CN114646813A - Photodiode junction capacitance measuring device and method - Google Patents
Photodiode junction capacitance measuring device and method Download PDFInfo
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- CN114646813A CN114646813A CN202210517981.1A CN202210517981A CN114646813A CN 114646813 A CN114646813 A CN 114646813A CN 202210517981 A CN202210517981 A CN 202210517981A CN 114646813 A CN114646813 A CN 114646813A
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- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
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- G01R31/2632—Circuits therefor for testing diodes
Abstract
The invention discloses a device and a method for measuring junction capacitance of a photodiode. Under the light-shading condition, one end of the photodiode to be tested is connected with the adjustable bias voltage module, the other end of the photodiode to be tested is connected with the inverting input end of the transimpedance amplification module, the sweep frequency signal output by the phase-locked amplifier is connected to the positive input end of the transimpedance amplification module to serve as an excitation signal, the output signal of the transimpedance amplification module is collected and uploaded to an upper computer, and the upper computer fits the junction capacitance of the photodiode to be tested according to a system response function. The invention can indirectly measure the junction capacitance of the photodiode under different bias voltages, and the fitting mean square error is only 10‑4The method has the advantages of simple measurement steps and high precision, is suitable for the applications of selecting the photodiodes, improving the parameter consistency and the like, and can improve the common mode rejection ratio of the balanced detector.
Description
Technical Field
The invention relates to the field of semiconductor parameter measurement, in particular to a photodiode junction capacitance measuring device and method.
Background
With the development of the field of weak signal detection, such as the field of weak force measurement based on light momentum, acceleration measurement, etc., indirect measurement 10 by laser is required-20The extremely weak force of N magnitude, so the noise performance of the photoelectric detection module is required to be higher. In general, the noise of the photodetection module originates from two aspects: optical noise and electrical noise. The optical noise is mainly derived from relative intensity noise caused by the fluctuation of the output light intensity of the laser and shot noise generated by the fluctuation of the optical quantum which is not related to the frequency. The electrical noise mainly comes from the input current noise, the input voltage noise and the resistance thermal noise of the active device of the photoelectric detection module, and is smaller than the optical noise by one order of magnitude or more. For the prior art, the relative intensity noise of the laser has become a major limiting factor for photodetection.
In order to suppress the influence of the relative intensity noise of the laser, a balanced detection method is generally used, that is, two photodiodes with completely consistent models and parameters are used for carrying out differential processing on laser signals, the relative intensity noise of the laser belongs to a common-mode signal, and the two paths of signals can be effectively suppressed after being differentiated. The better the amplitude and phase consistency of the two paths of differential signals is, the better the common mode rejection effect is. However, in real life, even if the photodiodes of the same model and batch are used, the responsivity, junction capacitance and other parameters may not be completely consistent, the difference in responsivity of the two photodiodes may cause the difference in amplitude of the differential signal, and the difference in junction capacitance may cause the difference in phase of the differential signal. In general, an amplitude difference caused by the responsivity of the photodiode can be compensated by adjusting the optical path system, but a phase difference caused by the junction capacitance is difficult to compensate by the optical path. And the junction capacitance of the photodiode changes with the change of the reverse bias voltage. Therefore, a simple and effective method is needed to select a photodiode from a batch of photodiodes with junction capacitance parameters close to each other as a balanced detector, or to find a reverse bias voltage value that makes the junction capacitance parameters of the two photodiodes consistent, so as to achieve a better common mode rejection effect and obtain a better signal-to-noise ratio.
Disclosure of Invention
In order to solve the problems in the prior art, an object of the present invention is to provide a device and a method for measuring junction capacitance of a photodiode, which can indirectly measure junction capacitance of photodiodes under different bias voltages, and have the advantages of fast measurement speed, simple steps, and high accuracy.
The purpose of the invention is realized by the following technical scheme:
a photodiode junction capacitance measuring device comprises a photodiode to be measured, an adjustable bias voltage module, a trans-impedance amplification module, a phase-locked amplifier and an upper computer module; one end of the photodiode to be tested is connected with the adjustable bias voltage module, and the other end of the photodiode to be tested is connected with the inverted input end of the transimpedance amplification module; the signal output end of the phase-locked amplifier is connected to the positive phase input end of the transimpedance amplification module and is used as an excitation signal, and the input end of the phase-locked amplifier collects an output signal of the transimpedance amplification module and is connected with the upper computer module; and the upper computer module is used for fitting the output signal of the transimpedance amplification module to obtain the junction capacitance parameter of the photodiode to be detected.
Furthermore, the adjustable bias voltage module comprises a low dropout regulator and an adjustable resistor, the output voltage of the low dropout regulator is adjusted by changing the resistance value of the adjustable resistor, and the adjustment range of the output voltage comprises all voltage values in the range of reverse bias voltage which can be borne by the photodiode to be tested.
Further, the transimpedance amplification module comprises an operational amplifier OPA1 and a feedbackResistance RFAnd a feedback capacitor CFSaid feedback resistance RFAnd said feedback capacitor CFAfter being connected in parallel, one end of the parallel connection is connected with the inverting input end of the operational amplifier OPA1, and the other end of the parallel connection is connected with the output end of the operational amplifier OPA 1.
Further, the feedback resistor RFUsing a precision resistor with precision better than or equal to 0.1%, the feedback capacitor CFPrecision capacitors with precision better than or equal to 1% are used.
Furthermore, the photodiode to be tested is electrically connected through a pluggable connector.
Furthermore, the frequency range of the frequency sweep signal of the phase-locked amplifier is greater than or equal to 1KHz to 500KHz, and the number of the collection points of the single frequency sweep at the input end of the phase-locked amplifier is greater than or equal to 100.
Further, the frequency response of the output signal of the transimpedance amplification moduleu 0 (f)= H(f)× u i (f)Whereinu i (f)Is representative of the frequency response of the input signal,H(f)representing a system response function of the photodiode junction capacitance measurement device, theH(f)And the feedback resistor RFThe feedback capacitor CFAnd the photodiode junction capacitance C to be measuredDTo determine the relationship:
wherein C represents the junction capacitance C of the photodiode to be testedDThe capacitance value generated in parallel with the input capacitance Cin of the operational amplifier OPA1, f represents the signal frequency.
Further, a junction capacitance measuring method of a photodiode junction capacitance measuring apparatus includes:
the method comprises the following steps:
inserting the photodiode to be tested into the photodiode junction capacitance measuring device, and shading the photodiode to be tested;
step two:
adjusting the adjustable bias voltage module to a target reverse bias voltage;
step three:
the signal output end of the phase-locked amplifier outputs a sweep frequency excitation signal, the input end of the phase-locked amplifier collects an output signal of the transimpedance amplification module, and the output signal of the transimpedance amplification module is uploaded to the upper computer module;
step four:
the upper computer module is based onH(f)And the feedback resistor RFThe feedback capacitor CFAnd the photodiode junction capacitance C to be measuredDThe least square method is utilized to carry out parameter fitting to obtain the junction capacitance C of the photodiode to be measuredDA capacitance value C generated in parallel with an input capacitance Cin of the operational amplifier OPA 1;
step five:
subtracting the input capacitor Cin from the capacitance value C generated by the parallel connection and measured in the fourth step to obtain the junction capacitance C of the photodiode to be measured when the target reverse bias voltage is obtainedDIs measured.
The invention has the beneficial effects that:
the invention discloses a photodiode junction capacitance measuring device and method, wherein sweep frequency signals are used as excitation, the least square method and the system response function of a photodiode and a trans-resistance amplifying circuit thereof are utilized, the junction capacitance values of the photodiode under different types and different reverse bias voltages are fitted in a nonlinear mode, and the fitting mean square error is only 10-4Magnitude. The photodiode junction capacitance measuring device disclosed by the invention is used for selecting the photodiodes of the same type and batch, so that the common mode rejection ratio of the balanced detection module can be improved by 21.76 dB; the junction capacitance parameters of the same photodiode under different reverse bias voltages are measured to obtain the optimal reverse bias voltage compensation value, so that the junction capacitance difference of the two photodiodes is reduced from 13% to 0.18%, and the common mode rejection ratio of the balanced detection module can be improved from 42.12dB to 61.66 dB. The method has the advantages of simple measurement steps and high precision, and is suitable for selecting the photodiode, improving the parameter consistency and the like.
Drawings
Fig. 1 is a schematic block diagram of a photodiode junction capacitance measuring device of the present invention.
Fig. 2 is a schematic circuit diagram of an adjustable bias voltage module according to an embodiment of the present invention.
Fig. 3 is a schematic circuit diagram of a photodiode junction capacitance measuring device according to the present invention.
FIG. 4 shows 9 same batches of the same model number in example 1 of the present inventionH(f)The fitted curve of (2) is compared with the figure.
Fig. 5 is a graph of the common mode rejection effect of different junction capacitance differences in embodiment 1 of the present invention.
FIG. 6 shows the voltage of different reverse biases in embodiment 2 of the present inventionH(f)The measured values of (a) and the fitted curve are compared.
FIG. 7 shows three types of photodiodes in example 3 of the present inventionH(f)The fitted curve of (2) is compared with the graph.
Detailed Description
The invention is further described in the following with reference to the drawings and examples of the description, without thereby limiting the scope of protection of the invention.
As shown in fig. 1, the photodiode junction capacitance measuring device provided by the present invention includes a photodiode to be measured, an adjustable bias voltage module, a transimpedance amplification module, a lock-in amplifier, and an upper computer module; one end of the photodiode to be tested is connected with the adjustable bias voltage module, and the other end of the photodiode to be tested is connected with the inverted input end of the transimpedance amplification module; the signal output end of the phase-locked amplifier is connected to the positive phase input end of the transimpedance amplification module and is used as an excitation signal, and the input end of the phase-locked amplifier collects an output signal of the transimpedance amplification module and is connected with the upper computer module through a serial port line; and the upper computer module is used for fitting the output signal of the transimpedance amplification module to obtain the junction capacitance parameter of the photodiode to be detected.
The adjustable bias voltage module comprises a low dropout linear regulator and an adjustable resistor, the output voltage of the low dropout linear regulator is adjusted by changing the resistance value of the adjustable resistor, and the voltage adjusting range comprises all electricity in the reverse bias voltage range which can be borne by the photodiode to be testedAnd (4) pressure value. Fig. 2 is a schematic circuit diagram of an adjustable bias voltage module provided by the present invention, which is applicable to embodiment 1 and embodiment 2, and it is obvious to those skilled in the art that devices with other models and parameters can be selected according to actual requirements. As shown in fig. 2, the low dropout linear regulator tps7a49 of texas instruments, tps7a49, has a large voltage input range (3V to 36V) and a good noise performance (15.4 μ Vrms), so that the design of the adjustable bias voltage module is more flexible, and no additional noise is introduced to the device. Output voltage V of tps7A49OUTCan be set by a resistor R1 and a resistor R2:
output voltage V of tps7A49OUTAfter being divided by the resistors R3 and R4, the voltage is input to a voltage follower formed by an operational amplifier OPA2, and finally the follower outputs a reverse bias voltage Vb. The voltage follower has the function that the output voltage Vb of the adjustable bias voltage module is not changed due to the change of the equivalent impedance of the subsequent stage of the photodiode to be tested by utilizing the characteristics of high input impedance and low output impedance of the voltage follower, so that the output voltage is more stable. The output voltage Vb of the adjustable bias voltage module can be changed by adjusting the resistance value of the adjustable resistor R4:
as shown in fig. 3, the transimpedance amplification module includes an operational amplifier OPA1 and a feedback resistor RFAnd a feedback capacitor CFSaid feedback resistance RFAnd said feedback capacitor CFAfter parallel connection, two ends are respectively connected with the inverting input end and the output end of the operational amplifier OPA 1. The output of the operational amplifier OPA1 is obtained by circuit principlesu o (f)And an input signalu i (f)The relation of (A) is as follows:
wherein C represents the junction capacitance C of the photodiode to be testedDThe capacitance value generated in parallel with the input capacitance Cin of the operational amplifier OPA1, f representing the frequency,H(f)representing a system response function of the photodiode junction capacitance measurement device.
Input signalu i (f)The output of the lock-in amplifier is a sine-swept signal of a particular amplitude, which can be selected to have any voltage value within the operating range of the operational amplifier OPA 1. Output signalu o (f)And signal acquisition is carried out through the input end of the phase-locked amplifier.
As can be seen from the formula (4),H(f)and the feedback resistor RFThe feedback capacitor CFAnd the photodiode junction capacitance C to be measuredDTo determine the relationship.
In order to reduce the errors caused by the resistor and capacitor precision and provide the fitting precision, the precise feedback resistor R with the precision of 0.1% is used in the embodimentFAnd a precision feedback capacitor C with a precision of 1%F。
In order to be able to quickly replace the photodiode to be measured and improve the measurement efficiency, the photodiode to be measured of the embodiment is electrically connected through a pluggable connector.
In order to improve the fitting precision and reduce errors, the frequency range of the frequency sweeping signals of the phase-locked amplifier is larger than or equal to 1KHz to 500KHz, and the number of collection points of single frequency sweeping at the input end of the phase-locked amplifier is larger than or equal to 100.
The specific application method of the invention comprises the following steps:
the method comprises the following steps:
and inserting the photodiode to be tested into the photodiode junction capacitance measuring device, and shading the photodiode to be tested. The purpose of shading treatment is to avoid the influence of photocurrent on the measurement result;
step two:
adjusting the adjustable bias voltage module to a target reverse bias voltage. The target reverse bias voltage can be any voltage value within the range of the reverse bias voltage borne by the photodiode to be tested;
step three:
the signal output end of the phase-locked amplifier outputs a sweep frequency excitation signal, the input end of the phase-locked amplifier collects an output signal of the transimpedance amplification module, and the output signal of the transimpedance amplification module is uploaded to the upper computer module;
step four:
the upper computer module is based onH(f)And the feedback resistor RFThe feedback capacitor CFAnd the photodiode junction capacitance C to be measuredDThe relation is determined by using mathematical analysis software such as Matlab, Mathemica and the like and using a least square method to perform parameter fitting to obtain the junction capacitance C of the photodiode to be measuredDA capacitance value C generated in parallel with an input capacitance Cin of the operational amplifier OPA 1;
step five:
subtracting the input capacitor Cin from the capacitance value C generated by the parallel connection and measured in the step four to obtain the junction capacitor C of the photodiode to be measured when the target reverse bias voltage is obtainedDIs measured. The value of the input capacitance Cin of the operational amplifier OPA1 can be obtained by referring to the manufacturer data manual of the operational amplifier OPA 1.
Example 1
The photodiode junction capacitance measuring device is used for measuring 9 photodiodes G8370 with the same batch and the same model, and two junction capacitance parameters which are closest to each other are selected from the photodiodes G8370 for balance detection.
The reverse bias voltage of the photodiode to be tested in this embodiment is in the range of 0V to 2V, so Vb is required to be set to any voltage value in the range of 0V to 2V. In this example, VIN=10V, R1=576K Ω, R2=100K Ω, R3=1K Ω, R4 is an adjustable resistance of 5K Ω. Then, V can be obtained from the equations (1) and (2)OUTAnd = 8.01V and Vb = 0V-6.67V, and the design requirement is met. This exampleIs 0V, the resistance of the adjustable resistor R4 is adjusted to 0 Ω. In the embodiment, the amplitude of the frequency sweeping signal is set to be 20mVpp, the frequency sweeping range is 1 KHz-500 KHz, and the number of collection points in a single frequency sweeping is 100. In this example, OPA1 model was selected as OPA657 from Texas instruments Inc., and Cin was found to be 4.5pF by referring to the data sheet. And (3) respectively testing and fitting the 9 photodiodes to be tested according to the steps from the first step to the fifth step, wherein the fitting curve is shown in figure 4, and the measured values of the junction capacitance are obtained as shown in the following table 1:
TABLE 1
From the measured values, even if the photodiodes of the same batch and the same model have large difference of the junction capacitance parameters, the difference of the junction capacitances of the numbers 6 and 7 reaches 16%, and the difference of the junction capacitances of the numbers 4 and 9 is the minimum, and is only 0.056%. The fitting mean square error of 9 photodiodes to be measured is 10-4Magnitude indicates that the model of the invention has high fitting precision under the current data. The circuit simulation software TI-TINA is used for simulation, the rest simulation conditions are the same, the common mode rejection effect of 16% of junction capacitance difference and 0.056% of junction capacitance difference is simulated, as shown in FIG. 5, VF1 represents a signal after rejection, VF2 represents a signal before rejection, and a common mode rejection ratio calculation formula is as follows:
the calculation result shows that when the junction capacitance difference is 16%, the common mode rejection ratio of the balanced detection module is 40.66 dB; the common mode rejection ratio of the balanced detection module is 62.42dB when the junction capacitance difference is 0.056%. The embodiment shows that the photodiode junction capacitance measuring device disclosed by the invention is used for selecting the photodiodes of the same type and batch, so that the common mode rejection ratio of the balanced detection module can be improved by 21.76dB, and the noise performance of photoelectric detection is greatly improved.
Example 2
When the photodiode with the same model and batch has no enough number to select or two photodiodes with the junction capacitance parameter difference smaller than 1%, the photodiode junction capacitance measuring device can be used for measuring the junction capacitance parameters of the same photodiode under different reverse bias voltages, and the junction capacitance difference is compensated in a reverse bias voltage adjusting mode.
In example 1, the junction capacitance measurement of number 5 was 368.4pF, the junction capacitance measurement of number 6 was 325.0pF, the initial difference was 13%, and the common mode rejection ratio of the balanced detection module was 42.12 dB. In this embodiment, the junction capacitance measured values of the photodiode to be measured with the number 5 in embodiment 1 under different reverse bias voltages are measured, and the junction capacitance difference between the number 5 and the number 6 is compensated.
The reverse bias voltage of the photodiode to be tested in this embodiment is in the range of 0V to 2V, so Vb is required to be set to any voltage value in the range of 0V to 2V. In this example, VIN=10V, R1=576K Ω, R2=100K Ω, R3=1K Ω, R4 is an adjustable resistance of 5K Ω. Then, V can be obtained from the equations (1) and (2)OUTAnd = 8.01V and Vb = 0V-6.67V, and the design requirement is met. In the embodiment, the amplitude of the frequency sweeping signal is set to be 20mVpp, the frequency sweeping range is 1 KHz-500 KHz, and 100 points are collected in a single frequency sweeping. In this example, OPA1 model was selected as OPA657 from Texas instruments Inc., and Cin was found to be 4.5pF by referring to the data sheet. In this embodiment, the reverse bias voltage of the photodiode to be tested is adjusted by a larger step, and generally, when the reverse bias voltage is smaller, the junction capacitance changes with the reverse bias voltage more, so in this embodiment, when the reverse bias voltage is equal to 0V, 0.1V, 0.5V, 1V, and 2V, the photodiode to be tested with the number 5 is tested and fitted according to the above steps one to five, and the measured values of the junction capacitance and the fitting curve pairs of h (f) under different reverse bias voltages are as shown in fig. 6, and the following table 2 is obtained:
TABLE 2
| Reverse bias voltage (V) | 0 | 0.1 | 0.5 | 1 | 2 |
| Measured value of junction capacitance (pF) | 368.4 | 332.5 | 267.47 | 233. 9 | 203.3 |
| Mean square error of fit | 4.1×10-4 | 3.3×10-4 | 4.2×10-4 | 3.8×10-4 | 2.81×10-4 |
From the measurement results, it can be seen that when the reverse bias voltage is 0.1V, the junction capacitance of number 5 is 332.5pF, which is slightly larger than 325.0 pF. Therefore, in this embodiment, after 0.1V, the reverse bias voltage is adjusted by small steps of 0.01V, and the photodiode to be tested with the number 5 is tested and fitted according to the above steps one to five, so as to obtain the measured values of the junction capacitance as shown in the following table 3:
TABLE 3
It can be seen from the measurement results that when the reverse bias voltage is 0.12V, the junction capacitance of number 5 is 325.6pF, which is 0.18% different from the junction capacitance of number 6, 325.0pF, and the common mode rejection ratio of the balanced detection module is 61.66dB at the compensation voltage. The embodiment shows that the photodiode junction capacitance measuring device measures the junction capacitance parameters of the same photodiode under different reverse bias voltages to obtain the optimal reverse bias voltage compensation value, so that the junction capacitance difference of the two photodiodes is reduced from 13% to 0.18%, the common mode rejection ratio of the balanced detection module can be increased from 42.12dB to 61.66dB, and the noise performance of the photoelectric detection is greatly improved.
Example 3
In this embodiment, the photodiode junction capacitance measuring device of the present invention is used to measure the junction capacitances of other types of photodiodes: s9055, G12180-020A and G6849 of an array structure. The method can measure the junction capacitance of the photodiodes with different models and structures, has good universality and practicability, and obtains a fitting curve as shown in figure 7.
The reverse bias voltage range of the photodiode to be tested of the model S9055 is 0V-20V, so Vb can be set to any voltage value within the range of 0V-20V. In this example, VIN=28V, R1=806K Ω, R2=40.2K Ω, R3=1K Ω, R4 is an adjustable resistance of 5K Ω. Then, V can be obtained from the equations (1) and (2)OUTAnd (4) the voltage is = 24.94V, and Vb = 0V-20.78V, so that the design requirement is met. In this embodiment, when the target reverse bias voltage is 0V, the resistance of the adjustable resistor R4 is adjusted to 0 Ω. In the embodiment, the amplitude of the frequency sweeping signal is set to be 20mVpp, the frequency sweeping range is 1 KHz-500 KHz, and the number of collection points in a single frequency sweeping is 100. In this example, OPA1 model was selected as OPA657 from Texas instruments Inc., and Cin was found to be 4.5pF by referring to the data sheet. And (4) respectively testing and fitting the two to-be-tested photodiodes of the type S9055 according to the steps from the first step to the fifth step to obtain 6.905pF and 6.910pF of measured values of the junction capacitance.
The reverse bias voltage range of the photodiode to be tested of the model g12180-020A is 0V-5V, so Vb is required to be set to any voltage value within the range of 0V-5V. The true bookIn the examples, VIN=10V, R1=576K Ω, R2=100K Ω, R3=1K Ω, R4 is an adjustable resistance of 5K Ω. Then, V can be obtained from the equations (1) and (2)OUTAnd 8.01V, and Vb = 0V-6.67V, so that the design requirement is met. In this embodiment, when the target reverse bias voltage is 0V, the resistance of the adjustable resistor R4 is adjusted to 0 Ω. In the embodiment, the amplitude of the frequency sweeping signal is set to be 20mVpp, the frequency sweeping range is 1 KHz-500 KHz, and the number of collection points in a single frequency sweeping is 100. In this example, OPA1 model was selected as OPA657 from Texas instruments Inc., and Cin was found to be 4.5pF by referring to the data sheet. And (4) respectively testing and fitting the two photodiodes to be tested with the model number of g12180-020A according to the first step to the fifth step to obtain the measured values of the junction capacitance of 555.7pF and 556.9 pF.
The four-quadrant photodiode to be tested of model G6849 has a structure completely different from that of the photodiode to be tested, and is a photodiode array formed by arranging and integrating four identical photodiodes according to four quadrants, and all N-poles are connected to a common terminal. The consistency of the junction capacitances of the four quadrants can directly influence the common mode rejection performance of the four-quadrant photodiode, the four-quadrant photodiode with better consistency of the four quadrants can be selected, the junction capacitances of the four quadrants under different bias voltages can be measured, and reference is provided for the design of the photoelectric detector circuit.
The reverse bias voltage of G6849 is in the range of 0V to 5V, so Vb is required to be set to any voltage value in the range of 0V to 5V. In this example, VIN=10V, R1=576K Ω, R2=100K Ω, R3=1K Ω, R4 is an adjustable resistance of 5K Ω. Then from equations (1) and (2), VOUTAnd = 8.01V and Vb = 0V-6.67V, and the design requirement is met. In the embodiment, the amplitude of the frequency sweeping signal is set to be 20mVpp, the frequency sweeping range is 1 KHz-500 KHz, and the number of collection points in a single frequency sweeping is 100. In this example, OPA1 model was selected as OPA657 from Texas instruments Inc., and Cin was found to be 4.5pF by referring to the data sheet. The two photodiodes to be tested of model G6849 are respectively tested and fitted according to the above steps one to five to obtain junction capacitance values of four quadrants (A, B, C, D) when the reverse bias voltage is 0V and 1V, as shown in table 4 below:
TABLE 4
From the test results, the consistency of the capacitance of the four-quadrant junction of No. 1 is better than that of No. 2, and the consistency of the reverse bias voltage of 1V is better than that of 0V, so that when the four-quadrant photoelectric detector circuit is designed, the design value of the reverse bias voltage is selected to be 1V, and better common mode rejection performance can be obtained.
According to the device and the method for measuring the junction capacitance of the photodiode, provided by the invention, the junction capacitances of the photodiodes and the photodiode arrays under different types and different bias voltages can be indirectly measured by performing least square parameter fitting on a system response function, and the fitting mean square error is only 10-4Magnitude, wide measurement range, and good universality and practicability. The photodiode junction capacitance measuring device disclosed by the invention is used for selecting the photodiodes of the same type and batch, so that the common mode rejection ratio of the balanced detection module can be improved by 21.76 dB; the junction capacitance parameters of the same photodiode under different reverse bias voltages are measured to obtain the optimal reverse bias voltage compensation value, so that the junction capacitance difference of the two photodiodes is reduced from 13% to 0.18%, and the common mode rejection ratio of the balanced detection module can be improved from 42.12dB to 61.66 dB. The invention is suitable for the application of selecting the photodiode, improving the parameter consistency and the like, and has the advantages of simple measurement steps and high precision.
The above-mentioned embodiments are merely preferred embodiments of the present invention, and are not intended to limit the present invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical spirit of the present invention should fall within the protection scope of the present invention, unless departing from the content of the technical scheme of the present invention.
Claims (8)
1. A photodiode junction capacitance measuring device characterized in that: the device comprises a photodiode to be tested, an adjustable bias voltage module, a transimpedance amplification module, a phase-locked amplifier and an upper computer module;
one end of the photodiode to be tested is connected with the adjustable bias voltage module, and the other end of the photodiode to be tested is connected with the inverted input end of the transimpedance amplification module;
the signal output end of the phase-locked amplifier is connected to the positive phase input end of the transimpedance amplification module and is used as an excitation signal, and the input end of the phase-locked amplifier collects an output signal of the transimpedance amplification module and is connected with the upper computer module;
and the upper computer module is used for fitting the output signal of the transimpedance amplification module to obtain the junction capacitance parameter of the photodiode to be detected.
2. The photodiode junction capacitance measuring device of claim 1, wherein: the adjustable bias voltage module comprises a low dropout linear regulator and an adjustable resistor, the output voltage of the low dropout linear regulator is adjusted by changing the resistance value of the adjustable resistor, and the adjustment range of the output voltage comprises all voltage values in a reverse bias voltage range which can be borne by the photodiode to be tested.
3. The photodiode junction capacitance measuring device of claim 1, wherein: the transimpedance amplification module comprises an operational amplifier OPA1 and a feedback resistor RFAnd a feedback capacitor CFSaid feedback resistance RFAnd said feedback capacitor CFAfter being connected in parallel, one end of the parallel connection is connected with the inverting input end of the operational amplifier OPA1, and the other end of the parallel connection is connected with the output end of the operational amplifier OPA 1.
4. The photodiode junction capacitance measuring device of claim 3, wherein: the feedback resistor RFUsing a precision resistor with a precision better than or equal to 0.1%, the feedback capacitor CFPrecision capacitors with precision better than or equal to 1% are used.
5. The photodiode junction capacitance measuring device of claim 1, wherein: the photodiode to be tested is electrically connected through a connector which can be plugged and unplugged.
6. The photodiode junction capacitance measuring device of claim 1, wherein: the frequency range of the frequency sweeping signals of the phase-locked amplifier is larger than or equal to 1KHz to 500KHz, and the number of the collection points of the single frequency sweeping at the input end of the phase-locked amplifier is larger than or equal to 100.
7. The photodiode junction capacitance measuring device of claim 3, wherein: frequency response of output signal of the transimpedance amplification moduleu 0 (f)= H(f)×u i (f)Whereinu i (f)Which is representative of the frequency response of the input signal,H (f)representing a system response function of the photodiode junction capacitance measurement device, theH(f)And the feedback resistor RFThe feedback capacitor CFAnd the photodiode junction capacitance C to be measuredDTo determine the relationship:
wherein C represents the junction capacitance C of the photodiode to be testedDThe capacitance value generated in parallel with the input capacitance Cin of the operational amplifier OPA1, f represents the signal frequency.
8. A junction capacitance measuring method of a photodiode junction capacitance measuring apparatus according to claim 7, characterized in that: the method comprises the following steps:
the method comprises the following steps:
inserting the photodiode to be tested into the photodiode junction capacitance measuring device, and shading the photodiode to be tested;
step two:
adjusting the adjustable bias voltage module to a target reverse bias voltage;
step three:
the signal output end of the phase-locked amplifier outputs a sweep frequency excitation signal, the input end of the phase-locked amplifier collects an output signal of the transimpedance amplification module, and the output signal of the transimpedance amplification module is uploaded to the upper computer module;
step four:
the upper computer module is based onH(f)And the feedback resistor RFThe feedback capacitor CFAnd the junction capacitance C of the photodiode to be measuredDThe least square method is utilized to carry out parameter fitting to obtain the junction capacitance C of the photodiode to be measuredDA capacitance value C generated in parallel with an input capacitance Cin of the operational amplifier OPA 1;
step five:
subtracting the input capacitor Cin from the capacitance value C generated by the parallel connection and measured in the step four to obtain the junction capacitor C of the photodiode to be measured when the target reverse bias voltage is obtainedDIs measured.
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