Weak signal detection system of ultraviolet photoelectron spectrum analyzer

Abstract

The application discloses a weak signal detection system of an ultraviolet photoelectron spectrum analyzer, and relates to the field of photoelectron spectrum analysis. A pulse protection circuit and a direct current protection circuit are connected with an electron multiplier through a selection circuit; the pulse protection circuit is connected with a weak pulse amplification circuit, and the direct current protection circuit is connected with a weak direct current amplification circuit. The weak pulse amplification circuit is connected with a discrimination and shaping circuit; and the weak direct current amplification circuit is connected with an AD conversion circuit. The selection circuit is connected with the pulse protection circuit and the weak pulse amplification circuit by default, and is connected with the direct current protection circuit and the weak direct current amplification circuit after receiving a switching signal from a control unit. The control unit processes a standard TTL signal to obtain the number of photoelectrons, sends the switching signal to the selection circuit when the number of photoelectrons exceeds a limit, and processes a digital quantity to obtain the number of photoelectrons. The application realizes accurate counting of high-frequency weak pulse signals and accurate measurement of weak direct current signals under high voltage.

Description

Technical Field

[0001] This application relates to the field of photoelectron spectroscopy analysis, and more specifically, to a weak signal detection system for an ultraviolet photoelectron spectroscopy analyzer. Background Technology

[0002] Currently, in fields such as aerospace, chemistry, semiconductors, and medicine, there is a need to sample and detect random high-speed pulses and weak DC signals output by electronic devices. For example, a CEM (electron multiplier) is an electronic device that multiplies the number and amplifies the amplitude of electronic signals. Depending on the working mode, it can generate random high-speed pulse signals and weak DC signals.

[0003] Random high-speed pulses are characterized by high speed, strong randomness, and small pulse width, while weak DC signals are characterized by low amplitude and susceptibility to interference. This places high demands on the counting of random high-speed pulses and the acquisition and conversion of weak DC signals.

[0004] High-speed random pulses have very narrow pulse widths, typically in the nanosecond range, and are highly random. Traditional microcontroller pulse counting methods struggle to guarantee real-time and accurate counting when the input pulse frequency is very high or the pulse width is very narrow, resulting in counting errors or even failure to detect pulses. Furthermore, traditional weak DC signal detection methods struggle to distinguish noise from useful signals when the current signal is very weak, and currently there are no devices for detecting weak currents accompanied by high voltage. Summary of the Invention

[0005] In view of the above problems, this application proposes a weak signal detection system for an ultraviolet photoelectron spectroscopy analyzer to overcome the shortcomings of the prior art.

[0006] This application provides a weak signal detection system for an ultraviolet photoelectron spectroscopy analyzer, including: The pulse protection circuit and the DC protection circuit are both connected to the output of the electron multiplier via a selection circuit. The output of the pulse protection circuit is connected to the weak pulse amplifier circuit, and the output of the DC protection circuit is connected to the weak DC amplifier circuit. Both are used to isolate the high voltage in the output signal of the electron multiplier and transmit the remaining signal to their respective circuits. The weak pulse amplification circuit is connected to the discrimination and shaping circuit, and is used to amplify the remaining signal to obtain a large pulse voltage signal and transmit it to the discrimination and shaping circuit. The discrimination and shaping circuit is connected to the control unit and is used to discriminate and shape the large pulse voltage signal to obtain a standard TTL signal and transmit it to the control unit. The weak DC amplifier circuit is connected to the AD conversion circuit to amplify the remaining signal, obtain a detectable voltage signal, and transmit it to the AD conversion circuit. The AD conversion circuit is connected to the control unit and is used to perform AD conversion on the detectable voltage signal to obtain the corresponding digital quantity and transmit it to the control unit. The selection circuit is connected by default to the output terminal of the pulse protection circuit and the weak pulse amplification circuit, and is used to connect the output terminal of the DC protection circuit and the weak DC amplification circuit after receiving a switching signal from the control unit. The control unit is used to process the standard TTL signal to obtain the number of photoelectrons, and to send a switching signal to the selection circuit when the number of photoelectrons exceeds the limit. It is also used to process the digital quantity to obtain the number of photoelectrons.

[0007] Optionally, the discrimination and shaping circuit includes: a first comparator, a second comparator, a first shaper, and a second shaper; The remaining signal is received at the non-inverting inputs of both the first comparator and the second comparator. The inverting input of the first comparator receives a high threshold value from the control unit. The inverting input of the second comparator receives a low threshold from the control unit; The output of the first comparator is connected to the positive terminal of the first shaper; The output of the second comparator is connected to the positive terminal of the second shaper; The output terminals of both the first shaper and the second shaper are connected to the control unit. The first comparator is used to filter out the photoelectron pulse signal corresponding to the photoelectron and the small-amplitude pulse signal generated by thermal noise in the remaining signal, and obtain a large-amplitude pulse signal. The thermal noise is generated by high-energy ray bombardment and the noise of the electron multiplier itself. The second comparator is used to filter out the small-amplitude pulse signal generated by the thermal noise in the remaining signal, and obtain the photoelectron pulse signal and the large-amplitude pulse signal; The first shaper is used to shape the large amplitude pulse signal to obtain a first standard TTL signal; The second shaper is used to shape the photoelectron pulse signal and the amplitude pulse signal to obtain a second standard TTL signal.

[0008] Optionally, the control unit includes: a controller and a DA conversion circuit; The controller controls the DA conversion circuit via the IIC communication protocol to generate the high threshold and the low threshold.

[0009] Optionally, it also includes: low-pass filtering and differential signal conversion; The input terminal of the low-pass filter is connected to the output terminal of the DC protection circuit, and its output terminal is connected to the weak DC amplifier circuit. It is used to perform low-pass filtering on the remaining signal to obtain a stable DC signal and transmit it to the weak DC amplifier circuit. The input terminal of the differential signal converter is connected to the output terminal of the weak DC amplifier circuit, and its output terminal is connected to the AD conversion circuit. It is used to perform differential conversion processing on the detectable voltage signal to obtain a precise voltage signal and transmit it to the AD conversion circuit.

[0010] Optionally, the weak DC amplifier circuit includes: an operational amplifier and a negative feedback structure; The positive input terminal of the operational amplifier receives the remaining signal, and the negative input terminal is connected to the output terminal through the negative feedback structure. The output terminal outputs the detectable voltage signal.

[0011] Optionally, the weak DC amplifier circuit further includes: an external protection ring; the external protection ring includes: a switching circuit, a 1 GΩ high-impedance resistor, and a digital-to-analog converter; The positive input terminal of the operational amplifier is grounded through the 1 GΩ high-impedance resistor and connected to the AD conversion circuit through the switching circuit; The negative input terminal of the operational amplifier receives the remaining signal and is connected to the output terminal through the negative feedback structure, and the output terminal outputs the detectable voltage signal. The two protection terminals of the operational amplifier are respectively connected to the digital-to-analog converter and receive protection reference voltages respectively. The switching circuit is controlled by the control unit. When it receives a weak DC signal, it closes for a preset time to collect the voltage at the positive input terminal and transmit it to the AD conversion circuit. After the preset time, it opens and maintains a high impedance state. The collected voltage is assigned to two protection terminals by the control unit as the initial protection voltage. After applying an initial protection voltage to the two protection terminals, the control unit automatically adjusts the initial protection voltage according to the detectable voltage signal and converts it into the protection reference voltage through the digital-to-analog converter.

[0012] Optionally, the control unit utilizes an automatic fine-tuning algorithm to automatically adjust the initial protection voltage and convert it into the protection reference voltage via the digital-to-analog converter. The automatic fine-tuning algorithm employs dynamic threshold valley prediction plus fuzzy adaptive step size calculation. It achieves automatic adjustment by searching for the protection reference voltage value that minimizes the peak-to-peak value of the detectable voltage signal. Specifically, it includes: Using peak-to-peak values ​​within a sliding window Vpp The changing trend of the peak-to-peak value is used to dynamically calculate and predict the valley voltage; whereby, it is assumed that the peak-to-peak value... Vpp With protection reference voltage VG If the relationship locally exhibits a single-valley quadratic curve, then the three most recent measurement points in the automatic fine-tuning algorithm are ( VG k-2 , Vpp k-2 ), ( VG k-1 , Vpp k-1 ), ( VG k , Vpp k Using quadratic interpolation, the predicted valley voltage is:

[0013]

[0014]

[0015] In the above formula, express VG The predicted value, This represents the difference between the peak-to-peak value Vpp within the (k-1)th window and the peak-to-peak value Vpp within the (k-2)th window. Vpp represents the difference between the peak-to-peak value Vpp in the k-th window and that in the (k-1)-th window, where a, b, and c represent the interpolation coefficients of the quadratic interpolation. like < and If the value is greater than 0, then the predicted valley value is in the middle. The linear approximation is:

[0016] If the prediction is reliable, jump directly to VG pred Skip multiple searches in the middle; The fuzzy adaptive step size is based on the peak-to-peak value. Vpp The three inputs are the rate of change, the direction reversal count, and the current step size. The step size adjustment coefficient is output in real time through fuzzy rules. Let the input variables be E, RC, and S, and the output be α, where E represents the peak-to-peak value. Vpp The rate of change is [-0.5, 0.5], that is:

[0017] RC represents the direction reversal count within the last 10 steps [0,10], S represents the ratio of the current step size to the initial step size [0.01,1], α represents the step size adjustment coefficient, and the final step size range is [0.2,2.0]. When the peak value of 5 consecutive steps Vpp Fluctuation Vpp noise When the value is ×2 and Step < 0.1 mV, the system enters a lockout mode and stops stepping. During automatic adjustment, the peak-to-peak value is checked every 100 ms. Vpp The increment is adjusted, and if the increment exceeds the threshold, the coarse adjustment is reactivated. Vpp noise Step represents the peak-to-peak noise floor at the output. VG The single adjustment step size of the voltage.

[0018] Optionally, the specific method for the control unit to process the standard TTL signal to obtain the number of photoelectrons includes: The control unit performs a difference operation between the second standard TTL signal and the first standard TTL signal to obtain the target TTL signal; The control unit performs pulse counting on the target TTL signal, and the pulse counting result is the number of photoelectrons.

[0019] Optionally, the specific method for the control unit to process the digital quantity to obtain the number of photoelectrons includes: The control unit obtains the detectable voltage corresponding to the digital quantity by using the relationship between the ADC digital quantity and voltage. The control unit performs a difference operation between the detectable voltage and the noise voltage to obtain the denoised voltage; The control unit divides the noise reduction voltage by the amplification gain of the weak DC amplifier circuit, and then subtracts the noise current of the weak DC amplifier circuit itself to obtain the weak DC current value input to the weak DC amplifier circuit. The control unit divides the weak DC current value by the gain of the electron multiplier to obtain the photocurrent input to the electron multiplier. The control unit divides the photocurrent by the fundamental charge to obtain the number of photoelectrons.

[0020] Optionally, the controller in the control unit is an FPGA, and the clock frequency of the FPGA can reach up to 200 MHz; The data communication between the FPGA and the host computer is carried out through UART serial communication. The number of photoelectrons is transmitted to the host computer in 4 groups according to a preset baud rate. Each group contains 4 data, and each data is an 8-bit binary number, totaling 32 bits, which is used as a count value. The host computer converts the 32-bit binary number into a decimal number and displays it visually.

[0021] The weak signal detection system of the ultraviolet photoelectron spectroscopy analyzer proposed in this application has both pulse protection circuit and DC protection circuit input terminals connected to the output terminal of the electron multiplier through selection circuits; the output terminal of the pulse protection circuit is connected to the weak pulse amplification circuit, and the output terminal of the DC protection circuit is connected to the weak DC amplification circuit. The protection circuits are used to isolate the high voltage in the output signal of the electron multiplier, thereby extracting the weak signal accompanied by the high voltage. These weak signals are transmitted as residual signals to their respective corresponding circuits.

[0022] The weak pulse amplifier circuit is connected to the discrimination and shaping circuit to amplify the remaining signal, obtain a large pulse voltage signal, and transmit it to the discrimination and shaping circuit; the weak DC amplifier circuit is connected to the AD conversion circuit to amplify the remaining signal, obtain a detectable voltage signal, and transmit it to the AD conversion circuit.

[0023] Since the entire system is unaware of whether the current signal is a weak pulse signal or a weak DC signal when the electron multiplier outputs a signal, the selection circuit is connected by default to the output of the pulse protection circuit and the weak pulse amplifier circuit. It is used to connect the output of the DC protection circuit and the weak DC amplifier circuit after receiving the switching signal from the control unit.

[0024] In other words, when the electron multiplier outputs a signal, it is assumed that the current signal is a weak pulse signal. The weak pulse amplification circuit amplifies the remaining signal to obtain a large pulse voltage signal and transmits it to the discrimination and shaping circuit. The discrimination and shaping circuit is connected to the control unit and is used to discriminate and shape the large pulse voltage signal to obtain a standard TTL signal and transmit it to the control unit. The dual threshold comparison technology is used to filter out noise interference, and the discrimination and shaping of the weak pulse signal is achieved by combining a high-bandwidth operational amplifier.

[0025] The control unit processes the standard TTL signal to obtain the number of photoelectrons (or a precise number of photoelectrons if it is a weak pulse signal), and sends a switching signal to the selection circuit when the number of photoelectrons exceeds the limit (this indicates that the current signal is a weak DC signal, not a weak pulse signal).

[0026] After receiving the switching signal, the selection circuit connects the output of the DC protection circuit to the weak DC amplifier circuit. The weak DC amplifier circuit amplifies the remaining signal to obtain a detectable voltage signal and transmits it to the AD conversion circuit. The AD conversion circuit is connected to the control unit and is used to perform AD conversion on the detectable voltage signal to obtain the corresponding digital quantity and transmit it to the control unit. The control unit processes the digital quantity to obtain the number of photoelectrons.

[0027] The weak signal detection system proposed in this application abandons the traditional single measurement method. For random high-speed pulse signals, it does not use a microcontroller for pulse counting. Even with high input pulse frequencies or narrow pulse widths, it ensures real-time and accurate counting, precisely detecting pulses and reducing counting errors. For weak DC signals, even with very weak current signals, it effectively distinguishes noise from useful signals and can detect weak currents while accompanied by high voltage. It achieves accurate counting of high-frequency weak pulse signals under high voltage and precise measurement of weak DC current signals. It features strong anti-interference capabilities, high counting accuracy, and a wide dynamic range, making it suitable for precise detection of weak current signals accompanied by high voltage in aerospace, semiconductor, and other fields. It has broad application prospects and high practicality. Attached Figure Description

[0028] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a modular schematic diagram of a weak signal detection system for an ultraviolet photoelectron spectroscopy analyzer proposed in an embodiment of this application; Figure 2 This is a schematic diagram illustrating a preferred pulse protection circuit in an embodiment of this application. Figure 3 This is a schematic diagram illustrating a preferred DC protection circuit in an embodiment of this application. Figure 4 This is a schematic diagram illustrating the structure of a preferred weak pulse amplifier circuit exemplified in the embodiments of this application; Figure 5 This is a schematic diagram of the structure of the discrimination and shaping circuit exemplified in the embodiments of this application; Figure 6 This is a schematic diagram illustrating the structure of the discrimination and shaping circuit of the DA conversion circuit as exemplified in the embodiments of this application; Figure 7 This is a schematic diagram illustrating a preferred weak DC amplifier circuit with a guard ring, as exemplified in the embodiments of this application. Figure 8This is a schematic diagram of the structure of a weak DC amplifier circuit using a low leakage current analog switch MAX4661 as the switching circuit Z, as exemplified in the embodiments of this application. Figure 9 This is an architectural diagram of a weak signal detection system of an ultraviolet photoelectron spectroscopy analyzer exemplified in the embodiments of this application. Detailed Implementation

[0029] The embodiments of this application will now be described in detail. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0030] This application discloses a weak signal detection system for an ultraviolet photoelectron spectroscopy analyzer, referencing... Figure 1 The modular schematic diagram shown illustrates that the weak signal detection system of the ultraviolet photoelectron spectroscopy analyzer includes: a pulse protection circuit, a DC protection circuit, a selection circuit, a weak pulse amplification circuit, a weak DC amplification circuit, a discrimination and shaping circuit, an AD conversion circuit, and a control unit.

[0031] The pulse protection circuit and DC protection circuit both have their inputs connected to the output of the electron multiplier (usually the anode terminal) via a selection circuit. When a single photoelectron strikes the sample, it generates photoelectrons, which are then amplified by the channel electron multiplier (CMM). Figure 1 (Represented by CEM in Chinese) The input is multiplied to 10 after attraction. 7 ~10 8 Each photoelectron is absorbed by the anode plate and forms a pulsed current. This usually corresponds to a weak pulse signal. However, when the number of photoelectrons is too large, the output signal of the electron multiplier will change from a weak pulse signal to a weak DC current signal, or simply a weak DC signal.

[0032] The output of the pulse protection circuit is connected to the weak pulse amplifier circuit, and the output of the DC protection circuit is connected to the weak DC amplifier circuit. Both are used to isolate the high voltage in the output signal of the electron multiplier, thereby extracting the weak signal accompanied by the high voltage. These weak signals are transmitted to their respective circuits as residual signals.

[0033] The weak pulse amplification circuit is connected to the discrimination and shaping circuit to amplify the remaining signal, obtain a large pulse voltage signal, and transmit it to the discrimination and shaping circuit. The discrimination and shaping circuit is connected to the control unit to discriminate and shape the large pulse voltage signal, obtain a standard TTL signal, and transmit it to the control unit.

[0034] The weak DC amplifier circuit is connected to the AD conversion circuit to amplify the remaining signal, obtain a detectable voltage signal, and transmit it to the AD conversion circuit; the AD conversion circuit is connected to the control unit to perform AD conversion on the detectable voltage signal, obtain the corresponding digital quantity, and transmit it to the control unit.

[0035] The selection circuit is by default connected to the output of the pulse protection circuit and the weak pulse amplifier circuit. It is used to connect the output of the DC protection circuit and the weak DC amplifier circuit only after receiving a switching signal from the control unit. This is because: Since the weak signal detection system is unaware of whether the signal is a weak pulse or a weak DC signal when the electron multiplier outputs a signal, the selection circuit is connected by default to the output of the pulse protection circuit and the weak pulse amplification circuit. The weak pulse amplification circuit amplifies the remaining signal to obtain a large pulse voltage signal, which is then transmitted to the discrimination and shaping circuit. The discrimination and shaping circuit discriminates and shapes the large pulse voltage signal to obtain a standard TTL signal, which is then transmitted to the control unit. It uses a dual threshold comparison technique to filter out noise interference and combines a high-bandwidth operational amplifier to achieve the discrimination and shaping of the weak pulse signal.

[0036] The control unit processes the standard TTL signal to obtain the number of photoelectrons (or a precise number of photoelectrons if it is a weak pulse signal), and when the number of photoelectrons exceeds the limit (this indicates that the current signal is a weak DC signal, not a weak pulse signal), the control unit sends a switching signal to the selection circuit.

[0037] After receiving the switching signal, the selection circuit connects the output of the DC protection circuit to the weak DC amplifier circuit. The weak DC amplifier circuit amplifies the remaining signal to obtain a detectable voltage signal and transmits it to the AD conversion circuit. The AD conversion circuit performs AD conversion on the detectable voltage signal to obtain the corresponding digital quantity and transmits it to the control unit. The control unit processes the digital quantity to obtain the number of photoelectrons.

[0038] In one embodiment of this application, the pulse protection circuit and the DC protection circuit can be implemented using various types of devices or integrated circuits. Below, only one circuit structure of each is briefly exemplified, without going into detail.

[0039] For pulse protection circuits, refer to Figure 2The diagram shows a preferred circuit structure. The SHV detector represents the signal output by the electron multiplier, which includes a high voltage and a residual signal. Capacitors C1 and C2 isolate the DC high voltage; preferably, 6000 V high-voltage 4.7 nF ceramic capacitors can be used. Resistors R1 and R2 are high-value resistors to reduce current shunting; preferably, 10 kV high-voltage 10 MΩ resistors can be used. This circuit structure ensures that the high voltage in the weak pulse signal SHV detector from the electron multiplier output is isolated, resulting in the residual signal BNC AMP. This residual signal is then transmitted to the weak pulse amplification circuit via a coaxial cable.

[0040] For DC protection circuits, refer to... Figure 3 The diagram shows a preferred circuit structure, where the coaxial cable serves as the high-voltage source. Figure 3 (Not shown) A cable that outputs high voltage; SHV detector indicates an electron multiplier (…). Figure 3 (Not shown in the image) The output signal, Figure 3 The diagram only shows a schematic of one path supplying power to the anode of the electron multiplier, as the current to be detected is also the anode current. The workflow is as follows: a high-voltage source supplies power to the anode of the electron multiplier. After the electron multiplier voltage is successfully configured, it collects photoelectrons. These photoelectrons multiply inside the electron multiplier, forming a weak current at the anode. This current appears in the circuit. The section consisting of the ADA4530-1 and ADS1256 can be understood as an ammeter, but this ammeter is connected in series on the high-voltage side. Therefore, the ADA4530-1 and its surrounding circuitry are designed with a floating ground to isolate the high voltage. The ADS1256 and FPGA are at a low potential and will not be damaged by the high voltage. This method achieves DC protection.

[0041] In one embodiment of this application, a weak pulse amplification circuit can employ various types of devices or integrated circuits to implement its pulse signal amplification function. Only one amplification circuit is briefly illustrated below. (Refer to...) Figure 4 The diagram shows a preferred weak pulse amplifier circuit, which consists of a first-stage amplifier and a second-stage amplifier. The first-stage amplifier employs a charge-sensitive amplifier circuit. Figure 4BNC represents the residual signal. The OPA657 amplifier and its peripheral structure form a charge-sensitive amplifier circuit, which features high sensitivity and low noise, capable of converting negative pulse currents with amplitudes in the microamplitude range into positive voltage signals with amplitudes in the hundreds of mV range. The OPA657's IN- and VOUT pins are designed with negative feedback, consisting of a 10 kΩ negative feedback resistor and a 2 pF negative feedback capacitor. The 10 kΩ negative feedback resistor primarily discharges the charge on the 2 pF negative feedback capacitor and generates negative feedback to stabilize the DC operating point of the OPA657 amplifier. Furthermore, this integral feedback structure effectively suppresses input capacitance, improving the signal-to-noise ratio and stability.

[0042] The second-stage amplification uses an in-phase voltage amplifier circuit, which takes the output of the first-stage amplification as its input. The MAX4414 amplifier amplifies the pulse voltage output from the previous stage by 2 times and outputs it through VOUT. This facilitates the identification and processing by the subsequent discrimination and shaping circuits. It also more effectively separates the photoelectronic signal and the noise signal, making it easier to set the threshold and extract the target pulse signal.

[0043] In one embodiment of this application, the structure of the discrimination and shaping circuit is referenced. Figure 5 As shown, it includes: a first comparator and a second comparator. Figure 5 In Chinese, it is directly represented by CMP. The first shaper and the second shaper are two shapers. Figure 5 They are denoted as L1 and L2 respectively.

[0044] The non-inverting inputs of both the first and second comparators CMP receive the remaining signal VOUT, where INA is the input of the first comparator and INB is the input of the second comparator; the inverting input INA of the first comparator receives the signal from the control unit ( Figure 5 The high threshold HIGH_GATE (not shown in the diagram) of the second comparator is received at the inverting input INB- of the control unit, which receives the low threshold LOW_GATE.

[0045] The output of the first comparator is connected to the positive terminal of the first shaper L1, and its output is OUTA; the output of the second comparator is connected to the positive terminal of the second shaper L2, and its output is OUTB; the outputs of the first shaper L1 and the second shaper L2 are both connected to the control unit.

[0046] The first comparator is used to filter out the photoelectron pulse signal corresponding to the photoelectron and the small-amplitude pulse signal generated by thermal noise in the remaining signal, and obtains the large-amplitude pulse signal OUTA. The thermal noise is generated by high-energy ray bombardment and the noise of the electron multiplier itself. The second comparator is used to filter out the small-amplitude pulse signal generated by thermal noise in the remaining signal, and obtains the photoelectron pulse signal and the large-amplitude pulse signal. That is, OUTB includes the photoelectron pulse signal and the large-amplitude pulse signal OUTA.

[0047] The first shaper is used to shape the large amplitude pulse signal OUTA to obtain the first standard TTL signal HIGH_OUT; the second shaper is used to shape the photoelectron pulse signal and the large amplitude pulse signal OUTB to obtain the second standard TTL signal LOW_OUT.

[0048] In one embodiment of this application, for the high threshold and the low threshold, a preferred approach is to use a control unit to set them. Therefore, the control unit preferably includes: a controller and a DA conversion circuit. The controller controls the DA conversion circuit via the IIC communication protocol to generate high and low threshold values. For a better understanding of this structure, refer to... Figure 6 The diagram shown illustrates the structure of the discrimination and shaping circuitry in the DA conversion circuit. Figure 6 The diagram uses two specific models, PCF8591T, as examples to represent the DA and shows its connection to the discrimination and shaping circuits.

[0049] Controller ( Figure 6 (Not shown in the image) This describes the IIC communication protocol controlling two D / A conversion chips, PCF8591, to output a certain analog voltage as input to two comparators to achieve adjustment of both large and small thresholds. At the high threshold, small-amplitude pulse signals generated by target photoelectron pulse signals and thermal noise are filtered out, and OUTA outputs large-amplitude pulse signals caused by high-energy ray bombardment, etc. At the low threshold, small-amplitude pulse signals generated by thermal noise are filtered out, and OUTB outputs large-amplitude pulse signals caused by target photoelectron pulse signals and high-energy ray bombardment, etc. Then, a shaper further shapes and transforms the two signals OUTA and OUTB output from the aforementioned circuit, transforming the distorted pulse signals caused by interference into standard TTL square wave signals with shorter rise and fall times, which are then input to the controller.

[0050] In one embodiment of this application, a preferred structure for a weak DC amplifier circuit may include an operational amplifier and a negative feedback structure. The positive input terminal of the operational amplifier receives a DC signal, and the negative input terminal is connected to the output terminal through the negative feedback structure. The output terminal outputs a detectable voltage signal. Preferably, an ultra-low bias current precision operational amplifier ADA4530-1 can be selected to construct a transimpedance amplifier circuit. It has an input bias current of 20 fA, an input offset voltage of 9 μV, and a current noise density of 6 fA / √Hz, exhibiting extremely low input bias current, low noise, and a wide output range.

[0051] In the negative feedback structure, the feedback resistor can preferably be either 10 kΩ or 10 GΩ, and the feedback capacitor can preferably be 1 μF. Connecting them in parallel forms the negative feedback structure, which also has a low-pass filtering function, retaining the target DC signal while filtering out high-frequency noise. With a 10 GΩ feedback resistor, the output current of the electron multiplier anode under test (10 pA~200 pA) can be amplified by 10 times, resulting in a voltage signal of 100 mV~2 V. With a 10 kΩ feedback resistor, the output current of the electron multiplier anode under test (200 pA~200 μA) can be amplified by 1000 times, resulting in a voltage signal of 2 μV~2 V.

[0052] The DC weak amplifier circuit composed of the above-mentioned operational amplifier and negative feedback structure can generally be used directly. However, considering the weak DC current input at the pA level, and to prevent the adverse effects of leakage current, capacitive coupling interference, and EMI at the circuit input, and to improve and ensure detection accuracy, this application creatively proposes an external protection ring design method. This protection ring has the following features: Reference Figure 7 The diagram shows a preferred weak pulse amplifier circuit with a guard ring. Figure 7 In this context, OPA represents an operational amplifier, with the ADA4530-1 being a preferred choice. The signal input via the coaxial cable is also the residual signal. The positive input terminal IN+ of the ADA4530-1 operational amplifier's OPA is grounded through a 1 GΩ high-impedance resistor and then connected to the AD conversion circuit via a switching circuit Z. Figure 7 (Not shown in the diagram) The negative input terminal IN- receives the remaining signal and is connected to the output terminal OUT through a negative feedback structure (composed of a 10kΩ and a 10GΩ feedback resistor and a 1μF feedback capacitor connected in parallel). The output terminal OUT outputs a detectable voltage signal VOUT. The two protection terminals GRD of the operational amplifier are connected to the digital-to-analog converter DACZ, respectively, and receive the protection reference voltage. VG This type of protection ring is an external protection ring, and is an automatic following protection ring creatively proposed in this application. It obtains the protection reference voltage by directly setting the initial protection voltage externally and then automatically adjusting it. VGThis is to achieve the aforementioned function of the follow-protection ring.

[0053] The switching circuit Z is controlled by the control unit. When it receives a weak DC signal, it closes for a preset time to collect the voltage at the positive input terminal IN+ and transmit it to the AD conversion circuit. After the preset time, it opens and maintains a high-impedance state. The collected voltage is assigned to the two protection terminals GRD by the control unit as the initial protection voltage; the protection reference voltage... VG The initial protection voltage is obtained after automatic adjustment. After the initial protection voltage is applied to the two protection terminals GRD, the initial protection voltage is automatically adjusted according to the detectable voltage signal VOUT and converted into a protection reference voltage by the digital-to-analog converter DACZ. VG A better approach is to use a digital-to-analog converter (DACZ) to convert the digital signal sent by the control unit into a corresponding analog signal to obtain the initial protection voltage. Utilizing the virtual short circuit of the operational amplifier IN+=IN-, after the current signal enters the system circuit, the IN+ voltage is detected within a preset time to obtain the approximate voltage range of the signal input terminal IN-. This initial protection voltage is then set as the initial protection reference voltage for the GRD. Immediately afterwards, the non-inverting voltage test circuit is disconnected to ensure that no other external inputs enter the weak current detection circuit.

[0054] It should be noted that some traditional technologies use a follower protection ring, also known as the traditional "GRD voltage follows the signal input voltage." The core logic of this follower protection ring is passive adaptation to the input potential, and its development focuses on manual, precise controllability and extremely simple, stable circuitry. Because this traditional follower protection ring solution connects the input signal terminal to the protection ring, forcing the protection ring voltage to be set to the input signal voltage, and using PCB routing to wrap the input signal line within the protection ring, causing PCB leakage current to flow into the follower protection ring instead of the signal line, those skilled in the art will inevitably pursue further research based on this traditional follower protection ring technology by using more precise operational amplifiers to make the GRD equal to the signal input voltage, thus eliminating following errors. This reflects a current technical bias in the field.

[0055] However, the inventors discovered that this technical bias faces technical limitations: the potential matching between GRD and IN- depends entirely on the follower op-amp, and the op-amp itself has an input offset voltage (usually in the μV range) and temperature drift (in the ppm / ℃ range), which will cause ΔV to fail to approach 0, ultimately leaving a residual pA-level leakage current, making it difficult to meet the requirements for weak current detection in the pA or even fA range; and once the circuit is deployed, the following relationship between GRD and the signal input terminal IN- is fixed, which cannot cope with changes in long-term use such as device aging and PCB surface contamination, and the deviation will accumulate over time, and the leakage current suppression effect will continue to decay.

[0056] To address the aforementioned technical biases and limitations of creative discovery, the inventors innovatively proposed an external protection ring, an automatic following protection ring designed for weak current detection scenarios with stringent requirements regarding cost, complexity, and reliability. By externally setting the protection ring voltage GRD, and directly matching the input port potential, it achieves high matching and long-term stable leakage current suppression. Its core principle is equipotential shielding and leakage current suppression: the core challenge in weak current detection is leakage current interference—PCB substrate, device packaging, or environmental humidity can create stray resistance paths, causing external leakage current to flow into the high-impedance input port (IN-), superimposed on the weak current being measured, resulting in measurement distortion. According to the leakage current calculation formula:

[0057] in, V in This is the input port potential. VG The protection reference voltage for the external protection ring. R leak This refers to stray insulation resistance. The core principle of this application is equipotential shielding: through automatic adjustment... VG ≈ V in This allows the potential difference between the external protection ring and the input port to approach zero, thereby reducing leakage current. I leak The signal is suppressed to below the pA level (ideally ≈0) to achieve the purpose of shielding leakage current interference. Simultaneously, the external protective copper ring forms a low-impedance "Faraday cage," surrounding the sensitive input node and feedback network, blocking external electric field coupling interference, and further ensuring signal integrity. The design was creatively implemented using the following design concept: For the non-inverting input IN+ reference potential design: a 1 GΩ high-impedance resistor is connected to AGND (ground) to provide a stable bias for the floating input signal and avoid... V in Potential drift, while the characteristics of a 1 GΩ high-resistance resistor do not affect weak current input.

[0058] For GRD voltage setting: The digital quantity sent by the control unit is converted into the corresponding analog quantity, i.e., the initial protection voltage, through the digital-to-analog converter (DAC).

[0059] For automatic voltage matching adjustment of GRD, the following applies: V in Voltage Measurement: A switching circuit is set up. After the signal enters the circuit, the voltage at the non-inverting input terminal is measured (this voltage is the analog voltage obtained after the digital quantity sent by the control unit is converted by the digital-to-analog converter (DACZ), which is also the initial protection voltage). By utilizing the virtual short of the op-amp, the approximate voltage range at the inverting terminal is obtained, and this voltage is set as... VG The initial voltage is then immediately determined, and the non-inverting voltage test circuit is immediately disconnected to ensure that no other external input enters the weak current detection circuit. Automatic adjustment is then performed afterward.

[0060] Reference Figure 8 The diagram shows the structure of a weak DC amplifier circuit that uses a low-leakage-current analog switch MAX4661 as the switching circuit Z. Figure 8 The DACZ (Digital-to-Analog Converter) is omitted. The low-leakage-current analog switch MAX4661's on-resistance does not affect high-resistance measurements. The MAX4661 four-channel analog switch has a low on-resistance of up to 2.5 Ω. It provides a maximum on-resistance matching between switches of up to 0.5 Ω, with a maximum shutdown leakage current of only 5 nA. Any normally closed switch of the MAX4661 can be used. It remains open when not in measurement mode, and a high level on the control pin in the non-measurement state opens the switch. When switched to DC mode (i.e., after receiving a weak DC signal), the control unit issues a low-level command, the MAX4661 closes, and samples the voltage at the positive input terminal IN+, inputting it to the AD conversion circuit. Subsequently, the control unit issues a high-level command to open the MAX4661, without affecting the current detection loop. The sampled voltage at the positive input terminal IN+ is assigned to the protection terminal GRD by the control unit as the initial protection voltage, determining the approximate range for subsequent protection loop voltage fine-tuning.

[0061] During automatic adjustment, the static potential can be matched first: establish VG and V in The reference equipotential is established to reduce initial leakage current; then, dynamic potential is matched: after the control unit obtains the detectable voltage signal VOUT, it calculates the peak-to-peak value Vpp of VOUT in real time. The initial protection voltage is automatically adjusted and converted into a protection reference voltage via a digital-to-analog converter. VG This minimizes the peak-to-peak value of VOUT (Vpp), indicating that the leakage current is minimized. I leak The situation has been effectively contained.

[0062] In one embodiment of this application, the control unit uses an automatic fine-tuning algorithm to automatically adjust the initial protection voltage and converts it into a protection reference voltage via a digital-to-analog converter. VGThe automatic fine-tuning algorithm uses dynamic threshold valley prediction plus fuzzy adaptive step size for calculation. It achieves automatic adjustment by searching for the protection reference voltage value that minimizes the peak-to-peak value of the detectable voltage signal. Specifically, it includes: Using peak-to-peak values ​​within a sliding window Vpp The changing trend of the valley voltage is dynamically calculated and predicted; this can directly skip large sections of invalid search areas and greatly reduce the number of iterations.

[0063] Assuming peak-to-peak value Vpp With protection reference voltage VG If the relationship locally exhibits a single-valley quadratic curve, then the three most recent measurement points in the automatic fine-tuning algorithm are ( VG k-2 , Vpp k-2 ), ( VG k-1 , Vpp k-1 ), ( VG k , Vpp k Using quadratic interpolation, the predicted valley voltage is:

[0064]

[0065]

[0066] In the above formula, express VG The predicted value, This represents the difference between the peak-to-peak value Vpp within the (k-1)th window and the peak-to-peak value Vpp within the (k-2)th window. Vpp represents the difference between the peak-to-peak value Vpp in the k-th window and that in the (k-1)-th window, where a, b, and c represent the interpolation coefficients of the quadratic interpolation. like < and If the value is greater than 0, then the predicted valley value is in the middle. The linear approximation is:

[0067] When the prediction is reliable (e.g., two consecutive reversals), jump directly to... VG pred Skip multiple searches in the middle.

[0068] Fuzzy adaptive step size based on peak-to-peak value VppThe three inputs are the rate of change, the direction reversal count, and the current step size. The step size adjustment coefficient is output in real time through fuzzy rules, thus realizing the adaptive switching from fast coarse adjustment to smooth fine adjustment to extremely low dead zone.

[0069] Let the input variables be E, RC, and S, and the output be α, where E represents the rate of change of the peak-to-peak value Vpp [-0.5, 0.5], i.e.:

[0070] RC represents the direction reversal count within the last 10 steps [0,10], S represents the ratio of the current step size to the initial step size [0.01,1], α represents the step size adjustment coefficient, and the final step size range is [0.2,2.0]. ,in Step now Indicates the latest step size. Step old Indicates the old step size.

[0071] A partial example of the fuzzy rule table is shown in Table 1 below:

[0072] Table 1 When the peak value of 5 consecutive steps Vpp Fluctuation Vpp noise When the value is ×2 and Step < 0.1 mV, the system enters a lockout mode and stops stepping. During automatic adjustment, the peak-to-peak value is checked every 100 ms. Vpp The increment is adjusted, and if the increment exceeds the threshold, the coarse adjustment is reactivated. Vpp noise Step represents the peak-to-peak noise level at the system output. VG The single adjustment step size of the voltage.

[0073] The above method achieves the function of the outer protection ring, preventing the adverse effects of leakage current, capacitive coupling interference and EMI at the circuit input terminal, thereby improving and ensuring detection accuracy.

[0074] In one embodiment of this application, the control unit processes a standard TTL signal to obtain the number of photoelectrons. The specific method includes: the control unit performs a difference operation between the second standard TTL signal and the first standard TTL signal to obtain a target TTL signal; the control unit performs pulse counting on the target TTL signal, and the pulse counting result is the number of photoelectrons.

[0075] In one embodiment of this application, the control unit processes digital quantities to obtain the number of photoelectrons using a specific method including: For digital quantities, the control unit uses the relationship between the ADC digital value and the voltage to obtain the detectable voltage corresponding to that digital value; this is equivalent to the ADC dividing the reference voltage into corresponding bits. For example, assuming the ADC is 24 bits and the reference voltage is 5 V, then 0000 0000 0000 0001, or 1 bit, is equivalent to 5 / 2. 24 This logic allows us to determine the detectable voltage corresponding to a digital quantity by relating it to the voltage through an ADC.

[0076] The control unit calculates the difference between the detectable voltage and the noise voltage to obtain the denoised voltage. The control unit divides the denoised voltage by the amplification gain of the weak DC amplifier circuit and then subtracts the noise current of the weak DC amplifier circuit itself (i.e., the thermal noise of the feedback resistor and the noise of the precision operational amplifier in the weak DC amplifier circuit) to obtain the weak DC current value input to the weak DC amplifier circuit.

[0077] The control unit then divides the weak DC current value by the gain of the electron multiplier to obtain the photocurrent input to the electron multiplier; finally, the control unit divides the photocurrent by the elementary charge to obtain the number of photoelectrons.

[0078] In one embodiment of this application, in order to obtain a more stable weak DC signal and accurate digital quantity, the weak signal detection system may preferably include: low-pass filtering and differential signal conversion.

[0079] The input of the low-pass filter is connected to the output of the DC protection circuit, and its output is connected to the weak DC amplifier circuit. It is used to perform low-pass filtering on the remaining signal to obtain a stable DC signal and transmit it to the weak DC amplifier circuit. The input of the differential signal converter is connected to the output of the weak DC amplifier circuit, and its output is connected to the AD conversion circuit. It is used to perform differential conversion processing on the detectable voltage signal to obtain a precise voltage signal and transmit it to the AD conversion circuit.

[0080] In one embodiment of this application, the controller of the control unit is preferably an FPGA, with a clock frequency of up to 200 MHz. Data communication between the FPGA and the host computer is conducted via UART serial communication. The FPGA transmits the number of photoelectrons to the host computer in four groups according to a preset baud rate. Each group contains four data points, with each data point being an 8-bit binary number (32 bits) used as a count value. The host computer converts the 32-bit binary number into a decimal number and displays it visually, allowing staff to intuitively understand the number of photoelectrons.

[0081] For an FPGA, its internal components mainly include a counting module, a D / A converter control module, an A / D converter control module, a UART serial communication module, a phase-locked loop module, and a clock divider module. The counting module internally generates a square wave gating signal with a high-level duration of 1 second and a duty cycle of 50%. During the high-level period, the count value increments by 1 after detecting the rising edge of the pulse signal; during the low-level period, the count value is sent to the host computer and then reset to zero for counting in the next cycle.

[0082] The D / A converter control module describes the IIC communication protocol to control the AD module to output the expected dual-threshold voltage, i.e., a high threshold and a low threshold. The A / D converter control module describes the SPI communication protocol to control the AD circuit to acquire the digital voltage value after passing through a weak DC amplification circuit. The UART serial communication module describes the UART communication protocol, which sends the count value to the host computer in four 32-bit binary numbers at the set baud rate for processing.

[0083] The phase-locked loop (PLL) module is used for frequency multiplication, multiplying the system clock from a base frequency of 50 MHz to 200 MHz, thereby increasing the system's sampling rate and reducing errors. The clock divider module is used to divide the system clock by different proportions to obtain sub-clocks that are provided to each module.

[0084] All the preferred structures described above can be referred to Figure 9 The diagram illustrates the architecture of a weak signal detection system for an ultraviolet photoelectron spectroscopy analyzer, providing a better understanding. The dual-mode channel electron multiplier, specifically the electron multiplier output, is connected to both a pulse protection circuit and a DC protection circuit via a selection circuit.

[0085] The output of the pulse protection circuit is connected to the weak pulse amplifier circuit, and the output of the DC protection circuit is connected to the weak DC amplifier circuit through a low-pass filter. The weak pulse amplifier circuit (preferably including charge-sensitive amplification and two-stage amplification) is connected to the discrimination and shaping circuit. The discrimination and shaping circuit first distinguishes between high and low threshold signals, and then shapes the pulse signal. The high and low thresholds used for high and low threshold signal discrimination are generated by the FPGA through a DAC. The discrimination and shaping circuit transmits the standard TTL signal to the control unit FPGA. Weak DC amplifier circuit ( Figure 9 (Taking a voltage follower-type protection loop as an example) It is connected to the AD conversion circuit through differential signal conversion, and the detectable voltage signal is differentially processed and then transmitted to the AD conversion circuit; the AD conversion circuit can be integrated with the FPGA. Figure 9 (The two are shown in a dashed box). Of course, they can also be separated from the FPGA. In either case, the AD conversion circuit is connected to the control unit and transmits the corresponding digital quantity to the control unit FPGA.

[0086] The selection circuit is connected by default to the output of the pulse protection circuit and the weak pulse amplifier circuit. It is used to connect the output of the DC protection circuit and the weak DC amplifier circuit after receiving the switching signal from the control unit FPGA.

[0087] Data communication between the control unit and the host computer is achieved through UART serial communication. Preferably, a communication module of model CH340C can be selected to transmit the photoelectron quantity to the host computer for conversion and visualization display.

[0088] A superior host computer can be used to design corresponding software. For example, in the Visual Studio integrated development environment, host computer software can be developed based on C# WinForms. The screen UI can be designed with three sections: parameter settings, data display, and result statistics. This allows the photoelectric counting system to display measurement results in both pulse and DC modes, meeting the needs of photoelectric signal acquisition scenarios and achieving the purpose of human-computer interaction.

[0089] In the host computer program, a `SerialPort` object is instantiated using the `SerialPort` class. Ideally, a serial port data reception event should be triggered when there are 4 bytes of data in the buffer, extracting the 4 bytes of data from the buffer into a predefined byte array. In pulse mode, these 4 sets of 32-bit binary numbers represent the FPGA count value; converting them to decimal gives the number of photoelectrons measured by the FPGA in pulse mode. In DC mode, these 4 sets of 32-bit binary numbers can be the voltage values ​​acquired by the AD conversion circuit; the number of photoelectrons in DC mode can be calculated using a formula (the FPGA can also perform the conversion and directly transmit the number of photoelectrons). In both modes, the host computer can dynamically plot a time-photon count scatter plot, simultaneously calculating the maximum, minimum, and average values. The program can provide automatic line wrapping, data clearing functions, and supports generating timestamp CSV files for data export based on a set number of sampling times.

[0090] The above Figures 2-8 All specific models and resistance and capacitance values ​​shown are merely exemplary examples for better understanding of the technical solutions proposed in this application, and do not imply that only these models of components and resistors and capacitors with these resistance and capacitance values ​​can be used. All other models of components or integrated circuits with different parameters that can achieve the above functions can be substituted, and all fall within the scope of protection of this application.

[0091] In summary, the weak signal detection system of the ultraviolet photoelectron spectroscopy analyzer proposed in this application has both pulse protection circuit and DC protection circuit input terminals connected to the output terminal of the electron multiplier through selection circuits; the output terminal of the pulse protection circuit is connected to the weak pulse amplification circuit, and the output terminal of the DC protection circuit is connected to the weak DC amplification circuit. The protection circuits are used to isolate the high voltage in the output signal of the electron multiplier, thereby extracting the weak signal accompanied by the high voltage. These weak signals are transmitted as residual signals to their respective corresponding circuits.

[0092] The weak pulse amplifier circuit is connected to the discrimination and shaping circuit to amplify the remaining signal, obtain a large pulse voltage signal, and transmit it to the discrimination and shaping circuit; the weak DC amplifier circuit is connected to the AD conversion circuit to amplify the remaining signal, obtain a detectable voltage signal, and transmit it to the AD conversion circuit.

[0093] Since the entire system is unaware of whether the current signal is a weak pulse signal or a weak DC signal when the electron multiplier outputs a signal, the selection circuit is connected by default to the output of the pulse protection circuit and the weak pulse amplifier circuit. It is used to connect the output of the DC protection circuit and the weak DC amplifier circuit after receiving the switching signal from the control unit.

[0094] In other words, when the electron multiplier outputs a signal, it is assumed that the current signal is a weak pulse signal. The remaining signal in the weak pulse amplifier circuit is amplified to obtain a large pulse voltage signal and transmitted to the discrimination and shaping circuit. The discrimination and shaping circuit is connected to the control unit and is used to discriminate and shape the large pulse voltage signal to obtain a standard TTL signal and transmit it to the control unit. The dual threshold comparison technology is used to filter out noise interference, and the discrimination and shaping of the weak pulse signal is achieved by combining a high-bandwidth operational amplifier.

[0095] The control unit processes the standard TTL signal to obtain the number of photoelectrons (or a precise number of photoelectrons if it is a weak pulse signal), and sends a switching signal to the selection circuit when the number of photoelectrons exceeds the limit (this indicates that the current signal is a weak DC signal, not a weak pulse signal).

[0096] After receiving the switching signal, the selection circuit connects the output of the DC protection circuit to the weak DC amplifier circuit. The weak DC amplifier circuit amplifies the remaining signal to obtain a detectable voltage signal and transmits it to the AD conversion circuit. The AD conversion circuit is connected to the control unit and is used to perform AD conversion on the detectable voltage signal to obtain the corresponding digital quantity and transmit it to the control unit. The control unit processes the digital quantity to obtain the number of photoelectrons.

[0097] The weak signal detection system proposed in this application abandons the traditional single measurement method. For random high-speed pulse signals, it does not use a microcontroller for pulse counting. Even with high input pulse frequencies or narrow pulse widths, it ensures real-time and accurate counting, precisely detecting pulses and reducing counting errors. For weak DC signals, even with very weak current signals, it effectively distinguishes noise from useful signals and can detect weak currents while accompanied by high voltage. It achieves accurate counting of high-frequency weak pulse signals under high voltage and precise measurement of weak DC current signals. It features strong anti-interference capabilities, high counting accuracy, and a wide dynamic range, making it suitable for precise detection of weak current signals accompanied by high voltage in aerospace, semiconductor, and other fields. It has broad application prospects and high practicality.

[0098] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0099] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0100] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims. All of these forms are within the protection scope of this application.

[0101] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0102] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0103] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims. All of these forms are within the protection scope of this application.

Claims

1. A weak signal detection system for an ultraviolet photoelectron spectroscopy analyzer, characterized in that, include: The pulse protection circuit and the DC protection circuit are both connected to the output of the electron multiplier via a selection circuit. The output of the pulse protection circuit is connected to the weak pulse amplifier circuit, and the output of the DC protection circuit is connected to the weak DC amplifier circuit. Both are used to isolate the high voltage in the output signal of the electron multiplier and transmit the remaining signal to their respective circuits. The weak pulse amplification circuit is connected to the discrimination and shaping circuit, and is used to amplify the remaining signal to obtain a large pulse voltage signal and transmit it to the discrimination and shaping circuit. The discrimination and shaping circuit is connected to the control unit and is used to discriminate and shape the large pulse voltage signal to obtain a standard TTL signal and transmit it to the control unit. The weak DC amplifier circuit is connected to the AD conversion circuit to amplify the remaining signal, obtain a detectable voltage signal, and transmit it to the AD conversion circuit. The AD conversion circuit is connected to the control unit and is used to perform AD conversion on the detectable voltage signal to obtain the corresponding digital quantity and transmit it to the control unit. The selection circuit is connected by default to the output terminal of the pulse protection circuit and the weak pulse amplification circuit, and is used to connect the output terminal of the DC protection circuit and the weak DC amplification circuit after receiving a switching signal from the control unit. The control unit is used to process the standard TTL signal to obtain the number of photoelectrons, and to send a switching signal to the selection circuit when the number of photoelectrons exceeds the limit. It is also used to process the digital quantity to obtain the number of photoelectrons.

2. The weak signal detection system according to claim 1, characterized in that, The discrimination and shaping circuit includes: a first comparator, a second comparator, a first shaper, and a second shaper; The remaining signal is received at the non-inverting inputs of both the first comparator and the second comparator. The inverting input of the first comparator receives a high threshold value from the control unit. The inverting input of the second comparator receives a low threshold from the control unit; The output of the first comparator is connected to the positive terminal of the first shaper; The output of the second comparator is connected to the positive terminal of the second shaper; The output terminals of both the first shaper and the second shaper are connected to the control unit. The first comparator is used to filter out the photoelectron pulse signal corresponding to the photoelectron and the small-amplitude pulse signal generated by thermal noise in the remaining signal, and obtain a large-amplitude pulse signal. The thermal noise is generated by high-energy ray bombardment and the noise of the electron multiplier itself. The second comparator is used to filter out the small-amplitude pulse signal generated by the thermal noise in the remaining signal, and obtain the photoelectron pulse signal and the large-amplitude pulse signal; The first shaper is used to shape the large amplitude pulse signal to obtain a first standard TTL signal; The second shaper is used to shape the photoelectron pulse signal and the amplitude pulse signal to obtain a second standard TTL signal.

3. The weak signal detection system according to claim 2, characterized in that, The control unit includes: a controller and a DA conversion circuit; The controller controls the DA conversion circuit via the IIC communication protocol to generate the high threshold and the low threshold.

4. The weak signal detection system according to claim 1, characterized in that, Also includes: Low-pass filtering and differential signal conversion; The input terminal of the low-pass filter is connected to the output terminal of the DC protection circuit, and its output terminal is connected to the weak DC amplifier circuit. It is used to perform low-pass filtering on the remaining signal to obtain a stable DC signal and transmit it to the weak DC amplifier circuit. The input terminal of the differential signal converter is connected to the output terminal of the weak DC amplifier circuit, and its output terminal is connected to the AD conversion circuit. It is used to perform differential conversion processing on the detectable voltage signal to obtain a precise voltage signal and transmit it to the AD conversion circuit.

5. The weak signal detection system according to claim 1, characterized in that, The weak DC amplifier circuit includes: an operational amplifier and a negative feedback structure; The positive input terminal of the operational amplifier receives the remaining signal, and the negative input terminal is connected to the output terminal through the negative feedback structure. The output terminal outputs the detectable voltage signal.

6. The weak signal detection system according to claim 5, characterized in that, The weak DC amplifier circuit also includes: an external protection ring; the external protection ring includes: a switching circuit, a 1 GΩ high-impedance resistor, and a digital-to-analog converter; The positive input terminal of the operational amplifier is grounded through the 1 GΩ high-impedance resistor and connected to the AD conversion circuit through the switching circuit; The negative input terminal of the operational amplifier receives the remaining signal and is connected to the output terminal through the negative feedback structure, and the output terminal outputs the detectable voltage signal. The two protection terminals of the operational amplifier are respectively connected to the digital-to-analog converter and receive protection reference voltages respectively. The switching circuit is controlled by the control unit. When it receives a weak DC signal, it closes for a preset time to collect the voltage at the positive input terminal and transmit it to the AD conversion circuit. After the preset time, it opens and maintains a high impedance state. The collected voltage is assigned to two protection terminals by the control unit as the initial protection voltage. After applying an initial protection voltage to the two protection terminals, the control unit automatically adjusts the initial protection voltage according to the detectable voltage signal and converts it into the protection reference voltage through the digital-to-analog converter.

7. The weak signal detection system according to claim 6, characterized in that, The control unit utilizes an automatic fine-tuning algorithm to automatically adjust the initial protection voltage and convert it into a protection reference voltage via the digital-to-analog converter. The automatic fine-tuning algorithm employs dynamic threshold valley prediction combined with fuzzy adaptive step size calculation. It achieves automatic adjustment by searching for the protection reference voltage value that minimizes the peak-to-peak value of the detectable voltage signal. Specifically, it includes: Using peak-to-peak values ​​within a sliding window Vpp The changing trend of the peak-to-peak value is used to dynamically calculate and predict the valley voltage; whereby, it is assumed that the peak-to-peak value... Vpp With protection reference voltage VG If the relationship locally exhibits a single-valley quadratic curve, then the three most recent measurement points in the automatic fine-tuning algorithm are ( VG k-2 , Vpp k-2 ), ( VG k-1 , Vpp k-1 ), ( VG k , Vpp k Using quadratic interpolation, the predicted valley voltage is: In the above formula, express VG The predicted value, Represents the peak-to-peak value within the (k-1)th window. Vpp The difference from the (k-2)th time, Represents the peak-to-peak value within the k-th window. Vpp The difference between the (k-1)th and the second interpolation, where a, b, and c represent the interpolation coefficients of the second interpolation; like < and If the value is greater than 0, then the predicted valley value is in the middle. The linear approximation is: If the prediction is reliable, jump directly to VG pred Skip multiple searches in the middle; The fuzzy adaptive step size is based on the peak-to-peak value. Vpp The three inputs are the rate of change, the direction reversal count, and the current step size. The step size adjustment coefficient is output in real time through fuzzy rules. Let the input variables be E, RC, and S, and the output be α, where E represents the peak-to-peak value. Vpp The rate of change is [-0.5, 0.5], that is: RC represents the direction reversal count within the last 10 steps [0,10], S represents the ratio of the current step size to the initial step size [0.01,1], α represents the step size adjustment coefficient, and the final step size range is [0.2,2.0]. When the peak value of 5 consecutive steps Vpp Fluctuation Vpp noise When the value is ×2 and Step < 0.1 mV, the system enters a lockout mode and stops stepping. During automatic adjustment, the peak-to-peak value is detected every 100 ms. Vpp The increment is adjusted, and if the increment exceeds the threshold, the coarse adjustment is reactivated. Vpp noise Step represents the peak-to-peak noise floor at the output. VG The single adjustment step size of the voltage.

8. The weak signal detection system according to claim 2, characterized in that, The control unit is used to process the standard TTL signal to obtain the number of photoelectrons. Specific methods for this include: The control unit performs a difference operation between the second standard TTL signal and the first standard TTL signal to obtain the target TTL signal; The control unit performs pulse counting on the target TTL signal, and the pulse counting result is the number of photoelectrons.

9. The weak signal detection system according to claim 1, characterized in that, The control unit is used to process the digital quantity to obtain the number of photoelectrons. Specific methods for this include: The control unit obtains the detectable voltage corresponding to the digital quantity by using the relationship between the ADC digital quantity and voltage. The control unit performs a difference operation between the detectable voltage and the noise voltage to obtain the denoised voltage; The control unit divides the noise reduction voltage by the amplification gain of the weak DC amplifier circuit, and then subtracts the noise current of the weak DC amplifier circuit itself to obtain the weak DC current value input to the weak DC amplifier circuit. The control unit divides the weak DC current value by the gain of the electron multiplier to obtain the photocurrent input to the electron multiplier. The control unit divides the photocurrent by the fundamental charge to obtain the number of photoelectrons.

10. The weak signal detection system according to claim 1, characterized in that, The controller in the control unit is an FPGA, and the clock frequency of the FPGA can reach up to 200MHz. The data communication between the FPGA and the host computer is carried out through UART serial communication. The number of photoelectrons is transmitted to the host computer in 4 groups according to a preset baud rate. Each group contains 4 data, and each data is an 8-bit binary number, totaling 32 bits, which is used as a count value. The host computer converts the 32-bit binary number into a decimal number and displays it visually.

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