Fluorescence imaging system and method for detecting a target molecule

Abstract

The present application relates to a spot position detection system based on a graphene-germanium position sensitive detector, belonging to the field of photoelectric technology. The system comprises a graphene / germanium photoconductive position sensitive detector module, an analog signal processing module, and a data acquisition and processing module. The analog signal processing circuit mainly includes a preamplifier and dark current compensation circuit, a second-order band-pass filter circuit, a post-automatic gain differential operation circuit, and a peak detection circuit, which realizes I / V conversion amplification, filtering, differential operation, and peak detection of the four-way photocurrent signals of the detector output under the bias condition. The data acquisition and processing module realizes digital processing of the peak voltage through FPGA control of the A / D module, and automatically adjusts the analog switch channel according to the converted voltage value, realizing automatic gain control. The present application improves the signal-to-noise ratio and optimizes the system structure, with separate design of analog and digital circuits, enhancing the scene applicability of the system.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of optoelectronic technology, and relates to a light spot position detection system based on a graphene-germanium-based position sensitive detector. BACKGROUND

[0002] A position sensitive detector (PSD) is a photoelectric position sensor for measuring the continuous position of a light spot on the surface of a photodiode by surface resistance. Unlike a CCD discrete element detector, a photoconductive position sensitive detector can provide continuous position data, high position resolution and high speed response. It is a new type of photoelectric device, also known as a coordinate photocell. It is a non-segmented device that can convert the position of a light spot on a photosensitive surface into an electrical signal. A PSD is composed of a p-substrate, a pin photodiode and surface resistance. It has the advantages of high position resolution, fast response speed and simple processing circuit. When a light spot is incident on the photosensitive region of the detector surface, the device converts the light signal into an electrical signal according to the lateral photoconductive effect and moves to the electrode regions in the four corners. Due to the different distances from the light spot to the electrode regions, the sizes of the final output photoelectric currents are different. Finally, the light spot position is calculated by a light spot position coordinate formula.

[0003] The signal processing circuit design mainly utilizes integrated operational amplifiers or special analog integrated circuits, and a small number of external components can be used to construct processing circuits with various functions. The main functions include signal amplification, signal filtering, impedance matching, level conversion, non-linear compensation, current / voltage conversion, voltage / frequency conversion, etc. The signal circuit finally converts various natural analog quantities into digital voltage signals that can be collected, realizing the detection and recognition of natural quantities. Generally, a PSD signal processing circuit is mainly composed of a front-stage operational amplifier circuit and a rear-stage differential operational amplifier circuit. A simple two-stage operational amplifier has no obvious effect on the processing of the dark current and noise of the detector. In order to improve the precision and stability of the position detection system, it is very important to design a dark current compensation and a special filter short circuit.

[0004] A peak detection circuit is designed to detect the positive peak or negative peak of an input alternating current signal or pulse signal, and can immediately output a direct current voltage substantially equal to the peak value. It is widely used in automatic gain control circuits and sensor maximum value detection circuits. In actual circuit design, a peak detection circuit generally includes a peak identification circuit, a peak sampling circuit and a peak holding circuit, and is affected by the amplitude and frequency of the measured signal. How to design a simple and effective circuit structure to realize a circuit structure with high detection frequency and small peak error is the key to the design of the circuit.

[0005] Automatic gain control (AGC) circuit, a special circuit that can keep the output signal amplitude stable or limit it to a very small range when the input signal amplitude changes greatly. AGC circuit is used to ensure the stability of the received amplitude, and has been widely used in various receivers, recorders and signal acquisition systems. In addition, it has also been widely used in optical fiber communication, microwave communication, satellite communication and other communication systems, as well as radar, broadcast television systems. SUMMARY

[0006] Therefore, the purpose of the present application is to provide a graphene-germanium-based position sensitive detector-based light spot position detection system. When the graphene / germanium detector detects the incident light of the corresponding waveband, the optical signal is finally converted into a weak current signal. According to the charging and discharging of the detector and the actual photoelectric current conduction characteristics, the detector can be equivalent to a circuit model composed of a resistor, a parasitic capacitor, a weak current output meter and a diode. In practical applications, according to the different incident light powers of the device responsivity, the output photoelectric current changes in a large range. At the same time, due to the necessity of working under bias conditions, the output of dark current and noise of the device is large. The dark current varies from 1 nanoampere to several microamperes according to the different detector materials and different device manufacturing structures and processes, which will affect the accuracy of the light spot position detection to some extent. The noise of the detection system mainly includes 1 / f noise, thermal noise and high-frequency oscillation noise generated by the device. Designing a signal processing circuit to reduce the influence of dark current and noise on the accuracy and stability of the system is one of the problems to be solved.

[0007] To achieve the above purpose, the present application provides the following technical solutions:

[0008] The graphene-germanium-based position sensitive detector-based light spot position detection system comprises a graphene / germanium-based photoconductive position sensitive detector, a bias circuit, a DC-DC power supply module, a preamplifier and a dark current compensation circuit, a second-order band-pass filter circuit, a post-automatic gain differential operational amplifier circuit, a peak detection circuit, an A / D conversion circuit and an analog switch.

[0009] The graphene / germanium-based photoconductive position sensitive detector completes photoelectric conversion of incident laser under the working condition of the bias circuit and outputs four photoelectric current signals.

[0010] The DC-DC power module, the pre-operational amplifier and dark current compensation circuit, the second-order band-pass filter circuit, the post-automatic gain differential operational amplifier circuit and the peak detection circuit constitute an analog signal processing module, realize I / V conversion amplification, filtering, differential operation and peak detection output of the photocurrent signal output by the bias circuit, the A / D conversion circuit controlled by the FPGA and the analog switch constitute a data acquisition and processing module, acquire the signal peak voltage detected by the peak detection circuit and convert it into a digital signal input to the FPGA, the FPGA adjusts the analog switch according to the sampling voltage value, realizes automatic gain control of the automatic gain differential operation circuit, and performs algorithm processing on the digital voltage value to output the spot position coordinates.

[0011] Optionally, in the graphene / germanium-based photoconductive position-sensitive detector, a device region is designed at each of four corners of a 10*10mm 2 intrinsic germanium substrate, the device includes a pair of gold electrodes and is connected through graphene, and an effective photosensitive area in the middle of the device is 8*8mm 2 :

[0012] The calculation formula of the detector spot position (x, y) algorithm is:

[0013]

[0014] Wherein, i x1 , i x2 , i y1 , i y2 are output current signals of the device regions at four corners of the graphene / germanium-based photoconductive position-sensitive detector; and L is the side length of the square effective photosensitive area of the detector.

[0015] Optionally, in the bias circuit, the device regions in the graphene / germanium-based photoconductive position-sensitive detector are connected to the 1V bias power supply output by the DC-DC power module in the analog signal processing module.

[0016] Optionally, in the DC-DC power module, the 24V voltage source input from the external DC power supply is converted into positive and negative 15V, 5V and 1V power supplies, which are used for power supply of each functional circuit chip in the system and bias voltage of the detector.

[0017] The pre-operational amplifier and dark current compensation circuit convert the photocurrent signal output by the bias circuit into a voltage signal and perform operational amplification;

[0018] The second-order band-pass filter circuit filters the voltage output by the pre-operational amplifier and dark current compensation circuit, reduces the high-frequency and 1 / f noise power in the signal, and outputs the signal voltage.

[0019] The post automatic gain differential operational amplifier circuit performs adaptive differential operational amplification on the signal voltage output by the second-order band-pass filter circuit according to the gain control signal transmitted by the analog switch.

[0020] The peak detection circuit is used for detecting the peak value of the signal voltage when the incident laser is a pulse spot, and outputting a stable direct current signal for spot position detection.

[0021] Optionally, the A / D conversion circuit samples two analog peak voltage signals and converts them into digital signals input into the FPGA for position data processing.

[0022] The analog switch receives the control signal transmitted by the FPGA, automatically adjusts the analog switch control signal and inputs it into the post automatic gain differential operational amplifier circuit to realize signal amplification.

[0023] According to the digital voltage signal, the coordinates of the spot position are calculated and converted into the spot coordinates of the UI interface, and finally the data are transmitted to the PC end through the serial port.

[0024] The beneficial effects of the present application are as follows:

[0025] (1) In the traditional position sensitive detection system, the signal processing circuit is a simple two-stage operational amplifier structure, which cannot meet the requirements of the 1550nm waveband communication system for spot position detection stability, accuracy and pulse laser detection. The analog signal processing circuit designed in the present system introduces dark current compensation and filter circuit and is optimized, thereby improving the signal-to-noise ratio, position detection accuracy and stability of the spot position detection system.

[0026] (2) The present application designs an automatic gain differential operational circuit, which realizes the differential operation of four photoelectric current signals and automatic gain control, and outputs a stable direct current signal with a suitable peak value for A / D acquisition. The designed peak detection circuit can detect the AC or pulse input spot, and the peak detection accuracy is high.

[0027] Other advantages, objects and features of the present application will be set forth in part in the following specification taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art from a consideration of the following specification and from the practice of the present application. The objects and other advantages of the present application will be realized and attained by means of the instrumentalities and combinations pointed out in the following specification. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to make the objects, technical solutions and advantages of the present application clearer, the preferred embodiments of the present application will be described in detail below with reference to the accompanying drawings, in which:

[0029] Figure 1 It is a designed graphene / germanium photoconductive position sensitive detector device structure diagram.

[0030] Figure 2 Equivalent model diagram of circuit drawn according to output characteristics of designed graphene / germanium photoconductive position sensitive detector;

[0031] Figure 3 Overall schematic diagram of designed light spot detection system. DETAILED DESCRIPTION

[0032] The present application will be described in greater detail by way of specific embodiments, and as such, those skilled in the art can easily understand other advantages and purposes of the present application from the contents disclosed in the specification. The present application can also be implemented or applied by other different embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present application in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0033] The drawings are only used for exemplary illustration, and the representation is only a schematic diagram, not a physical diagram, and should not be understood as a limitation on the present application. In order to better illustrate the embodiments of the present application, some components in the drawings may be omitted, enlarged or reduced, and do not represent the actual size of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0034] The same or similar reference numerals in the drawings of the embodiments of the present application correspond to the same or similar components; in the description of the present application, it should be understood that if the terms "upper", "lower", "left", "right", "front", "back" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are only used for exemplary illustration, and should not be understood as a limitation on the present application. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0035] Figure 1 is a top view and side view structure diagram of a graphene / germanium photoconductive position sensitive detector used in the designed light spot position detection system. The device area is designed at the four corners of the germanium substrate surface, and the graphene strip is laid between the metal electrodes to form a position sensitive detector. When the system is working, the detector is turned on by the bias circuit, at this time the signal generator is used to modulate the 1550nm laser to emit pulsed laser to irradiate the device, so that the detector outputs four photoelectric current signals.

[0036] Figure 2is the circuit model of the detector bias working condition. R1 is the bias circuit isolation resistor; IP is the equivalent current source of the photocurrent; D is an ideal diode; Cj is the parasitic capacitance; Rsh is the equivalent resistance of the graphene strip. A 1V bias voltage is provided by the analog signal processing circuit, and isolation resistors are connected in series in the x1, x2, y1, and y2 device regions, so that the bias voltage of the four device regions is isolated and the photocurrent signals are independently output.

[0037] The analog signal processing circuit comprises:

[0038] As shown in Figure 3 , the embodiments of the analog signal processing module and the data acquisition and processing module are described.

[0039] The DC-DC power module is provided with a 24V DC power input from the outside, and a switch and a power indicator lamp and an anti-reverse connection circuit are designed for the input. The anti-reverse connection circuit is composed of a self-restoring capacitor filament, a voltage stabilizing diode and a capacitor, which automatically disconnects the connection with the rear circuit when the positive and negative poles of the power supply are reversely connected. The 24V is converted into positive and negative 15V through a step-down conversion, which is used to provide power for the operational amplifier chip in the preamplifier, the dark current compensation circuit, the band-pass filter circuit and the post-amplification automatic gain differential operational amplifier circuit.

[0040] In addition, the first DC-DC step-down module is connected to the above-mentioned 15V power supply, and a positive and negative 5V power output is converted and output through a step-down chip and a supporting circuit. The power output has two main functions.

[0041] Function 1: 1V power output is realized by connecting a 5V to 1V step-down module to provide bias voltage for the detector bias circuit.

[0042] Function 2: providing power for the A / D conversion circuit and serving as a reference voltage, and providing power for the peak detection circuit operational chip.

[0043] Function 3: The second DC-DC step-down module is designed to convert 5V into positive and negative 3.3V, which is used to power the FPGA chip and as a reference voltage.

[0044] Thus, the function implementation of the DC-DC power module of the signal processing circuit is introduced. The power outputs of different amplitudes are designed to connect the probes, which is convenient for detecting the implementation of the power function in actual application.

[0045] In the following introduction of the function implementation process of the signal processing circuit, the four-way output signal processing process of the position-sensitive amplifier is the same except for the post-amplification operational amplifier module. Therefore, one of the ways is taken as an example to introduce the implementation process of the module.

[0046] The preamplifier and dark current compensation circuit receive four photocurrent signals from the bias circuit and input them to the inverting input of the instrumentation amplifier. A fixed-gain feedback circuit is used to convert the current signals into voltage signals and amplify them. Under no-light conditions, adjusting the potentiometer of the dark current compensation circuit at the inverting input adjusts the amplifier output voltage to within 100uV, thereby compensating for the detector's dark current.

[0047] The interstage second-order bandpass filter circuit mainly consists of an integrated low-pass filter chip and its matching resistor-capacitor network, and a second-order high-pass filter. The second-order high-pass filter removes 1 / f noise from the signal, while the integrated low-pass filter removes high-frequency noise. This circuit receives the effective voltage signal from the preamplifier and dark current compensation circuit, and through the combined action of the two filtering circuits, outputs a high signal-to-noise ratio voltage signal.

[0048] The post-amplifier automatic gain differential operational amplifier circuit first selects a four-input integrated operational amplifier chip as the core component. It then converts the voltage signals corresponding to the photocurrents output from each electrode region of the detector into voltage signals based on the terms (i) in the position-sensitive detector spot position calculation formula. x2 +i y1 )-(i x1 +i y2 ), (i x2 +i y2 )-(i x1 +i y1 ) and (i x2 +i x1 +i y2 +i y1 The differential operation is completed. Furthermore, the feedback circuit in this circuit consists of analog switching circuits combined with resistors of varying gains. Controlled by an FPGA, the output voltage after the differential operation is adjusted between 0.3V and 4.7V.

[0049] The peak detection circuit receives the effective voltage signal from the post-automatic gain differential operational amplifier circuit, extracts the peak value of the pulse signal or AC signal, and outputs it as an effective DC voltage signal. Test loops are designed at both the input and output terminals, and the waveforms of the input and output signals are compared by connecting an oscilloscope.

[0050] The automatic gain control circuit consists of analog switches and resistors with different gains. First, the FPGA controls the A / D sampling circuit to acquire the peak voltage V output by the peak detection circuit. (ix2+ix1+iy2+iy1)If the peak voltage is less than 0.3V, it indicates that the gain is small, and then the FPGA transmission control signal is good analog switch circuit to adjust to the next higher gain channel. If the peak voltage is greater than 4.7V, it indicates that the gain is large, and then automatically adjust to the previous lower gain channel. Finally, adjust the peak voltage V (ix2+ix1+iy2+iy1) between 0.3V and 4.7V.

[0051] The FPGA receives the digital peak signal voltage of the A / D conversion circuit, uses the average value algorithm to reduce the influence of invalid signals on the stability of the system spot position detection. At the same time, according to the spot position calculation formula, the signal output by the average value algorithm is position converted and output through the serial port.

[0052] In summary, the graphene / germanium-based photoconductive position-sensitive detector, the analog signal processing module, the bias circuit, and the data acquisition and processing module provided by the embodiments of the present application can realize the spot position detection of 1550nm communication waveband laser. The analog signal processing module realizes I / V conversion amplification, filtering, differential operation, and peak detection of the photodetector photocurrent signal, and the introduction of the dark current compensation circuit can reduce the influence of the dark current on the detection accuracy of the system. The data acquisition and processing module can convert the analog voltage signal into a digital signal, and adaptively adjust the gain channel of the analog switch according to the sampling value, and finally calculate and output the spot position coordinates. The introduction of the peak detection circuit can realize the response of the system to alternating current and pulse laser, and reduce the power consumption of the laser.

[0053] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should be covered in the scope of the claims of the present application.

Claims

1. A system for detecting the position of a light spot based on a graphene-germanium based position sensitive detector, characterized in that: The system comprises a graphene / germanium-based photoconductive position-sensitive detector, a bias circuit, a DC-DC power module, a preoperational amplifier and dark current compensation circuit, a second-order band-pass filter circuit, a post-automatic gain differential operational amplifier circuit, a peak detection circuit, an A / D conversion circuit and an analog switch; the graphene / germanium-based photoconductive position-sensitive detector completes photoelectric conversion on incident laser under the working condition of the bias circuit and outputs four photoelectric current signals, wherein, in the graphene / germanium-based photoconductive position-sensitive detector, a device region is designed in the four corners of a 10*10 mm 2 intrinsic germanium substrate; the DC-DC power module, the preoperational amplifier and dark current compensation circuit, the second-order band-pass filter circuit, the post-automatic gain differential operational amplifier circuit and the peak detection circuit constitute an analog signal processing module, realizing I / V conversion amplification, filtering, differential operation and peak detection output of the photoelectric current signal output by the bias circuit, wherein: The DC-DC power module converts the 24V voltage source input by the external DC power supply into positive and negative 15V, 5V and 1V power sources, which are used for power supply of functional circuit chips in the system and bias voltage of the detector. The preamplifier and dark current compensation circuit converts four photoelectric current signals output by the bias circuit into voltage signals and performs operational amplification, and realizes compensation of the dark current of the detector by adjusting the potentiometer. The second-order band-pass filter circuit filters the voltage output by the preamplifier and dark current compensation circuit, reduces high-frequency and 1 / f noise power in the signal, and outputs signal voltage. The post-amplification automatic gain differential operational amplifier circuit performs adaptive differential operational amplification on the signal voltage output by the second-order band-pass filter circuit according to the gain control signal transmitted by the analog switch. The peak detection circuit is used to detect the peak value of the signal voltage when the incident laser is a pulsed spot, and output a stable direct current signal.

2. The graphene-germanium based position sensitive detector based spot position detection system according to claim 1, characterized in that: In the graphene / germanium-based photoconductive position-sensitive detector, the formula for calculating the position of a light spot (x, y) on the detector is as follows: x , y ) ， wherein i x1 , i x2 , i y1 , i y2 are the output current signals of the four corner device regions of the graphene / germanium based photoconductive position sensitive detector, respectively, L is the side length of the square active light sensing area of the detector.

3. The graphene-germanium based position sensitive detector based spot position detection system according to claim 2, characterized in that: The A / D conversion circuit controlled by the FPGA and the analog switch constitute a data acquisition and processing module, wherein the A / D conversion circuit samples two analog peak voltage signals and converts them into digital signals input to the FPGA for position data processing; the analog switch receives the control signal transmitted by the FPGA, automatically adjusts the analog switch control signal and inputs it into the post-amplification automatic gain differential operational amplifier circuit to realize signal amplification; the FPGA adjusts the analog switch according to the sampling voltage value, realizes automatic gain control of the automatic gain differential operational amplifier circuit, and performs algorithm processing on the digital voltage value to output the spot position coordinates.

4. The graphene-germanium based position sensitive detector based spot position detection system according to claim 3, characterized in that: In the bias circuit, the device area in the graphene / germanium-based photoconductive position-sensitive detector is connected to the 1V bias power source output by the DC-DC power module in the analog signal processing module. The system calculates the coordinates of the spot position according to the digital voltage signal, converts the spot coordinates on the UI interface, and finally transmits the data to the PC end through the serial port.

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