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

Abstract

The invention 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] The present invention relates to the field of mass spectrometers, and particularly to a microcurrent multi-stage amplification circuit for a mass spectrometry ion detector. Background Art

[0002] A mass spectrometer is an instrument for measuring the mass of substances, with characteristics such as strong structure identification ability, high sensitivity, wide analysis range, and fast analysis speed, and has extremely wide applications in the fields of environmental detection, food safety, life science, etc.

[0003] A mass spectrometer mainly consists of an injection device, an ion source, a mass analyzer, an ion detector, etc., where the ion detector is responsible for receiving ion signals and performing signal conversion and amplification. Common ion detectors include a channel electron multiplier (CEM), a microchannel plate (MCP), and a Faraday cup, among which the channel electron multiplier and the microchannel plate are more commonly used.

[0004] When the concentration difference of the analyte detected by the mass spectrometer is very large (a difference of 6 orders of magnitude or even larger), it will result in the inability to simultaneously take into account high-concentration and low-concentration substances. Taking air components as an example, the nitrogen content is about 78%, the oxygen content is about 21%, while the concentration of trace gases is only at the ppm or even ppb level, with a difference of up to 9 orders of magnitude. When measuring simultaneously, either the low-concentration substances cannot be detected, or the high-concentration substances reach the detection upper limit of the circuit. Summary of the Invention

[0005] The present disclosure provides a flexible microcurrent multi-stage amplification circuit for a mass spectrometry ion detector, which can perform dynamic adjustment with variable gain on the microcurrent of the ion detector to meet the application requirements of simultaneously detecting high-concentration and low-concentration substances.

[0006] The microcurrent multi-stage amplification circuit for the 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 control circuit, where:

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

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

[0009] The second-stage amplification circuit receives the output signal of the voltage follower circuit and performs secondary signal amplification through a programmable gain instrumentation amplifier;

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

[0011] The analog-to-digital conversion circuit receives the output of the second-stage amplification circuit, converts it into a digital signal and outputs it to the microprocessor, and the microprocessor is used to calculate the signal strength of the analyte according to the signal value and the gain amplification factor.

[0012] Further, the first-stage amplification circuit receives the micro-current input of the ion detector, converts the current signal into a voltage signal through the 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 resistance module is connected in parallel between the negative input terminal and the output terminal of the operational amplifier.

[0014] The load resistance module includes: several paths of load resistors with different resistance values connected in parallel, and each path of resistor is provided with an access switch.

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

[0016] Further, the input control of the first-stage amplification circuit is 4 control pins with switchable states of 0V or -7.5V, which respectively control the on-off of 4 N-channel junction field effect transistors serving as access switches to control the connection of 4 paths of load resistors and achieve 4 different amplification multiples.

[0017] Further, the second-stage amplification circuit includes: a programmable gain amplifier, a second-stage operational amplifier and its peripheral circuits; among them:

[0018] The programmable gain amplifier provides four selectable gains through 2 input control signals A0 and A1.

[0019] The output of the programmable gain amplifier is input to the positive input terminal of the second-stage operational amplifier through the resistor R32.

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

[0021] Further, the gain adjustment control circuit includes: a microprocessor, a bidirectional isolation transceiver and a voltage comparator; among them:

[0022] Two of the microprocessor's IO signals are sent to a four-channel voltage comparator via the bidirectional isolation transceiver. Each comparator is set with a reference voltage of 1.5V, and its VCC and GND pins are connected to 7.5V and -7.5V respectively. High and low levels are output through two IO ports of the microprocessor, and the four-channel voltage comparator outputs 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] Another two of the microprocessor's output signals are sent to the A0 and A1 pins of the second-stage amplifier circuit via the bidirectional isolation transceiver to achieve four selectable gain state combinations.

[0024] Further, the resistors in the first-stage amplifier circuit use high-precision metal film low-temperature drift resistors. Among them, R1 is selected as a 10K resistor, the load resistor is at least 1M and at most 10G, and the maximum gain is 10 6 times.

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

[0026] Further, the voltage follower circuit uses an AD706JRZ operational amplifier chip. The non-inverting input terminal receives the output signal of the first-stage amplifier circuit, and the inverting input terminal is connected to the output terminal through a feedback resistor.

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

[0028] Before detection, first clarify what substance to measure. If the measurement signal of the substance is too low after the circuit measurement is completed, the amplification gain is increased; conversely, if the measurement signal reaches the detection upper limit of the microprocessor MCU, the gain is reduced.

[0029] Compared with the prior art, the beneficial effects of the present disclosure are: ① Signal conversion, filtering and amplification are carried out through the first-stage and second-stage amplifier circuits, and the gain levels of the first-stage and second-stage amplifier 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 in 9 orders of magnitude; ③ Greatly broaden the detection range of the mass spectrometer and improve the automatic control level of the mass spectrometer; ④ Simple and reliable, flexible and convenient to use, effectively improving the detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] By describing the exemplary embodiments of the present disclosure in more detail in conjunction with the accompanying drawings, the above and other objects, features and advantages of the present disclosure will become more obvious. Among them, in the exemplary embodiment mode of the present disclosure, the same reference numerals generally represent the same components.

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

[0032] Figure 2 Schematic diagram of an exemplary first-stage amplification circuit;

[0033] Figure 3 Schematic diagram of an exemplary second-stage amplification circuit;

[0034] Figure 4 Schematic diagram of an exemplary gain adjustment control circuit. Detailed implementation manners

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

[0036] The present disclosure provides a multi-stage amplification circuit for microcurrent of a mass spectrometer ion detector. In an exemplary implementation manner, the circuit structure is as shown in the accompanying Figure 1 drawings, and it is composed of a first-stage amplification circuit, a voltage follower circuit, a second-stage amplification circuit, a gain adjustment control circuit, and a high-precision analog-to-digital conversion circuit, where:

[0037] The first-stage amplification circuit receives the microcurrent input of the ion detector, converts the current signal into a voltage signal and performs high-frequency filtering, and performs primary amplification through an ultra-low input bias current operational amplifier; the first-stage amplification circuit receives the dynamic adjustment gear signal of the gain adjustment control circuit and can realize different amplification gain adjustments in 4 gears;

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

[0039] The second-stage amplification circuit receives the output signal of the voltage follower circuit and performs secondary signal amplification through a programmable gain instrumentation amplifier. The second-stage amplification circuit receives the dynamic adjustment gear signal of the gain adjustment control circuit and realizes different amplification gain adjustments in 4 gears;

[0040] The gain adjustment control circuit is controlled by a microprocessor (MCU) to dynamically adjust the gain gears of the first-stage amplification circuit and the second-stage amplification circuit, and can realize a total of 16 groups of different amplification gains, and the maximum gain can reach 10 9 ;

[0041] The high-precision analog-to-digital conversion circuit receives the output signal of the secondary amplification circuit, converts it into a digital signal through a high-precision analog-to-digital conversion chip, and outputs it to the microprocessor. The microprocessor further processes it according to the signal value and the gain amplification factor, and calculates the signal strength of the object to be measured, which can meet the requirements of simultaneously detecting substances with different concentrations in 9 orders of magnitude.

[0042] The further description of each part is as follows:

[0043] (1) Primary amplification circuit

[0044] Receives the micro-current input of the ion detector, converts the current signal into a voltage signal and performs high-frequency filtering, and performs primary amplification through an ultra-low input bias current operational amplifier. For details, see Figure 2 。

[0045] Preferably, all the resistors in the figure are selected as high-precision metal film low-temperature drift resistors, which have the advantages of high precision and low temperature drift. R1 is selected as a 10K resistor, and C1 is selected as a 1nf / 50V capacitor, which has the effect of high-frequency filtering. The 4-channel control signal is 4-channel control pins with switchable states of 0V or -7.5V, which control 4 N-channel junction field effect transistors (N-Channel JFETs) to realize the connection of different load resistors in 4 gears, and then control the amplification factor of the primary operational amplifier. It can be seen from the figure that the maximum gain of the primary amplification circuit is 10G / 10K = 10 6 times. The N-channel junction field effect transistor can be selected as 2N4117A, and the operational amplifier can be selected as AD549, which can realize ultra-low input bias current amplification at the fA level and improve the sensitivity of the mass spectrometer detection.

[0046] (2) The voltage follower circuit is mainly composed of an AD706JRZ operational amplifier chip. The non-inverting input terminal receives the output signal of the primary amplification circuit, and the inverting input terminal is connected to the output terminal through a feedback resistor. The voltage follower circuit plays the role of isolating the front and rear stage circuits and improving the load driving ability.

[0047] (3) The secondary amplification circuit is mainly composed of a programmable gain amplifier, an operational amplifier chip and its peripheral circuits. For details, see Figure 3 。

[0048] Preferably, the programmable gain amplifier uses a PGA204 chip, which provides four optional gains of 1, 10, 100, and 1000. The amplification factor can be flexibly adjusted through 2-channel control signals A0 and A1, and the appropriate gain can be selected according to actual needs to obtain an accurate amplification result. The operational amplifier chip uses a TLC272 single-power operational amplifier chip, which has the characteristics of high precision and wide voltage range, and plays the role of signal isolation and enhancing driving ability. The resistors R31 and R32 use 20K surface mount resistors, and the capacitor C44 uses a 100pf / 50V surface mount capacitor, which plays the role of input voltage safety protection and filtering.

[0049] (4) The gain adjustment control circuit mainly consists of a microprocessor (MCU), a bidirectional isolation transceiver, and a voltage comparator, dynamically adjusting the gain levels of the first-stage amplification circuit and the second-stage amplification circuit, and controlling the high-precision analog-to-digital conversion circuit through the SPI bus. For details, see Figure 4 .

[0050] The IO port of the microprocessor realizes the level conversion from 3.3V to 5V through the dual-power bidirectional isolation transceiver 74LVXC4245MTCX chip and conducts effective isolation.

[0051] The input control of the first-stage amplification circuit is 4 control pins with switchable states of 0V or -7.5V. There are many implementation methods. In this embodiment, the LM339 chip is adopted, which has 4 comparators. Its VCC and GND pins are respectively connected to 7.5V and -7.5V. A reference voltage of 1.5V is set for each comparator. By outputting high and low levels through 2 IO ports of the MCU, 4 outputs with states of 0V or -7.5V can be realized.

[0052] The second-stage amplification circuit is controlled through 2 IO ports of the microprocessor. Through the isolation transceiver 74LVXC4245MTCX chip, the level of the microprocessor IO port is converted from 0 / 3.3V to 0 / 5V and connected to the A0 and A1 pins of the PGA204 chip to realize four optional gain state combinations of 1, 10, 100, and 1000.

[0053] (5) The high-precision analog-to-digital conversion circuit mainly consists of a 16-bit analog-to-digital conversion chip ADS8341E. This chip collects the output of the second-stage amplification circuit and converts it into a digital signal, connects to the microprocessor of the gain adjustment control circuit through the SPI bus method, receives the control of the gain adjustment control circuit, and completes the acquisition and digital output of the micro-current signal.

[0054] The microprocessor of the gain adjustment control circuit collects the original micro-current signal of the ion detector, combines the current gains of the first-stage and second-stage amplification circuits, and finally calculates the actual concentration of the substance to be measured. The maximum gain of this scheme is: the maximum gain of the first-stage amplification circuit is 10 6 × the maximum gain of the second-stage amplification circuit is 10 3 =10 9 , which can meet the application requirements for simultaneously detecting substances with different concentrations in 9 orders of magnitude.

[0055] During specific detection, it is necessary to first clarify what substance is to be measured. If the measurement signal of this substance is too low, the microprocessor controls the first and second-stage operational amplifiers to increase the gain; conversely, if the measurement signal reaches the detection upper limit of the MCU, the gain is reduced, and finally an appropriate gain is found to calculate the substance concentration.

[0056] In this embodiment, a micro-current signal is received by a first-stage operational amplifier circuit for signal conversion, filtering, and primary amplification, and a second-stage programmable gain instrumentation amplifier is used for secondary amplification. Both the first-stage and second-stage amplification circuits are designed with 4 dynamic adjustment gears, achieving a total of 16 different gain combinations, and the maximum gain can reach 10 9 , meeting the application requirements for simultaneously detecting high-concentration and low-concentration substances.

[0057] The above technical solution is only an exemplary embodiment of the present invention. For those skilled in the art, based on the disclosed application methods and principles of the present invention, various types of improvements or deformations can be easily made, not limited to the methods described in the above specific embodiments of the present invention. Therefore, the foregoing description is only preferred and does not have a restrictive meaning.

Claims

1. A micro-current multi-stage amplifier circuit for a mass spectrometer ion detector, characterized in that: include: A primary amplifier circuit, a voltage follower circuit, a secondary amplifier circuit, an analog-to-digital conversion circuit, and a gain adjustment control circuit, wherein: The first-stage amplification circuit receives the micro-current input of the ion detector, converts the current signal into a voltage signal and performs high-frequency filtering, and performs primary amplification through an ultra-low input bias current operational amplifier; The voltage follower circuit receives the output voltage signal of the first-stage amplifier circuit and performs voltage following through the operational amplifier; The secondary amplifier circuit receives the output signal of the voltage follower circuit and performs secondary signal amplification through a programmable gain instrumentation amplifier; The gain adjustment control circuit includes: a microprocessor, which is used to adjust the gain gears of the primary amplification circuit and the secondary amplification circuit respectively, to achieve several groups of different amplification gains, and to meet the detection requirements of substances with different concentrations of multiple orders of magnitude; The analog-to-digital conversion circuit receives the output of the secondary amplification circuit, converts it into a digital signal and outputs it to the microprocessor. The microprocessor is used to convert the concentration of the object to be tested according to 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 of the ion detector, converts the current signal into a voltage signal through the resistor R1, performs high-frequency filtering, and then inputs the voltage signal into the ultra-low input bias current operational amplifier for primary amplification; A load resistance module is connected in parallel between the negative input terminal and the output terminal of the operational amplifier; The load resistor module comprises: a plurality of load resistors with different resistance values ​​connected in parallel with each other, each resistor being provided 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 is 4 control pins that can switch between 0V or -7.5V states, which respectively control the on and off of 4 N-channel junction field effect transistors used as access switches to control the connection of 4 load resistors to achieve 4 different amplification factors.

4. The circuit according to claim 3, characterized in that The secondary amplifier circuit comprises: a programmable gain amplifier, a secondary operational amplifier and its peripheral circuits; 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 secondary operational amplifier via resistor R32; A parallel resistor R31 and a filter capacitor are provided between the negative input terminal and the output terminal of the secondary operational amplifier.

5. The circuit according to claim 4, characterized in that The gain adjustment control circuit comprises: a microprocessor, a bidirectional isolation transceiver and a voltage comparator; wherein: Two of the microprocessor IO signals are transmitted to four voltage comparators through the bidirectional isolation transceiver. Each comparator is set to a reference voltage of 1.5V, and its VCC and GND pins are connected to 7.5V and -7.5V respectively. The high and low levels are output through the two IO ports of the microprocessor, and the four voltage comparators output four 0V or -7.5V control signals to the four control pins of the first-stage amplifier circuit, which are used to control the amplification factor of the first-stage operational amplifier. The other two channels of the microprocessor output signal are transmitted to the A0 and A1 pins of the secondary amplifier circuit via the bidirectional isolation transceiver to achieve four optional gain state combinations.

6. The circuit according to any one of claims 3 to 5, characterized in that: The resistors in the first-stage amplifier circuit are all high-precision metal film low-temperature drift resistors; among them, R1 is a 10K resistor, the minimum load resistance is 1M, the maximum is 10G, 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 adopts an AD706JRZ operational amplifier chip, the in-phase input terminal receives the output signal of the first-stage amplifier circuit, and the inverting input terminal is connected to the output terminal through a feedback resistor.

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

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