Broadband low-noise photoelectric detector based on cascade circuit structure

Abstract

The utility model provides a broadband low-noise photoelectric detector based on a cascade circuit structure. The broadband low-noise photoelectric detector comprises a photodiode (1), a transimpedance amplification circuit (2), a coupling capacitor (3), a first radio frequency amplification circuit (4) and a second radio frequency amplification circuit (5). A photocurrent signal of the photodiode (1) irradiated by laser is input into a negative input end of the transimpedance amplification circuit (2), and a positive input end of the transimpedance amplification circuit (2) is grounded; the output of the transimpedance amplification circuit (2) is connected with the first radio frequency amplification circuit (4) through the coupling capacitor (3), the output of the first radio frequency amplification circuit (4) is connected with the second radio frequency amplification circuit (5), and the output of the second radio frequency amplification circuit (5) is the alternating current signal output end of the broadband low-noise photoelectric detector. The cascade circuit structure can effectively expand the bandwidth of the existing photoelectric detector based on the transimpedance amplification circuit, but does not amplify the electronic noise of the photoelectric detector at the same time.

Description

Technical Field

[0001] The utility model relates to the technical field of photodetectors, and particularly relates to a broadband low-noise photodetector based on a cascaded circuit structure. Background Technique

[0002] Photodetectors have a wide range of applications in the fields of quantum communication, quantum precision measurement, and quantum optics. Among them, broadband low-noise photodetectors can collect more optical field information, making the collected information more comprehensive and accurate. At present, most photodetectors adopt the structure of a transimpedance amplifier circuit. However, in this structure, it is impossible to have both high bandwidth and high gain for the detector. If you want to increase the bandwidth, the signal gain and signal-to-noise ratio will decrease; if a cascaded structure of two-stage or multi-stage transimpedance amplifier circuits is adopted, the gain can be increased synchronously on the basis of increasing the bandwidth, but at the same time, the electronic noise of the photodetector will also increase. At present, there are also some photodetectors that adopt a cascaded structure of two-stage or multi-stage radio frequency amplifier circuits, but the electronic noise of such photodetectors is particularly large, often dozens of decibels higher than the shot noise benchmark. Summary of the Invention

[0003] In order to overcome the deficiencies of existing photodetectors, the purpose of the utility model is to provide a photodetector with broadband and low noise.

[0004] A broadband low-noise photodetector based on a cascaded circuit structure provided by the utility model includes a photodiode, a transimpedance amplifier circuit, a coupling capacitor, a first radio frequency amplifier circuit, and a second radio frequency amplifier circuit; the photocurrent signal after the photodiode is irradiated by laser is input to the negative input terminal of the transimpedance amplifier circuit, the positive input terminal of the transimpedance amplifier circuit is grounded, the output terminal of the transimpedance amplifier circuit is connected to the first radio frequency amplifier circuit through the coupling capacitor, the output terminal of the first radio frequency amplifier circuit is connected to the second radio frequency amplifier circuit, and the output terminal of the second radio frequency amplifier circuit is the AC signal output terminal of the broadband low-noise photodetector.

[0005] The coupling capacitor is used to effectively transmit the output signal of the transimpedance amplifier circuit to the first radio frequency amplifier circuit, and its capacitance value needs to be determined by theoretical calculation and ADS software simulation methods.

[0006] In the cascaded circuit of the transimpedance amplifier circuit, the first radio frequency amplifier circuit, and the second radio frequency amplifier circuit, the coupling capacitor between them determines whether the signal can be effectively transmitted. If the capacitance value of the coupling capacitor is not selected properly and is not matched with the input impedance of the first radio frequency amplifier circuit, it may cause signal transmission loss, reflection, or distortion, etc., thus affecting the performance of the entire detector circuit.

[0007] The theoretical calculation and ADS software simulation methods for determining the capacitance value of the coupling capacitor include the following steps:

[0008] 1) Calculate using the formula \(C = 1 / (2\pi Rf)\), where \(R\) in the formula is the load resistance after the transimpedance amplifier circuit, and \(f\) is the operating frequency of the experimental design. Calculate the capacitance value of the coupling capacitor according to the theoretical formula.

[0009] 2) Substitute the capacitance value of the coupling capacitor into the circuit model using the simulation software ADS for S-parameter simulation. In signal transmission, the S-parameters need to meet the following conditions: input return loss \(S_{11} \lt -10\ dB\), output return loss \(S_{22} \lt -10\ dB\), reverse transmission coefficient \(S_{12} \lt -20\ dB\), and gain \(S_{21} \gt 40\ dB\). When these conditions are met, the signal can be transmitted forward better.

[0010] 3) Select a capacitor that meets the capacitance values in steps 1) and 2) and weld it to the circuit board for experimental verification. The experimental effect is good, and thus determine the capacitance value of the capacitor.

[0011] The circuit board of the photodetector described above is wrapped with aluminum foil and fixed in an aluminum shielding box.

[0012] Compared with the prior art, the beneficial effects of the present utility model are as follows:

[0013] (1) The transimpedance amplifier circuit is a stable and reliable current-voltage converter. On this basis, the method of cascading a radio frequency amplifier circuit through a coupling capacitor in the transimpedance amplifier circuit is ingeniously used to realize a photodetector that takes into account both broadband and low-noise characteristics. This cascading method effectively expands the bandwidth of the existing photodetector based on the transimpedance amplifier circuit, but does not amplify the electronic noise of the photodetector.

[0014] (2) Compared with the existing photodetectors based on single-stage, two-stage or multi-stage transimpedance amplifier circuits, the bandwidth of the detector of this utility model is expanded a lot; compared with the existing photodetectors based on single-stage, two-stage or multi-stage radio frequency amplifier circuits, the electronic noise of the detector is reduced a lot, and it is basically close to the background noise of the spectrum analyzer.

[0015] (3) The operational amplifier ADA4817-1 in the transimpedance amplifier circuit has a gain-bandwidth product of 1050 MHz, an input voltage noise of 4 nV / √Hz, and an input current noise of 2.5 fA / √Hz; the radio frequency amplifier PSA-8A+ in the radio frequency amplifier circuit has a bandwidth of 4 GHz and a noise figure of 3.3 dB. The gain-bandwidth product of ADA4817-1 is relatively small, but both the input current noise and the input voltage noise are small; PSA-8A+ has a small noise figure, and these parameters provide a guarantee for the implementation of the broadband low-noise photodetector. Description of the Drawings

[0016] Figure 1Schematic diagram of the circuit structure of the broadband low-noise photodetector based on the cascaded circuit structure of the present utility model.

[0017] Figure 2 Detailed circuit diagram of the broadband low-noise photodetector based on the cascaded circuit structure of the present utility model.

[0018] In the figure: 1. Photodiode, 2. Transimpedance amplifier circuit, 3. Coupling capacitor, 4. First RF amplifier circuit, 5. Second RF amplifier circuit; 11. First resistor, 12. First capacitor; 21. Operational amplifier, 22. Second capacitor, 23. Second resistor, 24. Third capacitor, 25. Fourth capacitor, 26. Fifth capacitor, 27. Sixth capacitor; 41. Seventh capacitor, 42. Third resistor, 43. First RF amplifier, 44. First RF choke, 45. Fourth resistor, 46. Eighth capacitor, 47. Ninth capacitor; 51. Tenth capacitor, 52. Fifth resistor, 53. Second RF amplifier, 54. Second RF choke, 55. Sixth resistor, 56. Eleventh capacitor, 57. Twelfth capacitor, 58. Thirteenth capacitor, 59. Seventh resistor.

[0019] Figure 3 Output noise spectrum curve of the broadband low-noise photodetector based on the cascaded circuit structure in the implementation of the present utility model. Specific implementation mode

[0020] The present utility model will be further described in detail below with reference to the accompanying drawings.

[0021] As Figure 1 The schematic diagram of the circuit structure of the broadband low-noise photodetector based on the cascaded circuit structure shown, includes a photodiode 1, a transimpedance amplifier circuit 2, a coupling capacitor 3, a first RF amplifier circuit 4 and a second RF amplifier circuit 5; the photocurrent signal after the photodiode 1 is irradiated by laser is input to the negative input terminal of the transimpedance amplifier circuit 2, the positive input terminal of the transimpedance amplifier circuit 2 is grounded, the output terminal of the transimpedance amplifier circuit 2 is connected to the first RF amplifier circuit 4 through the coupling capacitor 3, the output terminal of the first RF amplifier circuit 4 is connected to the second RF amplifier circuit 5, and the output terminal of the second RF amplifier circuit 5 is the AC signal output terminal of the broadband low-noise photodetector; wherein: the model of the photodiode 1 is FD80W, the model of the operational amplifier in the transimpedance amplifier circuit 2 is ADA4817-1, and the models of the RF amplifiers in the first RF amplifier circuit 4 and the second RF amplifier circuit 5 are PSA-8A+.

[0022] The coupling capacitor 3 is used to effectively transmit the output signal of the transimpedance amplifier circuit 2 to the first RF amplifier circuit 4, and its capacitance value needs to be determined by theoretical calculation and ADS software simulation methods.

[0023] The method for theoretical calculation and ADS software simulation of determining the capacitance value of the coupling capacitor 3 includes the following steps:

[0024] 1) Calculate using the formula C = 1 / (2πRf), where R in the formula is the load resistance after the transimpedance amplifier circuit, and f is the operating frequency designed in the experiment. Calculate the capacitance value of the coupling capacitor according to the formula theoretically.

[0025] 2) Substitute the capacitance value of the coupling capacitor into the circuit model for S-parameter simulation using the simulation software ADS. In signal transmission, the S-parameters need to satisfy: input return loss S11 < -10 dB, output return loss S22 < -10 dB, reverse transmission coefficient S12 < -20 dB, and gain S21 > 40 dB; when these conditions are met, the signal can be transmitted forward better.

[0026] 3) Select a capacitor with a capacitance value that meets the requirements of steps (1) and (2) and weld it to the circuit board for experimental verification. If the experimental effect is good, the capacitance value of the capacitor is determined.

[0027] Such as Figure 2Circuit details of the broadband low-noise photodetector based on the cascaded circuit structure are shown. The cathode of the photodiode 1 is connected to the +5V power supply. The +5V power supply is connected to the first resistor 11 and the first capacitor 12 for filtering. The anode of the photodiode 1 is connected to the negative input terminal of the operational amplifier 21 of the transimpedance amplifier circuit 2. The positive input terminal of the operational amplifier 21 is grounded. The second capacitor 22 and the second resistor 23 are both connected across the negative input terminal and the output terminal of the operational amplifier 21. The output terminal of the operational amplifier 21 is connected to the first radio frequency amplifier circuit 4 through the coupling capacitor 3. The operational amplifier 21 is powered by ±5V power supplies. The +5V power supply is filtered by connecting the third capacitor 24 and the fourth capacitor 25. The -5V power supply is filtered by connecting the sixth capacitor 27 and the fifth capacitor 26. The first radio frequency amplifier circuit 4 is specifically that the seventh capacitor 41 is connected to the input terminal of the first radio frequency amplifier 43 through the third resistor 42. The first radio frequency amplifier 43 is powered by the +5V power supply. The power supply is filtered by connecting the ninth capacitor 47 and the eighth capacitor 46, and then connected to the fourth resistor 45 and the first radio frequency choke 44 to the output terminal of the first radio frequency amplifier 43. The output of the first radio frequency amplifier circuit 4 is connected to the second radio frequency amplifier circuit 5. The second radio frequency amplifier circuit 5 is specifically that the tenth capacitor 51 is connected to the input terminal of the second radio frequency amplifier 53 through the fifth resistor 52. The second radio frequency amplifier 53 is powered by the +5V power supply. The power supply is filtered by connecting the twelfth capacitor 57 and the eleventh capacitor 56, and then connected to the sixth resistor 55 and the second radio frequency choke 54 to the output terminal of the second radio frequency amplifier 53. The output terminal of the second radio frequency amplifier 53 is connected to the thirteenth capacitor 58 and the seventh resistor 59. The output terminal of the seventh resistor 59 is the AC signal output terminal of the broadband low-noise photodetector. The model of the photodiode 1 is FD80W. The model of the operational amplifier 21 in the transimpedance amplifier circuit 2 is ADA4817-1, with a gain-bandwidth product of 1050MHz, an input voltage noise of 4nV / √Hz, and an input current noise of 2.5fA / √Hz. The models of the radio frequency amplifiers 43 and 53 in the first radio frequency amplifier circuit 4 and the second radio frequency amplifier circuit 5 are both PSA-8A+, with a bandwidth of 4GHz and a noise figure of 3.3dB.

[0028] The coupling capacitor 3 is used to effectively transmit the output signal of the transimpedance amplifier circuit 2 to the first radio frequency amplifier circuit 4, and its capacitance value needs to be determined through theoretical calculation and ADS software simulation. In the present invention, the capacitance value of the coupling capacitor 3 is calculated to be 12pF through the formula. Then, the capacitance value of the coupling capacitor is substituted into the circuit model for S-parameter simulation using the simulation software ADS. The S-parameters obtained from the simulation are S11 < -15dB, S22 < -20dB, S12 < -20dB, and S21 > 45dB, which meet the S-parameter standard requirements, indicating that the signal can be effectively transmitted forward.

[0029] As Figure 3The figure shows the output noise spectrum curve of the broadband low-noise photodetector based on the cascade circuit structure in the implementation of the present utility model. In the figure, the m1 curve is the background noise of the spectrum analyzer, m2 is the electronics noise of the broadband low-noise photodetector, and m3 is the signal noise when the incident optical power is 6 mW. It can be seen from the figure that the noise spectrum of the photodetector is relatively flat; the electronics noise is extremely low, only a few dB higher than the background noise; the signal-to-noise ratio is relatively high, about 17 dB in the analysis frequency range of 0.1 to 0.75 GHz, and the working bandwidth of the photodetector is about 750 MHz.

Claims

1. A broadband low-noise photodetector based on a cascade circuit structure, characterized in that: The invention comprises a photodiode (1), a transimpedance amplifier circuit (2), a coupling capacitor (3), a first radio frequency amplifier circuit (4) and a second radio frequency amplifier circuit (5); a photocurrent signal of the photodiode (1) after being irradiated by laser is input into the negative input end of the transimpedance amplifier circuit (2), the positive input end of the transimpedance amplifier circuit (2) is grounded, the output end of the transimpedance amplifier circuit (2) is connected to the first radio frequency amplifier circuit (4) through the coupling capacitor (3), the output end of the first radio frequency amplifier circuit (4) is connected to the second radio frequency amplifier circuit (5), and the output end of the second radio frequency amplifier circuit (5) is the AC signal output end of the broadband low-noise photodetector.

2. A broadband low-noise photodetector based on a cascade circuit structure according to claim 1, characterized in that: The capacitance of the coupling capacitor (3) is determined by theoretical calculation and ADS software simulation.

3. A broadband low-noise photodetector based on a cascade circuit structure according to claim 1 or 2, characterized in that: The circuit board of the photoelectric detector is wrapped with aluminum foil and then fixed in an aluminum shielding box.

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