An automatically feedback-regulated balance detector

Abstract

The present invention provides a balanced detector with automatic feedback regulation, which includes a photoelectric detection circuit, a monitoring circuit, a voltage feedback regulation circuit, a transimpedance amplifier circuit, and a voltage amplifier circuit. The photoelectric detection circuit includes two series-connected photodiodes. A differential current is obtained at the connection node of the two series-connected photodiodes, and the differential current signal is input to the input end of the transimpedance amplifier circuit. The current signal is converted into a voltage signal by the transimpedance amplifier circuit and then output to the voltage amplifier circuit. The voltage signal is amplified and output by the voltage amplifier circuit. The monitoring circuit is used to monitor the voltages on both sides of the photodiode and input the voltage signal to the voltage comparator in the voltage feedback regulation circuit. The voltage signal is compared by the voltage comparator, and the output voltage of the voltage feedback regulation circuit is used to regulate the voltage in the photoelectric detection circuit. The present invention can effectively suppress common-mode noise and achieve high-bandwidth and high-gain photoelectric detection.

Description

Technical Field

[0001] The present invention relates to the technical field of photodetectors, and particularly to a balanced detector with automatic feedback regulation. Background Art

[0002] Balanced detection technology has the advantages of low noise and high sensitivity, and is widely used in fields such as quantum noise measurement, spectral measurement, heterodyne detection, and terahertz detection. Traditional balanced detectors are designed with symmetric optoelectronic detection circuits, and optoelectronic signal conversion is performed through two photodiodes. When the response parameters of the two phototubes are asymmetric, noise will be introduced during the optoelectronic conversion process, thus affecting the accuracy. There are also high requirements for the identity of the device and the voltage at both ends of the phototube. Therefore, designing a highly symmetric balanced detector circuit has become a key topic for current researchers.

[0003] In addition, high gain and high bandwidth are also key indicators for measuring the performance of balanced detectors. The generally used transimpedance amplifier circuit is applicable to the low-frequency range, and there is a contradiction between its gain and bandwidth. Increasing its bandwidth will result in a decrease in its gain. Therefore, a balanced detector circuit with single-stage amplification cannot meet the requirements of simultaneously increasing the circuit gain and bandwidth. So, designing a multi-stage amplification circuit is also a problem that needs to be solved in current research. Summary of the Invention

[0004] Aiming at the deficiencies in the prior art, the purpose of the present invention is to provide a balanced detector with automatic feedback regulation that can effectively suppress common-mode noise and achieve high-bandwidth and high-gain optoelectronic detection.

[0005] To solve the above problems, the technical solution of the present invention is as follows:

[0006] A balanced detector with automatic feedback regulation, the balanced detector includes an optoelectronic detection circuit, a monitoring circuit, a voltage feedback regulation circuit, a transimpedance amplifier circuit, and a voltage amplifier circuit. The optoelectronic detection circuit includes two serially connected photodiodes, a differential current is obtained at the connection node of the two serially connected photodiodes, and the differential current signal is input to the input end of the transimpedance amplifier circuit. The current signal is converted into a voltage signal by the transimpedance amplifier circuit and then output to the voltage amplifier circuit. The voltage signal is amplified and output by the voltage amplifier circuit. The monitoring circuit is used to monitor the voltages on both sides of the photodiode and input the voltage signal to a voltage comparator in the voltage feedback regulation circuit. The voltage signal is compared by the voltage comparator, and the output voltage of the voltage feedback regulation circuit is used to adjust the voltage in the optoelectronic detection circuit.

[0007] Optionally, the photoelectric detection circuit includes two first photodiodes and second photodiodes with exactly the same model and performance parameters. After converting the collected optical signal into a current signal through the photodiodes, the output is sent to the transimpedance amplifier circuit. The actually output current signal is the difference between the output current signals of the two photodiodes.

[0008] Optionally, the two photodiodes are PIN photodiodes with small dark current and junction capacitance and high responsivity. The cathode of the first photodiode is connected to a positive voltage of 10V after being in series with a resistor, and the anode of the second photodiode is connected to a negative voltage of -10V after being in series with a resistor.

[0009] Optionally, the transimpedance amplifier circuit is used to convert the current signal into a voltage signal. A feedback resistor and a feedback capacitor are connected in parallel to the inverting terminal of the transimpedance amplifier circuit, and the non-inverting terminal of the transimpedance amplifier circuit is grounded through a resistor.

[0010] Optionally, the voltage amplifier circuit is a proportional amplifier circuit composed of an operational amplifier. The inverting terminal of the voltage amplifier circuit is connected to the output terminal of the transimpedance amplifier circuit through a filter capacitor. The non-inverting terminal of the voltage amplifier circuit is grounded through a pull-down resistor, and the output terminal of the voltage amplifier circuit outputs an amplified voltage signal.

[0011] Optionally, the monitoring circuit includes two differential amplifiers with exactly the same structure, which respectively monitor the voltage signals at both ends of the resistors in series with the two photodiodes and output them.

[0012] Optionally, the voltage feedback adjustment circuit includes a voltage comparator and a voltage digital-to-analog conversion chip. The voltage signal is input to the voltage comparator in the voltage feedback adjustment circuit and compared through the voltage comparator. When the two monitored voltages are not equal, a voltage is output through the voltage digital-to-analog conversion chip for voltage feedback to adjust the voltage in the photoelectric detection circuit.

[0013] Optionally, the monitored negative voltage is first converted into a positive voltage through a voltage inverter follower and then connected to the input terminal of the voltage comparator for comparison through the voltage comparator.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] 1. The bias voltages at both ends of the photodiodes are adjusted through the monitoring circuit and the voltage feedback adjustment circuit, which can realize real-time voltage monitoring and compare the two voltages through the voltage comparator. When there is a voltage difference, the voltages at both ends of the photodiodes are automatically feedback-adjusted, so that the voltages at both ends are always kept equal, better realizing the symmetry and balance of the detector, reducing the influence of common-mode noise and electronics noise, and optimizing the performance of the balanced detector.

[0016] 2. Through the design of a two-stage amplifier circuit that combines a transimpedance amplifier circuit and a voltage amplifier circuit, the voltage gain and bandwidth of the circuit output signal are improved. Since the gain-bandwidth product of the amplifier is a fixed value, expanding the gain of the circuit will result in a decrease in bandwidth, which cannot meet the actual requirements. The design of the two-stage amplifier circuit avoids the limitation of the gain-bandwidth product. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments read in conjunction with the accompanying drawings:

[0018] Figure 1 It is a structural block diagram of an automatic feedback-regulated balanced detector provided by an embodiment of the present invention;

[0019] Figure 2 It is a circuit connection schematic diagram of an automatic feedback-regulated balanced detector provided by an embodiment of the present invention;

[0020] Figure 3 It is a schematic circuit diagram of the two-stage amplifier part of an automatic feedback-regulated balanced detector provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those of ordinary skill in the art can make several changes and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0022] Figure 1 It is a structural block diagram of an automatic feedback-regulated balanced detector provided by an embodiment of the present invention, Figure 2 It is a circuit connection schematic diagram of an automatic feedback-regulated balanced detector provided by an embodiment of the present invention, as Figure 1 and Figure 2 shown, the balanced detection device includes a photoelectric detection circuit 1, a monitoring circuit 2, a voltage feedback regulation circuit 3, a transimpedance amplifier circuit 4, and a voltage amplifier circuit 5.

[0023] The photoelectric detection circuit 1 includes two first photodiodes 11 and second photodiodes 12 with the same model and performance parameters, having high sensitivity and high-speed response characteristics. After connecting the two photodiodes in series with a resistor and connecting them to a DC power supply, the light signals collected by the photodiodes are converted into current signals and output. The actually output current signal is the difference between the output current signals of the two photodiodes. The two photodiodes are PIN photodiodes with the advantages of small dark current, small junction capacitance, and high responsivity, and the bandwidth of this photodiode is 2.5 GHz. In the circuit, the first photodiode 11 and the second photodiode 12 are connected in series. Using the working principle of reverse biasing of the PIN photodiode, a positive voltage of 10 V is connected after a resistor is connected in series at the cathode of the first photodiode 11, and a negative voltage of -10 V is connected after a resistor is connected in series at the anode of the second photodiode 12. According to Kirchhoff's current law, the current difference of the two series-connected photodiodes is obtained at the node connecting the anode of the first photodiode 11 and the cathode of the second photodiode 12, and the output difference current signal is connected to the input end of the transimpedance amplifier circuit 4.

[0024] The monitoring circuit 2 is used to collect the voltage signals at both ends of the resistor in series with the photodiode, monitor the voltage at both ends of the resistor in series with the photodiode in real time, and input the voltage signal to the voltage comparator in the voltage feedback adjustment circuit 3. The monitoring circuit 2 for monitoring the voltage signals at both ends of the photodiode is composed of a precision differential amplifier. The non-inverting input terminal and the inverting input terminal of one differential amplifier are respectively connected to both ends of the load resistor R1 connected to the cathode of the first photodiode 11, and the non-inverting input terminal and the inverting input terminal of the other differential amplifier are respectively connected to both ends of the load resistor R12 connected to the anode of the second photodiode 12. The structures of the two monitoring circuits composed of differential amplifiers are exactly the same, and the power supply is ±5V.

[0025] The voltage automatic feedback adjustment circuit 3 compares the monitored voltage signals through a voltage comparator. The monitored negative voltage needs to be first converted into a positive voltage through a voltage inverter follower 6 and then connected to the input terminal of the voltage comparator. When there is a voltage difference, the voltage comparator feeds back the output voltage through a programmable voltage digital-to-analog conversion chip to adjust the voltage in the photoelectric detection circuit, so as to keep the voltage at both ends of the photodiode the same and achieve circuit symmetry.

[0026] As Figure 3 shown, the transimpedance amplifier circuit 4 selects a bipolar input operational amplifier chip OPA855IDSGR with a gain bandwidth of 8 GHz. The inverting input terminal of the operational amplifier is connected in parallel with a feedback capacitor C8 and a feedback resistor R2. The feedback resistor R2 is used to increase the gain of the circuit, and the gain of the circuit is related to the resistance value of R2. The feedback capacitor C8 is used to improve the frequency response characteristics of the detector. The non-inverting input terminal of the operational amplifier is grounded after passing through a resistor R11.

[0027] The voltage amplification circuit 5 is composed of an OPA855IDSGR chip and its peripheral circuits. The inverting terminal of the voltage amplification circuit 5 is connected to the output terminal of the transimpedance amplification circuit 4 through a filtering capacitor C9. The inverting input terminal of the OPA855IDSGR chip is connected to the parallel resistors R3 and R6 to form a proportional amplification circuit, and the voltage amplification factor is R3 / R6. The non-inverting terminal is grounded after passing through a pull-down resistor R10.

[0028] In this embodiment, a two-stage amplification design concept of combining the transimpedance amplification circuit 4 and the voltage amplification circuit 5 is adopted. The voltage signal output after the current-voltage conversion is achieved by the transimpedance amplification circuit 4 is connected to the inverting terminal of the voltage amplification circuit 5 composed of a high-gain operational amplifier. After voltage amplification, the amplified voltage signal can be detected at the output terminal.

[0029] In addition, after the voltage signals are monitored by the two-way monitoring circuit 2 and output, they are compared by a voltage comparator. Because theoretically, to ensure the balance performance of the balance detector and the symmetry of the circuit structure, it is necessary to ensure that the voltage magnitudes at both ends of the photodiode are exactly equal. The voltage signal monitored from the negative voltage power supply terminal is first converted from a negative voltage to a positive voltage through an inverting follower and then connected to the input terminal of the voltage comparator. When the voltage at the non-inverting terminal of the voltage comparator is greater than the voltage at the inverting terminal, the output terminal of the voltage comparator outputs a high-level voltage. When the voltage at the non-inverting terminal is less than the voltage at the inverting terminal, the output terminal of the voltage comparator outputs a low-level voltage. When there is a voltage difference, the voltage feedback adjustment circuit 3 starts to work, and the bias voltage at both ends of the photodiode is dynamically adjusted through the output voltage of the voltage feedback adjustment circuit 3, so that the photodiode obtains consistent response parameters, thereby achieving the purpose of balanced measurement of the detector.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] 1. The bias voltage at both ends of the photodiode is adjusted through the monitoring circuit and the voltage feedback adjustment circuit, which can realize real-time voltage monitoring and compare the two voltages through a voltage comparator. When there is a voltage difference, the voltage at both ends of the photodiode is automatically feedback-adjusted, so that the voltages at both ends are always kept equal, better realizing the symmetry and balance of the detector, reducing the influence of common-mode noise and electronics noise, and optimizing the performance of the balance detector.

[0032] 2. Through the design of a two-stage amplification circuit combining the transimpedance amplification circuit and the voltage amplification circuit, the voltage gain and bandwidth of the circuit output signal are improved. Because the gain-bandwidth product of the amplifier is a fixed value, expanding the gain of the circuit will result in a decrease in bandwidth, which cannot meet the actual requirements. The design of the two-stage amplification circuit avoids the limitation of the gain-bandwidth product.

[0033] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Without conflict, the embodiments of the present application and the features in the embodiments can be combined arbitrarily with each other.

Claims

1. An automatically feedback-regulated balance detector, characterized in that, The balance detector includes a photoelectric detection circuit, a monitoring circuit, a voltage feedback adjustment circuit, a transimpedance amplifier circuit, and a voltage amplifier circuit. The photoelectric detection circuit includes two serially connected photodiodes. A differential current is obtained at the connection node of the two serially connected photodiodes, and the differential current signal is input to the input terminal of the transimpedance amplifier circuit. The current signal is converted into a voltage signal by the transimpedance amplifier circuit and then output to the voltage amplifier circuit. The voltage signal is amplified and output by the voltage amplifier circuit. The monitoring circuit is used to monitor the voltages on both sides of the photodiodes and input the voltage signal to the voltage comparator in the voltage feedback adjustment circuit. The voltage signal is compared by the voltage comparator, and the voltage in the photoelectric detection circuit is adjusted by the output voltage of the voltage feedback adjustment circuit; the photoelectric detection circuit includes a first photodiode and a second photodiode with exactly the same model and performance parameters. The optical signal collected is converted into a current signal by the photodiodes and then output to the transimpedance amplifier circuit. The actually output current signal is the difference between the output current signals of the two photodiodes. The monitoring circuit includes two differential amplifiers with exactly the same structure, which respectively monitor the voltage signals across the resistors serially connected to the two photodiodes and output them. The voltage feedback adjustment circuit includes a voltage comparator and a voltage digital-to-analog conversion chip. The voltage signal is input to the voltage comparator in the voltage feedback adjustment circuit and compared by the voltage comparator. When the two monitored voltages are not equal, a voltage is output through the voltage digital-to-analog conversion chip for voltage feedback to adjust the voltage in the photoelectric detection circuit.

2. The automatic feedback adjustment balance detector according to claim 1, characterized in that, The two photodiodes are PIN photodiodes with small dark current, small junction capacitance, and high responsivity. The cathode of the first photodiode is connected to a positive voltage of 10V after being serially connected with a resistor, and the anode of the second photodiode is connected to a negative voltage of -10V after being serially connected with a resistor.

3. The automatic feedback-adjusted balance detector according to claim 1, wherein, The transimpedance amplifier circuit is used to convert the current signal into a voltage signal. A feedback resistor and a feedback capacitor are connected in parallel to the inverting terminal of the transimpedance amplifier circuit, and the non-inverting terminal of the transimpedance amplifier circuit is grounded through a resistor.

4. The automatic feedback-adjusted balance detector according to claim 1, wherein The voltage amplifier circuit is a proportional amplifier circuit composed of an operational amplifier. The inverting terminal of the voltage amplifier circuit is connected to the output terminal of the transimpedance amplifier circuit through a filter capacitor. The non-inverting terminal of the voltage amplifier circuit is grounded through a pull-down resistor, and the output terminal of the voltage amplifier circuit outputs the amplified voltage signal.

5. The automatic feedback adjustment balance detector according to claim 1, characterized in that The monitored negative voltage is first converted into a positive voltage by a voltage inverter follower and then connected to the input terminal of the voltage comparator for comparison by the voltage comparator.

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