Balanced photoelectric detector based on differential technology

Abstract

The invention relates to the technical field of novel photoelectric detection, in particular to a balanced photoelectric detector based on a differential technology. Comprising a photoelectric conversion circuit, a first-stage operational amplifier circuit, a second-stage operational amplifier circuit and a power supply circuit, the photoelectric conversion circuit comprises two photodiodes which are connected in series, and a grounding resistor is arranged between the two photodiodes, so that a bias circuit is formed to provide bias voltage for the photodiodes; the output end of the primary operational amplifier circuit is connected with the input end of the secondary operational amplifier circuit to form a differential amplifier circuit; the power supply circuit comprises a 12v-to-5v power supply circuit and a 5v-to-5v power supply circuit. A magnetic bead filter, a pi-type low-pass filter circuit and a shunt capacitor filter circuit are arranged between the 12v-to-5v power supply circuit and the 5v-to-5v power supply circuit. According to the invention, the dark counting influence caused by the adoption of a single-ended phototube in the weak signal extraction process can be avoided, and the measurement precision and reliability are improved.

Description

Technical Field

[0001] The invention relates to the field of novel photoelectric detection technology, and in particular to a balanced photoelectric detector based on differential technology. Background Art

[0002] Photodetectors are devices that detect the intensity of light signals to generate corresponding electrical signals. Due to their advantages of fast response speed, small size and low dark current, they are widely used in fiber optic communication systems, fiber optic sensors, optical isolators, computer data transmission, photoelectric automatic control and light measurement. With the continuous development of detection technology, high-precision and high-sensitivity detection methods have become particularly important.

[0003] In the common detector modules currently used, a single-ended photodiode is usually used as a photoelectric conversion device. In the application of single-ended photodetectors, light is irradiated onto the photosensitive surface of the photodiode, converting a weak current signal. After the current signal is processed by external circuits such as amplifier circuits, a voltage value is output. However, the output voltage signal is not the expected pure signal value, and it is usually mixed with a certain amount of noise. If the light signal itself is very weak, the difference between the converted electrical signal and the noise of the detector is not very large, and it is difficult to distinguish the signal we need. The signal-to-noise ratio of this signal is low, and the low signal-to-noise ratio signal makes the subsequent collection work very troublesome to process. In addition, the quantum efficiency of the single-ended photodetector is low, and it usually does not have additional gain. Therefore, the ability to detect weak light is limited, and the response speed will also be limited. At the same time, when there is no light incident on the single-ended photodetector, the current output caused by the device itself will produce dark counts. Especially in the detection of weak light signals, the influence of dark counts is more significant. The additional signals generated by dark counts need to be identified and eliminated in the data processing stage, which increases the complexity and calculation of data processing. This is a major disadvantage of single-photon detectors. Since there is only one phototube, it is sensitive to external interference such as magnetic fields and electromagnetic interference, which will affect the stability and accuracy of the signal. Its spectral response range is limited, which limits their use in specific wavelength applications. At the same time, when designing single-ended photodiode detectors, it is often necessary to make a trade-off between responsivity and bandwidth. Increasing the absorption area can improve responsivity, but at the same time it will increase the RC time constant and limit the high-speed performance of the device. Therefore, there is an urgent need for a balanced photodetector based on differential technology to improve the ability to detect weak light, while reducing the impact of shot noise caused by the use of single-ended phototubes, and accurately distinguish the required signal from the noise of the detector to improve the signal-to-noise ratio of the detector. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a balanced photodetector based on differential technology. It includes: a photoelectric conversion circuit, a primary operational amplifier circuit, a secondary operational amplifier circuit, an RC filter circuit and a power supply circuit; the photoelectric conversion circuit includes two photodiodes connected in series, and a grounding resistor is arranged between the two photodiodes to form a bias circuit to provide a bias voltage for the photodiodes; the output end of the primary operational amplifier circuit and the input end of the secondary operational amplifier circuit are connected to form a differential amplifier circuit; the RC filter circuit is composed of a resistor and a capacitor; the power supply circuit includes a 12v to 5v power supply circuit and a 5v to -5v power supply circuit, and a magnetic bead filter, a π-type low-pass filter circuit and a parallel capacitor filter circuit are respectively arranged between the 12v to 5v power supply circuit and the 5v to -5v power supply circuit. The present invention can avoid the dark count influence caused by the use of a single-ended phototube in the process of weak signal extraction, and improve the accuracy and reliability of measurement.

[0005] The present invention adopts the following technical solution, a balanced photodetector based on differential technology, comprising:

[0006] It includes: a photoelectric conversion circuit, a primary operational amplifier circuit, a secondary operational amplifier circuit and a power supply circuit;

[0007] The photoelectric conversion circuit includes two photodiodes connected in series, and a grounding resistor is arranged between the two photodiodes to form a bias circuit to provide a bias voltage for the photodiodes; the output end of the first-level operational amplifier circuit and the input end of the second-level operational amplifier circuit are connected to form a differential amplifier circuit; the RC filter circuit is composed of a resistor and a capacitor; the power supply circuit includes a 12v to 5v power supply circuit and a 5v to -5v power supply circuit, and a magnetic bead filter, a π-type low-pass filter circuit and a parallel capacitor filter circuit are respectively arranged between the 12v to 5v power supply circuit and the 5v to -5v power supply circuit.

[0008] Furthermore, the response wavelength range of the two photodiodes in the photoelectric conversion circuit is 400nm-1100nm.

[0009] Furthermore, the first-stage operational amplifier circuit includes a first operational amplifier and a first resistor, and the first resistor is arranged between a feedback pin and a negative input terminal of the first operational amplifier.

[0010] Furthermore, the secondary operational amplifier circuit includes a second operational amplifier, an RC filtering circuit, a second resistor, a third resistor, a fourth resistor and a first capacitor, the positive input terminal of the second operational amplifier is connected to the second resistor to receive the signal output by the first operational amplifier, one end of the inverting input terminal is grounded through the third resistor, and the other end is connected to the output terminal through a parallel circuit of a fourth resistor and the first capacitor; the RC filtering circuit includes a fifth resistor and a second capacitor, the fifth resistor is connected between the output terminal of the secondary operational amplifier circuit and the second capacitor, one end of the second capacitor is connected to the fifth resistor, and the other end is grounded.

[0011] Further, the 12V to 5V power supply circuit includes a first linear regulator, a first magnetic bead, a third capacitor, a fourth capacitor, a fifth capacitor, a sixth capacitor, a seventh capacitor, a sixth resistor, and a seventh resistor;

[0012] The input end of the first linear regulator and the third capacitor are connected in parallel to a 12V voltage source, one end of the fourth capacitor and the fifth capacitor are grounded, and the other ends are respectively connected to the enable input end and the noise reduction pin of the first linear regulator; the sixth capacitor and the seventh resistor are connected in parallel between the output end and the feedback pin of the first linear regulator, one end of the sixth resistor is connected to the ground end of the first linear regulator, and the other end is connected to the output end; one end of the seventh capacitor is connected to the 5V output end, and the other end is grounded; the first magnetic bead is arranged between the first linear regulator and the 5V output end.

[0013] Further, the 5V to -5V power supply circuit includes a second linear regulator, a second magnetic bead, a parallel capacitor filter circuit, an eighth capacitor, a ninth capacitor, a tenth capacitor, an eleventh capacitor, an eighth resistor, a ninth resistor, and a tenth resistor;

[0014] One end of the eighth capacitor is connected to the voltage source input terminal of the second linear regulator, and the other end is grounded; the eighth resistor is connected between the open-drain output pin and the 5v voltage input terminal of the second linear regulator; one end of the ninth capacitor is grounded, and the other end is connected to the CAP pin of the second linear regulator; one end of the ninth resistor and the tenth resistor are respectively connected to the reference voltage pin and the feedback pin of the second linear regulator, and the other end is grounded; the parallel capacitor filter circuit is connected to the 5v voltage input terminal of the second linear regulator; the tenth capacitor and the eleventh capacitor are connected in parallel to the voltage output terminal of the second linear regulator, and the other ends are connected to the -5v voltage output terminal through the second magnetic bead.

[0015] Furthermore, the π-type low-pass filter circuit includes a twelfth capacitor, a thirteenth capacitor and a first inductor. The twelfth capacitor and the thirteenth capacitor are connected in parallel to form a parallel loop. One end of the parallel loop is connected to the first inductor, and the other end is grounded.

[0016] Furthermore, the balanced photodetector of the present invention also includes a detector housing, which includes an upper layer and a lower layer for placing the detector circuit and the power supply circuit, and the upper layer and the lower layer are separated by a layer of metal plate; the housing is provided with circular holes around which are used to fix the power input connector and the BNC connector of the photodetection circuit, as well as circular holes for inputting optical signals.

[0017] The beneficial effects of the present invention are as follows: the balanced photodetector based on differential technology proposed by the present invention has multiple beneficial effects:

[0018] Improved sensitivity and anti-interference ability: The balanced photodetector proposed in the present invention uses an amplifier to enhance the differential signal and suppress the common-mode signal, thereby improving the signal quality. This design can eliminate the unevenness and differences in light source intensity and photodiode performance, and improve the sensitivity and anti-interference ability of the detector;

[0019] Suppressing common mode noise: The balanced detector of the present invention suppresses the common mode signal, suppresses the noise of the local oscillation light, and increases the energy of the useful signal and reduces the noise, thereby improving the sensitivity of the detector;

[0020] Improve signal-to-noise ratio: Differential detection technology uses two photodiodes with very well-matched responsivities to achieve excellent common-mode rejection ratio, eliminate common-mode noise, and obtain small changes in effective signals from interference noise. This technology can improve signal strength and signal-to-noise ratio;

[0021] Expand the measurement range: The use of differential detection technology can improve the signal-to-noise ratio of the beat frequency signal, thereby expanding the measurement range;

[0022] Avoiding the influence of dark current: The present invention avoids the influence of dark count caused by the use of single-ended photoelectric tubes in the process of weak signal extraction, improves the accuracy and reliability of measurement, and makes subsequent data processing more convenient;

[0023] Improved frequency response: The photodetector composed of two photodiodes with matching performance has better frequency response characteristics, can support higher signal transmission rates, and is suitable for high-speed optical communication and data transmission applications;

[0024] Improve system performance and reliability: Balanced photodetectors can suppress the relative intensity noise of lasers and the spontaneous emission noise in erbium-doped fiber amplifiers, and are also widely used in analog optical links and microwave photonic systems;

[0025] Integrated design: Dual photodiode detectors can be integrated on a single chip, simplifying the design and manufacturing process and reducing packaging costs. This integrated design helps improve device reliability and stability.

[0026] In summary, the balanced photodetector based on differential technology proposed in the present invention has obvious advantages in signal-to-noise ratio, common mode rejection ratio, sensitivity, measurement range, frequency response, anti-interference ability, high integration and low loss, and provides an effective technical solution for high-speed optical communication and precision measurement, and brings significant technological progress to coherent detection systems and precision measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0028] Figure 1 A schematic diagram of a balanced photodetector structure based on differential technology according to an embodiment of the present invention;

[0029] Figure 2 A schematic diagram of the structure of a photoelectric conversion circuit according to an embodiment of the present invention;

[0030] Figure 3 A schematic diagram of a two-stage operational amplifier cascade circuit connection according to an embodiment of the present invention;

[0031] Figure 4 A schematic diagram of a power supply circuit principle of an embodiment of the present invention;

[0032] Figure 5 This is a schematic diagram of a 12V to 5V circuit connection according to an embodiment of the present invention;

[0033] Figure 6 A 5V to -5V circuit connection diagram according to an embodiment of the present invention;

[0034] Figure 7 A schematic diagram of a π-type filter circuit connection according to an embodiment of the present invention;

[0035] Figure 8 The figure is a schematic diagram of the structure of a balanced photodetector housing according to an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The present invention provides a high-sensitivity, low-noise balanced photoelectric detector capable of detecting weak light signals. Two highly consistent photodiodes matched to each other are used for photoelectric conversion. The weak current signals converted by the two photodiodes are then differentially subtracted. The obtained differential signal is amplified by an amplifier, and the working points of the two photodiodes are adjusted through a feedback loop so that their output signals are always equal, thereby eliminating the unevenness and differences in light source intensity and photodiode performance, and improving the sensitivity and anti-interference ability of the detector. The differential amplifier amplifies the difference between the two input signals and suppresses the common-mode signal, thereby improving the signal-to-noise ratio and measurement accuracy of the signal. At the same time, the balanced detectors are integrated together, thereby improving the integration level and reducing the packaging difficulty and cost.

[0038] A flow chart of a balanced photodetector based on differential technology according to an embodiment of the present invention is as follows: Figure 1 As shown, it includes a photoelectric conversion circuit, a primary operational amplifier circuit, a secondary operational amplifier circuit and a power supply circuit, which specifically includes: the photoelectric conversion circuit includes two photodiodes connected in series, and a grounding resistor is arranged between the two photodiodes to form a bias circuit to provide a bias voltage for the photodiodes; the output end of the primary operational amplifier circuit and the input end of the secondary operational amplifier circuit are connected to form a differential amplifier circuit; the power supply circuit includes a 12V to 5V power supply circuit and a 5V to -5V power supply circuit, and a magnetic bead filter, a π-type low-pass filter circuit and a parallel capacitor filter circuit are respectively arranged between the 12V to 5V power supply circuit and the 5V to -5V power supply circuit.

[0039] In the embodiment of the present invention, the bias circuit is connected in series between the positive and negative power supplies and the photodiodes through bias resistors to provide the necessary bias voltage for the photodiodes to ensure that they can work normally. The bias circuit provides the necessary voltage or current for the semiconductor device to ensure that the device operates stably under a specific working state, so that it can maintain a stable operating point under different process drifts, temperature changes or power supply voltage fluctuations.

[0040] The two photodiodes in the photoelectric conversion circuit are composed of PIN photodiodes with similar performance. The light signals received by the two photodiodes are in opposite phases, and their output currents are also opposite. A differential signal is obtained by subtraction, and then enters the amplifier circuit part to amplify the differential signal.

[0041] The first-stage operational amplifier circuit is a high-gain amplifier circuit, which adopts a low-noise, high-speed operational amplifier design. Resistors are connected between the feedback pin and the negative input terminal. By adjusting the value of the feedback resistor, the gain can be increased while maintaining a high loop gain, thereby avoiding the limitation of fixed gain bandwidth. In addition, the feedback resistor can help suppress high-frequency noise caused by parasitic capacitance. By introducing a resistor in the feedback path, the high-frequency noise gain can be reduced, thereby improving the signal quality of the circuit.

[0042] The two-stage operational amplifier circuit is a high-speed FET input single-channel amplifier circuit. It adopts a high-performance, fast field-effect transistor operational amplifier design. After the first-stage operational amplifier amplifies the current signal, it enters the positive input terminal of the second-stage amplifier. One end of the inverting input terminal is connected to the ground with a resistor, and the other end is connected to the resistor to the output terminal. The current signal is converted into a voltage signal and amplified. The amplification factor can be adjusted by changing the ratio of the feedback resistor to the input resistor. The chip is powered by positive and negative dual power supplies. The signals entering the positive and negative power supplies of the operational amplifier will be filtered by a magnetic bead filter to filter out unnecessary high-frequency noise signals. The capacitor parallel filter consists of three parallel capacitors, which can filter signals in a specific frequency range as needed.

[0043] The RC low-pass filter circuit is composed of a resistor and a capacitor, with its signal input end connected to a series combination of a resistor and a capacitor, the other end of the resistor connected to the output end of the circuit, and the other end of the capacitor connected to the ground. Its specific structure can also refer to the existing circuit structure. Under this configuration, low-frequency signals can smoothly pass through the resistor to reach the output end due to the high capacitive reactance of the capacitor, while high-frequency signals will be short-circuited to the ground by the capacitor due to the low capacitive reactance of the capacitor, thereby reducing the high-frequency components reaching the output end. The values ​​of the resistor and the capacitor can be calculated to obtain the noise within the frequency band to be filtered out.

[0044] The π-type low-pass filter circuit consists of two capacitors and an inductor. The two capacitors are connected in parallel, and an inductor is connected at both ends of them. At low frequencies, the impedance of the inductor is higher, and the signal is mainly transmitted through the capacitor. As the frequency increases, the impedance of the capacitor decreases, and more high-frequency signals are short-circuited to the ground by the capacitor, thereby being filtered out; the inductor has a smaller hindering effect on low-frequency signals, but a greater hindering effect on high-frequency signals, so it can prevent high-frequency signals from passing through. At the same time, the two parallel capacitors can further reduce the high-frequency noise at the output end.

[0045] The parallel capacitor filter circuit is composed of three capacitors with different capacitance values ​​connected in parallel. Capacitors with different capacitance values ​​have different degrees of response to signals of different frequencies. Large-capacitance capacitors have better filtering effects on low-frequency signals, while small-capacitance capacitors have better filtering effects on high-frequency signals. Therefore, three capacitors with different capacitance values ​​connected in parallel can provide a wider frequency response range, so that the circuit can respond better to signals of different frequencies.

[0046] The 12V to 5V power supply circuit is composed of a linear voltage regulator and peripheral circuits. Its output voltage is adjustable. The voltage output can be adjusted by adjusting the size of the feedback loop resistance ratio. Its output 5V is finally filtered by a magnetic bead filter to remove the high-frequency noise part in the power supply, completing the 12V to 5V voltage conversion and obtaining a pure 5V power supply.

[0047] The 5v to negative 5v power supply circuit consists of a 5v to negative 5v charge pump and peripheral circuits. Its output voltage is adjustable. The charge pump completes the conversion from 5v to negative 5v, and then the signal ripple is reduced by the LDO linear regulator. Finally, the high-frequency noise in the power supply signal is further filtered out by the π-type filter circuit to obtain a pure negative 5v power supply.

[0048] The voltage stabilization circuit includes positive and negative power supplies to stabilize the power supply part of the secondary operational amplifier. The positive and negative 5V power supplies are connected to the detector circuit. After the power supply voltage is stabilized by the linear regulator, a stable voltage is provided for the positive and negative power supplies required by the operational amplifier, protecting the operational amplifier from voltage fluctuations or instantaneous voltage spikes, ensuring the service life of the operational amplifier. At the same time, the voltage stabilization circuit can also reduce noise and ripple on the power line, providing a clean power supply for the amplifier circuit.

[0049] In another specific embodiment of the present invention:

[0050] Photoelectric conversion circuit such as Figure 2 As shown, it includes two photodiodes with matched performance. The response wavelength range of the two photodiodes in the photoelectric conversion circuit is 400nm-1100nm. The two photodiodes are reversely connected in series between positive and negative 5V. The power supply signal is filtered by three capacitors in parallel before being input to the photodiode. Three capacitors with different capacitances are connected in parallel to filter out signal noise in a wider frequency range. A 10kΩ resistor is connected between the two diodes to ground. The grounding resistor can provide the necessary bias current for the photodiode to ensure that it operates in the best working state, while reducing the noise generated by the photodiode and stabilizing the working point of the photodiode.

[0051] The first-stage operational amplifier circuit includes a first operational amplifier and a first resistor, wherein the first resistor is arranged between the feedback pin and the negative input terminal of the first operational amplifier. Specifically, it adopts a single-channel amplifier of unit gain stability, ultra-high-speed voltage feedback type, model ADA4817-1ARDZ, with FET input. The weak current signal entering the chip is amplified, and the amplification factor can be adjusted by changing the resistance value between the negative input and the feedback. The chip is powered by positive and negative dual power supplies. The signals entering the positive and negative power supplies of the operational amplifier will be filtered by capacitor parallel connection to filter out unnecessary high-frequency noise signals. The capacitor parallel connection filter is composed of three parallel capacitors, and the signals in a specific frequency range can be filtered out as needed.

[0052] The secondary operational amplifier circuit includes a second operational amplifier, an RC filtering circuit, a second resistor, a third resistor, a fourth resistor and a first capacitor. The positive input end of the second operational amplifier is connected to the second resistor to receive the signal output by the first operational amplifier. One end of the inverting input end is grounded through the third resistor, and the other end is connected to the output end through a fourth resistor and a first capacitor parallel circuit; the RC filtering circuit includes a fifth resistor and a second capacitor. The fifth resistor is connected between the output end of the secondary operational amplifier circuit and the second capacitor. One end of the second capacitor is connected to the fifth resistor and the other end is grounded. The RC filter can filter out noises of different frequency bands by modifying the values ​​of the resistors and capacitors. The secondary operational amplifier circuit adopts a high-performance, high-speed, FET input single-channel amplifier of model AD8065ARZ. The output of the FET input operational amplifier The input bias current is usually very low, which is very important for precision amplification applications that require low noise and low distortion. At the same time, FET input op amps have higher bandwidth and lower input capacitance, and are also suitable for amplifying and processing high-frequency signals. After the first-stage operational amplifier amplifies the signal, it enters the positive input terminal of the second-stage amplifier. One end of the inverting input terminal is connected to the ground with a resistor, and the other end is connected to the output terminal. The current signal is converted into a voltage signal by the transimpedance amplifier and amplified. The amplification factor can be adjusted by changing the ratio of the feedback resistor to the input resistor. The chip uses positive and negative dual power supplies. The signals entering the positive and negative power supplies of the operational amplifier will be filtered by a magnetic bead filter to filter out unnecessary high-frequency noise signals. The capacitor parallel filter consists of three parallel capacitors, which can filter signals in a specific frequency range as needed. It should be noted that these two operational amplifiers constitute the following: Figure 3The differential amplifier shown in the figure, one of them is used as an inverting amplifier and the other is used as a non-inverting amplifier. The output ends of the two operational amplifiers are connected through resistors to form a differential amplifier, which can significantly suppress common-mode signals and provide a high common-mode rejection ratio. In addition, the differential amplifier can improve the dynamic range of the signal because it can effectively suppress common-mode noise, thereby allowing a larger signal swing without introducing additional noise. The two operational amplifiers solve the problem of the gain-bandwidth product limitation of the first-stage sampling amplifier by adopting a two-stage amplification cascade method, alleviate the contradiction between the mutual constraints between the gain and bandwidth of the balanced detector, improve the response bandwidth of the detector, and improve the gain and signal-to-noise ratio of the detection system. At the same time, it can improve the common-mode rejection ratio of the detector, thereby improving the purity and quality of the signal.

[0053] Figure 4 The figure shows a schematic diagram of the principle of constructing a power supply circuit in an embodiment of the present invention, which includes a 12V to 5V power supply circuit, a magnetic bead filter, a 5V to -5V power supply circuit, a voltage stabilizing circuit, and a π-type filter circuit. After the 12V power supply voltage enters the circuit, it is first connected to the ground in parallel with a Schottky diode and a voltage stabilizing diode. The Schottky diode has a low noise characteristic, and its voltage noise and current noise are relatively low, so as to reduce the noise of the signal. The voltage stabilizing diode can clamp the signal voltage to prevent the signal voltage from exceeding its set stable voltage, thereby protecting the subsequent circuit from being damaged by excessively high voltage. At the same time, the Schottky diode connected to the ground in parallel The diode and Zener diode can suppress common-mode signals and reduce the impact of electromagnetic interference on signals. For high-frequency signals, the fast response characteristics of the Schottky diode can reduce signal distortion and improve signal fidelity. The signal then passes through the fuse. The main function of the fuse in the circuit is to protect the circuit from damage by excessive current. When the current in the circuit exceeds the maximum current that the fuse can withstand, the fuse will blow, thereby cutting off the circuit and preventing components in the circuit from being damaged due to overheating. The rated current of the fuse is usually slightly higher than the normal operating current of the circuit, so that it will not blow during normal operation and will only work under abnormal circumstances.

[0054] Specifically, the 12v to 5v power supply circuit diagram is as follows Figure 5 As shown, it includes a first linear regulator, a first magnetic bead, a third capacitor, a fourth capacitor, a fifth capacitor, a sixth capacitor, a seventh capacitor, a sixth resistor, and a seventh resistor; the input end of the first linear regulator and the third capacitor are connected in parallel to a 12V voltage source, one end of the fourth capacitor and the fifth capacitor are grounded, and the other ends are respectively connected to the enable input end and the noise reduction pin of the first linear regulator; the sixth capacitor and the seventh resistor are connected in parallel between the output end and the feedback pin of the first linear regulator, one end of the sixth resistor is connected to the ground end of the first linear regulator, and the other end is connected to the output end; one end of the seventh capacitor is connected to the 5V output end, and the other end is grounded; the first magnetic bead is arranged between the first linear regulator and the 5V output end.

[0055] In a specific embodiment of the present invention, the first linear regulator adopts a low-dropout linear regulator chip model TPS7A4901DGNR, which has an input range of 3v to 36v, an adjustable output voltage range from 1.194v to 33v, a maximum output current of 150mA, and a noise of 15.4uvRMS in the frequency range of 10Hz to 100kHz. It has a high power supply rejection ratio, in which a clean voltage rail is critical to maximizing system performance and can provide maximum system performance in sensitive circuits. The chip and the peripheral circuit are designed to convert 12v voltage into 5v.

[0056] 5v to -5v power supply circuit diagram Figure 6 As shown, it includes a second linear regulator, a second magnetic bead, a parallel capacitor filtering circuit, an eighth capacitor, a ninth capacitor, a tenth capacitor, an eleventh capacitor, an eighth resistor, a ninth resistor, and a tenth resistor; one end of the eighth capacitor is connected to the voltage source input end of the second linear regulator, and the other end is grounded; the eighth resistor is connected between the open-drain output pin and the 5V voltage input end of the second linear regulator; one end of the ninth capacitor is grounded, and the other end is connected to the CAP pin of the second linear regulator; one end of the ninth resistor and the tenth resistor are respectively connected to the reference voltage pin and the feedback pin of the second linear regulator, and the other end is grounded; the parallel capacitor filtering circuit is connected to the 5V voltage input end of the second linear regulator; the tenth capacitor and the eleventh capacitor are connected in parallel to the voltage output end of the second linear regulator, and the other end is connected to the -5V voltage output end through the second magnetic bead.

[0057] In a specific embodiment of the present invention, the second linear regulator adopts a chip of model LM27762DSSR, which integrates a low-noise charge pump and a low-dropout linear regulator, with an input voltage range of 2.7v to 5.5v, capable of generating a low-noise, adjustable positive power supply voltage of 1.5V to 5V and a negative power supply voltage of -5V to -1.5V, an output current range of ±250mA, and a dedicated enable input for the positive and negative voltage outputs, supporting independent positive and negative power rail timing to meet specific system power sequencing requirements, capable of independently outputting a -5v power supply, which has current limiting and thermal protection, as well as a thermal shutdown mechanism triggered when overheating, which can protect the device from damage. This chip uses negative enable, negative feedback, and negative output pins, and adjusts the output voltage by adjusting the size of the feedback resistance, so that it outputs a -5v voltage source.

[0058] The voltage stabilization circuit uses TPS7A3001DGNR, a negative high-voltage, ultra-low-noise linear regulator chip. This device can very effectively suppress the ripple and noise of the input power supply, thereby providing a clean and stable power supply for sensitive analog circuits. Its input voltage range is: -3V to -36V, and the output voltage range is adjustable from -1.18V to -33V. The maximum output current is 200mA. It has a high power supply rejection ratio and is particularly suitable for circuit applications that are sensitive to power supply noise. Its input and enable are connected to a high level of 5v, and the feedback pin is connected to the chip output through a resistor and a capacitor in parallel. The feedback pin is connected to a resistor and grounded. The output voltage of 5v is adjusted by adjusting the feedback resistance.

[0059] The π-type filter consists of two capacitors and an inductor, such as Figure 7 As shown, it includes a twelfth capacitor, a thirteenth capacitor and a first inductor. The twelfth capacitor and the thirteenth capacitor are connected in parallel to form a parallel loop. One end of the parallel loop is connected to the first inductor, and the other end is grounded. It adopts an LC filter structure, and eliminates or weakens unnecessary frequency components through the combination of capacitors and inductors. The working principle of the filter circuit of L1 and C12 is that the voltage filtered by C1 is added to the filter circuit of L1 and C12. For DC voltage, since the DC resistance of inductor L1 is very small, the DC voltage drop generated on L1 when DC current flows through L1 is very small, which is better than the filter resistor; for AC components, In other words, because of the existence of the inductive reactance of inductor L1, and this inductive reactance is very large, this inductive reactance and the capacitive reactance of capacitor C2 (capacitive reactance is very small) form a voltage divider attenuation circuit, which has a great attenuation effect on the AC component, achieving the purpose of filtering. The cut-off frequency of the π-type LC filter is affected by the values ​​of inductance and capacitance. Larger capacitance and inductance values ​​lead to lower cut-off frequencies, thereby better filtering out high-frequency noise. Through calculation, it is obtained that when the capacitance value of C11 is 0.1uF, the capacitance value of C12 is 330nF, and the inductance value is 1uH, high-frequency noise above 1Mhz can be filtered out, thereby reducing the interference of high-frequency noise of the power supply on the signal part, so that the detector circuit can have a clean power supply.

[0060] like Figure 8 As shown, the balanced photodetector in the embodiment of the present invention also includes a detector housing, which includes an upper layer and a lower layer for placing the detector circuit and the power supply circuit, and the upper layer and the lower layer are separated by a layer of metal plate; the housing is provided with circular holes around the power input connector and the BNC connector for fixing the photodetection circuit, as well as circular holes for inputting optical signals. The design of these interfaces takes into account the stability and reliability of signal transmission. The housing is made of all-metal material to provide good shielding performance and reduce the impact of external electromagnetic interference on the internal circuit of the detector.

[0061] In summary, the technical solution of the present invention integrates two photodiodes with matched performance to obtain a differential signal with high sensitivity and strong anti-interference ability. The differential signal is amplified by a differential amplifier composed of two cascaded operational amplifiers, and the operating points of the two photodiodes are adjusted through a feedback loop so that their output signals are always equal. Finally, the processed signal is obtained for observation to obtain information about the light signal detected by the detector.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A balanced photodetector based on differential technology, characterized in that: include: Photoelectric conversion circuit, primary operational amplifier circuit, secondary operational amplifier circuit and power supply circuit; The photoelectric conversion circuit includes two photodiodes connected in series, and a grounding resistor is arranged between the two photodiodes to form a bias circuit to provide a bias voltage for the photodiodes; the output end of the first-level operational amplifier circuit and the input end of the second-level operational amplifier circuit are connected to form a differential amplifier circuit; the power supply circuit includes a 12v to 5v power supply circuit and a 5v to -5v power supply circuit, and a magnetic bead filter, a π-type low-pass filter circuit and a parallel capacitor filter circuit are respectively arranged between the 12v to 5v power supply circuit and the 5v to -5v power supply circuit.

2. The balanced photodetector based on differential technology according to claim 1, characterized in that: The response wavelength range of the two photodiodes in the photoelectric conversion circuit is 400nm-1100nm.

3. The balanced photodetector based on differential technology according to claim 1, characterized in that: The first-stage operational amplifier circuit includes a first operational amplifier and a first resistor, and the first resistor is arranged between a feedback pin and a negative input terminal of the first operational amplifier.

4. The balanced photodetector based on differential technology according to claim 1, characterized in that: The secondary operational amplifier circuit includes a second operational amplifier, an RC filtering circuit, a second resistor, a third resistor, a fourth resistor and a first capacitor. The positive input end of the second operational amplifier is connected to the second resistor to receive the signal output by the first operational amplifier. One end of the inverting input end is grounded through the third resistor, and the other end is connected to the output end through a parallel circuit of the fourth resistor and the first capacitor; the RC filtering circuit includes a fifth resistor and a second capacitor. The fifth resistor is connected between the output end of the secondary operational amplifier circuit and the second capacitor. One end of the second capacitor is connected to the fifth resistor, and the other end is grounded.

5. The balanced photodetector based on differential technology according to claim 1, characterized in that: The 12V to 5V power supply circuit includes a first linear regulator, a first magnetic bead, a third capacitor, a fourth capacitor, a fifth capacitor, a sixth capacitor, a seventh capacitor, a sixth resistor, and a seventh resistor; The input end of the first linear regulator and the third capacitor are connected in parallel to a 12V voltage source, one end of the fourth capacitor and the fifth capacitor are grounded, and the other ends are respectively connected to the enable input end and the noise reduction pin of the first linear regulator; the sixth capacitor and the seventh resistor are connected in parallel between the output end and the feedback pin of the first linear regulator, one end of the sixth resistor is connected to the ground end of the first linear regulator, and the other end is connected to the output end; one end of the seventh capacitor is connected to the 5V output end, and the other end is grounded; the first magnetic bead is arranged between the first linear regulator and the 5V output end.

6. The balanced photodetector based on differential technology according to claim 1, characterized in that: The 5V to -5V power supply circuit includes a second linear regulator, a second magnetic bead, a parallel capacitor filter circuit, an eighth capacitor, a ninth capacitor, a tenth capacitor, an eleventh capacitor, an eighth resistor, a ninth resistor, and a tenth resistor; One end of the eighth capacitor is connected to the voltage source input terminal of the second linear regulator, and the other end is grounded; the eighth resistor is connected between the open-drain output pin and the 5v voltage input terminal of the second linear regulator; one end of the ninth capacitor is grounded, and the other end is connected to the CAP pin of the second linear regulator; one end of the ninth resistor and the tenth resistor are respectively connected to the reference voltage pin and the feedback pin of the second linear regulator, and the other end is grounded; the parallel capacitor filter circuit is connected to the 5v voltage input terminal of the second linear regulator; the tenth capacitor and the eleventh capacitor are connected in parallel to the voltage output terminal of the second linear regulator, and the other ends are connected to the -5v voltage output terminal through the second magnetic bead.

7. The balanced photodetector based on differential technology according to claim 1, characterized in that: The π-type low-pass filter circuit includes a twelfth capacitor, a thirteenth capacitor and a first inductor. The twelfth capacitor and the thirteenth capacitor are connected in parallel to form a parallel loop. One end of the parallel loop is connected to the first inductor, and the other end is grounded.

8. The balanced photodetector based on differential technology according to claim 1, characterized in that: It also includes a detector housing, which includes an upper layer and a lower layer for placing the detector circuit and the power supply circuit, and the upper layer and the lower layer are separated by a layer of metal plate; the housing is provided with circular holes around which are used to fix the power input connector and the BNC connector of the photoelectric detection circuit, as well as circular holes for inputting optical signals.

Images