Photoelectric detector circuit capable of adaptively eliminating DC bias influence of photodiode

Abstract

The invention discloses a photoelectric detector circuit capable of adaptively eliminating the direct current bias influence of a photodiode. The photoelectric detector circuit comprises a photodiode module, a TIA module, a power divider module, a low-pass filter module, an inverse proportion amplification module, a reference voltage module, a summing circuit module and a band-pass filter module. When the photodiode module outputs changed direct current bias current, the low-pass filter module and the inverse proportion amplification module extract direct current bias components and feed the direct current bias components back to the in-phase end of the TIA module, and the band-pass filter module filters interference signals outside the bandwidth and retains detection alternating current signals. And the feedback voltage and the reference voltage are added to serve as the N-stage bias voltage of the photodiode module. The reference voltage connected with the in-phase end of the TIA module and the N pole of the photodiode module is self-adaptive change voltage, signal saturation caused by direct current bias is avoided, the voltage difference between the N pole and the P pole of the photodiode module is stabilized, and the stability and noise performance of the photoelectric detection circuit are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of photoelectric detectors, and in particular relates to a photoelectric detector circuit capable of adaptively eliminating the influence of direct current bias of a photodiode. Background Art

[0002] A photodiode (PD) is a photoelectric conversion device. When it is exposed to light, its output current changes with the change of light intensity. When a photodiode is used in combination with a transimpedance amplifier (TIA), the output current of the photodiode can be converted into a voltage signal to form a photoelectric detection device. By detecting the output voltage of the transimpedance amplifier, the characteristic parameters of the optical signal can be indirectly obtained, and the measurement of parameters such as light intensity and spectrum can be realized. It is widely used in photoelectric sensing, communication, medicine, security, environmental monitoring and other fields. Therefore, the photoelectric detection technology of photodiode combined with transimpedance amplifier has broad application prospects and market demand. At the same time, it also puts forward higher requirements for its detection performance and stability.

[0003] In the field of photoelectric detector technology, in order to obtain higher sensitivity and stability, the photodiode is usually reverse biased for use, and the subsequent transimpedance amplifier generally selects a high-resistance negative feedback resistor to achieve a high amplification factor and obtain a high-power voltage signal, thereby ensuring the detection signal-to-noise ratio of the photoelectric sensing system. However, in practical applications, the average power of the optical signal will cause a DC bias current output, thereby introducing a DC bias voltage in the output of the transimpedance amplifier. With the complexity of the current application environment of photoelectric sensing, the average power of the optical signal often produces unpredictable drift due to fluctuations in the optical signal transmission process, which also causes a time-varying DC bias voltage in the output voltage of the transimpedance amplifier. At present, there are some methods for optimizing the DC bias voltage in the output, such as automatic correction of DC bias voltage: by adding correction circuits or algorithms, the DC bias voltage is measured and corrected in real time to ensure the accuracy and stability of the output signal; signal de-DC: by adding methods such as capacitor coupling or AC coupling, the DC signal is isolated or removed to avoid the influence of the DC bias voltage on the system performance; software digital processing: the output signal is de-DC, filtered and gain processed by digital signal processing algorithms to eliminate interference such as DC bias voltage and noise. However, such methods are only analyzed from the perspective of post-stage compensation or filtering, and do not really eliminate the time-varying DC bias voltage in the TIA output, making the TIA unable to perform at its best performance. Specifically, due to the limited power supply range of the transimpedance amplifier, when the time-varying DC bias voltage produces a large offset, the original amplifier circuit output will be saturated at the positive power supply voltage or negative power supply voltage of the op amp, causing signal distortion, thus failing to fully utilize the working range of the op amp. The result is that the gain of the transimpedance amplifier is reduced to improve the stability of the detection system to avoid signal saturation distortion, which sacrifices the detection range of the TIA and limits the improvement of the detection signal-to-noise ratio of the photoelectric sensor system.

[0004] In order to truly eliminate the time-varying DC bias voltage in the TIA output, a method of constructing a DC current to offset the DC bias current of the photodiode itself, thereby eliminating the DC bias voltage output by the TIA, has been proposed and applied. This method obtains the DC bias current of the photodiode through the photodiode monitoring circuit detection, and then feeds back this DC bias current to the output end of the photodiode through the current mirror circuit to offset the DC component in the photodiode current output, thereby suppressing the DC bias voltage in the TIA output. However, this method greatly increases the complexity of the system, and the additional devices introduced will produce additional load effects in the electrical connection between the photodiode and the TIA, such as additional capacitance, which will affect the performance and stability of the system. It can be seen that the current method cannot effectively solve the problem that the detection range, gain, and signal-to-noise ratio of the photodiode combined with the TIA are limited by the DC bias voltage. Summary of the invention

[0005] The present invention provides a photodetector circuit that adaptively eliminates the influence of DC bias on photodiodes to solve the above-mentioned technical problems, and specifically adopts the following technical solutions: A photoelectric detector circuit for adaptively eliminating the influence of direct current bias of a photodiode comprises: a photodiode module, a TIA module, a power divider module, a low-pass filter module, an inverting proportional amplification module, a reference voltage module, an addition circuit module and a band-pass filter module; The photodiode module generates a current signal under the input of the light signal And connected to the inverting input pin of the TIA module, the TIA module converts the current signal of the photodiode module into a voltage The power divider module divides the output of the TIA module into two signals, one of which is a feedback path signal input into the low-pass filter module. The low-pass filter module performs low-pass filtering on the feedback path signal of the power divider module and then inputs it into the inverting proportional amplification module. The inverting proportional amplification module performs inverting proportional amplification on the voltage output by the low-pass filter to obtain a feedback voltage , feedback voltage One path is fed back to the in-phase input pin of the TIA module as the in-phase terminal reference voltage of the operational amplifier of this stage, thereby forming a negative feedback loop, and the other path is input to the addition circuit module, and the reference voltage module generates a reference voltage The adding circuit module adds the feedback voltage output by the inverting proportional amplification module The reference voltage module outputs a reference voltage The voltage output after addition is fed back to the N-stage of the photodiode module as the bias voltage of the N-stage. The other main path signal of the power divider module passes through the bandpass filter module, and the bandpass filter module performs bandpass filtering on the signal on the main signal path, retains the signal in the frequency band where the target detection signal is located, filters out the signal outside the signal bandwidth, and finally outputs the detection target AC signal .

[0006] Furthermore, the power divider module adopts an unequal power distribution method, and the signal attenuation of the main signal path is less than the signal attenuation of the feedback path.

[0007] Furthermore, the power divider module uses a directional coupler to split the output of the TIA module.

[0008] Furthermore, a first-stage voltage follower is connected after the feedback path of the power divider module.

[0009] Furthermore, the low-pass filter module adopts a fifth-order LC Butterworth low-pass filter.

[0010] Furthermore, the bandpass filter module adopts a fifth-order LC Butterworth bandpass filter.

[0011] Furthermore, the passband of the bandpass filter module is set to the frequency band where the target detection signal is located.

[0012] Furthermore, the cut-off frequency of the low-pass filter module is greater than the frequency of the average power fluctuation of the optical signal, and has a large attenuation at the signal carrier frequency.

[0013] Furthermore, the inverting proportional amplification module and the low-pass filter module are integrated into an active inverting proportional amplification low-pass filter module.

[0014] Furthermore, the reference voltage module adopts a low-noise LDO power chip, and the total power input outputs a low-noise reference voltage through the LDO power chip. .

[0015] The benefit of the present invention lies in that the photodetector circuit provided can adaptively eliminate the influence of the DC bias of the photodiode, introduces the adaptive elimination of the DC bias voltage and the adaptive adjustment of the bias voltage of the photodiode module, on the one hand, the stability of the TIA circuit is improved by adaptively eliminating the DC bias voltage output by the TIA module, avoiding the signal saturation caused by the DC bias, and maximizing the gain of the TIA; on the other hand, the voltage difference between the P level and the N level of the photodiode module is stabilized by adaptively adjusting the bias voltage of the photodiode module, avoiding the fluctuation of the measurement bandwidth and the fluctuation of the photoelectric conversion sensitivity caused by the fluctuation of the voltage difference between the P level and the N level, and ensuring the stable working state and noise performance of the photodiode module during the photoelectric conversion. Thereby, the problem that the DC bias current output by the photodiode module in the existing photodetector drifts, resulting in the limited improvement of the TIA detection range, gain, and signal-to-noise ratio, can be solved, and the performance and stability of the photodetector system in harsh application environments can be ensured.

[0016] Specifically, the photodetector circuit of the present invention adaptively eliminates the influence of the DC bias of the photodiode. When the average optical power received by the photodiode module fluctuates due to long-distance transmission or changes in the application environment, the DC bias current generated by the photodiode module changes accordingly, causing the DC bias voltage component in the output of the transimpedance amplifier to fluctuate. By constructing the negative feedback loop proposed by the present invention, the DC bias voltage is conditioned and fed back to the in-phase input pin of the transimpedance amplifier, and the DC bias voltage caused by the DC component of the photodiode module in the TIA output can be adaptively eliminated, avoiding the problem of the output DC bias current of the photodiode module in the photodetector drifting, resulting in the limited improvement of the TIA detection range, gain, and signal-to-noise ratio, and ensuring the performance and stability of the photodetector system in harsh application environments. At the same time, by adding the voltage fed back to the in-phase input pin of the transimpedance amplifier and the reference voltage, and inputting the N-stage of the photodiode module, the reverse bias voltage between the N-stage and the P-stage of the photodiode module can be stabilized at a fixed value, avoiding the sensitivity fluctuation and signal-to-noise ratio deterioration caused by the change of the reverse bias voltage of the photodiode module. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application 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 application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0018] Figure 1 It is a block diagram of a photodetector circuit for adaptively eliminating the influence of direct current bias of a photodiode according to the present invention; Figure 2 is a circuit connection diagram of an embodiment of a photodetector circuit for adaptively eliminating the influence of a photodiode DC bias of the present invention; Figure 3 is a frequency domain simulation result diagram of an embodiment of the present invention; Figure 4 It is a time domain simulation result diagram of an embodiment of the present invention.

[0019] Photodiode module 1, TIA module 2, power divider module 3, low-pass filter module 4, inverting proportional amplifier module 5, reference voltage module 6, adding circuit module 7, band-pass filter module 8. DETAILED DESCRIPTION

[0020] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0021] like Figure 1 As shown, a photodetector circuit for adaptively eliminating the influence of DC bias of a photodiode comprises: a photodiode module 1, a TIA module 2, a power divider module 3, a low-pass filter module 4, an inverting proportional amplifier module 5, a reference voltage module 6, an addition circuit module 7 and a bandpass filter module 8. The photodiode module 1 generates a current signal under the input of an optical signal. And connected to the inverting input pin of TIA module 2, TIA module 2 converts the current signal of photodiode module 1 into voltage The power divider module 3 divides the output of the TIA module 2 into two signals, one of which is a feedback path signal input to the low-pass filter module 4. The low-pass filter module 4 performs low-pass filtering on the feedback path signal of the power divider module 3 and then inputs it into the inverting proportional amplifier module 5. The inverting proportional amplifier module 5 performs inverting proportional amplification on the voltage output by the low-pass filter to obtain a feedback voltage , feedback voltage One path is fed back to the non-inverting input pin of TIA module 2 as the non-inverting terminal reference voltage of this stage of op amp, thus forming a negative feedback loop, and the other path is input to the addition circuit module 7, and the reference voltage module 6 generates a reference voltage The adding circuit module 7 converts the feedback voltage output by the inverting proportional amplification module 5 into The reference voltage output by the reference voltage module 6 The voltage output after addition is fed back to the N-th level of the photodiode in the photodiode module 1 as the bias voltage of the N-th level. The P-stage of the photodiode in the photodiode module 1 is connected to the TIA module 2. The other main path signal of the power divider module 3 passes through the bandpass filter module 8, which performs bandpass filtering on the signal on the main signal path, retains the signal in the frequency band of the target detection signal, filters out the signal outside the signal bandwidth, and finally outputs the detection target AC signal. Compared with the conventional circuit combining a photodiode with a TIA for optical signal detection, in the present invention, the reference voltage connected to the in-phase input pin of the transimpedance amplifier 1 in the TIA module and the N-pole of the photodiode is an adaptively variable voltage.

[0022] like Figure 2 An exemplary circuit diagram of a photodetector circuit for adaptively eliminating the effect of DC bias on a photodiode is shown.

[0023] The photodiode module 1 has a photodiode and a junction capacitor . Photodiode Working in reverse bias state, the N-stage is connected to the voltage output by the addition circuit module 7 , the P level is connected to the inverting input pin of the transimpedance amplifier in TIA module 2. Due to the virtual short characteristic of the op amp, the voltage of this pin is equal to the feedback voltage output by the inverting proportional amplifier module 5 , the voltage difference between the N level and the P level is . is the junction capacitance of the photodiode module 1 when it is reverse conducting.

[0024] The non-inverting input pin of the transimpedance amplifier in TIA module 2 is connected to the feedback voltage , the negative feedback loop is fed back by a feedback resistor and feedback capacitor , and Feedback resistor The resistance value is 1kΩ, so this stage of op amp The amplification factor is 60dB. , and A T-type capacitor network is formed, and its equivalent capacitance is Compared with the single capacitor method, it is easier to accurately realize small capacitance values. Under the effect of , the output voltage of TIA module 2 can be expressed as .

[0025] In the implementation mode of the present application, the power divider module 3 adopts an unequal power distribution method, and the signal attenuation of the main signal path is less than the signal attenuation of the feedback path. The signal attenuation of the main signal path is small, and the signal attenuation of the feedback path is large, thereby ensuring the signal power on the main signal path and avoiding the deterioration of the detection signal-to-noise ratio caused by excessive attenuation. Specifically, the power divider module 3 uses a directional coupler to split the output of the TIA module 2. The signal attenuation on the main path is small and close to the original signal power. The signal power attenuation on the feedback path is large to ensure the signal power on the main path. The output of the directional coupler is connected to a voltage follower. , and series resistor Then input the low pass filter module 4. Series resistor The impedance of the output end of the transmission line is 50Ω, which ensures the impedance matching of the transmission line. The high impedance isolation between the input and output of the voltage follower can effectively isolate the circuit between the input signal source and the output load, ensuring the signal quality on the main signal path.

[0026] The low-pass filter module 4 performs low-pass filtering on the feedback path signal of the power divider module 3, filters out the high-frequency component, that is, the AC component in the TIA output, retains the low-frequency component, that is, the low-frequency part in the TIA output, and inputs this low-frequency signal into the inverting proportional amplifier module 5. The cut-off frequency of the low-pass filter module 4 is greater than the frequency of the average power fluctuation of the optical signal. Therefore, the DC bias voltage output of the transimpedance amplifier caused by the DC bias current of the photodiode is transmitted to the feedback path without attenuation within the passband of the low-pass filter, while the target detection signal is outside the passband of the low-pass filter, so it experiences significant out-of-band attenuation when transmitted to the feedback path. In this way, the feedback voltage output by the feedback path is Based on the negative feedback principle, the TIA DC bias voltage component caused by the average optical power fluctuation can be filtered out to the maximum extent in the main signal path, and the carrier AC signal component can be guaranteed to be attenuated. Specifically, the low-pass filter module 4 adopts a fifth-order LC Butterworth low-pass filter with a cut-off frequency set to 1kHz, performs low-pass filtering on the feedback path signal, filters out the high-frequency component, that is, the AC component in the TIA output, retains the low-frequency component, that is, the low-frequency part in the TIA output, and inputs this low-frequency signal into the inverting proportional amplifier module 5.

[0027] The inverse proportional amplification module 5 performs inverse proportional amplification on the output signal of the low-pass filter module 4 to obtain a feedback voltage , the magnification factor is ,in The resistance is 50Ω, and It forms impedance matching to avoid signal reflection caused by impedance discontinuity. Feedback voltage The output is connected to the op amp in TIA module 2 The non-inverting input pin of the TIA module 2 serves as an additional reference bias voltage for the output of TIA module 2.

[0028] The reference voltage module 6 uses an extremely low-noise reference voltage source chip to convert the total power input into a reference voltage. , and input to the adding circuit module 7, the output of the adding circuit module 7 is used as the reverse bias voltage of the photodiode. Specifically, the reference voltage module 6 adopts a low-noise LDO power chip, and the total power input outputs a low-noise reference voltage through the LDO power chip. .

[0029] The adding circuit module 7 converts the reference voltage With feedback voltage Perform unit gain in-phase addition operation, that is, the amplification factor is 1, that is, , output voltage , and connect this voltage to the N-stage of the photodiode.

[0030] The passband of the bandpass filter module 8 is set to the frequency band where the target detection signal is located. On the one hand, it can further filter out the residual DC bias voltage caused by the circuit imperfection, and on the other hand, it can filter out the stray harmonic interference caused by the nonlinearity of the photodiode and TIA. Specifically, the bandpass filter module 8 adopts a fifth-order LC Butterworth bandpass filter, the passband center frequency is set to 80MHz, the passband is set to 80MHz±10MHz, the 80MHz frequency band information of the carrier signal is retained, the out-of-band interference is filtered out, and the target signal to be detected is output. , is the matching resistance at the load end.

[0031] The DC bias negative feedback loop of the photodiode module 1 composed of the power divider module 3, the low-pass filter module 4, the inverting proportional amplifier module 5, the reference voltage module 6 and the adding circuit module 7 can offset the DC bias voltage caused by the DC bias current of the photodiode module 1 in the TIA module 2, thereby completing the adaptive elimination of the DC component of the photodiode module 1, and the voltage generated by the adding circuit module 7 The N-level provided to the photodiode can adaptively ensure that the voltage difference between the N-level and the P-level is stable at the reference voltage when the P-level voltage fluctuates. In this way, a photodetector circuit that adaptively eliminates the DC component of the photodiode can be realized.

[0032] The frequency domain simulation results of this circuit are as follows Figure 3 , which shows the output voltage of TIA module 2 , the target signal to be detected output by the bandpass filter module 8 and feedback voltage Respectively with the output current of photodiode module 1 From the simulation results, it can be seen that the present invention can offset the DC bias in the photodiode module 1, so that the output voltage of the TIA module 2 The low-frequency components are filtered out and the high-frequency components are retained. The target signal to be detected output by the bandpass filter module 8 The output current of the photodiode module 1 The frequency response curve between the two shows a bandpass characteristic due to the existence of the bandpass filter. The signal gain in the passband causes a 6dB power attenuation at the output end due to the 50Ω impedance matching at the load end, and the TIA gain of 60dB is finally changed to an output gain of 54dB.

[0033] The time domain simulation results of this circuit are shown in Figure 4 , which shows the output voltage of TIA module 2 , the target signal to be detected output by the bandpass filter module 8 , feedback voltage And the voltage generated by the adding circuit module 7 The output current of the photodiode module 1 is composed of a 1mA DC bias current and an 80MHz, 1mA amplitude sinusoidal current. From the simulation results, we can see that the output of the TIA module 2 The DC bias voltage component is eliminated, and the voltage difference between the N-level and P-level of the photodiode is stabilized at the reference voltage. .

[0034] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form, and any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A photodetector circuit for adaptively eliminating the influence of DC bias of a photodiode, characterized in that: Contains: photodiode module, TIA module, power divider module, low-pass filter module, inverting proportional amplifier module, reference voltage module, addition circuit module and band-pass filter module; The photodiode module generates a current signal under the input of the light signal And connected to the inverting input pin of the TIA module, the TIA module converts the current signal of the photodiode module into a voltage The power divider module divides the output of the TIA module into two signals, one of which is a feedback path signal input into the low-pass filter module. The low-pass filter module performs low-pass filtering on the feedback path signal of the power divider module and then inputs it into the inverting proportional amplification module. The inverting proportional amplification module performs inverting proportional amplification on the voltage output by the low-pass filter to obtain a feedback voltage , feedback voltage One path is fed back to the in-phase input pin of the TIA module as the in-phase terminal reference voltage of the operational amplifier of this stage, thereby forming a negative feedback loop, and the other path is input to the addition circuit module, and the reference voltage module generates a reference voltage The adding circuit module adds the feedback voltage output by the inverting proportional amplification module The reference voltage module outputs a reference voltage The voltage output after addition is fed back to the N-stage of the photodiode module as the bias voltage of the N-stage. The other main path signal of the power divider module passes through the bandpass filter module, and the bandpass filter module performs bandpass filtering on the signal on the main signal path, retains the signal in the frequency band where the target detection signal is located, filters out the signal outside the signal bandwidth, and finally outputs the detection target AC signal .

2. A photodetector circuit for adaptively eliminating the influence of photodiode DC bias according to claim 1, characterized in that: The power divider module adopts an unequal power distribution method, and the signal attenuation of the main signal path is less than the signal attenuation of the feedback path.

3. A photodetector circuit for adaptively eliminating the influence of photodiode DC bias according to claim 1, characterized in that: The power divider module uses a directional coupler to split the output of the TIA module.

4. A photodetector circuit for adaptively eliminating the influence of photodiode DC bias according to claim 3, characterized in that: The feedback path of the power divider module is connected to a first-stage voltage follower.

5. The photodetector circuit for adaptively eliminating the influence of DC bias of a photodiode according to claim 1, characterized in that: The low-pass filter module adopts a fifth-order LC Butterworth low-pass filter.

6. A photodetector circuit for adaptively eliminating the influence of photodiode DC bias according to claim 1, characterized in that: The bandpass filter module adopts a fifth-order LC Butterworth bandpass filter.

7. A photodetector circuit for adaptively eliminating the influence of DC bias of a photodiode according to claim 1, characterized in that: The passband of the bandpass filter module is set to the frequency band where the target detection signal is located.

8. The photodetector circuit for adaptively eliminating the influence of DC bias of a photodiode according to claim 1, characterized in that: The cut-off frequency of the low-pass filter module is greater than the frequency of fluctuation of the average power of the optical signal.

9. The photodetector circuit for adaptively eliminating the influence of DC bias of a photodiode according to claim 1, characterized in that: The inverting proportional amplification module and the low-pass filter module are integrated into an active inverting proportional amplification low-pass filter module.

10. The photodetector circuit for adaptively eliminating the influence of photodiode DC bias according to claim 1, characterized in that: The reference voltage module adopts a low-noise LDO power chip, and the total power input outputs a low-noise reference voltage through the LDO power chip. .

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