Photoelectric balance detection circuit

Abstract

The utility model discloses a photoelectric balance detection circuit, which relates to the technical field of photoelectric balance detection and comprises an optical detector unit, a bias voltage adjusting unit, a sampling amplifying unit, a transimpedance amplifying unit and a filtering amplifying unit. The optical detectors are cascaded and then led out from a common point to be connected with the trans-impedance amplifier; according to the utility model, the input optical power detection circuit of the optical detector and the bias voltage regulation circuit of the optical detector are designed, the characteristic difference between the optical detectors is effectively reduced, an optical power monitoring and acquisition function is provided, in the aspect of radio frequency signals, low-noise amplification of signals is realized through a high-gain filtering and amplifying circuit, and the signal quality is improved. Zero adjustment of the operational amplifier is achieved through the zero adjustment circuit, filtering configurations such as magnetic beads are added through the power supply circuit, and the anti-interference capacity of the operational amplifier is enhanced.

Description

Technical Field

[0001] This utility model relates to the field of photoelectric balance detection technology, and specifically to a photoelectric balance detection circuit. Background Technology

[0002] Photodetection is an essential process in high-speed optical communication, optical sensing and other fields. Compared with direct detection, the advantages of balanced photodetection are high detection sensitivity, high signal-to-noise ratio and strong ability to suppress common-mode noise, which leads to its widespread application. Balanced photodetection uses two photodetectors (PDs) connected in parallel to convert the two received optical signals into electrical signals to form a photocurrent difference. Then, the difference is amplified by transimpedance and the output radio frequency signal is generated, thus realizing balanced detection of two optical signals. The main indicators of balanced detectors are: operating wavelength, operating bandwidth, responsivity, common-mode rejection ratio (CMRR), output transimpedance gain (Gain) and equivalent noise power (NEP).

[0003] In existing balanced detection systems, power imbalance between the two input optical signals, inconsistent photoelectric responsivity of the detector, power supply noise, operational amplifier noise floor, and error output can all affect the performance of the balanced detector. These factors mainly affect the three basic performance characteristics: sensitivity, signal-to-noise ratio, and common-mode rejection. While conventional solutions on the market have optimized the parameters for these influencing factors, they have also brought about problems such as complex circuit design, system instability, long debugging process, and system crosstalk. Utility Model Content

[0004] The purpose of this invention is to provide a photoelectric balanced detection circuit to solve the problems mentioned in the background art. In existing balanced detection systems, the power imbalance of the two input optical signals, the inconsistent photoelectric responsivity of the detector, power supply noise, operational amplifier noise floor and error output will affect the performance of the balanced detector, mainly affecting the three basic performances of sensitivity, signal-to-noise ratio and common-mode rejection. The conventional solutions on the market have optimized the parameters for these influencing factors, but at the same time, they have brought problems such as complex circuit design, system instability, long debugging process and system crosstalk.

[0005] A photoelectric balanced detection circuit includes a photodetector unit, a bias voltage adjustment unit, a sampling amplification unit, a transimpedance amplification unit, and a filtering amplification unit. The photodetector unit is connected to a corresponding filtering circuit and a sampling circuit through the bias side of the photodetector. The cascaded photodetectors are led out from a common point and connected to a transimpedance amplifier. The sampling amplification unit includes a differential amplifier under negative adjustable bias and a differential amplifier under positive adjustable bias. The differential amplifiers are respectively connected to the two ends of a corresponding precision sampling resistor and output as a monitoring signal. The transimpedance amplification unit and the filtering amplification unit are implemented through the transimpedance amplifier and the filtering amplifier, respectively. The filtering amplifier is connected to the transimpedance amplifier and outputs through a port.

[0006] Preferably, the photodetector is used to receive the laser signal to be measured and convert the laser signal into photocurrent. The photodetector unit consists of two indium gallium arsenide photodiodes, and its main indicators include photosensitive area, response bandwidth, photoelectric conversion responsivity and dark current.

[0007] Preferably, the bias voltage adjustment unit adjusts the bias voltage to ensure that the two photodetectors have the same operating bandwidth characteristics. The bias voltage adjustment unit achieves stable and reliable voltage regulation through resistor voltage division and output filtering.

[0008] Preferably, the sampling amplification unit calculates the photocurrent by acquiring the precision resistor signal and calculates the input optical power based on the detector's responsivity, thereby providing adjustment feedback to the bias voltage adjustment unit. The sampling amplification unit mainly consists of a precision sampling resistor and a differential amplifier.

[0009] Preferably, the transimpedance amplification unit amplifies and converts the differential current of the two photodetectors into a radio frequency voltage signal of a certain multiple. The transimpedance amplification unit consists of an input filter circuit, a transimpedance operational amplifier, and a corresponding zero-point adjustment circuit.

[0010] Preferably, the filtering and amplification unit filters and amplifies the output RF voltage signal of the transimpedance amplification unit to eliminate harmonic interference from the preceding stage and finally outputs it. The filtering and amplification unit is a second-order Butterworth filter composed of an operational amplifier and auxiliary circuitry.

[0011] Compared with the prior art, the beneficial effects of the present invention are:

[0012] An input optical power detection circuit and a bias voltage adjustment circuit for a photodetector were designed, which effectively reduced the characteristic differences between photodetectors and provided the function of monitoring and acquiring optical power. In terms of radio frequency signals, a high-gain filter amplification circuit was used to achieve low-noise signal amplification. A zero-point adjustment circuit was used to achieve zero-point adjustment of the operational amplifier. By adding filtering configurations such as ferrite beads to the power supply circuit, the anti-interference capability of the operational amplifier was enhanced. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the circuit structure of a photoelectric balance detection circuit according to the present invention;

[0014] Figure 2 This is a circuit diagram illustrating the transimpedance amplification and filtering amplification of a photoelectric balanced detection circuit according to this utility model.

[0015] Figure 3 This is a circuit diagram of a differential amplification circuit under forward bias adjustment for a photoelectric balance detection circuit according to this utility model.

[0016] Figure 4 This is a circuit diagram of a differential amplification circuit under negative bias adjustment for a photoelectric balanced detection circuit according to this utility model. Detailed Implementation

[0017] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0018] Please see Figure 1-4 As shown, a photoelectric balanced detection circuit includes a photodetector unit, a bias voltage adjustment unit, a sampling amplification unit, a transimpedance amplification unit, and a filtering amplification unit. The photodetector unit is connected to the corresponding filtering circuit and sampling circuit through the bias side of the photodetector. After cascading, the photodetectors are led out from the common point and connected to the transimpedance amplifier. The sampling amplification unit includes a differential amplifier under negative adjustable bias and a differential amplifier under positive adjustable bias. The upper and lower sampling differential amplifiers are respectively connected to the two ends of the corresponding precision sampling resistor and output as a monitoring signal. The transimpedance amplification unit and the filtering amplification unit are implemented through the transimpedance amplifier and the filtering amplifier. The filtering amplifier is connected to the transimpedance amplifier and outputs through the port.

[0019] In this embodiment, the photodetector is used to receive the laser signal to be measured and convert it into photocurrent. The photodetector unit consists of two indium gallium arsenide photodiodes. Its main indicators include photosensitive area, response bandwidth, photoelectric conversion responsivity, and dark current. The lower the dark current, the lower the system noise and the higher the detection sensitivity. The operating bandwidth determines the operating bandwidth of the balanced detector, which is affected by the photodetector material and bias voltage. The responsivity refers to the photoelectric conversion capability of the photodetector. The more consistent the indicators of the two detectors are, the stronger the common-mode rejection capability of the balanced detector. However, it is actually difficult to produce two photodiodes with completely identical performance indicators. This solution, based on the selection of photodiodes, also adds a circuit bias voltage adjustment function, which can further shorten the difference in indicators between the two photodetectors.

[0020] In this embodiment, the bias voltage adjustment unit adjusts the bias voltage to ensure that the two photodetectors have the same operating bandwidth characteristics. The bias voltage adjustment unit achieves stable and reliable voltage regulation through resistor voltage division and output filtering. The adjusted voltage is applied to the photodetector, thereby improving the response bandwidth of the photodetector. This solution is configured with two sets of bias voltage adjustments, so that the bias voltage of the two detectors can be adjusted independently, thereby adjusting the response of the photodetectors to achieve consistency.

[0021] In this embodiment, the sampling amplification unit calculates the photocurrent by acquiring the precision resistor signal and calculates the input optical power based on the detector's responsivity, thereby providing adjustment feedback to the bias voltage adjustment unit. The sampling amplification unit mainly consists of a precision sampling resistor and a differential amplifier. The precision sampling resistor is selected with a resistance value error of less than 0.1% and a temperature drift of less than 100ppm, thereby achieving consistency in acquisition between the upper and lower photodetectors and insensitivity to ambient temperature. The differential amplifier is selected as the INA128U differential amplifier, which has a high common-mode rejection capability of at least 120dB, as well as low temperature drift (less than 0.5μV / ℃), low noise (700μA), and high gain (1000 times) performance. Only one resistor value needs to be adjusted to achieve a wide range of gain adjustment, which has the advantage of simple structure. The sampling amplification unit can accurately detect the input optical power of the two photodetectors, thereby providing information for bias voltage adjustment and user monitoring.

[0022] In this embodiment, the transimpedance amplifier unit amplifies and converts the differential current of the two photodetectors into a radio frequency voltage signal of a certain multiple. The transimpedance amplifier unit consists of an input filter circuit, a transimpedance operational amplifier, and a corresponding zero-point adjustment circuit. The photocurrent of the photodetector enters the transimpedance amplifier after filtering out noise. The transimpedance amplifier selected is the LTC6228 transimpedance amplifier, which has ultra-low voltage noise: 0.88nV / √Hz, high voltage slew rate: 500V / μs, operating frequency (AV=+1): 730MHz, offset drift: 0.4μV / ℃, and a common-mode rejection ratio greater than 100dB. Because the transimpedance amplifier circuit transmits high radio frequency signals, this solution adopts a 4-layer circuit design and performs 50-ohm impedance matching to effectively maintain the integrity of signal transmission. Since the operational amplifier has offset characteristics, it may cause the output to be not at zero. This solution is equipped with a zero-point adjustment circuit, which can effectively adjust the output to zero, making the system output more accurate.

[0023] In this embodiment, the filtering and amplification unit filters and amplifies the output RF voltage signal of the transimpedance amplification unit, eliminating harmonic interference from the previous stage and finally outputting the signal. The filtering and amplification unit is a second-order Butterworth filter composed of an operational amplifier and auxiliary circuits. Its greatest advantage is its high flatness of in-band response and high out-of-band rejection capability. It can also further amplify the signal. Considering the complexity of the circuit and design requirements, a higher-order filtering structure can also be selected. The amplifier is the same model LTC6228. The optimal values ​​of the auxiliary circuit are calculated using filter simulation software to achieve the best effect. The operational amplifier uses ferrite beads and configuration capacitors for power supply filtering, effectively suppressing interference from the power supply.

[0024] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A photoelectric balance detection circuit, characterized in that, The system includes a photodetector unit, a bias voltage adjustment unit, a sampling amplification unit, a transimpedance amplification unit, and a filtering amplification unit. The photodetector unit is connected to the corresponding filtering circuit and sampling circuit through the bias side of the photodetector. The cascaded photodetectors are led out from the common point and connected to the transimpedance amplifier. The sampling amplification unit includes a differential amplifier under negative adjustable bias and a differential amplifier under positive adjustable bias. The differential amplifier is connected to both ends of the corresponding precision sampling resistor and outputs a monitoring signal. The transimpedance amplification unit and the filtering amplification unit are implemented through the transimpedance amplifier and the filtering amplifier, respectively. The filtering amplifier is connected to the transimpedance amplifier and outputs through a port.

2. The photoelectric balance detection circuit according to claim 1, characterized in that, The photodetector is used to receive the laser signal to be measured and convert the laser signal into photocurrent. The photodetector unit consists of two indium gallium arsenide photodiodes.

3. The photoelectric balance detection circuit according to claim 1, characterized in that, The bias voltage adjustment unit adjusts the bias voltage to ensure that the two photodetectors have the same operating bandwidth characteristics. The bias voltage adjustment unit achieves stable and reliable voltage regulation through resistor voltage division and output filtering.

4. The photoelectric balance detection circuit according to claim 1, characterized in that, The sampling amplification unit calculates the photocurrent by acquiring the precision resistor signal and calculates the input optical power based on the detector's responsivity, thereby providing adjustment feedback to the bias voltage adjustment unit. The sampling amplification unit mainly consists of a precision sampling resistor and a differential amplifier.

5. The photoelectric balance detection circuit according to claim 1, characterized in that, The transimpedance amplifier unit amplifies and converts the differential current of the two photodetectors into a radio frequency voltage signal of a certain multiple. The transimpedance amplifier unit consists of an input filter circuit, a transimpedance operational amplifier, and a corresponding zero-point adjustment circuit.

6. The photoelectric balance detection circuit according to claim 1, characterized in that, The filtering and amplification unit filters and amplifies the output RF voltage signal of the transimpedance amplifier unit, eliminates harmonic interference from the preceding stage, and finally outputs the signal. The filtering and amplification unit is a second-order Butterworth filter composed of an operational amplifier and auxiliary circuitry.

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