US20200400796A1

US20200400796A1 - Time of flight device and time of flight method

Info

Publication number: US20200400796A1
Application number: US16/898,405
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: 2019-06-21
Filing date: 2020-06-10
Publication date: 2020-12-24
Also published as: TWI714508B; CN112114328A; TWI775092B; US11525902B2; TW202101025A; TWI748460B; US11474217B2; US20200400819A1; CN112114322A; CN112114323A; CN112114328B; TW202101024A; TW202101026A; US20200400793A1

Abstract

A time of flight device and a time of flight method are provided. The time of flight device includes a first time-to-digital converter, a second time-to-digital converter, a driving circuit, a sensing light source, a sensing pixel and a processing circuit. The driving circuit provides a pulse signal and a reference pulse signal simultaneously. The first time-to-digital converter determines first depth data based on the reference pulse signal. The sensing light source emits a light pulse to a sensing object based on the pulse signal. The sensing pixel receives a reflected light pulse reflected by the sensing object and outputs a reflected pulse signal to the second time-to-digital converter so that the second time-to-digital converter determines second depth data based on the reflected pulse signal. The processing circuit subtracts the first depth data from the second depth data to obtain real depth data.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of U.S. provisional application no. 62/864,516, filed on Jun. 21, 2019. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

TECHNICAL FIELD

The invention relates to a distance measurement technology, and more particularly, to a time of flight device and a time of flight method.

BACKGROUND

For a general time-of-flight (ToF) circuit, the ToF circuit includes a time-to-digital converter (TDC), and the TDC is used for a time-to-depth data conversion. However, a conversion characteristic curve of the TDC is usually nonlinear in a period of time after being enabled. Because a sensing period for time of flight is often short, a time length measurement can be easily affected by jitter. In other words, since the general ToF circuit is often affected by the nonlinear conversion characteristic curve and jitter, a distorted conversion result of time to depth data may be obtained. Therefore, several solutions are provided in the following embodiments.

SUMMARY

The invention provides a time of flight device and a time of flight method that can provide a reliable distance measurement effect.
The time of flight device of the invention includes a first time-to-digital converter, a second time-to-digital converter, a driving circuit, a sensing light source, a sensing pixel and a processing circuit. The driving circuit is configured to provide a pulse signal and a reference pulse signal simultaneously. The driving circuit is coupled to the first time-to-digital converter. The reference pulse signal is provided to the first time-to-digital converter so that the first time-to-digital converter determines first depth data based on the reference pulse signal. The sensing light source is coupled to the driving circuit, and configured to emit a light pulse to a sensing object based on the pulse signal. The sensing pixel is coupled to the second time-to-digital converter, and configured to receive a reflected light pulse reflected by the sensing object and output a reflected pulse signal to the second time-to-digital converter so that the second time-to-digital converter determines second depth data based on the reflected pulse signal. The processing circuit is coupled to the first time-to-digital converter and the second time-to-digital converter, and configured to subtract the first depth data from the second depth data to obtain real depth data.
The time of flight method of the invention includes the following steps: simultaneously providing a reference pulse signal to a first time-to-digital converter and a pulse signal to a sensing light source; determining first depth data based on the reference pulse signal by the first time-to-digital converter; emitting a light pulse to a sensing object based on the pulse signal by the sensing light source; receiving a reflected light pulse reflected by the sensing object and outputting a reflected pulse signal to a second time-to-digital converter by a sensing pixel; determining second depth data based on the reflected pulse signal by the second time-to-digital converter; and subtracting the first depth data from the second depth data to obtain real depth data by a processing circuit.
Based on the above, the time of flight device and the time of flight method can correct the depth data by the two time-to-digital converters to effectively obtain the real depth data.
To make the aforementioned more comprehensible, several embodiments accompanied with drawings are described in detail as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a time of flight device according to an embodiment of the invention.

FIG. 2 is a signal timing diagram of various signals and a light pulse according to an embodiment of the invention.

FIG. 3 is a flowchart of a time of flight method according to an embodiment of the invention.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.
In order to make content of the invention more comprehensible, embodiments are described below as the examples to prove that the invention can actually be realized. Moreover, elements/components/steps with same reference numerals represent same or similar parts in the drawings and embodiments.
FIG. 1 is a block diagram of a time of flight device according to an embodiment of the invention. Referring to FIG. 1, a time of flight device 100 includes a driving circuit 110, a sensing light source 120, a first time-to-digital converter 130, a sensing pixel 140, a second time-to-digital converter 150 and a processing circuit 160. The driving circuit 110 is coupled to the sensing light source 120 and the first time-to-digital converter 130. The second time-to-digital converter 150 is coupled to the sensing pixel 140. The processing circuit 160 is coupled to the first time-to-digital converter 130 and the second time-to-digital converter 150. In this embodiment, the driving circuit 110 may simultaneously provide a pulse signal PL to the sensing light source 120 and a reference pulse signal RPL to the first time-to-digital converter 130. The first time-to-digital converter 130 may determine first depth data D1 based on the reference pulse signal RPL and provide the first depth data D1 to the processing circuit 160. The sensing light source 120 emits a light pulse LP to a sensing object 200 based on the pulse signal PL. The sensing pixel 140 receives a reflected light pulse RLP reflected by the sensing object 200 and outputs a reflected pulse signal RP to the second time-to-digital converter 150. The second time-to-digital converter 150 determines second depth data D2 based on the reflected pulse signal RP and provide the second depth data D2 to the processing circuit 160. In this embodiment, the processing circuit 160 may subtract the first depth data D1 from the second depth data D2 to obtain real depth data.
In this embodiment, the sensing light source 120 may be, for example, a pulse light emitter or a laser diode, and the sensing light source 120 may be configured to emit the light pulse LP of infrared radiation (IR) to the sensing object 200. In this embodiment, the sensing pixel 140 may be, for example, a complementary metal-oxide-semiconductor image sensor (CMOS Image Sensor; CIS), and the sensing pixel 140 may received or sense the reflected light pulse RLP of IR reflected by the sensing object 200. Further, it should be noted that, the first depth data D1 of the present embodiment is reference data (or known as correcting data) instead of a real sensing result. Furthermore, the second depth data D2 of the present embodiment refers to a sensing result of a distance between the time of flight device 100 and the sensing object 200 or surface depth information of the sensing object 200.
In the present embodiment, the driving circuit 110 may further include a timing circuit. The timing circuit may be configured to provide a timing to the first time-to-digital converter 130 and the second time-to-digital converter 150 so that the first time-to-digital converter 130 and the second time-to-digital converter 150 may be simultaneously enabled according to the timing. Further, that the first time-to-digital converter 130 and the second time-to-digital converter 150 may be enabled before the driving circuit 110 simultaneously provides the pulse signal PL and the reference pulse signal RPL.
In addition, the time of flight device 100 of the present embodiment may also include a pixel array which includes the sensing pixel 140 and a dark pixel, and the dark pixel is coupled to the first time-to-digital converter 130. The dark pixel refers to a pixel element located in the pixel array that is not used for sensing. In other words, the time of flight device 100 of this embodiment may directly receive the reference pulse signal RPL of the driving circuit 110 through the time-to-digital converter provided in the area of one or more dark pixels in the pixel array where the one or more dark pixels are not used fro sensing, so as to obtain the first depth data D1 . In one embodiment, a plurality of pixels in the pixel array may be classified into a plurality of pixel groups, and each of the pixel groups includes the sensing pixel 140 and the dark pixel. For example, the pixel group may be, for example, four pixels adjacent to each other in a two-by-two manner, where three pixels may be used for distance measurement to obtain three pieces of depth data and the remaining one pixel may be used to obtain the first depth data D1. The first depth data D1 may be used to correct said three pieces of depth data. Alternatively, multiple pixels in one entire row or one entire column of the pixel array may all be used as the dark pixels described above, and configured to correct the depth data obtained by the sensing pixels in each corresponding row or column.
FIG. 2 is a signal timing diagram of various signals and a light pulse according to an embodiment of the invention. Referring to FIG. 1 and FIG. 2, FIG. 2 is a signal timing diagram of various signals and the light pulse shown in FIG. 1. First of all, with reference to an enabling timing TDC1_EN of the first time-to-digital converter 130 and an enabling timing TDC2_EN of the second time-to-digital converter 150 shown in FIG. 2, the first time-to-digital converter 130 and the second time-to-digital converter 150 are simultaneously enabled at a first time T1 to starting counting, and a counting result is a characteristic conversion curve TDC_C shown in FIG. 2. It should be noted that, the characteristic conversion curve TDC_C shown in FIG. 2 has a non-linear curve change at an initial stage of enabling. Next, the driving circuit 110 may provide the pulse signal PL and the reference pulse signal RPL at a second time T2 simultaneously. In this regard, the driving circuit 110 outputs the pulse signal PL to the sensing light source 120 so that the sensing light source 120 emits the light pulse LP to the sensing object 200 based on the pulse signal PL. Moreover, since a time difference between the pulse signal PL outputted by the driving circuit 110 and the light pulse LP emitted by the sensing light source 120 is extremely short, for convenience of explanation, they are considered as being generated simultaneously in FIG. 2. Nonetheless, whether the pulse signal PL and the light pulse LP are generated simultaneously or not does not affect the operation of the invention. Meanwhile, the driving circuit 110 outputs the reference pulse signal RPL to the first time-to-digital converter 130 so that the first time-to-digital converter 130 determines the first depth data D1 based on the first time T1 and the second time T2 for receiving the reference pulse signal RPL. As shown in FIG. 2, the first depth data D1 corresponds to depth information of the characteristic conversion curve TDC_C between the first time T1 and the second time T2 that may be distorted.
Then, over a period of time, the light pulse LP is emitted on a surface of the sensing object 200 so that the sensing pixel 140 senses or receives the reflected light pulse RLP at a third time T3. Accordingly, the sensing pixel 140 provides the reflected pulse signal RP to the second time-to-digital converter 150. In this regard, since a time difference between the reflected light pulse RLP received or sensed by the sensing pixel 140 and the reflected pulse signal RP outputted by the sensing pixel 140 is extremely short, they are considered as being generated simultaneously in FIG. 2. Nonetheless, whether the reflected light pulse RLP and the reflected pulse signal RP are generated simultaneously or not does not affect the operation of the invention. The second time-to-digital converter 150 determines the second depth data D2 based on the first time T1 and the third time T3 for receiving the reflected pulse signal RP. The second time T2 is between the first time T1 and the third time T3. As shown in FIG. 2, the second depth data D2 corresponds to depth information of the characteristic conversion curve TDC_C between the first time T1 and the third time T3. Lastly, the processing circuit 160 of the present embodiment may receive the first depth data D1 and the second depth data D2 provided by the first time-to-digital converter 130 and the second time-to-digital converter 150, and then the processing circuit 160 may subtract the first depth data D1 from the second depth data D2 to obtain real depth data D3. In other words, after the processing circuit 160 of the present embodiment deduces the part of the second depth data D2 that may have distorted depth information, the depth information corresponding to the characteristic conversion curve TDC_C between the second time T2 and the third time T3 may be obtained. In this regard, the characteristic conversion curve TDC_C has a linear curve change between the second time T2 to the third time T3. Therefore, the time of flight device 100 of the present embodiment can accurately obtain depth information of the sensing object 200.
It should be noted here that, since an enabling time (the first time T1) of the time-to-digital converter 100 is not the same as the time (the second time T2) for the drive circuit to output the pulse signal PL, a time length (T2−T1) between the enabling time (the first time T1) and the time for outputting the pulse signal PL (the second time T2) will be affected by jitter. In other words, if the reference pulse signal RPL and the architecture design of the second time-to-digital converter 150 as described in this embodiment are not used, the result of time of flight will be different each time due to jitter. Moreover, since the traditional time of flight architecture cannot obtain information regarding jitter, the impact of jitter cannot be deducted. In this regard, since the present embodiment uses the architectural design of the reference pulse signal RPL and the second time-to-digital converter 150, the time of flight device 100 of the present embodiment can obtain the information regarding jitter through the reference pulse signal RPL and the output result D1 of the second time-to-digital converter 150. Moreover, since the pulse signal PL and the reference pulse signal RPL are generated simultaneously, the time of flight device 100 of the present embodiment can obtain jitter information of the pulse signal PL, and can deduct the impact of jitter to obtain real depth information. That is to say, for the time of flight device 100 of the present embodiment, in a fixed scene, the result of time of flight will be the same each time without being affected by jitter.
FIG. 3 is a flowchart of a time of flight method according to an embodiment of the invention. Referring to FIG. 1 and FIG. 3, the time of flight method of the present embodiment is applicable to the time of flight device 100 in the embodiment of FIG. 1. In step S310, the driving circuit 110 simultaneously provides the reference pulse signal RPL to the first time-to-digital converter 130 and the pulse signal PL to the sensing light source 120. In step S320, the first time-to-digital converter 130 determines the first depth data D1 based on the reference pulse signal RPL. In step S330, the sensing light source 120 emits the light pulse LP to the sensing object 200 based on the pulse signal PL. In step S340, the sensing pixel 140 receives the reflected light pulse RLP reflected by the sensing object 200 and outputs the reflected pulse signal RP to the second time-to-digital converter 150. In step S350, the second time-to-digital converter 150 determines the second depth data D2 based on the reflected pulse signal RP. In step S360, the processing circuit 160 subtracts the first depth data D1 from the second depth data D2 to obtain the real depth data. Therefore, the time of flight method of the present embodiment can allow the time of flight device 100 to accurately obtain depth information of the sensing object 200.
Nevertheless, enough teaching, suggestion, and implementation regarding other device features and technical details of the time of flight device 100 of this embodiment may be obtained from the foregoing embodiments of FIG. 1 and FIG. 2, and thus related descriptions thereof are not repeated hereinafter.
In summary, the time of flight device and time of flight method of the invention can simultaneously enable the first time-to-digital converter and the second time-to-digital converter before the time of flight sensing begins, and provide the reference data (or the correcting data) between the enabling and sensing times through the first time-to-digital converter to correct the depth data generated by the second-time to digital converter. Therefore, after the part that may have distortion information in a previous stage of depth data is deducted from the depth data generated by the second-time-to-digital converter, the real depth data without distortion or with low distortion may be obtained.
Although the invention has been described with reference to the above embodiments, it will be apparent to one of ordinary skill in the art that modifications to the described embodiments may be made without departing from the spirit of the invention. Accordingly, the scope of the invention will be defined by the attached claims and not by the above detailed descriptions.

Claims

1. A time of flight device, comprising:

a first time-to-digital converter;

a second time-to-digital converter;

a driving circuit, coupled to the first time-to-digital converter, and configured to simultaneously provide a pulse signal and a reference pulse signal, wherein the reference pulse signal is provided to the first time-to-digital converter so that the first time-to-digital converter determines first depth data based on the reference pulse signal;

a sensing light source, coupled to the driving circuit, and configured to emit a light pulse to a sensing object based on the pulse signal;

a sensing pixel, coupled to the second time-to-digital converter, and configured to receive a reflected light pulse reflected by the sensing object and output a reflected pulse signal to the second time-to-digital converter so that the second time-to-digital converter determines second depth data based on the reflected pulse signal; and

a processing circuit, coupled to the first time-to-digital converter and the second time-to-digital converter, and configured to subtract the first depth data from the second depth data to obtain real depth data.

2. The time of flight device of claim 1, wherein the first time-to-digital converter is enabled at a first time, and determines the first depth data based on the first time and a second time for receiving the reference pulse signal.

3. The time of flight device of claim 2, wherein the second time-to-digital converter is enabled at the first time, and determines the second depth data based on the first time and a third time for receiving the reflected pulse signal.

4. The time of flight device of claim 3, wherein the second time is between the first time and the third time.

5. The time of flight device of claim 1, wherein the driving circuit comprises a timing circuit, and the driving circuit is further coupled to the second time-to-digital converter to separately provide a timing to the first time-to-digital converter and the second time-to-digital converter so that the first time-to-digital converter and the second time-to-digital converter are simultaneously enabled.

6. The time of flight device of claim 1, further comprising a pixel array, wherein the pixel array comprises the sensing pixel and a dark pixel, and the dark pixel is coupled to the first time-to-digital converter.

7. The time of flight device of claim 6, wherein the pixel array comprises a plurality of pixel groups, and each of the pixel groups comprises the sensing pixel and the dark pixel.

8. A time of flight method, comprising:

simultaneously providing a reference pulse signal to a first time-to-digital converter and a pulse signal to a second time-to-digital converter;

determining first depth data based on the reference pulse signal by the first time-to-digital converter;

emitting a light pulse to a sensing object based on the pulse signal by a sensing light source;

receiving a reflected light pulse reflected by the sensing object and outputting a reflected pulse signal to the second time-to-digital converter by a sensing pixel;

determining second depth data based on the reflected pulse signal by the second time-to-digital converter; and

subtracting the first depth data from the second depth data to obtain real depth data by a processing circuit.

9. The time of flight method of claim 8, wherein the first time-to-digital converter is enabled at a first time, and the first time-to-digital converter determines the first depth data based on the first time and a second time for receiving the reference pulse signal.

10. The time of flight method of claim 9, wherein the second time-to-digital converter is enabled at the first time, and the second time-to-digital converter determines the second depth data based on the first time and a third time for receiving the reflected pulse signal.