Photodetector Circuit for Adaptive Elimination of the Influence of the DC Bias of a Photodiode

Abstract

The present invention discloses a photodetector circuit for adaptively eliminating the influence of the DC bias of a photodiode, comprising: 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. When there is a varying DC bias current in the output of the photodiode module, the low-pass filter module and the inverting proportional amplification module extract the DC bias component and feedback it to the non-inverting input terminal of the TIA module. The band-pass filter module filters out the interference signals outside the bandwidth and retains the detected AC signals. The feedback voltage and the reference voltage are added together as the bias voltage of the N-th stage of the photodiode module. The reference voltage connected to the non-inverting input terminal of the TIA module and the N-th pole of the photodiode module is an adaptively varying voltage, which avoids signal saturation caused by the DC bias, stabilizes the voltage difference between the N-th and P-th stages of the photodiode module, and improves the stability and noise performance of the photodetection circuit.

Description

Technical Field

[0001] The present invention belongs to the technical field of photodetectors, and particularly relates to a photodetector circuit for adaptively eliminating the influence of the DC bias of a photodiode. Background Art

[0002] A photodiode (PD) is a photoelectric conversion device. When it is irradiated by light, its output current changes with the change of light intensity. When the photodiode is combined 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, which are widely used in the fields of photoelectric sensing, communication, medicine, security, environmental monitoring, etc. Therefore, the photoelectric detection technology combining a photodiode with a transimpedance amplifier has broad application prospects and market demands. At the same time, higher requirements are also put forward for its detection performance and stability.

[0003] In the field of photodetector technology, in order to obtain higher sensitivity and stability, a photodiode is usually used in reverse bias. For the subsequent transimpedance amplifier, a high-value negative feedback resistor is generally selected to achieve a high amplification factor and obtain a high-power voltage signal, so as to ensure 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, which will in turn introduce a DC bias voltage in the output of the transimpedance amplifier. With the complication of the application environment of current photoelectric sensing, the average power of the optical signal often produces unpredictable drift due to the fluctuations in the optical signal transmission process, which makes there be a time-varying DC bias voltage in the output voltage of the transimpedance amplifier. At present, there are already some methods for optimizing the DC bias voltage in the output, such as automatic correction of the DC bias voltage: by adding a correction circuit or algorithm, the DC bias voltage is measured and corrected in real time to ensure the accuracy and stability of the output signal; signal DC removal: by adding methods such as capacitive 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: by performing processing such as DC removal, filtering, and gain on the output signal through digital signal processing algorithms to eliminate interference such as DC bias voltage and noise. However, such methods only analyze from the perspective of post-stage compensation or filtering, and do not really eliminate the time-varying DC bias voltage existing in the TIA output, making the TIA unable to exert its best performance. Specifically, due to the limited power supply range of the transimpedance amplifier, when the time-varying DC bias voltage has a large offset, it will cause the output of the original amplifier circuit to saturate at the positive power supply voltage or negative power supply voltage of the operational amplifier, resulting in signal distortion, and thus the working range of the operational amplifier cannot be fully utilized. The resulting consequence is that in order to improve the stability of the detection system, the gain of the transimpedance amplifier is reduced to avoid signal saturation distortion, sacrificing the detection range of the TIA and limiting the improvement of the detection signal-to-noise ratio of the photoelectric sensing 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 cancel the DC bias current of the photodiode itself and thus eliminate the DC bias voltage in the TIA output has been proposed and applied. This method detects the DC bias current of the photodiode through a photodiode monitoring circuit, and then feeds this DC bias current back to the output end of the photodiode through a current mirror circuit to cancel the DC component in the current output of the photodiode, 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, such as additional capacitance, in the electrical connection between the photodiode and the TIA, affecting the performance and stability of the system. It can be seen that the current methods cannot well solve the problem that the detection range, gain, and signal-to-noise ratio improvement of the combination of the photodiode and the TIA are limited by the DC bias voltage. Summary of the Invention

[0005] The present invention provides a photodetector circuit for adaptively eliminating the influence of the DC bias of a photodiode to solve the above-mentioned technical problems, and specifically adopts the following technical solutions:

[0006] A photodetector circuit for adaptively eliminating the influence of the DC bias of a photodiode includes: a photodiode module, a TIA module, a power splitter module, a low-pass filter module, an inverting proportional amplifier module, a reference voltage module, an adder circuit module, and a band-pass filter module;

[0007] The photodiode module generates a current signal under the input of an optical signal and is 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 splitter module divides the output of the TIA module into two paths of signals. One path of feedback path signal is input to the low-pass filter module. The low-pass filter module performs low-pass filtering on the feedback path signal of the power splitter module and then inputs it to the inverting proportional amplifier module. The inverting proportional amplifier module performs inverting proportional amplification on the voltage output by the low-pass filter to obtain a feedback voltage . The feedback voltage is fed back to the non-inverting input pin of the TIA module as the non-inverting terminal reference voltage of this stage of operational amplifier, thereby forming a negative feedback loop. The other path is input to the adder circuit module. The reference voltage module generates a reference voltage . The adder circuit module adds the feedback voltage output by the inverting proportional amplifier module and the reference reference voltage output by the reference voltage module . The voltage output after addition is fed back to the Nth stage of the photodiode module as the bias voltage of the Nth stage . The other path of the main path signal of the power splitter module passes through the band-pass filter module. The band-pass filter module performs band-pass 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 signals outside the signal bandwidth, and finally outputs the detected target AC signal .

[0008] Further, the power splitter module adopts a non-equal power distribution method, and the attenuation of the signal on the main signal path is less than the attenuation of the feedback path signal.

[0009] Further, the power splitter module uses a directional coupler to split the output of the TIA module.

[0010] Further, a voltage follower is connected after the feedback path of the power splitter module.

[0011] Further, the low-pass filter module adopts a fifth-order LC Butterworth low-pass filter.

[0012] Further, the band-pass filter module adopts a fifth-order LC Butterworth band-pass filter.

[0013] Further, the passband of the band-pass filter module is set to the frequency band where the target detection signal is located.

[0014] Further, the cut-off frequency of the low-pass filter module is greater than the frequency of the optical signal average power fluctuation, and there is a large attenuation at the signal carrier frequency.

[0015] Further, the inverting proportional amplification module and the low-pass filter module are integrated into an active inverting proportional amplification low-pass filter module.

[0016] Further, the reference voltage module adopts a low-noise LDO power supply chip, and the total power supply input outputs a low-noise reference reference voltage through the LDO power supply chip 。

[0017] The beneficial effect of the present invention lies in the provided photodetector circuit for adaptively eliminating the influence of the DC bias of the photodiode, introducing 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 output DC bias voltage of the TIA module, avoiding signal saturation caused by the DC bias, and the gain of the TIA can be maximally increased; on the other hand, by adaptively adjusting the bias voltage of the photodiode module, the voltage difference between the P and N levels of the photodiode module is stabilized, avoiding the measurement bandwidth fluctuation and the optoelectronic conversion sensitivity fluctuation caused by the voltage difference fluctuation between the P and N levels, and ensuring the stable working state and noise performance of the photodiode module during optoelectronic conversion. Thus, the problem that the output DC bias current of the photodiode module in the existing photodetector drifts, resulting in 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 a harsh application environment can be ensured.

[0018] Specifically, for the photodetector circuit of the present invention that 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 fluctuations in the DC bias voltage component in the output of the transimpedance amplifier. By constructing the negative feedback loop proposed in the present invention, the DC bias voltage is conditioned and then fed back to the non-inverting input pin of the transimpedance amplifier, which can adaptively eliminate the DC bias voltage caused by the DC component of the photodiode module in the output of the TIA, avoiding the problem that the drift of the DC bias current output by the photodiode module in the photodetector limits the improvement of the detection range, gain, and signal-to-noise ratio of the TIA, 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 non-inverting input pin of the transimpedance amplifier to the reference voltage and inputting it to the N-stage of the photodiode module, the reverse bias voltage between the N-stage and 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. Description of the Drawings

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0020] Figure 1 is the block diagram of the photodetector circuit of the present invention that adaptively eliminates the influence of the DC bias of the photodiode;

[0021] Figure 2 is the circuit connection diagram of the embodiment of the photodetector circuit of the present invention that adaptively eliminates the influence of the DC bias of the photodiode;

[0022] Figure 3 is the frequency-domain simulation result diagram of an embodiment of the present invention;

[0023] Figure 4 is the time-domain simulation result diagram of an embodiment of the present invention.

[0024] Photodiode module 1, TIA module 2, power splitter module 3, low-pass filter module 4, inverting proportional amplifier module 5, reference voltage module 6, adder circuit module 7, band-pass filter module 8. Detailed Embodiments

[0025] Embodiments of the present application will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where like or similar reference numerals denote like or similar elements or elements having like or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present application, but should not be construed as limiting the present application.

[0026] As Figure 1 shown, a photodetector circuit for adaptively eliminating the influence of the DC bias of a photodiode includes: a photodiode module 1, a TIA module 2, a power splitter module 3, a low-pass filter module 4, an inverting proportional amplifier module 5, a reference voltage module 6, an adder circuit module 7, and a band-pass filter module 8. The photodiode module 1 generates a current signal under the input of an optical signal and accesses the inverting input pin of the TIA module 2. The TIA module 2 converts the current signal of the photodiode module 1 into a voltage . The power splitter module 3 divides the output of the TIA module 2 into two paths of signals. One path of feedback path signal is 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 splitter module 3 and then inputs it to 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 . The feedback voltage is fed back to the non-inverting input pin of the TIA module 2 as the non-inverting terminal reference voltage of this stage of operational amplifier, thereby forming a negative feedback loop. The other path is input to the adder circuit module 7. The reference voltage module 6 generates a reference voltage . The adder circuit module 7 adds the feedback voltage output by the inverting proportional amplifier module 5 with the reference reference voltage output by the reference voltage module 6 . The voltage output after addition is fed back to the N pole of the photodiode in the photodiode module 1 as the bias voltage of the N pole . The P pole of the photodiode in the photodiode module 1 is connected to the TIA module 2. The other path of main path signal of the power splitter module 3 passes through the band-pass filter module 8. The band-pass filter module 8 performs band-pass 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 signals outside the signal bandwidth, and finally outputs the detected target AC signal

[0027] As Figure 2 shown is an exemplary circuit diagram of a photodetector circuit for adaptively eliminating the influence of the DC bias of a photodiode.

[0028] The photodiode module 1 has a photodiode and a junction capacitance . The photodiode operates in a reverse-biased state, with the N terminal connected to the voltage output by the addition circuit module 7 , and the P terminal connected to the inverting input pin of the transimpedance amplifier in the TIA module 2. According to the virtual short characteristic of the operational amplifier, the voltage of this pin is equal to the feedback voltage output by the inverting proportional amplification module 5 , and the voltage difference between the N terminal and the P terminal is . is the junction capacitance when the photodiode module 1 is reverse-conducted.

[0029] The non-inverting input pin of the transimpedance amplifier in the TIA module 2 is connected to the feedback voltage , and the negative feedback loop is composed of the feedback resistor and the feedback capacitor , and . The resistance value of the feedback resistor is 1 kΩ, so the amplification factor of this stage of the operational amplifier is 60 dB. , and constitute a T-type capacitance network, and its equivalent capacitance is , and it is easier to accurately implement a small capacitance value compared to the single-capacitance method. Under the action of the feedback voltage , the output voltage of the TIA module 2 can be expressed as .

[0030] In the embodiment of the present application, the power splitter module 3 adopts an unequal power distribution method, and the signal attenuation of the main signal path is less than that of the feedback path signal. This makes the signal attenuation of the main signal path small and the signal attenuation of the feedback path 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 splitter 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 on the feedback path is attenuated greatly to ensure the signal power on the main path. The output of the directional coupler is connected to a voltage follower , and after being connected in series with the resistor , it is input to the low-pass filter module 4. The series resistor is 50 Ω to ensure impedance matching at the output end of the transmission line. Utilizing the high-impedance isolation effect between the input and output of the voltage follower can effectively isolate the circuit between the input signal source and the output load and ensure the signal quality on the main signal path.

[0031] The low-pass filter module 4 performs low-pass filtering on the feedback path signal of the power splitter module 3 to filter out high-frequency components, that is, the AC component in the TIA output, retain low-frequency components, that is, the low-frequency part in the TIA output, and input this low-frequency signal into the inverting proportional amplification module 5. The cut-off frequency of the low-pass filter module 4 is greater than the frequency of the optical signal average power fluctuation. 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. Therefore, it experiences significant out-of-band attenuation when transmitted to the feedback path. Thus, the feedback voltage output by the feedback path can, based on the principle of negative feedback, filter out the DC bias voltage component of the TIA caused by the average optical power fluctuation to the greatest extent in the main signal path and ensure the non-attenuation of the carrier AC signal component. Specifically, the low-pass filter module 4 uses a fifth-order LC Butterworth low-pass filter with a cut-off frequency set to 1 kHz to perform low-pass filtering on the feedback path signal, filter out high-frequency components, that is, the AC component in the TIA output, retain low-frequency components, that is, the low-frequency part in the TIA output, and input this low-frequency signal into the inverting proportional amplification module 5.

[0032] The inverting proportional amplification module 5 performs inverting proportional amplification on the output signal of the low-pass filter module 4 to obtain the feedback voltage , and the amplification factor is , where has a resistance value of 50 Ω, and constitutes impedance matching to avoid signal reflection caused by impedance discontinuity. The feedback voltage is output and connected to the non-inverting input pin of the operational amplifier in the TIA module 2 as an additional reference bias voltage for the output of the TIA module 2.

[0033] The reference voltage module 6 uses an extremely low-noise reference voltage source chip to convert the total power supply input into a reference voltage , and inputs it into the adder circuit module 7. The output of the adder circuit module 7 is used as the reverse bias voltage of the photodiode. Specifically, the reference voltage module 6 uses a low-noise LDO power supply chip, and the total power supply input is output as a low-noise reference voltage through the LDO power supply chip.

[0034] The adder circuit module 7 performs a unity-gain non-inverting addition operation on the reference voltage and the feedback voltage , that is, the amplification factor is 1, that is , and the output voltage is obtained and this voltage is connected to the N pole of the photodiode.

[0035] The passband of the band-pass 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 circuit imperfections. On the other hand, it can filter out the spurious harmonic interference caused by the non-linearity of the photodiode and the TIA. Specifically, the band-pass filter module 8 uses a fifth-order LC Butterworth band-pass filter, with the center frequency of the passband set to 80 MHz and the passband set to 80 MHz ± 10 MHz, retaining the 80 MHz frequency band information where the carrier signal is located, filtering out out-of-band interference, and outputting the target signal to be detected. , is the matching resistor at the load end.

[0036] The DC bias negative feedback loop of the photodiode module 1 composed of the power splitter module 3, the low-pass filter module 4, the inverting proportional amplification module 5, the reference voltage module 6, and the adder circuit module 7 can cancel 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. Moreover, the voltage provided to the N-stage of the photodiode can adaptively ensure that the voltage difference between the N-stage and the P-stage remains stable at the reference voltage when the P-stage voltage fluctuates. . In this way, a photodetector circuit that can adaptively eliminate the DC component of the photodiode can be realized.

[0037] The frequency-domain simulation results of this circuit are as Figure 3 shown, which shows the output voltage of the TIA module 2, the target signal to be detected output by the band-pass filter module 8 and the feedback voltage respectively and the amplitude-frequency response curves between the output current of the photodiode module 1. From the simulation results, it can be seen that the present invention can cancel the DC bias in the photodiode module 1, so that the output voltage of the TIA module 2 will filter out the low-frequency components and retain the high-frequency components. The frequency response curve between the target signal to be detected output by the band-pass filter module 8 and the output current of the photodiode module 1 shows a band-pass characteristic due to the presence of the band-pass filter. The signal gain within the passband causes a 6 dB power attenuation at the output due to the 50 Ω impedance matching at the load end, and the output gain finally becomes 54 dB from the 60 dB TIA gain.

[0038] The time-domain simulation results of this circuit are as Figure 4 shown, which shows the output voltage of the TIA module 2, the target signal to be detected output by the band-pass filter module 8 , feedback voltage and the voltage generated by the adder circuit module 7 . The output current of the photodiode module 1 consists of a DC bias current of 1 mA and a sinusoidal current with a frequency of 80 MHz and an amplitude of 1 mA. It can be seen from the simulation results that the output of the TIA module 2 eliminates the DC bias voltage component, and at the same time, the voltage difference between the N and P levels of the photodiode is stabilized at the reference voltage .

[0039] 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. Any technical solutions obtained by using equivalent replacements or equivalent transformations fall 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 primary voltage follower, and the primary voltage follower is arranged between the power divider module and the low-pass filter module.

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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