Micro-current multi-stage amplification circuit of mass spectrum ion detector

Abstract

The utility model relates to a mass spectrometer ion detector micro-current multistage amplification circuit, which comprises a primary amplification circuit, a voltage following circuit, a secondary amplification circuit, a gain adjustment control circuit and an analog-to-digital conversion circuit, the gain adjustment control circuit can dynamically adjust the gain gears of the first-stage amplification circuit and the second-stage amplification circuit, 16 groups of different amplification gains can be achieved in total, and the application requirement for simultaneous detection of nine orders of magnitude of substances with different concentrations is met. The circuit is simple and reliable, is flexible and convenient to use, greatly widens the detection range of the mass spectrometer, and improves the automatic control level and detection efficiency of the mass spectrometer.

Description

Technical Field

[0001] This utility model relates to the field of mass spectrometers, and in particular to a microcurrent multi-stage amplification circuit for a mass spectrometer ion detector. Background Technology

[0002] Mass spectrometers are instruments used to determine the mass of substances. They are characterized by strong structural identification capabilities, high sensitivity, wide analytical range, and fast analysis speed, and have extremely wide applications in environmental monitoring, food safety, life sciences, and other fields.

[0003] A mass spectrometer mainly consists of a sample introduction device, an ion source, a mass analyzer, and an ion detector. The ion detector is responsible for receiving ion signals and performing signal conversion and amplification. Common ion detectors include electron multipliers (CEMs), microchannel plates (MCPs), and Faraday cups, with electron multipliers and microchannel plates being the most commonly used.

[0004] When the concentrations of analytes detected by a mass spectrometer differ significantly (by six orders of magnitude or more), it becomes impossible to simultaneously measure both high and low concentrations. For example, air contains approximately 78% nitrogen and 21% oxygen, while trace gas concentrations are only at the ppm or even ppb level—a difference of up to nine orders of magnitude. Simultaneous measurement will either render the low-concentration substance undetectable or cause the high-concentration substance to reach the circuit's detection limit. Summary of the Invention

[0005] This disclosure provides a flexible multi-stage microcurrent amplification circuit for a mass spectrometer ion detector, which can dynamically adjust the gain of the ion detector microcurrent to meet the application requirements of simultaneously detecting high-concentration and low-concentration substances.

[0006] The microcurrent multi-stage amplification circuit for this mass spectrometry ion detector mainly includes: a first-stage amplification circuit, a voltage follower circuit, a second-stage amplification circuit, an analog-to-digital conversion circuit, and a gain adjustment and control circuit, wherein:

[0007] The first-stage amplifier circuit receives the micro-current input from the ion detector, converts the current signal into a voltage signal and performs high-frequency filtering, and then performs primary amplification through an ultra-low input bias current operational amplifier.

[0008] The voltage follower circuit receives the voltage signal output from the first-stage amplifier circuit and performs voltage following through an operational amplifier.

[0009] The secondary amplifier circuit receives the output signal from the voltage follower circuit and amplifies the signal in the second stage through a programmable gain instrumentation amplifier.

[0010] The gain adjustment control circuit includes a microprocessor, used to adjust the gain levels of the first-stage amplifier circuit and the second-stage amplifier circuit respectively, to achieve several different amplification gains and meet the detection requirements of substances with different concentrations of multiple orders of magnitude.

[0011] The analog-to-digital converter circuit receives the output of the two-stage amplifier circuit, converts it into a digital signal, and outputs it to the microprocessor. The microprocessor is used to calculate the signal strength of the object under test based on the signal value and the gain amplification factor.

[0012] Furthermore, the first-stage amplifier circuit receives the micro-current input from the ion detector, converts the current signal into a voltage signal through resistor R1, performs high-frequency filtering, and then inputs it into an ultra-low input bias current operational amplifier for primary amplification.

[0013] A load resistor module is connected in parallel between the negative input terminal and the output terminal of the operational amplifier.

[0014] The load resistor module includes: several load resistors with different resistance values ​​connected in parallel, and each resistor is equipped with an access switch;

[0015] The gain adjustment control circuit outputs a control signal to the first-stage amplifier circuit, and adjusts the amplification gain of the first-stage amplifier circuit by controlling the connection or disconnection of each load resistor.

[0016] Furthermore, the input control of the first-stage amplifier circuit consists of four control pins that can switch between 0V and -7.5V states, which respectively control the on / off state of four N-channel junction field-effect transistors used as access switches, thereby controlling the connection of four load resistors and achieving four different amplification factors.

[0017] Furthermore, the secondary amplifier circuit includes: a programmable gain amplifier, a secondary operational amplifier, and its peripheral circuitry; wherein:

[0018] The programmable gain amplifier provides four selectable gains through two input control signals A0 and A1;

[0019] The output of the programmable gain amplifier is input to the positive input terminal of the second operational amplifier via resistor R32;

[0020] A resistor R31 and a filter capacitor are connected in parallel between the negative input terminal and the output terminal of the two-stage operational amplifier.

[0021] Furthermore, the gain adjustment control circuit includes: a microprocessor, a bidirectional isolated transceiver, and a voltage comparator; wherein:

[0022] Two of the microprocessor's I / O signals are transmitted to four voltage comparators via the bidirectional isolated transceiver. Each comparator is set with a 1.5V reference voltage, and its VCC and GND pins are connected to 7.5V and -7.5V, respectively. The microprocessor outputs high and low levels through its two I / O ports, and the four voltage comparators output four 0V or -7.5V control signals to the four control pins of the first-stage amplifier circuit to control the amplification factor of the first-stage operational amplifier.

[0023] The other two output signals from the microprocessor are sent to the A0 and A1 pins of the secondary amplifier circuit via the bidirectional isolation transceiver, enabling four selectable gain state combinations.

[0024] Furthermore, the resistors in the first-stage amplifier circuit are high-precision metal film low-temperature drift resistors; among them, R1 is selected as a 10K resistor, the minimum load resistance is 1MΩ, the maximum is 10GΩ, and the maximum gain is 10. 6 times;

[0025] The N-channel junction field-effect transistor is 2N4117A, and the operational amplifier is AD549.

[0026] Furthermore, the voltage follower circuit uses an AD706JRZ operational amplifier chip, with the non-inverting input receiving the output signal from the first-stage amplifier circuit and the inverting input connected to the output through a feedback resistor.

[0027] Furthermore, the analog-to-digital conversion circuit is connected to the microprocessor via an SPI bus to complete the acquisition of micro-current signals and digital output.

[0028] Before testing, it is first necessary to determine what substance needs to be measured. If the measurement signal of the substance is too low after the circuit completes the measurement, the gain is amplified; conversely, if the measurement signal reaches the detection limit of the microprocessor MCU, the gain is reduced.

[0029] Compared with the prior art, the beneficial effects of this disclosure are: ① Signal conversion, filtering and amplification are performed through first-stage and second-stage amplification circuits, and the gain levels of the first-stage and second-stage amplification circuits are dynamically adjusted through the gain adjustment control circuit; ② A total of 16 different amplification gains can be achieved, which can meet the application requirements of simultaneous detection of substances with different concentrations of 9 orders of magnitude; ③ The detection range of the mass spectrometer is greatly expanded and the level of automation control of the mass spectrometer is improved; ④ It is simple, reliable, flexible and convenient to use, and effectively improves detection efficiency. Attached Figure Description

[0030] The above and other objects, features and advantages of this disclosure will become more apparent from the more detailed description of exemplary embodiments of this disclosure taken in conjunction with the accompanying drawings, in which the same reference numerals generally represent the same components.

[0031] Figure 1 This is an overall circuit structure diagram according to an exemplary embodiment of the present disclosure;

[0032] Figure 2 This is an example of a single-stage amplifier circuit schematic.

[0033] Figure 3 This is a schematic diagram of an exemplary two-stage amplifier circuit;

[0034] Figure 4 This is a schematic diagram of an exemplary gain adjustment control circuit. Detailed Implementation

[0035] Preferred embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0036] This disclosure provides a microcurrent multi-stage amplification circuit for an ion detector in a mass spectrometer. In one exemplary embodiment, the circuit structure is shown in the attached figure. Figure 1 As shown, it consists of a first-stage amplifier circuit, a voltage follower circuit, a second-stage amplifier circuit, a gain adjustment and control circuit, and a high-precision analog-to-digital converter circuit, wherein:

[0037] The first-stage amplifier circuit receives the micro-current input from the ion detector, converts the current signal into a voltage signal and performs high-frequency filtering, and then performs primary amplification through an ultra-low input bias current operational amplifier; the first-stage amplifier circuit receives the dynamic adjustment level signal from the gain adjustment control circuit, which can realize four different amplification gain adjustments.

[0038] The voltage follower circuit receives the output voltage signal from the first-stage amplifier circuit, performs voltage following through an operational amplifier, and enhances the load driving capability of the signal.

[0039] The second-stage amplifier circuit receives the output signal from the voltage follower circuit and amplifies it through a programmable gain instrumentation amplifier. The second-stage amplifier circuit also receives the dynamic adjustment range signal from the gain adjustment control circuit, enabling four different gain adjustment levels.

[0040] The gain adjustment control circuit is controlled by a microprocessor (MCU) to dynamically adjust the gain levels of the first-stage and second-stage amplifier circuits, achieving a total of 16 different amplification gains, with a maximum gain of 10. 9 ;

[0041] The high-precision analog-to-digital converter circuit receives the output signal from the two-stage amplifier circuit, converts it into a digital signal through the high-precision analog-to-digital converter chip, and outputs it to the microprocessor. The microprocessor further processes the signal value and gain amplification factor to calculate the signal intensity of the analyte, which can meet the needs of simultaneous detection of substances with different concentrations of up to nine orders of magnitude.

[0042] Further explanation of each part is as follows:

[0043] (1) First-stage amplifier circuit

[0044] The system receives the microcurrent input from the ion detector, converts the current signal into a voltage signal, performs high-frequency filtering, and then amplifies it through an ultra-low input bias current operational amplifier. See details... Figure 2 .

[0045] Preferably, all resistors in the diagram are high-precision metal film low-temperature drift resistors, which have the advantages of high precision and low temperature drift. R1 is a 10K resistor, and C1 is a 1nF / 50V capacitor, which serves as a high-frequency filter. The four control signals are four control pins that can be switched between 0V and -7.5V states, controlling four N-channel junction field-effect transistors (N-Channel JFETs) to achieve the connection of four different load resistance levels, thereby controlling the amplification factor of the first-stage operational amplifier. As shown in the diagram, the maximum gain of the first-stage amplifier circuit is 10G / 10K = 10. 6 The N-channel junction field-effect transistor can be selected as 2N4117A, and the operational amplifier can be selected as AD549, which can achieve ultra-low input bias current amplification at the fA level, thereby improving the detection sensitivity of the mass spectrometer.

[0046] (2) The voltage follower circuit mainly uses the AD706JRZ operational amplifier chip. The non-inverting input receives the output signal of the first-stage amplifier circuit, and the inverting input is connected to the output through a feedback resistor. The voltage follower circuit isolates the preceding and following stages and improves the load driving capability.

[0047] (3) The secondary amplifier circuit mainly consists of a programmable gain amplifier, an operational amplifier chip, and its peripheral circuits. See details. Figure 3 .

[0048] Preferably, the programmable gain amplifier uses the PGA204 chip, which offers four selectable gain values: 1, 10, 100, and 1000. The amplification factor can be flexibly adjusted via two control signals, A0 and A1, allowing selection of the appropriate gain to achieve accurate amplification results based on actual needs. The operational amplifier chip used is the TLC272 single-supply operational amplifier chip, characterized by high precision and a wide voltage range, serving to isolate signals and enhance drive capability. Resistors R31 and R32 are 20K surface-mount resistors, and capacitor C44 is a 100pF / 50V surface-mount capacitor, providing input voltage safety protection and filtering.

[0049] (4) The gain adjustment control circuit mainly consists of a microprocessor (MCU), a bidirectional isolated transceiver, and a voltage comparator. It dynamically adjusts the gain levels of the first-stage and second-stage amplifier circuits and controls the high-precision analog-to-digital converter circuit via the SPI bus. See details. Figure 4 .

[0050] The microprocessor I / O port uses a dual-power bidirectional isolated transceiver chip, 74LVXC4245MTCX, to switch between 3.3V and 5V levels and achieve effective isolation.

[0051] The input control of the first-stage amplifier circuit has four control pins that can switch between 0V and -7.5V states. There are many ways to achieve this. This embodiment uses the LM339 chip, which has four comparators. Its VCC and GND pins are connected to 7.5V and -7.5V respectively. Each comparator is set with a 1.5V reference voltage. The high and low levels are output through the two I / O ports of the MCU, which can realize four 0V or -7.5V state outputs.

[0052] The secondary amplifier circuit is controlled by two I / O ports of the microprocessor. The microprocessor I / O port level is converted from 0 / 3.3V to 0 / 5V by the 74LVXC4245MTCX isolated transceiver chip and connected to the A0 and A1 pins of the PGA204 chip to realize four selectable gain state combinations of 1, 10, 100 and 1000.

[0053] (5) The high-precision analog-to-digital conversion circuit is mainly composed of a 16-bit analog-to-digital conversion chip ADS8341E. This chip collects the output of the secondary amplifier circuit and converts it into a digital signal. It is connected to the gain adjustment control circuit microprocessor through the SPI bus, receives the control of the gain adjustment control circuit, and completes the acquisition of micro-current signals and digital output.

[0054] The gain adjustment control circuit microprocessor acquires the raw signal of the microcurrent from the ion detector, combines it with the current gain of the first and second stage amplifier circuits, and finally calculates the actual concentration of the analyte. The maximum gain of this scheme is: the maximum gain of the first stage amplifier circuit is 10. 6 × Maximum gain of the second-stage amplifier circuit 10 3 =10 9 It can meet the application needs of simultaneous detection of substances with concentrations of 9 different orders of magnitude.

[0055] In specific testing, it is necessary to first determine what substance needs to be measured. If the measurement signal of the substance is too low, the microprocessor will control the first and second stage operational amplifiers to amplify the gain; conversely, if the measurement signal reaches the upper limit of the MCU detection, the gain will be reduced. Finally, a suitable gain is found, and the concentration of the substance is calculated.

[0056] This embodiment receives a micro-current signal through a first-stage operational amplifier circuit, performs signal conversion, filtering, and primary amplification, and then performs secondary amplification through a second-stage programmable gain instrumentation amplifier. Both the first and second-stage amplifier circuits are designed with four dynamically adjustable levels, achieving a total of 16 different gain combinations, with a maximum gain of 10. 9 This meets the application requirements for simultaneously detecting high and low concentrations of substances.

[0057] The above technical solutions are merely exemplary embodiments of this utility model. For those skilled in the art, based on the application methods and principles disclosed in this utility model, it is easy to make various types of improvements or modifications, and not limited to the methods described in the specific embodiments of this utility model. Therefore, the methods described above are only preferred and not restrictive.

Claims

1. A microcurrent multi-stage amplification circuit for a mass spectrometry ion detector, characterized in that, include: The circuit includes a first-stage amplifier circuit, a voltage follower circuit, a second-stage amplifier circuit, an analog-to-digital converter circuit, and a gain adjustment and control circuit, among which: The first-stage amplifier circuit receives the micro-current input from the ion detector, converts the current signal into a voltage signal and performs high-frequency filtering, and then performs primary amplification through an ultra-low input bias current operational amplifier. The voltage follower circuit receives the voltage signal output from the first-stage amplifier circuit and performs voltage following through an operational amplifier. The secondary amplifier circuit receives the output signal from the voltage follower circuit and amplifies the signal in the second stage through a programmable gain instrumentation amplifier. The gain adjustment control circuit includes a microprocessor, used to adjust the gain levels of the first-stage amplifier circuit and the second-stage amplifier circuit respectively, to achieve several different amplification gains and meet the detection requirements of substances with different concentrations of multiple orders of magnitude. The analog-to-digital converter circuit receives the output of the two-stage amplifier circuit, converts it into a digital signal, and outputs it to the microprocessor. The microprocessor is used to calculate the concentration of the analyte based on the signal value and the gain amplification factor.

2. The circuit according to claim 1, characterized in that, The first-stage amplifier circuit receives the micro-current input from the ion detector, converts the current signal into a voltage signal through resistor R1, performs high-frequency filtering, and then inputs it into an ultra-low input bias current operational amplifier for primary amplification. A load resistor module is connected in parallel between the negative input terminal and the output terminal of the operational amplifier. The load resistor module includes: several load resistors with different resistance values ​​connected in parallel, and each resistor is equipped with an access switch; The gain adjustment control circuit outputs a control signal to the first-stage amplifier circuit, and adjusts the amplification gain of the first-stage amplifier circuit by controlling the connection or disconnection of each load resistor.

3. The circuit according to claim 2, characterized in that, The input control of the first-stage amplifier circuit consists of four control pins that can switch between 0V and -7.5V states. These pins control the on / off state of four N-channel junction field-effect transistors that act as access switches, thereby controlling the connection of four load resistors and achieving four different amplification levels.

4. The circuit according to claim 3, characterized in that, The secondary amplifier circuit includes: a programmable gain amplifier, a secondary operational amplifier, and its peripheral circuitry; wherein: The programmable gain amplifier provides four selectable gains through two input control signals A0 and A1; The output of the programmable gain amplifier is input to the positive input terminal of the second operational amplifier via resistor R32; A resistor R31 and a filter capacitor are connected in parallel between the negative input terminal and the output terminal of the two-stage operational amplifier.

5. The circuit according to claim 4, characterized in that, The gain adjustment control circuit includes: a microprocessor, a bidirectional isolated transceiver, and a voltage comparator; wherein: Two of the microprocessor's I / O signals are transmitted to four voltage comparators via the bidirectional isolated transceiver. Each comparator is set with a 1.5V reference voltage, and its VCC and GND pins are connected to 7.5V and -7.5V, respectively. The microprocessor outputs high and low levels through its two I / O ports, and the four voltage comparators output four 0V or -7.5V control signals to the four control pins of the first-stage amplifier circuit to control the amplification factor of the first-stage operational amplifier. The other two output signals from the microprocessor are sent to the A0 and A1 pins of the secondary amplifier circuit via the bidirectional isolation transceiver, enabling four selectable gain state combinations.

6. The circuit according to any one of claims 3-5, characterized in that, All resistors in the primary amplifier circuit are high-precision metal film low-temperature drift resistors; among them, R1 is a 10K resistor, the minimum load resistance is 1MΩ, the maximum is 10GΩ, and the maximum gain is 10. 6 times; The N-channel junction field-effect transistor is 2N4117A, and the operational amplifier is AD549.

7. The circuit according to claim 1, characterized in that, The voltage follower circuit uses an AD706JRZ operational amplifier chip. The non-inverting input receives the output signal from the first-stage amplifier circuit, and the inverting input is connected to the output through a feedback resistor.

8. The circuit according to claim 1, characterized in that, The analog-to-digital converter circuit is connected to the microprocessor via the SPI bus to complete the acquisition of micro-current signals and digital output.

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