CN110488174B

CN110488174B - Breakdown voltage testing of photodiodes

Info

Publication number: CN110488174B
Application number: CN201910788935.3A
Authority: CN
Inventors: 王陈銮; 向少卿
Original assignee: Hesai Technology Co Ltd
Current assignee: Hesai Technology Co Ltd
Priority date: 2019-08-26
Filing date: 2019-08-26
Publication date: 2021-05-04
Anticipated expiration: 2039-08-26
Also published as: CN113189466B; CN110488174A; CN113189466A

Abstract

The present disclosure relates to an analog front end circuit capable of testing a breakdown voltage of a photodiode, a method of testing a breakdown voltage of a photodiode, and a receiving circuit for a laser radar. According to the present disclosure, the reverse bias voltages of the photodiodes of the respective channels are independently adjusted by adjusting the voltage at the anodes of the photodiodes by the voltage-type DAC and/or by adjusting the supply voltage at the cathodes of the photodiodes under the control of the controller, so that the test of the breakdown voltages of the photodiodes can be completed and the photodiodes can be adjusted to the optimum operating voltage.

Description

Breakdown voltage testing of photodiodes

Technical Field

The present disclosure relates generally to the field of photoelectric sensors and, more particularly, to testing of breakdown voltage of a photodiode, and more particularly, to an analog front end circuit capable of testing breakdown voltage of a photodiode, a method of testing breakdown voltage of a photodiode, and a receiving circuit for a lidar.

Background

An Avalanche Photodiode (APD) is a P-N junction type light detecting diode in which an avalanche multiplication effect of carriers is utilized to amplify a photoelectric signal to improve detection sensitivity. With the addition of a higher reverse bias voltage (typically 100-200V in silicon), an internal current gain of about 100 can be achieved in the APD by the ionizing collision (avalanche breakdown) effect. Some silicon APDs employ doping techniques other than conventional APDs, allowing higher voltages (>1500V) to be applied without breakdown, and thus greater gain (>1000) can be achieved. In general, the higher the reverse voltage, the greater the gain.

Fig. 1 illustrates a diagram of the relationship between the output current I and the reverse bias voltage V of a photodiode in the prior art. It can be seen from the figure (third quadrant) that as the reverse bias voltage increases, the initial photocurrent remains substantially constant, but when the reverse bias voltage increases to a certain value, the photocurrent increases rapidly, and finally the photodiode breaks down, which is referred to as the breakdown voltage U_B. In fig. 1, three I-V characteristics under different illumination conditions are shown, wherein the I-V characteristic labeled "without illumination" is the I-V characteristic corresponding to the dark current of the photodiode. The dark current refers to a current flowing in the photodiode in a state where no light is irradiated. Photoelectric deviceThe breakdown voltage of the diode is directly related to the dark current. For example, in voltage tuning of an APD, a reverse bias voltage corresponding to a dark current Id of 10uA is regarded as a breakdown voltage U of the APD_B。

In the production process of the light receiving module using the photodiode as a receiving end, the sensitivity of the light receiving module can be ensured only by correctly setting the working point of the photodiode. The reasonable reverse photodiode operating voltage Vapd (representing the optimal sensitivity) is generally equal to the breakdown voltage U of the photodiode_BClosely coupled (usually Vapd at breakdown voltage U_BNearby), so U for the photodiode is found_BIs critical to setting the optimal operating voltage for the photodiode.

When the photodiodes are shipped from a factory, the breakdown voltage of each photodiode may be different, and the product specification may have a reference breakdown voltage of the photodiode and an error range, for example, the breakdown voltage of the photodiode is 200V, and the error range is ± 10V, that is, the actual breakdown voltage of each photodiode is different, but should be within a range of 190V to 210V.

Currently, before actually using the photodiodes, the breakdown voltage of each photodiode is measured and then classified by voltage range. Such work tasks are typically performed by the purchaser or the user of the photodiode, and include, for example: after the breakdown voltage of each photodiode is measured, the photodiodes are divided into a plurality of groups, and the measured breakdown voltage of each group is within a certain voltage interval, such as 2V or 3V. Therefore, for a batch of photodiodes with the reference breakdown voltage of 200V and the error range of ± 10V, the photodiode is divided into 10 steps for every 2V interval, and the total number of steps is 10 steps. In actual use and system design, the photodiodes within each bin are considered to have a uniform breakdown voltage.

The existing method for measuring the breakdown voltage of the photodiode comprises the following steps: the method comprises the steps of connecting a photodiode plate to a male plate to be tested through a connector, wherein the male plate is provided with a test area corresponding to each photodiode, applying different bias voltages to two ends of each photodiode by a method of performing a pricking test on the test area corresponding to each photodiode, scanning the bias voltages to obtain an I-V characteristic curve, and measuring a reverse bias voltage of which the dark current is equal to a specified value (10 uA for APD), so that the actually measured breakdown voltage of the photodiode is obtained.

According to such a scheme, in order to pursue stability and reliability of a designed circuit system, it is necessary to subdivide as much as possible a batch of photodiodes having the same reference breakdown voltage and error range. In addition, such a scheme does not take into account aging of the photodiode. However, since the breakdown voltage of the photodiode after power-on aging is not consistent and is wider than the breakdown voltage of the newly assembled photodiode, such a solution of the prior art may test the aged photodiode (for example, repeat the aforementioned method of the pin test), but cannot overcome the problem that the breakdown voltage of the aged photodiode exceeds the previously selected filing interval.

The statements in this background section merely represent techniques known to the public and are not, of course, representative of the prior art.

Disclosure of Invention

In view of at least one of the drawbacks of the prior art, one of the objectives of the technical solutions described in the present disclosure is to solve one or more of the problems described above. According to the present disclosure, the reverse bias voltages of the photodiodes of the respective channels are independently adjusted by adjusting the voltage at the anodes of the photodiodes by the voltage-type DAC and/or by adjusting the supply voltage at the cathodes of the photodiodes under the control of the controller, so that the test of the breakdown voltages of the photodiodes can be completed and the photodiodes can be adjusted to the optimum operating voltage.

In one aspect, an analog front end circuit capable of testing a breakdown voltage of a photodiode is provided, including a controller and a plurality of channels, wherein each channel includes:

a photodiode having a cathode for coupling to a supply voltage common to all channels;

the input end of the transimpedance amplification circuit is coupled with the anode of the photodiode, and the output end of the transimpedance amplification circuit is used for outputting an amplified electric signal; and

a voltage-mode digital-to-analog converter (DAC) configured to generate an analog voltage based on a digital control input provided by the controller, whereby the photodiode is reverse biased between the supply voltage and the analog voltage generated by the DAC,

wherein the controller is configured to vary the output voltage of the DAC in each channel by providing a digitally controlled input to each channel and to adjust the supply voltage in order to test the breakdown voltage of the photodiode in each channel.

In one embodiment, the supply voltage may be provided by a program controlled source table, and the program controlled source table is in communication with and controlled by the controller.

In one embodiment, the controller may be configured to read a current reading of the programmable source meter and adjust the output voltage of the DAC of each channel in accordance with the current reading.

In one embodiment, the photodiode may be an avalanche photodiode, APD.

In one embodiment, the analog front end circuit is implemented using an integrated circuit.

In one embodiment, the reference breakdown voltages of the photodiodes of the respective channels may be different by a range of 5V to 10V.

In another aspect, a method of testing the breakdown voltage of photodiodes is provided, wherein a plurality of photodiodes are arranged with their cathodes coupled to a common supply voltage and their anodes coupled to separate voltage-mode digital-to-analog converters, DACs, to form a plurality of channels, wherein the DACs in each channel are configured to generate an analog output voltage in accordance with a digitally controlled input provided by a controller. The method comprises the following steps:

adjusting the analog output voltages of a plurality of DACs to an adjustable minimum voltage;

adjusting the supply voltage to a first supply voltage value to ensure that none of the plurality of photodiodes is in a broken down state, wherein the first supply voltage value is dependent on a reference breakdown voltage and an associated error range of the plurality of photodiodes;

increasing the supply voltage and detecting a total current of dark currents of the plurality of channels such that the detected total current equals a first current value, thereby determining that a voltage across one of the plurality of photodiodes reaches a breakdown voltage, wherein the first current value is a dark current value corresponding to a known breakdown voltage for the photodiode;

adjusting the analog output voltages of a plurality of DACs to a highest voltage that is adjustable;

increasing the supply voltage to a second supply voltage value, a difference between the second supply voltage value and the first supply voltage value being equal to a maximum adjustable range of the plurality of DACs; and

in each of the plurality of channels, an analog output voltage of a corresponding one of the plurality of DACs is individually reduced, and a dark current flowing through a photodiode in each channel is detected so that the detected dark current is equal to the first current value, thereby enabling determination of a breakdown voltage of the photodiode in each channel.

In one embodiment, the supply voltage may be adjusted by a program controlled source table.

In one embodiment, the photodiode may be an avalanche photodiode, APD, and the first current value is equal to 10 μ Α.

In one embodiment, the method is initiated when the photodiode is in a non-operational state.

In yet another aspect, a receive circuit for a lidar includes a controller and a plurality of channels, wherein each channel includes:

wherein the controller is configured to perform the aforementioned method.

According to the present disclosure, a batch of photodiodes with close reference breakdown voltages may be arranged with their cathodes coupled to a common supply voltage and their anodes coupled to separate voltage-mode digital-to-analog converters DAC, respectively, to form a plurality of independent channels. Since the output analog voltage of the voltage-type digital-to-analog converter DAC is adjustable within a range, the bias voltage of the photodiode of each channel is correspondingly adjustable under the condition of a certain supply voltage. In addition, the supply voltage is also controllably adjustable. Thus, the present disclosure takes advantage of the adjustable range of the output analog voltage of the DAC and/or the adjustable supply voltage, compared to the above-described test schemes of the prior art, which brings the advantage that the bias voltage across the photodiodes is adjustable, thereby making it possible, compared to the prior art, to directly use a plurality of photodiodes with substantially the same reference breakdown voltage and error range (error range may be 5V or 10V) in the design and device selection of the circuitry, without categorizing the diodes, e.g. in the voltage interval of 2V, as described in the background art, without affecting the stability and reliability of the designed system.

The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings and specification. Moreover, it should be noted that the terminology used in the description has been chosen primarily for readability and instructional purposes, and may not have been chosen to delineate or circumscribe the inventive subject matter.

Drawings

The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and are not to limit the disclosure. In the drawings:

FIG. 1 illustrates a graph of the output current I and reverse bias voltage V of a photodiode in the prior art;

FIG. 2 schematically illustrates a schematic diagram of an analog front end circuit 200 capable of testing the breakdown voltage of a photodiode according to one embodiment of the invention; and

fig. 3 schematically shows a flow chart of a method of testing breakdown voltages of a plurality of photodiodes according to an embodiment of the present invention.

Detailed Description

In the following, only certain exemplary embodiments are briefly described. As those skilled in the art can appreciate, the described embodiments can be modified in various different ways, without departing from the spirit or scope of the present disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of apparatus, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

In the description of the present disclosure, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "straight", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and therefore should not be considered as limiting the present disclosure. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", may explicitly or implicitly include one or more of the described features. In the description of the present disclosure, "a plurality" means two or more unless specifically limited otherwise.

In the description of the present disclosure, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and the like are to be construed broadly and may be, for example, fixedly connected, detachably connected, or integrally connected: may be mechanically connected, may be electrically connected or may be in communication with each other; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meaning of the above terms in the present disclosure can be understood by those of ordinary skill in the art as appropriate. For example, the present disclosure uses the term "coupled" to indicate that the connection between two terminals can be direct connection, indirect connection through an intermediate medium, electrically wired connection, or wireless connection.

In the present disclosure, unless expressly stated or limited otherwise, the first feature "on" or "under" the second feature may comprise the first and second features being in direct contact, or may comprise the first and second features being in contact, not directly, but via another feature in between. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly above and obliquely above the second feature, or simply meaning that the first feature is at a lesser level than the second feature.

The following disclosure provides many different embodiments or examples for implementing different features of the disclosure. To simplify the disclosure of the present disclosure, specific example components and arrangements are described below. Of course, they are merely examples and are not intended to limit the present disclosure. Moreover, the present disclosure may repeat reference numerals and/or reference letters in the various examples, which have been repeated for purposes of simplicity and clarity and do not in themselves dictate a relationship between the various embodiments and/or arrangements discussed. In addition, the present disclosure provides examples of various specific processes and materials, but one of ordinary skill in the art may recognize applications of other processes and/or use of other materials.

It is to be noted that, unless otherwise specified, technical or scientific terms used in the present disclosure shall have the ordinary meaning as understood by those skilled in the art to which the present invention pertains.

Specific embodiments of the present disclosure are described below in conjunction with the appended drawings, it being understood that the preferred embodiments described herein are merely for purposes of illustrating and explaining the present disclosure and are not intended to limit the present disclosure.

Fig. 2 schematically illustrates a schematic diagram of an analog front end circuit 200 capable of testing the breakdown voltage of a photodiode according to one embodiment of the invention. The analog front end circuit 200 includes a controller 210 and a plurality of channels. Channels ch.0, ch.k, and ch.n are shown in fig. 2. Each channel includes a photodiode 212, a voltage-mode digital-to-analog converter (voltage-mode DAC)214, and a transimpedance amplification circuit 220. The cathodes of the photodiodes of the individual channels are coupled to a supply voltage HV common to all channels. The anodes of the photodiodes of each channel are coupled to a separate voltage source DAC 214 and transimpedance amplifier circuit 220 in each channel, respectively. The transimpedance amplifier circuit 220 has an input coupled to the anode of the photodiode and an output for outputting an amplified electrical signal, which may be coupled to a subsequent signal analysis circuit. The voltage-mode DACs in each channel are coupled between the common controller 210 and the anode of the photodiodes of each channel and are configured to generate analog voltages in accordance with a digitally controlled input provided by the controller 210. For a voltage-mode DAC, the input is a series of binary digital sequences and the output is an analog voltage corresponding to the binary digital sequence. The adjustable output voltage can be output along with the change of the numerical control input of the voltage type DAC.

Thus, the photodiode can be reverse biased between the supply voltage and the analog voltage generated by the voltage source DAC. The controller 210 may be configured to individually vary the output voltage of the voltage-mode DAC in each channel by providing a digitally controlled input to each channel. It will be appreciated that the output of the voltage mode DAC may provide an adjustable range of analogue voltages, for example from 0V to 5V, and thus an adjustable range of analogue voltages at the anode of the photodiode of each channel. That is, by using the voltage-type DAC, the voltage at the anode of the photodiode is adjustable, and the maximum adjustable range thereof is the maximum adjustable range of the output voltage of the voltage-type DAC, for example, also from 0V to 5V. Thus, the phase difference range of the possible breakdown voltages of the photodiodes in the respective channels can be the adjustable analog voltage range, and by individually adjusting the outputs of the DACs of the respective channels, the photodiodes of the respective channels can be made to operate at the optimum operating voltage (highest sensitivity). For example, the range of possible breakdown voltages of the photodiodes of each channel, i.e., the difference between the maximum possible breakdown voltage minus the minimum possible breakdown voltage of the photodiodes, may be within 5V.

Further, the controller 210 may also be configured to regulate the supply voltage HV of the respective channels. For example, the supply voltage HV may be provided by a program-controlled source meter, and the program-controlled source meter is in communication with and controlled by the controller. The controller may be configured to read a current reading of the program controlled source meter and adjust the output voltage of the DAC of each channel in accordance with the current reading.

According to embodiments of the present invention, the voltage at the anode of the photodiode in each channel, and/or the supply voltage at the cathode of the photodiode, is adjustable, thereby providing dynamic adjustment of the reverse bias voltage of the photodiode over a range. Thus, as described in detail below, the breakdown voltage of the photodiode in each channel may be tested using analog front end circuit 200, and/or the bias voltage of the photodiode in each channel may be individually adjusted to flexibly improve the sensitivity of the circuit when needed. Meanwhile, in the case of aging of the photodiode, the aged photodiode can be operated at an optimum operating voltage by adjusting the output voltage of the DAC and/or by adjusting the supply voltage.

According to the embodiment of the invention, the phase difference range of the reference (nominal) breakdown voltage of the photodiode of each optional channel depends on the adjustable analog voltage range, such as 10V, of the output of the voltage-type DAC selected in the circuit design, and the voltage range is larger than the voltage range, such as 2V (reference background art), which is classified by the DAC in the prior art. Because the voltage-type DAC is added and can be used for adjusting the reverse bias voltage of the photodiodes of each channel, when the devices of the photodiodes are selected, the photodiodes can be roughly classified according to 10V, for example, and then the photodiodes in each 10V range are finely adjusted in each channel by using the voltage-type DAC, so that each photodiode can work at the optimal working voltage representing the maximum sensitivity. Therefore, each photodiode can work at the optimal working voltage reflecting the maximum sensitivity, and compared with the scheme that the breakdown voltages of all the photodiodes with the actually measured breakdown voltages in a classification interval are regarded as the same in the prior art, the working efficiency of the photodiodes of each channel can be improved. The uniformity of the breakdown voltage and the operating voltage of the photodiode according to the present disclosure is limited by the smallest voltage step that the DAC can adjust, e.g. 0.1V, but this value is significantly smaller than such interval values as 2V that are used in the prior art to classify.

With continued reference to fig. 2, the transimpedance amplification circuit 220 may include: an operational amplifier 222, an RC circuit connected in parallel with the amplifier 224 (e.g., by a resistor R)_fAnd a capacitor C_fFormed), and optionally a capacitor Cb connected in parallel with the amplifier 224.

In one embodiment, the photodiode may be an avalanche photodiode, APD. It should be understood that the circuit described with reference to fig. 2 may also work in conjunction with other kinds of diodes, such as other PN junction photodiodes, and PIN junction photodiodes.

In one embodiment, the analog front-end circuit according to the embodiment of the present invention may be implemented by using an integrated circuit. For example, a plurality of photodiodes may be disposed on one side of a chip substrate, and a transimpedance amplifier circuit and a DAC may be disposed on the other side, so that the photodiodes, the transimpedance amplifier circuit, and the DAC are integrated in one chip, thereby forming an analog front-end chip, and the chip integrates a plurality of signal channels. The integrated circuit has the advantage that the chip can be placed directly on a PCB circuit board without the use of intermediate connectors between the plurality of photodiodes and the transimpedance amplifier circuit. On the contrary, when the analog front-end circuit is built by using discrete devices, because of many independent measurement channels, the discrete photodiode and the elements of the transimpedance amplifier circuit cannot be placed on the same PCB, and a plurality of PCBs are required to be used, and they are connected by connectors (connectors). The use of too many connectors will affect the accuracy of the breakdown voltage test. In addition, the discrete devices used to build the analog front-end circuit consume a larger area of the PCB, and increase the difficulty of board layout. In addition, integration can enable each photodiode to be correspondingly integrated with one DAC to adjust the problem of inconsistent breakdown voltage of the APD, so that consistency among channels is better. Further, since the voltage type DAC is integrated in the analog front end circuit, the breakdown voltages of the photodiodes before and after aging can be tested using the test method according to the present disclosure, and the problem that the variation range of the breakdown voltage becomes large due to aging of the photodiodes can be solved by DAC adjustment.

FIG. 3 schematically illustrates a flow chart of a method 300 of testing the breakdown voltage of a plurality of photodiodes according to one embodiment of the invention. The plurality of photodiodes are arranged such that cathodes of the plurality of photodiodes are coupled to a common supply voltage and anodes of the plurality of photodiodes are coupled to outputs of the individual voltage-type digital-to-analog converters DAC, thereby forming a plurality of channels. The input terminals of the voltage-mode DACs in each channel are connected to a common controller and are configured to generate an analog output voltage in accordance with a digitally controlled input provided by the controller. The method 300 may include the following steps.

In step S310, the analog output voltages of the plurality of voltage-mode DACs are all adjusted to the adjustable minimum voltage. For example, the adjustable output voltage range of the voltage-mode DAC may be in the range of 1V to 11V. Here, the analog output voltages of all voltage-mode DACs are regulated to the lowest voltage that can be regulated, i.e., 1V.

In step S320: and adjusting the power supply voltage to the first power supply voltage value to ensure that the plurality of photodiodes are not in a broken-down state. The first supply voltage value depends on the reference breakdown voltages of the plurality of photodiodes and the associated error range. At this time, the total current of the dark currents of the plurality of channels is detected, and the detected total current is substantially zero. The photodiodes to be tested may have substantially the same reference (nominal) breakdown voltage and their error range should have an interval value within the voltage adjustable range of the employed voltage-mode DAC. For example, for a plurality of photodiodes with a reference breakdown voltage of 200V and a nominal error range of ± 5V (with an error range of 10V), a possible breakdown voltage is in the range of 195V to 205V, if a voltage-type DAC with an adjustable output voltage in the range of 1V to 11V is used and the output of the voltage-type DAC has been adjusted to 1V in the aforementioned step S310, the supply voltage may be initially adjusted to 196V or less. At this time, the reverse bias voltage of the plurality of photodiodes is 196V-1V-195V.

In step S330: the method includes increasing a supply voltage and detecting a total current of dark currents of a plurality of channels such that the detected total current equals a first current value, thereby determining that a voltage across one of a plurality of photodiodes reaches a breakdown voltage, wherein the first current value is a dark current value corresponding to a known breakdown voltage for the photodiode. Here, the reverse bias voltage of the photodiode is increased by increasing the supply voltage while keeping the output voltage of the voltage-type DAC coupled to the anode side of the photodiode at an adjustable minimum value, for example, 1V. According to the current-voltage characteristic of the photodiode (refer to fig. 1), in the absence of light, when the reverse bias voltage of the photodiode increases to a certain value, the current sharply increases. For example, in the case where the photodiode is an avalanche photodiode APD, the reverse bias voltage at a dark current value equal to 10 μ a is the measured breakdown voltage of the APD. In the example where the photodiode is an APD, at this time, if it is detected that a dark current having a current value equal to 10 μ a occurs on the supply voltage side when the supply voltage is increased to 198V, it can be determined that one APD among the APDs at this time is in a state of being broken down, and the measured breakdown voltage of the APD should be 198V-1V — 197V.

In step S340: the analog output voltages of the plurality of voltage-mode DACs are all regulated to a maximum voltage that is adjustable. At this time, since the output voltage of the DAC is adjusted to the highest voltage that can be adjusted while the supply voltage is kept constant, the reverse bias voltage of the plurality of photodiodes is reduced, so that all the photodiodes are in a state of not being broken down at this time. For example, continuing the foregoing example, keeping the supply voltage 198V constant, increasing the analog output voltages of the plurality of voltage-type DACs from 1V to 11V, the reverse bias voltage of the photodiode is 198V-11V — 187V, and the reference breakdown voltage of the photodiode is in the range of 195V to 205V, so no photodiode breaks down.

In step S350: increasing a supply voltage to a second supply voltage value, a difference between the second supply voltage value and the first supply voltage value being equal to a maximum adjustable range of the plurality of DACs. For example, continuing the previous example, the supply voltage is increased accordingly by 10V, reaching 198V + 10V-208V, by a value equal to the maximum adjustable range of the analog output voltage of the voltage-mode DAC, i.e. 11V-1V-10V. The reverse bias voltage of the photodiode is 208V-11V-197V and the reference breakdown voltage is in the range of 195V to 205V, but the minimum measured breakdown voltage of the photodiode in step S330 is 197V, and only one of the photodiodes may be in a breakdown state.

In step S360: in each of a plurality of channels, an analog output voltage of a corresponding one of the DACs is individually reduced, and a dark current flowing through a photodiode in each channel is detected so that the detected dark current is equal to the first current value, whereby a breakdown voltage of the photodiode in each channel can be determined. At this time, for example, continuing the foregoing example, keeping the supply voltage 208V unchanged, the DACs of the respective channels are individually adjusted, the adjustable range of the output voltage thereof is from 11V to 1V, the adjustable range of the reverse bias voltage of the photodiodes of the respective channels is from 197V (208V-11V) to 207V (208V-1V), and the breakdown voltages of the photodiodes to be tested are in the range of 197V to 205V, so that the breakdown voltages of the respective photodiodes can be tested.

Further, in each channel, after the breakdown voltage of the photodiode therein is individually tested, the analog output voltage of the DAC in each channel can be adjusted back to the state in which the photodiode therein is not broken down, so as to avoid breakdown damage of the photodiode due to the fact that the reverse bias voltage of the photodiode in each channel may be above the breakdown voltage during the test process. For example, continuing the foregoing example, the analog output voltage of the DAC is adjusted back to 11V, or the output voltage of the DAC is increased by 1V or 2V, etc.

It will be appreciated that the accuracy of the breakdown voltage tested according to embodiments of the invention depends on the step voltage adjustable by the output voltage of the voltage-mode DAC, for example 0.1V, which is significantly smaller than the range of intervals of the prior art, for example 2V, in which the supply diode is classified. By introducing adjustable DAC output voltages and supply voltages, a method of adjustment of the breakdown voltage for the photodiodes in each of the multiple channels is provided, so there is no need to subdivide the multiple photodiodes labeled with the same reference breakdown voltage into many bins as in the prior art (e.g., see background, where the bins are one by 2V).

In one example, a method according to an embodiment of the present invention may be performed in conjunction with the circuit configuration shown in FIG. 2 described above, and the testing of the breakdown voltages of the plurality of photodiodes may be performed during periods when the circuit 200 of FIG. 2 is inactive. In addition, if the breakdown voltage of the aged photodiode is still within the adjustable range of the reverse bias voltage of the photodiode by using the DAC, the DAC can be adjusted to enable the aged photodiode of each channel to independently operate at the optimal operating voltage.

In one embodiment, the supply voltage may be adjusted by programming the source table. The program control source table may have a function of testing a current or a voltage flowing therethrough while supplying a supply voltage to the photodiode, and a value of the supply voltage thereof may be controlled by the controller.

It should be understood that although in some examples of the disclosure the photodiode is described as being an avalanche photodiode, APD, the circuits and methods presented by the present disclosure may be used with other types of photodiodes, such as PIN junction photodiodes.

The present disclosure also provides a receiving circuit for a lidar comprising a controller and a plurality of channels, wherein each channel comprises: a photodiode having a cathode for coupling to a supply voltage common to all channels; the input end of the transimpedance amplification circuit is coupled with the anode of the photodiode, and the output end of the transimpedance amplification circuit is used for outputting an amplified electric signal; and a voltage-mode digital-to-analog converter (DAC) configured to generate an analog voltage based on a digital control input provided by the controller, whereby the photodiode is reverse biased between the supply voltage and the analog voltage generated by the DAC. The controller may be configured to perform the aforementioned method.

The present disclosure also provides a computer-readable storage medium comprising computer-executable instructions stored thereon which, when executed by a processor or controller, perform a method according to the foregoing.

According to the present disclosure, a batch of photodiodes with close reference breakdown voltages may be arranged with their cathodes coupled to a common supply voltage and their anodes coupled to separate voltage-mode digital-to-analog converters DAC, respectively, to form a plurality of independent channels. Since the output analog voltage of the voltage-type digital-to-analog converter DAC is adjustable within a range, the bias voltage of the photodiode of each channel is correspondingly adjustable under the condition of a certain supply voltage. In addition, the supply voltage is also controllably adjustable. Thus, the present disclosure utilizes the adjustable range of the output analog voltage of the DAC and/or the adjustable supply voltage, which brings the advantage that the bias voltage across the photodiodes is adjustable, compared to the above-described test schemes in the prior art, thereby allowing a coarser granularity classification of a plurality of photodiodes having substantially the same reference breakdown voltage and error range without affecting the stability and reliability of the designed system, when designing the circuitry and selecting the devices, compared to the prior art.

It should be appreciated that the foregoing exemplary methods may be implemented in various ways, for example, in some embodiments, the foregoing methods may be implemented using software and/or firmware modules, as well as hardware modules. Other ways, now known or later developed, are also feasible, and the scope of the present invention is not limited in this respect. In particular, embodiments of the invention may be implemented in the form of a computer program product, in addition to hardware embodiments.

It should be noted that the embodiments of the present invention can be realized by hardware, software, or a combination of software and hardware. The hardware portion may be implemented using dedicated logic; the software portions may be stored in a memory and executed by a suitable instruction execution system, such as a microprocessor or specially designed hardware. Those skilled in the art will appreciate that the apparatus and methods described above may be implemented using computer executable instructions and/or embodied in processor control code, such code being provided on a carrier medium such as a disk, CD-or DVD-ROM, programmable memory such as read only memory (firmware), or a data carrier such as an optical or electronic signal carrier, for example. The apparatus and modules thereof of the present invention may be implemented by hardware circuits such as very large scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., or by software executed by various types of processors, or by a combination of hardware circuits and software, such as firmware.

It should be noted that although in the above detailed description several modules or sub-modules of the apparatus are mentioned, this division is only not mandatory. Indeed, the features and functions of two or more of the modules described above may be implemented in one module according to embodiments of the invention. Conversely, the features and functions of one module described above may be further divided into embodiments by a plurality of modules.

While the invention has been described with reference to what are presently considered to be the embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Although the present disclosure has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the disclosure. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. An analog front end circuit capable of testing a breakdown voltage of a photodiode, comprising a controller and a plurality of channels, wherein each channel comprises:

wherein the controller is configured to:

changing the output voltage of the DAC in each channel by providing a digitally controlled input to each channel and adjusting the supply voltage to test the breakdown voltage of the photodiode in each channel and adjust the output voltage of the DAC in each channel to an adjustable minimum voltage, adjusting the supply voltage to a first supply voltage value, ensuring that the photodiode is not in a breakdown state; increasing the supply voltage such that a total current of dark currents of the plurality of channels is equal to a dark current corresponding to a breakdown voltage of the photodiode; adjusting the output voltage of the DAC in each channel to an adjustable maximum voltage, increasing the supply voltage to a second supply voltage value; the analog output voltage of each DAC is reduced, the dark current in each channel is detected, and the breakdown voltage of the photodiode in each channel is determined.

2. The analog front end circuit of claim 1, wherein the supply voltage is provided by a programmed source meter, and the programmed source meter is in communication with and controlled by the controller.

3. The analog front end circuit of claim 2, wherein the controller is configured to read a current reading of the programmed source meter and adjust the output voltage of the DAC of each channel according to the current reading.

4. The analog front end circuit according to any one of claims 1-3, wherein the photodiode is an Avalanche Photodiode (APD).

5. The analog front-end circuit according to any of claims 1-3, wherein the analog front-end circuit is implemented using an integrated circuit.

6. The analog front-end circuit according to any one of claims 1-3, wherein reference breakdown voltages of the photodiodes of the respective channels differ by a range of 5V to 10V.

7. A method of testing the breakdown voltage of photodiodes, wherein a plurality of photodiodes are arranged with their cathodes coupled to a common supply voltage and their anodes coupled to separate voltage-mode digital-to-analog converters, DACs, to form a plurality of channels, wherein the DACs in each channel are configured to generate an analog output voltage in accordance with a digitally controlled input provided by a controller, wherein the method comprises:

8. The method of claim 7, wherein the supply voltage is adjusted by a programmed source meter.

9. The method according to any of claims 7-8, wherein the photodiode is an avalanche photodiode, APD, and the first current value is equal to 10 μ Α.

10. The method of any of claims 7-8, wherein the method is initiated when the photodiode is in a non-operational state.

11. A receive circuit for a lidar comprising a controller and a plurality of channels, wherein each channel comprises:

wherein the controller is configured to perform the method of any one of claims 7-10.