic signal processing system includes an electronic IV conversion module and an electronic signal conditioning module, and the electronic IV conversion module is connected to the electronic signal conditioning module; the positive ion signal conditioning module and the electronic signal conditioning module are both connected to the signal acquisition module; the signal acquisition module is connected to the isolation module.
[0006] Furthermore, the positive ion IV conversion module includes a first operational amplifier, a first multiplexer and a first conversion resistor, wherein: the first operational amplifier is connected in parallel with the first multiplexer; the first multiplexer is connected in series with the first conversion resistor; the first conversion resistor is connected in parallel with the first operational amplifier to form a closed-loop structure.
[0007] Furthermore, the positive ion signal conditioning module includes a first follower and a first single-ended to differential chip, and the first follower is connected to the first single-ended to differential chip.
[0008] Furthermore, the electronic IV conversion module includes a second operational amplifier, a second multiplexer and a second conversion resistor, wherein: the second operational amplifier is connected in parallel with the second multiplexer; the second multiplexer is connected in series with the second conversion resistor; and the second conversion resistor is connected in parallel with the second operational amplifier to form a closed-loop structure.
[0009] Furthermore, the electronic signal conditioning module includes a second follower and a second single-ended to differential chip, and the second follower is connected to the second single-ended to differential chip.
[0010] Furthermore, the signal acquisition module is a 24-bit, 250KSPS analog-to-digital converter of AD7175.
[0011] Furthermore, the isolation module is an ADUM3151 SPI digital isolator.
[0012] Furthermore, the first operational amplifier and the second operational amplifier are both ADA4530-1 femtoampere input bias current operational amplifiers; and the first multiplexer and the second multiplexer are both ADG1608 multi-channel analog switches.
[0013] Furthermore, the first follower and the second follower are both ADA4522-2 dual-channel, zero-drift, low-noise rail-to-rail operational amplifiers; the first single-ended to differential chip and the second single-ended to differential chip are both TLC6362 precision, low-noise, low-power, rail-to-rail, input / output differential operational amplifiers.
[0014] The present application provides a fA-class small signal amplifier for a four-stage mass spectrometer, which has the following beneficial effects:
[0015] The present invention does not need to collect two sets of signals separately through two sets of small signal amplifiers, but can directly and effectively amplify and collect the positive ion signal at the Faraday cup end of the quadrupole mass spectrometer and the electronic signal at the electron multiplier end, achieving a positive ion 1×10 -14 A~1×10 -8 A. Electronics 1×10 -12 A~1×10 -6 The measurement of A range spans 8 ranges with excellent amplification gain and acquisition accuracy. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The drawings that constitute part of this application are used to provide a further understanding of this application and make other features, objects and advantages of this application more apparent. The illustrative embodiment drawings of this application and their descriptions are used to explain this application and do not constitute an improper limitation of this application. In the drawings:
[0017] Figure 1 Schematic diagram of a fA-class small signal amplifier for a four-stage mass spectrometer provided according to an embodiment of the present application;
[0018] Figure 2 Schematic diagram of a positive ion IV conversion module provided according to an embodiment of the present application;
[0019] Figure 3 is a schematic diagram of a positive ion signal conditioning module provided according to an embodiment of the present application;
[0020] Figure 4 is a schematic diagram of an electronic IV conversion module provided according to an embodiment of the present application;
[0021] Figure 5 is a schematic diagram of an electronic signal conditioning module provided according to an embodiment of the present application;
[0022] In the figure: 1-positive ion IV conversion module, 11-first operational amplifier, 12-first multiplexer, 13-first conversion resistor, 2-positive ion signal conditioning module, 21-first follower, 22-first single-ended to differential chip, 3-electronic IV conversion module, 31-second operational amplifier, 32-second multiplexer, 23-second conversion resistor, 4-electronic signal conditioning module, 41-second follower, 42-second single-ended to differential chip, 5-signal acquisition module, 6-isolation module. DETAILED DESCRIPTION
[0023] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.
[0024] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.
[0025] In this application, terms such as "upper," "lower," "left," "right," "front," "back," "top," "bottom," "inner," "outer," "center," "vertical," "horizontal," "transverse," and "longitudinal" indicate positions or locations based on the positions or locations shown in the accompanying drawings. These terms are primarily intended to better describe this application and its embodiments and are not intended to limit the devices, elements, or components indicated to having a specific orientation, or to being constructed or operated in a specific orientation.
[0026] Furthermore, some of the above terms may be used to express other meanings besides indicating a position or location. For example, the term "on" may also be used to indicate a dependency or connection in certain circumstances. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.
[0027] Additionally, the term "plurality" shall mean two or more.
[0028] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.
[0029] like Figure 1 As shown, the present application provides an fA-class micro-signal amplifier for a four-stage mass spectrometer, including a positive ion signal processing system, an electronic signal processing system, a signal acquisition module 5 and an isolation module 6, wherein: the positive ion signal processing system includes a positive ion IV conversion module 1 and a positive ion signal conditioning module 2, and the positive ion IV conversion module 1 is connected to the positive ion signal conditioning module 2; the electronic signal processing system includes an electronic IV conversion module 3 and an electronic signal conditioning module 4, and the electronic IV conversion module 3 is connected to the electronic signal conditioning module 4; the positive ion signal conditioning module 2 and the electronic signal conditioning module 4 are both connected to the signal acquisition module 5; the signal acquisition module 5 is connected to the isolation module 6.
[0030] Specifically, a quadrupole mass spectrometer is a dynamic mass spectrometer that uses a quadrupole electric field for mass separation. Usually, after mass separation is performed in the quadrupole electric field, the tiny electrical signal generated is detected by a Faraday cup or an electron multiplier. The signal detected by the Faraday cup is a positively charged ion signal, while the signal detected by the electron multiplier is a negatively charged electron signal. The minimum signal intensity is only on the order of fA, so the signal is extremely susceptible to noise interference. The fA-level tiny signal amplifier for a quadrupole mass spectrometer provided in the embodiment of the present application can realize the collection of positively charged ion signals and negatively charged electron signals through the various modules set up, and has excellent anti-interference ability.
[0031] More specifically, the input signal at the Faraday tube end is a positive ion signal, which is amplified by the positive ion IV conversion module 1 and transmitted to the positive ion signal conditioning module 2, and then output to the signal acquisition module 5 after follower buffering and signal conversion of the single-ended to differential chip. The signal acquisition module 5 converts the differential analog signal into a digital signal, which is finally collected; the input signal at the electron multiplier tube end is an electronic signal, which is amplified by the electronic IV conversion module 3 and transmitted to the electronic signal conditioning module 4, and then output to the signal acquisition module 5 after follower buffering and signal conversion of the single-ended to differential chip. The signal acquisition module 5 performs single-ended to differential conversion on the secondary amplified signal, and converts the analog signal into a digital signal, which is finally collected; finally, the signal acquisition module 5 is connected to the isolation module 6 to effectively prevent interference with the signal and improve the collection accuracy.
[0032] Further, such as Figure 2 As shown, the positive ion IV conversion module 1 includes a first operational amplifier 11, a first multiplexer 12, and a first conversion resistor 13. The first operational amplifier 11 is connected in parallel with the first multiplexer 12; the first multiplexer 12 is connected in series with the first conversion resistor 13; and the first conversion resistor 13 is connected in parallel with the first operational amplifier 11, forming a closed-loop structure. The positive ion IV conversion module 1 performs primary amplification on the positive ions at the Faraday cage end and transmits the primary amplified signal to the positive ion signal conditioning module 2.
[0033] Further, such as Figure 3 As shown, the positive ion signal conditioning module 2 includes a first follower 21 and a first single-ended to differential conversion chip 22, with the first follower 21 connected to the first single-ended to differential conversion chip 22. The follower has high input impedance and low output impedance, which can isolate and buffer the signal. The first follower 21 is connected to the first single-ended to differential conversion chip 22 to convert the positive ion single-ended signal into a differential signal. This ensures that the subsequent circuits can be laid out in the form of high-speed differential routing, thereby improving the signal's anti-interference ability.
[0034] Further, such as Figure 4As shown, the electronic IV conversion module 3 includes a second operational amplifier 31, a second multiplexer 32, and a second conversion resistor 23, wherein: the second operational amplifier 31 is connected in parallel with the second multiplexer 32; the second multiplexer 32 is connected in series with the second conversion resistor 23; and the second conversion resistor 23 is connected in parallel with the second operational amplifier 31, forming a closed loop structure. Through the electronic IV conversion module 3, the electrons at the electron multiplier end can be primary amplified and the primary amplified signal can be transmitted to the electronic signal conditioning module 4
[0035] Further, such as Figure 5 As shown, the electronic signal conditioning module 4 includes a second follower 41 and a second single-ended to differential conversion chip 42, and the second follower 41 is connected to the second single-ended to differential conversion chip 42. The second follower 41 is connected to the second single-ended to differential conversion chip 42 to convert the electronic single-ended signal into a differential signal. This ensures that the subsequent circuits can be laid out in the form of high-speed differential routing, thereby improving the signal's anti-interference ability.
[0036] Furthermore, the signal acquisition module 5 is a 24-bit, 250KSPS AD7175 analog-to-digital converter. The preferred model of the signal acquisition module 5 is a 24-bit, 250KSPS AD7175 analog-to-digital converter, which has a 20us settling time, can effectively suppress electromagnetic interference, and also has advantages such as accurate timing positioning.
[0037] Furthermore, the isolation module 6 is an ADUM3151 SPI digital isolator. The isolation module 6 is preferably an ADUM3151 SPI digital isolator, which is composed of a 7-channel dedicated 3.75kVrms digital isolator, which can effectively protect the digital signal of the signal acquisition module 5 from interference.
[0038] Furthermore, the first operational amplifier 11 and the second operational amplifier 31 are both ADA4530-1 fA-level input bias current operational amplifiers; the first multiplexer 12 and the second multiplexer 32 are both ADG1608 multi-way analog switches.
[0039] Specifically, in order to ensure the measurement accuracy, the first operational amplifier 11 uses the fA (10 - 15 A) Input bias current operational amplifier, according to the "virtual short" and "virtual open" characteristics of the ideal model of the operational amplifier, the output voltage can be expressed as:
[0040] V out =I f ′R=I s 'A f =-I s ′R (1)
[0041] Among them, V out is the output voltage, V; I f is the feedback current, A; R is the resistance of the first conversion resistor 13, Ω; I S is the input current, A; A f As can be seen from the above formula, the amplification factor of the IV conversion method is determined by the resistance value of the feedback resistor.
[0042] More specifically, since the signal range of positive ions is 1×10 -14 A~1×10 -8 A. The signal range is too large, so using only a fixed resistance first conversion resistor 13 cannot meet the range of all signal tests. The voltage converted by IV will exceed the output voltage range of the device. At the same time, the output voltage after IV conversion cannot be too small. According to calculations, when the first conversion resistor 13 is selected as a 100GΩ resistor, according to the minimum current 1×10 -14 A, substituting into formula (1), the voltage after IV conversion is 1mV. When the first conversion resistor 13 is selected as 100MΩ, according to the current 1×10 -8 Substituting A into formula (1) yields an output voltage of 1V. It is known that the maximum output of the first operational amplifier 11 at a resistance of 100GΩ is 2V. According to I = V / R = 2V / 100GΩ = 20pA, the minimum voltage at a resistance of 100MΩ is 0.1mV. According to I = V / R = 0.1mV / 100MΩ = 10pA. Therefore, when a positive ion signal within the range of 10pA-20pA is collected, the first multiplexer 12 is required to switch the first conversion resistor 13. The first multiplexer 12 uses a multi-way analog switch of model ADG1608 to adjust the size of the first conversion resistor 13 according to the size of the positive ions.
[0043] Similarly, since the signal range of electrons is 1×10 -12 A~1×10 -6 A. The signal range is too large, so using only a fixed resistance second conversion resistor 23 cannot meet the range of all signal tests. The voltage converted by IV will exceed the output voltage range of the device. At the same time, the output voltage after IV conversion cannot be too small. According to calculations, when the second conversion resistor 23 is selected as a 1GΩ resistor, according to the minimum current 1×10 -12 A, substituting into formula (1), the voltage after IV conversion is 1mV. When the second conversion resistor 23 is selected as 1MΩ, according to the current 1×10 -6A, substitute into formula (1) to calculate the output voltage is 1V. It is known that the maximum output of the second operational amplifier 31 is 2V at 1GΩ resistance, according to I=V / R=2V / 1GΩ=2nA, the minimum voltage is 0.1mV at 1MΩ resistance, according to I=V / R=0.1mV / 1MΩ=1nA. Therefore, when the electronic signal within 1nA-2nA is collected, the second switching resistor 23 needs to be switched by the second multiplexer 32, and the second multiplexer 32 also selects the type ADG1608 analog switch.
[0044] Further, the first follower 21 and the second follower 41 are both double-channel, zero-drift, low-noise rail-to-rail operational amplifiers of ADA4522-2; the first single-ended to differential chip 22 and the second single-ended to differential chip 42 are both precision, low-noise, low-power, rail-to-rail, input / output differential operational amplifiers of TLC6362.
[0045] Specifically, the first follower 21 is a double-channel, zero-drift, low-noise rail-to-rail operational amplifier of ADA4522-2, which uses the buffering and isolation characteristics of the follower to prevent the influence of the impedance of the front-end small signal collection and the back-end amplification circuit; considering the first follower 21, since the output of the follower is directly connected to the inverting input of the follower, according to the "virtual short" and "virtual open" characteristics, we have:
[0046] V in =V out (2)
[0047] According to formula (2), the first follower 21 will not amplify the input signal, and the voltage gain is 1. However, the first follower 21 has the function of impedance transformation, which specifically affects the first follower 21 to have high input impedance and low output impedance. When the input impedance is very large, according to Ohm's law, when the resistance increases, the current drawn from the power supply decreases, so if the power supply has a high impedance load, the output power will not be affected. The first single-ended to differential chip 22 is a precision, low-noise, low-power, rail-to-rail, input / output differential operational amplifier of TLC6362, which can convert single-ended input signals into differential output signals to improve measurement accuracy. By processing the signal through the single-ended to differential chip, the interference of the single-ended signal is avoided.
[0048] Similarly, the second follower 41 uses a dual-channel, zero-drift, low-noise rail-to-rail operational amplifier, model ADA4522-2. The follower's buffering and isolation characteristics are used to prevent the influence of the impedance of the front-end small signal acquisition and back-end amplification circuits. Considering the second follower 41, since the follower output is directly connected to the follower's inverting input, according to the "virtual short" and "virtual open" characteristics, the relationship between the input and output is also shown in formula (2). The second single-ended to differential chip 42 also uses a precision, low-noise, low-power, rail-to-rail, input / output differential operational amplifier, model TLC6362.
[0049] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.
Claims
1. A fA-level small signal amplifier for a four-stage mass spectrometer, characterized in that: It includes a positive ion signal processing system, an electronic signal processing system, a signal acquisition module and an isolation module, among which: The positive ion signal processing system includes a positive ion IV conversion module and a positive ion signal conditioning module, wherein the positive ion IV conversion module is connected to the positive ion signal conditioning module; The electronic signal processing system includes an electronic IV conversion module and an electronic signal conditioning module, wherein the electronic IV conversion module is connected to the electronic signal conditioning module; The positive ion signal conditioning module and the electronic signal conditioning module are both connected to the signal acquisition module; The signal acquisition module is connected to the isolation module.
2. The fA-level small signal amplifier for a quadruple mass spectrometer according to claim 1, characterized in that: The positive ion IV conversion module includes a first operational amplifier, a first multiplexer, and a first conversion resistor, wherein: The first operational amplifier is connected in parallel with the first multiplexer; The first multiplexer is connected in series with the first conversion resistor; The first conversion resistor is connected in parallel with the first operational amplifier to form a closed-loop structure.
3. The fA-level small signal amplifier for a quadruple mass spectrometer according to claim 2, characterized in that: The positive ion signal conditioning module includes a first follower and a first single-ended to differential chip, and the first follower is connected to the first single-ended to differential chip.
4. The fA-level small signal amplifier for a quadruple mass spectrometer according to claim 3, characterized in that: The electronic IV conversion module includes a second operational amplifier, a second multiplexer, and a second conversion resistor, wherein: The second operational amplifier is connected in parallel with the second multiplexer; The second multiplexer is connected in series with the second conversion resistor; The second conversion resistor is connected in parallel with the second operational amplifier to form a closed-loop structure.
5. The fA-level small signal amplifier for a quadruple mass spectrometer according to claim 4, characterized in that: The electronic signal conditioning module includes a second follower and a second single-ended to differential conversion chip, and the second follower is connected to the second single-ended to differential conversion chip.
6. The fA-level small signal amplifier for a quadruple mass spectrometer according to claim 1, characterized in that: The signal acquisition module is a 24-bit, 250KSPS analog-to-digital converter of AD7175.
7. The fA-level small signal amplifier for a quadruple mass spectrometer according to claim 1, characterized in that: The isolation module is an ADUM3151 SPI digital isolator.
8. The fA-level small signal amplifier for a quadruple mass spectrometer according to claim 5, characterized in that: The first operational amplifier and the second operational amplifier are both ADA4530-1 femtoampere input bias current operational amplifiers; the first multiplexer and the second multiplexer are both ADG1608 multi-channel analog switches.
9. The fA-level small signal amplifier for a quadruple mass spectrometer according to claim 8, characterized in that: The first follower and the second follower are both ADA4522-2 dual-channel, zero-drift, low-noise rail-to-rail operational amplifiers; the first single-ended to differential chip and the second single-ended to differential chip are both TLC6362 precision, low-noise, low-power, rail-to-rail, input / output differential operational amplifiers.