US20220011413A1

US20220011413A1 - Light sensor and ranging method

Info

Publication number: US20220011413A1
Application number: US17/367,444
Authority: US
Inventors: Ping-Hung Yin; Jia-Shyang Wang
Original assignee: Guangzhou Tyrafos Semiconductor Technologies Co Ltd
Current assignee: Guangzhou Tyrafos Semiconductor Technologies Co Ltd
Priority date: 2020-07-10
Filing date: 2021-07-05
Publication date: 2022-01-13
Also published as: US20220011412A1; TWI777602B; US11747451B2; CN113923384A; TW202202805A; US20220011159A1; TW202202870A; TWI808431B; TW202208887A; CN113917440A; CN113917441A; US11953629B2; US11320521B2; CN113923384B; TW202203419A; TWI759213B; US20220011158A1; TWI780757B; CN113917442A

Abstract

A light sensor and a ranging method are provided. The light sensor includes a light source, a sensing sub-pixel, and a control circuit. The sensing sub-pixel includes a diode. The control circuit operates the diode in a Geiger mode or an avalanche linear mode. The control circuit includes a time-to-digital converter. The control circuit sequentially delays multiple light emission times of the light source in consecutive multiple sensing periods according to delay times during the consecutive multiple sensing periods. The control circuit sequentially monitors whether multiple digital values sequentially outputted by the time-to-digital converter corresponding to the consecutive multiple sensing periods have changed. The control circuit calculates a distance value according to the multiple digital values and a corresponding delay sequence when the control circuit determined that the multiple digital values have changed for a first time.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of U.S. provisional application Ser. No. 63/050,120, filed on Jul. 10, 2020, and U.S. provisional application Ser. No. 63/058,502, filed on Jul. 30, 2020. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND

Technical Field

This disclosure relates to a sensing technology, and in particular to a light sensor and a ranging method.

Description of Related Art

Currently, there is a high demand for high-sensitivity ranging sensors in various application fields, such as the medical field or the automotive field. In particular, a light sensor that may be used to sense extremely low light is currently one of the main sensor designs under development. However, a ranging result of a ranging sensor is limited by a bin resolution (or also known as a counting resolution) of a digital converter 330, and cannot provide a more precise ranging result. In view of this, how to enable a light sensor to effectively sense extremely low light while having high precision remains a challenge for those skilled in the art.

SUMMARY

This disclosure provides a light sensor and a ranging method, which can provide a high-precision ranging result.
The light sensor of the disclosure includes a light source, a sensing sub-pixel, and a control circuit. The sensing sub-pixel includes a diode. The control circuit is coupled to the light source and the sensing sub-pixel, and is configured to operate the diode in a Geiger mode or an avalanche linear mode. The control circuit includes a time-to-digital converter. The time-to-digital converter is coupled to the diode. The control circuit sequentially delays multiple light emission times of the light source in multiple consecutive sensing periods according to multiple delay times during the multiple consecutive sensing periods. The control circuit sequentially monitors whether multiple digital values sequentially outputted by the time-to-digital converter corresponding to the multiple sensing periods have changed. The control circuit calculates a distance value according to the multiple digital values and a corresponding delay sequence when the control circuit determined that the multiple digital values have changed for a first time.
The ranging method of the disclosure is applicable to a light sensor. The light sensor includes a light source, a sensing sub-pixel, and a control circuit. The sensing sub-pixel includes a diode. The control circuit includes a time-to-digital converter. The ranging method includes the following steps. The diode is operated in a Geiger mode or an avalanche linear mode through the control circuit. Multiple light emission times of the light source in multiple consecutive sensing periods are sequentially delayed through the control circuit according to multiple delay times during the multiple consecutive sensing periods. Whether multiple digital values sequentially outputted by the time-to-digital converter corresponding to the multiple sensing periods have changed is sequentially monitored through the control circuit. And, the control circuit calculates a distance value according to the multiple digital values and a corresponding delay sequence when the control circuit determined that the multiple digital values have changed for a first time.
Based on the above, the light sensor and the ranging method of the disclosure may determine whether the sensing result corresponding to the multiple light emission times have changed according to the adjustment of the multiple light emission times, so as to obtain the converted result with higher precision.
To make the above features and advantages more comprehensible, several embodiments accompanied by drawings are described in detail as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram of a light sensor according to an embodiment of the disclosure.

FIG. 2 is a schematic diagram of a sensing array according to an embodiment of the disclosure.

FIG. 3 is a schematic circuit diagram of a sensing circuit according to an embodiment of the disclosure.

FIG. 4 is a characteristic curve diagram of a diode according to an embodiment of the disclosure.

FIG. 5 is a flowchart of a ranging method according to an embodiment of the disclosure.

FIG. 6 is an operation time sequence diagram of a light sensor according to an embodiment of the disclosure.

FIG. 7 is an operation time sequence diagram of a light sensor according to another embodiment of the disclosure.

DESCRIPTION OF THE EMBODIMENTS

In order to make the content of the disclosure more comprehensible, the following embodiments are specifically cited as examples as to how the disclosure may be implemented. In addition, wherever possible, elements/components/steps with the same reference numerals in the drawings and the embodiments represent the same or similar components.
FIG. 1 is a schematic structural diagram of a light sensor according to an embodiment of the disclosure. FIG. 2 is a schematic diagram of a sensing array according to an embodiment of the disclosure. With reference to FIGS. 1 and 2, a light sensor 100 includes a control circuit 110, a sensing array 120, and a light source 130. The control circuit 110 is coupled to the sensing array 120 and the light source 130. The sensing array 120 includes multiple sensing sub-pixels 121_1 to 121_N, where N is a positive integer. Each of the sensing sub-pixels 121_1 to 121_N includes at least one diode (photodiode). The diode may be a pn junction diode. In the embodiment, the control circuit 110 may control the sensing array 120 to operate the diodes in the sensing sub-pixels 121_1 to 121_N in a Geiger mode or an avalanche linear mode, so as to perform a light sensing operation.
In the embodiment, the light source 130 may be an infrared laser light source, but the disclosure is not limited thereto. In other embodiments of the disclosure, the light source 130 may be a visible light source or an invisible light source. In the embodiment, the control circuit 110 may respectively operate the multiple diodes of the sensing sub-pixels 121_1 to 121_N in a single-photon avalanche diode (SPAD) state of the Geiger mode or the avalanche linear mode to sense a sensing light (pulsing light) emitted by the light source 130, thereby realizing a ranging sensing function having a low light amount and a high sensing sensitivity characteristic.
In the embodiment, the control circuit 110 may be, for example, an internal circuit or a chip of a light sensor, and includes digital circuit elements and/or analog circuit elements. The control circuit 110 may control an operation mode of the diodes in the sensing sub-pixels 121_1 to 121_N and/or an operation mode of the sensing sub-pixels 121_1 to 121_N through changing a bias voltage of the diodes in the sensing sub-pixels 121_1 to 121_N and/or a control voltage of multiple transistors. The control circuit 110 may control the light source 130 to emit the sensing light, and may perform related signal processing and sensing data calculations on a sensing signal outputted by the sensing sub-pixels 121_1 to 121_N. In other embodiments of the disclosure, the control circuit 110 may also be, for example, an external circuit or a chip of a light sensor, for example, a processing circuit or a control circuit in a certain terminal device such as a central processing unit (CPU), a microprocessor control unit (MCU), or a field programmable gate array (FPGA), but the disclosure is not limited thereto.
FIG. 3 is a schematic circuit diagram of a sensing circuit according to an embodiment of the disclosure. With reference to FIG. 3, a sensing circuit 300 of the embodiment may be applicable to the control circuit and the sensing sub-pixel described in various embodiments of the disclosure. In the embodiment, the sensing sub-pixel 300 includes a diode 310 and a cut-off resistor Rq. The control circuit includes an amplifier 320 and a time-to-digital converter 330. The time-to-digital converter 330 includes a count circuit 331. In the embodiment, a first terminal of the diode 310 is coupled to a working voltage V_OP(V_OP=V_BD+V_EB), where V_BDis a breakdown voltage, and V_EBis an excess bias voltage. The cut-off resistor Rq is coupled between a second terminal of the diode 310 and a ground terminal voltage. There is a node voltage V_Abetween the cut-off resistor Rq and the second terminal of the diode 310. An input terminal of the amplifier 320 is coupled to the second terminal of the diode 310. An output terminal of the amplifier 320 is coupled to the time-to-digital converter 330. In the embodiment, a control circuit (such as the control circuit 110 in FIG. 1) may control a bias voltage of the diode 310, to enable the diode 310 to operate in the Geiger mode or the avalanche linear mode to receive a ranging light emitted by a specific light source (such as the light source 130 in FIG. 1). In this regard, the input terminal of the amplifier 320 may receive a sensing signal provided by the diode 310 when the diode 310 sensed a single photon or several photons (trace photons) of the ranging light. The sensing signal may be a single photon sensing signal. In addition, the output terminal of the amplifier 320 may output an amplified sensing signal V_OUTto the time-to-digital converter 330. The amplified sensing signal V_OUTmay be, for example, a square wave pulse signal.
FIG. 4 is a characteristic curve diagram of a diode according to an embodiment of the disclosure. With reference to FIGS. 1, 2 and 4, the diode of the sub-sensing pixel according to the embodiment may have a characteristic curve 401 as shown in FIG. 4. A horizontal axis in FIG. 4 is a bias voltage V of the diode, and a vertical axis is a current I that the diode may generate due to photoelectric conversion under a corresponding bias voltage. The diode may operate in a solar cell mode when the bias voltage V of the diode is greater than 0 (a voltage range M1 as shown in FIG. 4). The diode may operate in a photodiode mode when the bias voltage V of the diode is between 0 and the avalanche breakdown voltage V_APD (a voltage range M2 as shown in FIG. 4). The diode may operate in the avalanche linear mode when the bias voltage V of the diode is between the avalanche breakdown voltage V_APD and a breakdown voltage V_SPAD (a voltage range M3 as shown in FIG. 4). The diode may operate in the Geiger mode when the bias voltage V of the diode is less than the breakdown voltage V_SPAD (a voltage range M4 as shown in FIG. 4). In the embodiment, the control circuit 110 controls the bias voltages of the multiple diodes of the sensing sub-pixel 121_1 to 121_N, so that the multiple diodes operate in the Geiger mode or the avalanche linear mode to receive the sensing light emitted by the light source 130.
FIG. 5 is a flowchart of a ranging method according to an embodiment of the disclosure. FIG. 6 is an operation time sequence diagram of the light sensor 100 according to an embodiment of the disclosure. With reference to FIGS. 1, 3, and 5, the light sensor 100 of the disclosure may execute Steps S510 to S540 as follows to perform ranging. In the Step S510, the control circuit 110 may operate the diode 310 in the Geiger mode or the avalanche linear mode. In the Step S520, the control circuit 110 may sequentially delay multiple light emission times of the light source 130 in multiple consecutive sensing periods according to multiple delay times during the multiple consecutive sensing periods. In the Step S530, the control circuit 110 may sequentially monitors whether multiple digital values sequentially outputted by the time-to-digital converter corresponding to the multiple sensing periods have changed. When the control circuit 110 determines that the multiple digital values have changed for a first time, in the Step S540, the control circuit 110 may calculate a distance value according to the multiple digital values and a corresponding delay sequence.
For example, with reference to FIG. 6, the control circuit 110 may sequentially delay the multiple light emission times of the light source 130 in the consecutive sensing periods according to delay times Td1 to Td10 during ten consecutive sensing periods. As shown in a count time sequence EP shown in FIG. 6, the control circuit 110 may operate the time-to-digital converter 330 to respectively start performing a count operation after a delay time length TA in each of the light emission times. TA is a delay time of the circuit, and it may also be zero. As shown in FIG. 6 in a preset light emission time sequence LP, preset light emission times of the light source 130 have an interval of equal time length. In this regard, as shown in an adjusted light emission time sequence LP′ shown in FIG. 6, the preset light emission times of the light source 130 are respectively adjusted according to the delay times Td1 to Td10, so that the light source 130 delays the emission. It should be noted that the delay times Td1 to Td10 may be determined according to a (minimum) bin resolution (a sub-bin resolution or a sub-counting resolution) Tb of the time-to-digital converter 330. In this example, the delay time Td1 may be, for example, 1×Tb. The delay time Td2 may be, for example, 0.9×Tb. The delay time Td3 may be, for example, 0.8×Tb. The delay time Td4 may be, for example, 0.7×Tb. The delay time Td5 may be, for example, 0.6×Tb. The delay time Td6 may be, for example, 0.5×Tb. The delay time Td7 may be, for example, 0.4×Tb. The delay time Td8 may be, for example, 0.3×Tb. The delay time Td9 may be, for example, 0.2×Tb. The delay time Td10 may be, for example, 0.1×Tb. The delay times Td1 to Td10 are less than the (minimum) bin resolution (counting resolution) Tb of the digital converter 330, therefore the disclosure may realize accuracy and precision of the sub-bin resolution.
In the example, the diode 310 may receive, for example, a reflected light of the sensing light emitted by the light source 130 and reflected from a sensing target surface during the first to the sixth sensing periods. Therefore, the time-to-digital converter 330 may output the multiple digital values corresponding to a first to a sixth distance sensing results according to count results of the first to the sixth sensing periods. The first to the sixth distance sensing results may all be, for example, 91 milliseconds (ms). In addition, since the diode 310 receives other multiple reflected lights of other multiple sensing lights emitted by the light source 130 and reflected from the sensing target surface during the seventh to the tenth sensing periods, the time-to-digital converter 330 may output the multiple digital values corresponding to a seventh to a tenth distance sensing results according to multiple count results of the seventh to the tenth sensing periods. The seventh to the tenth distance sensing results may be, for example, 90 milliseconds (ms). Therefore, the control circuit 110 may rely on, for example, the digital value and the delay sequence (the delay sequence of a seventh sensing period is 7, and a difference between the delay in the seventh sensing period and the delay in the first sensing period is (7−1)×0.1 ms) corresponding to 91 milliseconds to calculate the distance value when the control circuit 110 monitors that the multiple digital values obtained above have changed for a first time during the seventh sensing period. Taking time calculation as an example (actually it may be calculated using the digital value), the control circuit 110 may, for example, calculate a distance sensing result D according to a formula: D−6×0.1=91. Therefore, the control circuit 110 may calculate the distance sensing result D=91+6×0.1=91.6 ms, where 0.1 (0.1=1/10) is a reciprocal of total number of delays.
In this way, the control circuit 110 may obtain a sensing result that is 10 times of the (minimum) bin resolution of the time-to-digital converter 330. In other words, the disclosure may realize the accuracy and precision of the sub-bin resolution. However, the sensing periods and the number of delays in the disclosure are not limited to the above-mentioned examples. The sensing periods of the disclosure and the number of delays of the light source 130 may be determined according to a multiplication of an expected to be obtained (minimum) bin resolution of the digital converter 330. For example, if the expected bin resolution is 100 times, the sensing periods and the number of delays may be 100 times respectively, so that the distance sensing result calculated by the control circuit 110 may be, for example, 91.65. Therefore, the light sensor 100 of the embodiment may provide a high-precision ranging result. For a general ranging circuit, a storage space of the circuit is proportional to the resolution of the ranging. When the resolution is to be increased by 10 times, the storage space of the circuit has to be increased by 10 times. However, the disclosure may increase the resolution by, for example, 10 times or 100 times without increasing the circuit storage space. From another perspective, the control circuit 110 of the embodiment only has to monitor whether the digital values outputted by the digital converter 330 change from time to time, and calculate the distance value immediately when the digital values have changed. In other words, since the control circuit 110 of the embodiment does not have to record the sensing results of each of the sensing periods, the light sensor 100 of the embodiment further obtains the high-precision ranging result in a storage space saving means.
FIG. 7 is an operation time sequence diagram of a light sensor according to another embodiment of the disclosure. With reference to FIGS. 1, 2, and 7, it should be noted that since the multiple diodes of the sensing sub-pixels 121_1 to 121_N respectively serve as the single-photon avalanche diodes (operating in the Geiger mode or the avalanche linear mode), when the multiple diodes respectively sense the photons and an avalanche event occurs, the sensing sub-pixels 121_1 to 121_N have to respectively re-bias the multiple diodes, causing there to be a period of time (may be known as dead time) when the photons are unable to be sensed. In this regard, in order to reduce impact of the dead time, the control circuit 110 of the embodiment may, for example, set some of the sensing sub-pixels of the sensing sub-pixels 121_1 to 121_N of the embodiment as a sensing pixel (or macro-pixel). For example, with reference to FIG. 1, the four sensing sub-pixels 121_A to 121_D may serve as a sensing pixel 122, where A to D are positive integers, and less than or equal to N. The control circuit 110 may determine whether the sensing sub-pixels 121_A to 121_D respectively sense one or more photons in a corresponding same exposure time interval and concurrently generate multiple sensing currents, to serve as a pixel sensing result. For example, the control circuit 110 may perform a calculation on the distance sensing result (a time difference or a distance value) of the sensing sub-pixels 121_A to 121_D, to serve as the pixel sensing result.
Specifically, when the four diodes of the sensing sub-pixels 121_A to 121_D are operating in the Geiger mode or the avalanche linear mode, the control circuit 110 may sequentially expose the sensing sub-pixels 121_A to 121_D belonging to the same pixel in a frame sensing period (that is, corresponding to the sensing period in the above-mentioned embodiment). That is, each of the sensing periods in the above-mentioned embodiment may further include t0 to t6. Emission time sequences PH1 to PH4 of the sensing light are shown in FIG. 7, in which during the period from the time t0 to the time t6, for example, there are four sensing light signals (photons) P1 to P4 being emitted to the sensing pixel 122. Exposure operation time sequences EP1 to EP4 are shown in FIG. 7, in which when the sensing sub-pixel 121_1 receives the sensing light signal P1 at the time t1 in an exposure period T1, the sensing sub-pixel 121_1 may only proceed to perform the next exposure operation after a delay time Td.
In this regard, if exposure periods T2 to T4 of the sensing sub-pixels 121_2 to 121_4 are the same as the exposure period T1, then the sensing sub-pixels 121_1 to 121_4 may only receive the sensing light signal P1, and the sensing light signals P2 to P4 would not be sensed due to the sensing sub-pixels 121_1 to 121_4 being in the dead time.
Therefore, in the embodiment, an exposure starting time of the exposure periods T2 to T4 of the sensing sub-pixels 121_2 to 1214 may be respectively sequentially delayed to the times t1 to t3, and two sequentially adjacent exposure periods of the exposure periods T1 to may partially overlap. In this way, the sensing sub-pixel 121_2 may receive the sensing light signal P2 between the time t1 and the time t2 in the exposure period T2. The sensing sub-pixel 121_3 may receive the sensing light signal P3 between the time t3 and the time t4 in the exposure period T3. The sensing sub-pixel 121_4 may receive the sensing light signal P4 between the time t5 and the time t6 in the exposure period T4. Therefore, the sensing sub-pixel 121_2 to 121_4 may effectively receive all of the sensing light signals P1 to P4 and provide accurate sensing results.
In summary, the light sensor and the ranging method of the disclosure may delay the multiple light emission times of the light source according to the delay times that are gradually changing, and calculate the ranging results with higher precision according to the sensing results of the light sensor corresponding to the multiple light emission times. In addition, the light sensor and the ranging method of the disclosure may also effectively reduce the impact of the dead time of the sensing sub-pixels and provide accurate sensing results.
Although the disclosure has been described with reference to the above-mentioned embodiments, they are not intended to limit the disclosure. It is apparent that any one of ordinary skill in the art may make changes and modifications to the described embodiments without departing from the spirit and the scope of the disclosure. Accordingly, the scope of the disclosure is defined by the claims appended hereto and their equivalents in which all terms are meant in their broadest reasonable sense unless otherwise indicated.

Claims

What is claimed is:

1. Alight sensor, comprising:

a light source;

a sensing sub-pixel, comprising a diode; and

a control circuit, coupled to the light source and the sensing sub-pixel, and configured to operate the diode in a Geiger mode or an avalanche linear mode,

wherein the control circuit comprises a time-to-digital converter, and the time-to-digital converter is coupled to the diode,

wherein the control circuit sequentially delays a plurality of light emission times of the light source in a plurality of consecutive sensing periods according to a plurality of delay times during the plurality of consecutive sensing periods, wherein the control circuit sequentially monitors whether a plurality of digital values sequentially outputted by the time-to-digital converter corresponding to the plurality of sensing periods have changed,

wherein the control circuit calculates a distance value according to the plurality of digital values and a corresponding delay sequence when the control circuit determined that the plurality of digital values have changed for a first time.

2. The light sensor according to claim 1, wherein the plurality of delay times are sequentially decreased or increased at an equal time interval.

3. The light sensor according to claim 1, wherein there is a delay time with a longest time length among the plurality of delay times, and a time length of the delay time with the longest time length is equal to a time length of one count bit of the time-to-digital converter.

4. The light sensor according to claim 1, wherein a time length difference between any two adjacent delay times among the plurality of delay times is less than a time length of one count bit of the time-to-digital converter.

5. The light sensor according to claim 1, further comprising at least another sensing sub-pixel, wherein the at least another sensing sub-pixel and the sensing sub-pixel belong to a same pixel, and the sensing sub-pixel and the at least another sensing sub-pixel are sequentially exposed in each of the plurality of sensing periods.

6. The light sensor according to claim 5, wherein a plurality of exposure periods of the sensing sub-pixel and the at least another sensing sub-pixel in the each of the plurality of sensing periods are partially overlapped.

7. A ranging method, suitable for a light sensor, the light sensor comprising a light source, a sensing sub-pixel, and a control circuit, wherein the sensing sub-pixel comprises a diode, and the control circuit comprises a time-to-digital converter, the ranging method comprising:

operating the diode through the control circuit in a Geiger mode or an avalanche linear mode;

sequentially delaying a plurality of light emission times of the light source in a plurality of consecutive sensing periods through the control circuit according to a plurality of delay times during the plurality of consecutive sensing periods;

sequentially monitoring whether a plurality of digital values sequentially outputted by the time-to-digital converter corresponding to the plurality of sensing periods have changed through the control circuit; and

calculating a distance value according to the plurality of digital values and a corresponding delay sequence through the control circuit when the control circuit determined that the plurality of digital values have changed for a first time.

8. The ranging method according to claim 7, wherein the plurality of delay times are sequentially decreased or increased at an equal time interval.

9. The ranging method according to claim 7, wherein there is a delay time with a longest time length among the plurality of delay times, and a time length of the delay time with the longest time length is equal to a time length of one count bit of the time-to-digital converter.

10. The ranging method according to claim 7, wherein a time length difference between any two adjacent delay times among the plurality of delay times is less than a time length of one count bit of the time-to-digital converter.

11. The ranging method according to claim 7, further comprising at least another sensing sub-pixel, wherein the at least another sensing sub-pixel and the sensing sub-pixel belong to a same pixel, and the sensing sub-pixel and the at least another sensing sub-pixel are sequentially exposed in each of the plurality of sensing periods.

12. The ranging method according to claim 11, wherein a plurality of exposure periods of the sensing sub-pixel and the at least another sensing sub-pixel in the each of the plurality of sensing periods are partially overlapped.