A photodiode current detection device and method with charge enrichment

Abstract

This invention provides a photodiode current detection device and method with charge enrichment, enabling real-time acquisition and detection of both strong and weak signals. For strong signals, the real-time photocurrent signal can be directly acquired; for weak signals, the photodiode junction capacitance is used as a charge storage device. By exposing the photodiode to weak light for a period of time, the photocurrent will integrate and accumulate on the junction capacitance, resulting in a stronger accumulated signal, which is then measured, thus achieving weak signal detection. Applying this detection device and method to the chemiluminescence reaction principle for NO gas detection, the charge enrichment mode for detecting low-concentration NO gas yields a high signal-to-noise ratio signal, improving sensitivity. The direct measurement mode for detecting high-concentration NO gas does not affect the upper concentration limit of NO detection. The combination of these two operating modes significantly improves the detection performance and concentration range of the miniaturized NO detector.

Description

Technical Field

[0001] This invention relates to the technical field of photoelectric detection of chemiluminescence reactions, and more particularly to a photodiode current detection device and method with charge enrichment. Background Technology

[0002] A photodiode is a device that converts received light signals into photocurrent using the photoelectric effect. The photoelectric conversion efficiency is affected by the structure of the photodiode and the wavelength of the light. There are many types of photodiodes, including APD, PN, and PIN, and they are widely used in optical communication, precision optoelectronic detection, and other fields.

[0003] Currently, the main methods for measuring NO include electrochemical methods and chemiluminescence reactions, but their sensitivity is still not satisfactory. The principle of chemiluminescence reaction for detecting NO gas is that NO reacts with O3 to produce NO2, of which approximately 10% is in an excited state. * NO2 within 1 nanosecond * When NO transitions back to its ground state, it emits photons, generating light with wavelengths between 600-3000 nm. The light intensity is proportional to the NO concentration. A photoelectric converter is used as a detector to absorb photons and generate a photocurrent. The photocurrent intensity is linearly related to the NO concentration, and the NO concentration is determined using the photocurrent intensity. Most photoelectric converters for NO gas detection use photomultiplier tubes (PMTs), mainly because the light intensity generated by chemiluminescence detection of NO is too weak, especially for low concentrations of NO below 100 ppb. PMTs can multiply photons, thus enabling the detection of ultra-low concentrations (1-0.1 ppb) of NO. However, PMTs are large and complex, making them unsuitable for small instruments. Photodiodes, with their small size and low dark current, can replace PMTs as photoelectric converters, enabling miniaturized NO detection (CN109283172A). However, due to the smaller photosensitive area and weaker response signal of photodiodes, their sensitivity for NO detection is more than an order of magnitude lower than that of PMTs. In miniaturized instruments, photodiodes are used as photoelectric converters to detect ultra-low concentrations of NO. This can be achieved by increasing the intensity of the response signal. If the photocurrent generated by the photodiode is stored and enriched to achieve charge enrichment, the intensity of the response signal can be improved.

[0004] A photodiode is a semiconductor photosensitive device with a PN junction. When illuminated, the charge carriers within the photodiode flow directionally, forming a photocurrent, which is directly proportional to the light intensity. Therefore, treating the output of the photodiode as a current source and performing current-to-voltage conversion on it can greatly improve its energy efficiency and characteristics. A current-to-voltage converter using an operational amplifier becomes a basic photodiode amplifier (CN109283172A, CN202111527785.4), see... Figure 1This circuit isolates the photodiode from the signal voltage. While simple in structure, it presents several limitations in photodiode applications. The output current of a photodiode is very small, ranging from pA to μA. To increase the output amplitude, a large photosensitive area and a large feedback resistor are required, which leads to problems such as high offset, low bandwidth, poor stability, and high noise. Especially in NO detection applications, this circuit makes it difficult to detect current signals below 10 pA generated by low-concentration NO.

[0005] Based on the characteristics of a photodiode, it can be equivalent to a current source I. p Shunt resistor R D junction capacitance C D ,like Figure 2 As shown, the shunt resistor R D The values ​​are generally quite large, typically above tens of megohms, and their impact on the current source I can be ignored. p The shunting effect. This patent proposes a low-concentration NO weak light detection device and method, utilizing the junction capacitance C D As a charge storage device, when the photodiode is exposed to weak light for a period of time during detection, the current I... p The junction capacitance C D By integrating and accumulating the signal to obtain a stronger accumulated signal, measurement can be performed. Repeating this process continuously enables continuous signal measurement. The averaged accumulated signal is linearly correlated with the intensity of the light being measured, enabling the detection of NO concentration. The integration and accumulation process significantly suppresses noise and improves the signal-to-noise ratio, making this detection method particularly suitable for detecting extremely weak signals. Summary of the Invention

[0006] In view of the technical problems mentioned in the background section, a photodiode current detection device and method with charge enrichment is provided. In the detection of low concentration NO, a photodiode is used as a converter. This method can achieve average accumulation of signals and improve the detection sensitivity and signal-to-noise ratio in weak light.

[0007] The technical means employed in this invention are as follows:

[0008] A photodiode current detection device with charge enrichment is characterized by comprising: a reaction chamber, a filter, a photodiode, a sampling switch, a reset switch, an amplification circuit, and a signal processing and signal acquisition module; the reaction chamber is a cylindrical hollow cavity with an open bottom; the top of the reaction chamber is provided with an NO gas inlet, and the two sides of the reaction chamber are respectively provided with an ozone inlet and a tail gas outlet; the ozone entering the reaction chamber through the ozone inlet and the NO gas entering the reaction chamber through the NO gas inlet undergo a chemiluminescence reaction in the reaction chamber, generating weak infrared light, and the tail gas after the reaction is discharged from the tail gas outlet.

[0009] Furthermore, the filter is disposed at the opening of the reaction chamber to seal the reaction chamber and filter the light generated by the chemiluminescence reaction, removing stray light interference.

[0010] Furthermore, the photodiode is disposed at the bottom of the reaction chamber, and the filter physically isolates the photodiode from the reaction chamber and is photo-sealed with the reaction chamber; the photodiode is used in reverse to realize photoelectric conversion, and the photodiode has a junction capacitance inside to realize photocurrent accumulation and charge storage.

[0011] Furthermore, the reset switch is connected in parallel with the photodiode, one end of the sampling switch is connected to the cathode of the photodiode, and the other end is connected to the input terminal of the amplifier circuit; the reset switch realizes the reset of the stored charge, and the sampling switch realizes signal acquisition.

[0012] Furthermore, the amplification circuit includes a current-to-voltage converter consisting of a feedback resistor and a feedback capacitor to proportionally amplify the stored charge signal. The signal processing module performs smoothing filtering on the amplified signal, and the signal acquisition module acquires the processed signal using an ADC or TDC, converting it into a digital signal.

[0013] The present invention also provides a method for detecting the current of a photodiode with charge enrichment using the apparatus described in claims 1 to 4, characterized by comprising the following steps:

[0014] Step 1: Charge enrichment mode; During the weak signal phase, the reset switch is closed, the acquisition switch is open, the amplifier circuit and photodiode are isolated, the photodiode is short-circuited, and the charge on the junction capacitance inside the photodiode is zero, resulting in no signal generation. During the charge enrichment phase, the reset switch and acquisition switch are open, the amplifier circuit and photodiode are isolated, the photodiode generates photocurrent, charges the junction capacitance, and enriches the charge. After 0.1-300 seconds, the data acquisition phase begins, the reset switch remains open, the acquisition switch is closed, and the amplifier circuit begins amplifying the accumulated charge on the junction capacitance. After signal processing and acquisition, the desired accumulated weak signal is obtained.

[0015] Step 2: Repeat the detection method described in Step 1 to continuously obtain the signal after charge enrichment.

[0016] Step 3: Direct Measurement Mode; When there is a strong signal, the reset switch remains open, the acquisition switch is closed, the amplifier circuit is directly connected to the photodiode, and the real-time photocurrent signal is directly measured.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] This patent proposes a photodiode current detection device and method with charge enrichment, enabling real-time acquisition and detection of both strong and weak signals. For strong signals, the real-time photocurrent signal can be directly acquired; for weak signals, the photodiode junction capacitance is used as a charge storage device. By exposing the photodiode to weak light for a period of time, the photocurrent will integrate and accumulate on the junction capacitance, resulting in a stronger accumulated signal, which is then measured, thus achieving weak signal detection. At low concentrations, the light signal generated during the chemiluminescent reaction of ozone and NO gas is very weak. Utilizing the charge enrichment mode can obtain a high signal-to-noise ratio signal, greatly improving sensitivity. At high concentrations, the direct measurement mode can obtain a strong signal without affecting the high concentration limit of NO detection. The combination of these two operating modes greatly improves the detection performance and concentration range of the miniaturized NO detector.

[0019] In charge accumulation mode, the signal is smoothed due to the average accumulation process, which greatly suppresses noise and improves the signal-to-noise ratio. The longer the charge accumulation time, the stronger the signal, which is beneficial for detecting extremely weak photocurrent signals. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 It is a basic photodiode amplifier.

[0022] Figure 2 This is the equivalent circuit diagram of a photodiode.

[0023] Figure 3 The diagram shows the current detection device with charge enrichment of a photodiode proposed in this invention.

[0024] Figure 4 This is a sequence diagram and signal diagram of photocurrent enrichment acquisition under the charge enrichment mode of the present invention.

[0025] Figure 5 This is a signal acquisition diagram in the direct measurement mode of the present invention.

[0026] In the diagram: 1. Reaction chamber; 2. NO gas inlet; 3. Ozone inlet; 4. Exhaust gas outlet; 5. Photodiode; 6. Filter. Detailed Implementation

[0027] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0028] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0029] like Figure 3-5 As shown, the present invention provides a photodiode current detection device with charge enrichment, comprising: a reaction chamber, a filter, a photodiode, a sampling switch, a reset switch, an amplifier circuit, and a signal processing and signal acquisition module.

[0030] The reaction chamber is a cylindrical hollow cavity with an open bottom. An NO gas inlet is located at the top of the chamber, and an ozone inlet and a tail gas outlet are located on its two sides. Ozone entering the chamber through the ozone inlet and NO gas entering through the NO gas inlet undergo a chemiluminescence reaction within the chamber, producing weak infrared light. The resulting tail gas is discharged from the tail gas outlet. A filter is positioned at the opening of the reaction chamber to seal it and filter the light generated by the chemiluminescence reaction, removing light interference. A photodiode is located at the bottom of the reaction chamber. The filter physically isolates the photodiode from the reaction chamber and provides a photoelectric seal. The photodiode is used in reverse to achieve photoelectric conversion. An internal junction capacitance allows for photocurrent accumulation and charge storage. A reset switch is connected in parallel with the photodiode. One end of a sampling switch is connected to the cathode of the photodiode, and the other end is connected to the input of the amplifier circuit. The reset switch resets the stored charge, and the sampling switch acquires the signal.

[0031] The amplification circuit includes a feedback resistor and a current-to-voltage converter with a feedback capacitor; it proportionally amplifies the stored charge signal. The signal processing module performs smoothing filtering on the amplified signal, and the signal acquisition module acquires the processed signal using an ADC or TDC, converting it into a digital signal.

[0032] In this application, the interior of the reaction chamber can be flat or curved, and the interior can be plated with aluminum or silver mirror finish to obtain more photons. The reaction chamber can be heated and kept at a constant temperature to accelerate the reaction.

[0033] The lower the dark current of the photodiode, the better, generally in the range of 0.1pA-1000nA. The junction capacitance should be larger, generally in the range of 1pF-10uF. If the junction capacitance is not large enough, an external parallel capacitor can be connected to accumulate more charge and obtain a larger signal.

[0034] In a preferred embodiment, both the reset switch and the sampling switch in this application are configured with switching speeds in the range of nanoseconds to milliseconds; the reset switch and the sampling switch are analog switches or mechanical switches.

[0035] This application also includes a method for detecting the current of a photodiode with charge enrichment, characterized by comprising the following steps:

[0036] Step 1: Charge enrichment mode; When there is a weak signal, it is the preparation stage. The reset switch is closed, the acquisition switch is open, the amplifier circuit and the photodiode are isolated, the photodiode is short-circuited, the charge on the junction capacitance inside the photodiode is zero, and no signal is generated.

[0037] During the charge accumulation stage, the reset switch is turned on, the acquisition switch is turned on, the amplifier circuit and the photodiode are isolated, the photodiode generates photocurrent, charges the junction capacitance, and accumulates charge;

[0038] After a duration of 0.1-300 seconds, the system enters the data acquisition state. The reset switch remains open, the acquisition switch is closed, and the amplifier circuit begins to amplify the accumulated charge on the junction capacitor. After signal processing and signal acquisition, the desired weak signal after accumulation is obtained.

[0039] Step 2: Repeat the detection method described in Step 1 to continuously obtain the signal after charge enrichment;

[0040] Step 3: Direct Measurement Mode; When there is a strong signal, the reset switch remains open, the acquisition switch is closed, the amplifier circuit is directly connected to the photodiode, and the real-time photocurrent signal is directly measured.

[0041] The preferred timing of the preparation phase, charge enrichment phase, and data acquisition phase can be dynamically adjusted. The longer the charge enrichment phase lasts, the more charge accumulates and the stronger the signal becomes. The strongest signal is limited by the junction capacitance.

[0042] Example 1

[0043] Figure 3 A photodiode current detection device with charge enrichment is provided, comprising: a reaction chamber 1, a filter 6, a photodiode 5, a sampling switch, a reset switch, an amplifier circuit, and a signal processing and signal acquisition module;

[0044] The reaction chamber 1 is a cylindrical hollow cavity with an open bottom. The top of the cavity has an NO gas inlet 2, and the two sides of the cavity have an ozone inlet 3 and a tail gas outlet 4, respectively. After ozone and NO gas enter the reaction chamber, a chemiluminescent reaction occurs, producing weak infrared light. The resulting tail gas is discharged from the tail gas outlet 4.

[0045] The filter 6 is located on the bottom surface of the reaction chamber 1 to seal the reaction chamber 1 and filter the light generated by the chemiluminescence reaction to eliminate light interference.

[0046] Photodiode 5 is positioned on one side of the bottom surface of reaction chamber 1. Filter 6 physically isolates photodiode 5 from reaction chamber 1 and provides a photo-sealed connection. Photodiode 5 is used in reverse to achieve photoelectric conversion. Internally, photodiode 5 contains a junction capacitance C. D It can achieve photocurrent I p Accumulation and charge storage.

[0047] The reset switch (Reset) is connected in parallel with photodiode 5. One end of the sampling switch (Sample) is connected to the cathode of photodiode 5, and the other end is connected to the input of the amplifier circuit. The reset switch (Reset) resets the stored charge, and the sampling switch (Sample) acquires the signal.

[0048] The amplifier circuit is a current-to-voltage converter composed of a feedback resistor Rf and a feedback capacitor Cf. L The load resistor is used to proportionally amplify the stored charge signal. The signal processing module smooths and filters the amplified signal, and the signal acquisition module acquires the processed signal using an ADC or TDC, converting it into a digital signal. The amplifier circuit can be a transimpedance amplifier, a combination amplifier, or other types of amplifier circuits.

[0049] The interior of reaction chamber 1 can be flat or curved, and the interior should be plated with aluminum or silver mirror finish to obtain more photons.

[0050] Reaction chamber 1 can be heated to maintain a constant temperature to accelerate the reaction.

[0051] It is better that the dark current of the photodiode 5 is smaller, and the junction capacitance C D is larger. If the capacitance of the junction capacitance C D is not large enough, an external parallel capacitor can be connected, which can accumulate more charges and obtain a larger signal.

[0052] For the reset switch Reset and the sampling switch Sample, the switch speed is selected in the range of microseconds to milliseconds or even nanoseconds, and the faster the better. The on-resistance R on is smaller the better, and the off-resistance R off is larger the better. The switch type can be an analog switch or a mechanical switch.

[0053] The method for detecting the current of a photodiode with charge enrichment implemented by using the above device is as follows:

[0054] (1) When the signal is weak, it is divided into three stages, as shown in Figure 4 (left): Preparation stage (t1 < t < t2), the reset switch Reset is closed, the acquisition switch Sample is open, the amplifier circuit is isolated from the photodiode 5, the photodiode 5 is in a short-circuit state, and the charge on the junction capacitance C D inside the photodiode 5 is zero and no signal is generated; Charge enrichment stage (t2 < t < t3), the reset switch Reset is open, the acquisition switch Sample is open, the amplifier circuit is isolated from the photodiode 5, and the photodiode 5 generates a photocurrent I p , charges the junction capacitance CD and enriches the charges. After a period of time, it enters the data acquisition state (t3 < t < t4), the reset switch Reset remains open, the acquisition switch Sample is closed, and the amplifier circuit starts to amplify the accumulated charges on the junction capacitance C D . After signal processing and signal acquisition, the required weak signal after accumulation is obtained. Continuously cycling the above detection method can continuously obtain the signal after charge enrichment. This process is called the charge enrichment mode, and the obtained signal is shown in Figure 4 (right) as a series of bar graphs, and the difference between the baseline and the detection signal is the measured photocurrent I p signal.

[0055] (2) When the signal is strong, as shown in Figure 5 , the reset switch Reset always remains open, the acquisition switch Sample is closed, the amplifier circuit is directly connected to the photodiode 5, and the real-time photocurrent I p signal is directly measured, and there is no need to accumulate charges again to obtain a strong signal. This process is called the direct measurement mode.

[0056] The times of the preparation stage, the charge enrichment stage, and the data acquisition state can be dynamically adjusted. According to the capacitor charging formula: V t=E(1-e -t / RC ), where V t Let be the capacitor voltage at time t, E be the final voltage of the capacitor, t be time, R be the charging resistance (in this patent, it is a very small resistance value), and C be the capacitance value. Therefore, the longer the charge accumulation phase, the more charge accumulates and the stronger the signal. The strongest signal is affected by the junction capacitance C. D Capacity limitations.

[0057] When ozone and NO gas undergo a chemiluminescent reaction, the resulting light signal is extremely weak at low concentrations, especially below 100 ppb. Using direct measurement mode results in a very low signal-to-noise ratio or even no detectable signal. However, utilizing charge enrichment mode can yield a high signal-to-noise ratio, reducing the detection limit to below 10 ppb and significantly improving sensitivity. At high concentrations, direct measurement mode provides a strong signal without affecting the upper concentration limit for NO detection. The combination of these two operating modes greatly expands the concentration range of miniaturized NO detectors.

[0058] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments. In the above embodiments of the present invention, the descriptions of each embodiment have their own emphasis; parts not described in detail in a certain embodiment can be referred to in the relevant descriptions of other embodiments. It should be understood that the disclosed technical content in the several embodiments provided in this application can be implemented in other ways.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A photodiode current detection device with charge enrichment, characterized in that, include: The reaction chamber, filters, photodiodes, sampling switches, reset switches, amplifier circuits, and signal processing and acquisition modules are included. The reaction chamber is a cylindrical hollow cavity with an open bottom. The top of the reaction chamber is provided with an NO gas inlet, and the two sides of the reaction chamber are respectively provided with an ozone inlet and a tail gas outlet. The ozone entering the reaction chamber through the ozone inlet and the NO gas entering the reaction chamber through the NO gas inlet undergo a chemiluminescence reaction in the reaction chamber, producing weak infrared light. The tail gas after the reaction is discharged from the tail gas outlet. The filter is disposed at the opening of the reaction chamber to seal the reaction chamber and to filter the light generated by the chemiluminescence reaction, thereby removing stray light interference. The photodiode is disposed at the bottom of the reaction chamber. The filter physically isolates the photodiode from the reaction chamber and is photo-sealed with the reaction chamber. The photodiode is used in reverse to achieve photoelectric conversion. The photodiode has a junction capacitance inside to achieve photocurrent accumulation and charge storage. The reset switch is connected in parallel with the photodiode, one end of the sampling switch is connected to the cathode of the photodiode, and the other end is connected to the input terminal of the amplifier circuit; The reset switch resets the stored charge, and the sampling switch acquires the signal. The amplification circuit includes: a current-to-voltage converter consisting of a feedback resistor and a feedback capacitor; a proportional amplification of the stored charge signal; a signal processing module that performs smoothing and filtering on the amplified signal; and a signal acquisition module that acquires the processed signal by an ADC or a TDC and converts it into a digital signal.

2. The photodiode current detection device with charge enrichment according to claim 1, characterized in that: The reaction chamber is internally plated with aluminum or silver mirror finish to obtain more photons.

3. The photodiode current detection device with charge enrichment according to claim 1, characterized in that: The dark current of the photodiode ranges from 0.1pA to 1000nA, and the junction capacitance ranges from 1pF to 10uF.

4. The photodiode current detection device with charge enrichment according to claim 1, characterized in that: Both the reset switch and the sampling switch are configured with switching speeds in the range of nanoseconds to milliseconds; the reset switch and the sampling switch are either analog switches or mechanical switches.

5. A method for detecting current in a photodiode with charge enrichment using the apparatus described in claims 1-4, characterized in that, Includes the following steps: Step 1: Charge enrichment mode; When there is a weak signal, it is the preparation stage. The reset switch is closed, the acquisition switch is open, the amplifier circuit and the photodiode are isolated, the photodiode is short-circuited, the charge on the junction capacitance inside the photodiode is zero, and no signal is generated. During the charge accumulation stage, the reset switch is turned on, the acquisition switch is turned on, the amplifier circuit and the photodiode are isolated, the photodiode generates photocurrent, charges the junction capacitance, and accumulates charge; After a duration of 0.1-300 seconds, the system enters the data acquisition state. The reset switch remains open, the acquisition switch is closed, and the amplifier circuit begins to amplify the accumulated charge on the junction capacitor. After signal processing and signal acquisition, the desired weak signal after accumulation is obtained. Step 2: Repeat the detection method described in Step 1 to continuously obtain the signal after charge enrichment; Step 3: Direct Measurement Mode; When there is a strong signal, the reset switch remains open, the acquisition switch is closed, the amplifier circuit is directly connected to the photodiode, and the real-time photocurrent signal is directly measured.

6. The method for detecting current in a photodiode with charge enrichment according to claim 5, characterized in that: The duration of the preparation phase, charge enrichment phase, and data acquisition phase can be dynamically adjusted. The longer the charge enrichment phase lasts, the more charge accumulates and the stronger the signal becomes. The strongest signal is limited by the junction capacitance.

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