Gain self-adjusting ion signal detection circuit based on trans-impedance amplifier

Abstract

The utility model provides a trans-impedance amplifier-based gain self-adjusting ion signal detection circuit, comprising an electron multiplier CEM which converts an ion signal into an electron beam and transmits the electron beam to a low-gain signal amplification circuit and a high-gain signal amplification circuit through a trans-impedance amplifier U1. The output amplitude recognition and transmission circuit is used for judging the amplitude output by the low-gain signal amplification circuit and the high-gain signal amplification circuit and transmitting a signal generated after comparison to the control unit through an ADC, and the control unit controls the I / V conversion resistance adjustable circuit to switch the resistance value of the transimpedance amplifier U1 according to the collected signal. And transmitting to a PC end to form a mass spectrum. According to the gain self-adjusting ion signal detection circuit based on the trans-impedance amplifier, the accuracy and the applicability of mass spectrum detection are improved; meanwhile, the problem of mass spectrum peak shape abnormity caused by large change of the concentration range of the sample to be detected is solved.

Description

Technical Field

[0001] The utility model belongs to the technical field of signal detection, and in particular relates to a gain self-adjusting ion signal detection circuit based on a transimpedance amplifier. Background Art

[0002] A mass spectrometer is generally composed of several main parts, such as an ion source system, an ion optical system, a radio frequency power supply system, and a signal detection system. It is an instrument used to analyze particles. Its basic principle is to ionize microscopic particles into ions (through an ion source), and then separate ions of different mass-to-charge ratios through a mass analyzer (quadrupole mass analyzer, time-of-flight mass analyzer, magnetic mass analyzer, etc.), thereby performing ion quantitative / qualitative analysis. The mass spectrometer signal detection system generally uses an electron multiplier as a detector. When it is working, a DC voltage V is applied to both ends of the electron multiplier. CEM , a uniform axial electric field is established. After the charged particles such as ions enter the electron multiplier, they collide with the inner surface of the tube and stimulate secondary electrons. CEM The generated axial electric field accelerates and generates enough secondary electrons, which generate a gain of 10 at the high potential end of the electron multiplier after repeated collisions. 8 The electron beam is a pulsed signal or an analog current signal. The signal is coupled to the signal detection circuit through a coupling circuit. The signal detection circuit amplifies and compares the signal and transmits it to the signal counting unit, which finally calculates the mass spectrum signal intensity of the sample. In the daily operation of the mass spectrometer, the concentrations of the samples it detects are different, and there will be several orders of magnitude differences in the dynamic range. Because the electron multiplier has its own response dead time, it will have response saturation or excessive response when the sample concentration is high. The saturated response will be identified by the subsequent signal processing circuit as an ion-free pulse, resulting in the mass spectrum displaying no peak shape; the excessively high response will cause the subsequent signal processing circuit to be unable to process normally, exceeding the output range of the operational amplifier itself, resulting in the mass spectrometer being unable to display the peak shape normally. Both of these phenomena will prevent the experimenter from obtaining correct test results.

[0003] Currently, manufacturers typically address the issue of inaccurate mass spectrometry results caused by excessively high sample concentrations by using dual-mode ion detectors. These detectors operate in pulse counting mode at low sample concentrations and in analog mode at high sample concentrations. However, these ion detectors are expensive and primarily used in inductively coupled plasma mass spectrometers (ICP-MS), which have a dynamic range of nine orders of magnitude. They are not suitable for liquid chromatography-mass spectrometry (LC-MS) or gas chromatography-mass spectrometry (GC-MS). Furthermore, these detectors place high demands on the signal processing circuitry, making their design difficult. Summary of the Invention

[0004] In view of this, the utility model aims to propose a gain self-adjusting ion signal detection circuit based on a transimpedance amplifier to solve the problem of abnormal mass spectrum peak shape caused by large changes in the concentration range of the sample to be tested, resulting in low accuracy of mass spectrometry detection.

[0005] In order to achieve the above-mentioned purpose, the technical solution of the utility model is achieved as follows:

[0006] A gain self-adjusting ion signal detection circuit based on a transimpedance amplifier includes an electron multiplier (CEM). The electron multiplier (CEM) receives ions transmitted from the ion optics of a mass spectrometer and converts them into an electron beam. The electron beam is converted into a processable voltage signal by a transimpedance amplifier (U1). The voltage signal is amplified by a low-gain signal amplification circuit and a high-gain signal amplification circuit and connected to an output amplitude recognition and output circuit respectively. The output amplitude recognition and transmission circuit is used to determine the amplitudes of the outputs of the low-gain signal amplification circuit and the high-gain signal amplification circuit, and transmits the signals generated after comparison to a control unit via an ADC. The control unit controls an I / V conversion resistor adjustable circuit to switch the resistance value of the transimpedance amplifier (U1) according to the signal returned by the output amplitude recognition and transmission circuit, and transmits the generated mass spectrum ion information to a PC software for processing to form a mass spectrum.

[0007] Furthermore, the gain self-adjusting ion signal detection circuit based on the transimpedance amplifier also includes a noise floor subtraction circuit, which is used to compare and subtract the noise generated by the circuit itself with the noise signal generated by the dark current of the electron multiplier.

[0008] Furthermore, the noise floor subtraction circuit includes an operational amplifier U5, a negative input terminal of the operational amplifier U5 is connected to the output terminal of the transimpedance amplifier U1 through R5, and a positive input terminal of the operational amplifier U5 is connected to GND.

[0009] Furthermore, the I / V conversion resistance adjustable circuit includes R1, R2 and a relay switch S1, the first end of R1 is connected to the negative output end of the transimpedance amplifier U1, the second end is connected to R2, the two ends of R2 are connected in parallel with the two sides of the contact of the relay switch S1, and the coil of the relay switch S1 is connected to the control unit.

[0010] Furthermore, the low-gain signal amplification circuit includes a comparator U2, the negative input of the comparator U2 is connected to the output of the comparator U2, and the positive input of the comparator U2 is connected to the negative input of the operational amplifier U5 and the output of the operational amplifier U5 via R6.

[0011] Furthermore, the high-gain signal amplification circuit includes a comparator U3, the positive input of the comparator U3 is connected to the output of the operational amplifier U5, the output of the comparator U3 is connected to the negative input of the comparator U3 via R4, and the negative input of the comparator U3 is connected to GND via R3.

[0012] Furthermore, the output amplitude identification and transmission circuit includes a comparator U4, the negative input of which is connected to the output of comparator U3, and the output of which is connected to the control unit. The output amplitude identification and transmission circuit compares the amplitudes output by the low-gain signal amplification circuit and the high-gain signal amplification circuit with an internal threshold voltage Vref1, generating a signal that is transmitted to the control unit.

[0013] Furthermore, the ADC circuit includes an ADC chip and a switching switch S2, the output end of the ADC chip is connected to the control unit, the input end of the ADC chip is connected to the static contact of the switching switch S2, one moving contact of the switching switch S2 is connected to the output end of the comparator U2, and the other moving contact is connected to the output end of the comparator U3, and the coil of the switching switch S2 is connected to the control unit; the switching switch S2 transmits the amplified ion signal ION_SIGNAL output by the high-gain signal amplification circuit to the ADC chip for collection according to the control signal output by the control unit.

[0014] Furthermore, the DAC circuit includes a DAC chip and a comparator U6, the first end of the DAC chip is connected to the control unit, and the second end is connected to the positive input end of the comparator U4 and the negative input end of the comparator U6 via R9, the positive input end of the comparator U6 is connected to GND, the negative input end of the comparator U6 is connected to the output end of the comparator U6 via R8, and the output end of the comparator U6 is connected to the negative input end of the comparator U5 via R7.

[0015] Furthermore, the control unit is an MCU or FPGA.

[0016] Compared with the prior art, the gain self-adjusting ion signal detection circuit based on the transimpedance amplifier described in the present invention has the following advantages:

[0017] (1) The gain self-adjusting ion signal detection circuit based on the transimpedance amplifier described in the present invention is provided with a resistance switching circuit, which makes the gain of the transimpedance amplifier adjustable to adapt to the detection of different samples, thereby improving the accuracy and applicability of mass spectrometry detection; at the same time, it solves the problem of abnormal mass spectrum peak shape caused by large changes in the concentration range of the sample to be tested.

[0018] (2) The gain self-adjusting ion signal detection circuit based on the transimpedance amplifier described in the utility model is designed to design two low-gain signal amplification circuits, high-gain signal amplification circuits and output amplitude recognition and transmission circuits for the output signals of the transimpedance amplifier, which can identify the sample concentration range and thus adjust the gain working state of the transimpedance amplifier.

[0019] (3) The gain self-adjusting ion signal detection circuit based on the transimpedance amplifier described in the present invention can be adapted to the ion signal processing of various mass spectrometers. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0021] Figure 1 This is a principle block diagram of a gain self-adjusting ion signal detection circuit based on a transimpedance amplifier according to an embodiment of the present utility model;

[0022] Figure 2 This is a circuit diagram of a gain self-adjusting ion signal detection circuit based on a transimpedance amplifier according to an embodiment of the present utility model. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein can be combined with each other.

[0024] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0025] In the description of this utility model, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections, electrical connections; direct connections, indirect connections through an intermediate medium, and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this utility model based on specific circumstances.

[0026] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0027] Glossary:

[0028] ADC: Analog-to-digital converter, also known as A / D converter, or ADC for short.

[0029] DAC: Digital-to-analog converter, also known as D / A converter, abbreviated as DAC.

[0030] MCU: Microcontroller Unit microcontroller unit.

[0031] FPGA: Field Programmable Gate Array.

[0032] A gain self-adjusting ion signal detection circuit based on a transimpedance amplifier, such as Figure 1 and Figure 2 As shown, it includes electron multiplier CEM, transimpedance amplifier U1, background noise subtraction circuit, low gain signal amplification circuit, high gain signal amplifier circuit, output amplitude recognition and transmission circuit, ADC circuit, control unit, DAC circuit and I / V conversion resistor adjustable circuit.

[0033] The electron multiplier (CEM) receives ions transmitted from the mass spectrometer's ion optics and converts them into an electron beam. The electron beam is converted into a processable voltage signal No. 1 by a transimpedance amplifier. The converted voltage signal No. 1 is amplified to a processable amplitude by a low-gain signal amplifier circuit and a high-gain signal amplifier circuit respectively.

[0034] Specifically, the voltage signals of the low-gain signal amplification circuit and the high-gain signal amplification circuit are respectively connected to the output amplitude recognition and output circuit;

[0035] The output amplitude recognition and transmission circuit is used to determine the amplitude of the outputs of the low-gain signal amplification circuit and the high-gain signal amplification circuit, and transmits the signal generated after comparison to the control unit through the ADC. The control unit controls the I / V conversion resistor adjustable circuit to switch the resistance value of the transimpedance amplifier circuit according to the signal returned by the output amplitude recognition and transmission circuit, and at the same time transmits the generated mass spectrum ion information to the PC software after calculation for processing to form a mass spectrum.

[0036] A gain self-adjusting ion signal detection circuit based on a transimpedance amplifier also includes a background noise subtraction circuit, which is used to compare and subtract the noise generated by the circuit itself with the noise signal generated by the dark current of the electron multiplier.

[0037] The control unit is an MCU or an FPGA. In one or more embodiments, the FPGA model is XC7S100;

[0038] The noise floor subtraction circuit includes an operational amplifier U5, the negative input terminal of the operational amplifier U5 is connected to the output terminal of the transimpedance amplifier U1 through R5, and the positive input terminal of the operational amplifier U5 is connected to GND;

[0039] The I / V conversion resistance adjustable circuit includes R1, R2 and a relay switch S1. The first end of R1 is connected to the negative output end of the transimpedance amplifier U1, and the second end is connected to R2 respectively. The two ends of R2 are connected in parallel with the two sides of the contact of the relay switch S1, and the coil of the relay switch S1 is connected to the control unit.

[0040] The low-gain signal amplification circuit includes a comparator U2, wherein the negative input terminal of the comparator U2 is connected to the output terminal, and the positive input terminal of the comparator U2 is connected to the negative input terminal of the operational amplifier U5 and the output terminal of the operational amplifier U5 via R6.

[0041] The high-gain signal amplification circuit includes a comparator U3, the positive input of the comparator U3 is connected to the output of the operational amplifier U5, the output of the comparator U3 is connected to the negative input of the comparator U3 via R4, and the negative input of the comparator U3 is connected to GND via R3.

[0042] The output amplitude identification and transmission circuit includes a comparator U4, whose negative input is connected to the output of comparator U3, and whose output is connected to the control unit. The output amplitude identification and transmission circuit compares the amplitudes of the outputs of the low-gain signal amplifier circuit and the high-gain signal amplifier circuit with an internal threshold voltage Vref1, generating a signal that is transmitted to the control unit.

[0043] The ADC circuit includes an ADC and a switch S2. In one or more embodiments, the ADC model is LTC2374-16BIT. The ADC output is connected to the control unit, the ADC input is connected to the static contact of switch S2, one movable contact of switch S2 is connected to the output of comparator U2, and the other movable contact is connected to the output of comparator U3. The coil of switch S2 is connected to the control unit. Switch S2 transmits the amplified ion signal ION_SIGNAL output by the high-gain signal amplifier circuit to the ADC chip LTC2374-16BIT for acquisition based on the control signal output by the control unit.

[0044] The DAC circuit includes a DAC and a comparator U6. In one or more embodiments, the DAC model is AD5628. The first end of the DAC is connected to the control unit, and the second end is connected to the positive input end of the comparator U4 and the negative input end of the comparator U6 via R9. The positive input end of the comparator U6 is connected to GND, the negative input end of the comparator U6 is connected to the output end of the comparator U6 via R8, and the output end of the comparator U6 is connected to the negative input end of the comparator U5 via R7.

[0045] The working principle of a gain self-adjusting ion signal detection circuit based on a transimpedance amplifier is as follows:

[0046] Since the concentration range of the sample to be tested varies greatly, the electron multiplier CEM receives ions transmitted from the mass spectrometer ion optics and converts them into electron beams. After the current is converted into voltage through the transimpedance amplifier U1, the amplitude of the output voltage signal will also change with the change of sample concentration.

[0047] When a sample with an unknown concentration range is subjected to mass spectrometry detection, the relay switch S1 of the I / V conversion resistor adjustable circuit is first kept in the disconnected state, so that the transimpedance amplifier U1 operates in a high-gain state. The signal is compared with the threshold voltage Vref2 of the background noise subtraction circuit, and the noise generated by the circuit itself and the noise signal generated by the dark current of the electron multiplier are compared and subtracted at the operational amplifier U5. The voltage signal after background noise subtraction enters the low-gain signal amplification circuit and the high-gain signal amplification circuit respectively. The output signals of the low-gain signal amplification circuit and the high-gain signal amplification circuit are both output to the switching switch S2. The comparator U4 compares the signal output by the high-gain signal amplification circuit with the internal threshold voltage Vref1, and outputs a transimpedance amplifier U1 working state control signal suitable for the sample concentration to the control unit. The control unit controls the working state of the I / V conversion resistor adjustable circuit and the switching switch S2 according to the control signal, whether to continue to remain disconnected or switch to a closed state.

[0048] Meanwhile, the control unit controls the generation of threshold voltages Vref1 and Vref2 using the AD5628 digital-to-analog converter chip. The AD5628 boasts 12-bit accuracy, ensuring the accuracy of the threshold voltages. Comparator U6 inverts the polarity of the threshold voltage signal generated by the AD5628.

[0049] When a low-concentration sample is subjected to mass spectrometry, relay switch S1 of the adjustable I / V conversion resistor circuit is disconnected, and transimpedance amplifier U1 operates simultaneously with two resistors, placing it in a high-gain operating state. After deducting the noise floor from operational amplifier U5, the voltage signal enters comparator U2 of the low-gain signal amplification circuit and comparator U3 of the high-gain signal amplification circuit. The control unit switches switch S2 to a low-gain output state and transmits the amplified signal from comparator U2 of the low-gain signal amplification circuit to the ADC for sampling. Comparator U4 outputs a low-concentration control signal to the control unit, which controls relay switch S1 and switch S2. The ADC chip converts the collected analog signal into a digital signal and transmits it to the controller, ultimately generating a mass spectrum on the host computer.

[0050] When a high-concentration sample undergoes mass spectrometry, relay switch S1 of the adjustable I / V conversion resistor circuit closes, and transimpedance amplifier U1 operates in a single-resistance simultaneous mode, placing transimpedance amplifier U1 in a low-gain operating state. The voltage signal, after deducting the noise floor from operational amplifier U5, enters comparator U2 of the low-gain signal amplification circuit and comparator U3 of the high-gain signal amplification circuit. The controller switches switch S2 to a high-gain output state and transmits the amplified signal from comparator U3 of the high-gain signal amplification circuit to the ADC for sampling. Comparator U4 outputs a low-concentration control signal to the control unit, which controls relay switch S1 and switch S2. The ADC chip converts the collected analog signal into a digital signal and transmits it to the MCU. The MCU calculates the generated mass spectrometry ion information and transmits it to the PC software for processing to form a mass spectrum.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A gain self-adjusting ion signal detection circuit based on a transimpedance amplifier, characterized in that: It includes an electron multiplier CEM, which receives ions transmitted from the mass spectrometer ion optics and converts them into an electron beam. The electron beam is converted into a voltage signal that can be processed by a transimpedance amplifier U1. The voltage signal is amplified by a low-gain signal amplifier circuit and a high-gain signal amplifier circuit respectively and connected to the output amplitude recognition and output circuit respectively; the output amplitude recognition and transmission circuit is used to judge the amplitude of the output of the low-gain signal amplifier circuit and the high-gain signal amplifier circuit, and transmits the signal generated after comparison to the control unit through the ADC. The control unit controls the I / V conversion resistor adjustable circuit to switch the resistance value of the transimpedance amplifier U1 according to the signal returned by the output amplitude recognition and transmission circuit, and transmits the generated mass spectrum ion information to the PC software after calculation for processing to form a mass spectrum.

2. The gain self-adjusting ion signal detection circuit based on a transimpedance amplifier according to claim 1, characterized in that: It also includes a background noise subtraction circuit, which is used to compare and subtract the noise generated by the circuit itself with the noise signal generated by the dark current of the electron multiplier.

3. The gain self-adjusting ion signal detection circuit based on a transimpedance amplifier according to claim 2, characterized in that: The noise floor subtraction circuit includes an operational amplifier U5, a negative input terminal of the operational amplifier U5 is connected to the output terminal of the transimpedance amplifier U1 through R5, and a positive input terminal of the operational amplifier U5 is connected to GND.

4. The gain self-adjusting ion signal detection circuit based on a transimpedance amplifier according to claim 1, characterized in that: The I / V conversion resistance adjustable circuit includes R1, R2 and a relay switch S1. The first end of R1 is connected to the negative output end of the transimpedance amplifier U1, and the second end is connected to R2. The two ends of R2 are connected in parallel with the two sides of the contact of the relay switch S1. The coil of the relay switch S1 is connected to the control unit.

5. The gain self-adjusting ion signal detection circuit based on a transimpedance amplifier according to claim 2, characterized in that: The low-gain signal amplification circuit includes a comparator U2, wherein the negative input terminal of the comparator U2 is connected to the output terminal of the comparator U2, and the positive input terminal of the comparator U2 is connected to the negative input terminal of the operational amplifier U5 and the output terminal of the operational amplifier U5 via R6.

6. The gain self-adjusting ion signal detection circuit based on a transimpedance amplifier according to claim 3, characterized in that: The high-gain signal amplification circuit includes a comparator U3, the positive input of the comparator U3 is connected to the output of the operational amplifier U5, the output of the comparator U3 is connected to the negative input of the comparator U3 via R4, and the negative input of the comparator U3 is connected to GND via R3.

7. The gain self-adjusting ion signal detection circuit based on a transimpedance amplifier according to claim 6, characterized in that: The output amplitude recognition and transmission circuit includes a comparator U4, the negative input end of the comparator U4 is connected to the output end of the comparator U3, and the output end of the comparator U4 is connected to the control unit. The output amplitude recognition and transmission circuit compares the amplitudes output by the low-gain signal amplification circuit and the high-gain signal amplification circuit with the internal threshold voltage Vref and transmits the generated signal to the control unit.

8. The gain self-adjusting ion signal detection circuit based on a transimpedance amplifier according to claim 6, characterized in that: The ADC circuit includes an ADC chip and a switching switch S2. The output end of the ADC chip is connected to the control unit, the input end of the ADC chip is connected to the static contact of the switching switch S2, one moving contact of the switching switch S2 is connected to the output end of the comparator U2, and the other moving contact is connected to the output end of the comparator U3. The coil of the switching switch S2 is connected to the control unit; the switching switch S2 transmits the amplified ion signal ION_SIGNAL output by the high-gain signal amplification circuit to the ADC chip for collection according to the control signal output by the control unit.

9. The gain self-adjusting ion signal detection circuit based on a transimpedance amplifier according to claim 6, characterized in that: The DAC circuit includes a DAC chip and a comparator U6. The first end of the DAC chip is connected to the control unit, and the second end is connected to the positive input end of the comparator U4 and the negative input end of the comparator U6 via R9. The positive input end of the comparator U6 is connected to GND, the negative input end of the comparator U6 is connected to the output end of the comparator U6 via R8, and the output end of the comparator U6 is connected to the negative input end of the comparator U5 via R7.

10. The gain self-adjusting ion signal detection circuit based on a transimpedance amplifier according to claim 1, characterized in that: The control unit is an MCU or FPGA.

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