Range imaging device and range imaging method

Patent metadata

Field	Value
Publication number	US-12581214-B2
Application number	US-202318460743-A
Country	US
Kind code	B2
Filing date	Sep 5, 2023
Priority date	Mar 5, 2021
Publication date	Mar 17, 2026
Grant date	Mar 17, 2026

Abstract

A range imaging device includes a light source unit that emits light pulses to a measurement space; a light-receiving unit including a photoelectric conversion element that generates charge according to light incident from the space, a pixel circuit including charge storage units in which the charge is integrated in a frame cycle, and a pixel drive circuit that performs switching operation of transfer transistors to distribute the charge to the storage units for integration at integration timing synchronizing with emission of the pulses; and a distance calculation unit that calculates a distance between object in the space and the light-receiving unit based on charge determined by a first charge integrated in each storage unit. The calculation unit calculates the distance by subtracting a second charge from each first charge, the second charge being noise charge as an integrated charge other than the charge distributed and integrated by the switching operation.

First claim

The invention claimed is:

1 . A range imaging device, comprising:
a light source configured to emit light pulses to a measurement space; a light-receiving unit comprising a pixel drive circuit and at least one pixel circuit including a photoelectric conversion element and a plurality of charge storage units; and circuity that calculates a distance between an object in the measurement space and the light-receiving unit based on a charge determined by a first charge of a charge integrated in each of the charge storage units, wherein the photoelectric conversion element of the light-receiving unit generates the charge according to light incident from the measurement space, the plurality of charge storage units of the light-receiving unit integrates the charge in a frame cycle comprising one or more frames, the pixel drive circuit in the light-receiving unit is configured to perform switching operation of transfer transistors to distribute the charge to each of the charge storage units for integration therein at a predetermined integration timing synchronizing with emission of the light pulses, the circuity calculates the distance by subtracting a second charge from each of the first charges such that the second charge is noise charge as an integrated charge other than the charge distributed and integrated by the switching operation of the transfer transistors, any of the frames is a noise charge acquisition frame that acquires the second charge, in the noise charge acquisition frame after emission of the light pulses from the light source, in a state in which no charge is integrated in the charge storage units from the photoelectric conversion element in response to the pixel drive circuit turning off the transfer transistors, the charge integrated in each of the charge storage units is the second charge, and in frames following the noise charge acquisition frame, in response to the pixel drive circuit turning on or off the transfer transistors, the charge is distributed to each of the charge storage units for integration therein as the first charge.

2 . The range imaging device according to claim 1 , wherein
each of the frames is divided into a first sub-frame and a second sub-frame; in the first sub-frame after emission of the light pulses from the light source, in a state in which no charge is integrated in the charge storage units from the photoelectric conversion element in response to the pixel drive circuit turning off the transfer transistors, the charge integrated in each of the charge storage units is the second charge; and in the second sub-frame, in response to the pixel drive circuit turning on or off the transfer transistors, the charge is distributed to each of the charge storage units for integration therein as the first charge.

3 . The range imaging device according to claim 2 , wherein
the frames are each configured by an integration period in which the charge is distributed to each of the charge storage units for integration therein, and a reading period in which integrated charge is read from each of the charge storage units; and the integration period is shortened to provide the first sub-frame and the second sub-frame.

4 . The range imaging device according to claim 1 , wherein
in a state in which no charge is integrated in the charge storage units from the photoelectric conversion element in response to the pixel drive circuit turning off the transfer transistors with no light pulses emitted from the light source unit, a frame in which charge is integrated in each of the charge storage units as third charge is a first noise charge acquisition frame; in a state in which no charge is integrated in the charge storage units from the photoelectric conversion element in response to the pixel drive circuit turning off the transfer transistors after emission of the light pulses from the light source unit, a frame in which charge is integrated in each of the charge storage units as the second charge is a second noise charge acquisition frame; and the circuity subtracts the third charge from the second charge to calculate a fourth charge generated in areas other than in the photoelectric conversion element due to the light pulses.

5 . The range imaging device according to claim 4 , wherein
the circuity
calculates a fifth charge, in the case where a second distribution count of the distribution in each of the frames following the noise charge acquisition frame is changed from a first distribution count of the distribution in each of the first noise charge acquisition frame and the second noise charge acquisition frame, by dividing the second distribution count by the first distribution count, and multiplying the fourth charge by the division result as an adjustment factor; and
adds the fifth charge to the third charge to correct the second charge for use in the circuity.

6 . The range imaging device according to claim 1 , wherein the light pulses emitted from the light source are pulses in a near infrared wavelength band with a predetermined width.

7 . The range imaging device according to claim 1 , wherein the at least one pixel circuit has a back side illumination structure.

8 . The range imaging device according to claim 1 , wherein the at least one pixel circuit has three or more charge storage units.

9 . The range imaging device according to claim 1 , wherein the at least one pixel circuit is provided with one or more charge discharge transistors that discharge charge from the photoelectric conversion element other than in a period of distributing charge to each of the charge storage units for integration therein.

10 . The range imaging device according to claim 1 , wherein
the circuitry estimates the second charge from ambient light charge using a noise charge inflow ratio between the ambient light charge and noise charge such that the ambient light charge is generated due to ambient light in the measurement space and distributed from the photoelectric conversion element to the charge storage units for integration therein via the transfer transistors and that the noise charge is generated due to the ambient light and flowing into the charge storage units for integration therein without passing through the transfer transistors.

11 . The range imaging device according to claim 10 , wherein
the pixel drive circuit is configured to execute a first ratio acquisition frame and a second ratio acquisition frame before executing the frame cycle for measuring the distance such that the first ratio acquisition frame is a frame in which reference integrated charge is acquired by distributing the charge from the photoelectric conversion element to the charge storage units for integration therein through switching operation of the transfer transistors without emission of the light pulses and that the second ratio acquisition frame is a frame in which a reference noise charge that flows into the charge storage units for integration therein is acquired without switching operation of the transfer transistors and emission of the light pulses, and the circuitry calculates the noise charge inflow ratio based on a reference ambient light charge and the reference noise charge such that the reference ambient light charge is obtained by subtracting the reference noise charge from the reference integrated charge.

12 . The range imaging device according to claim 11 , wherein the circuitry
calculates a unit reference ambient light charge by dividing the reference ambient light charge by a total transfer period of time obtained by multiplying a first distribution count that is a number of times of distribution in the first ratio acquisition

Assignees

• Toppan Inc

Inventors

• Ookubo Yu
• Nakagome Tomohiro
• Hatakeyama Kunihiro
• Goto Hiroshige
• Takahashi Satoshi
• Hitsuoka Yasuyuki

Classifications

• G06T7/514

  from specularities · CPC title

• H04N23/671

  in combination with active ranging signals, e.g. using light or sound signals emitted toward objects · CPC title

• H04N25/61

  the noise originating only from the lens unit, e.g. flare, shading, vignetting or "cos4" · CPC title

• G03B13/20

  Rangefinders coupled with focusing arrangements, e.g. adjustment of rangefinder automatically focusing camera · CPC title

• G06T7/521

  from laser ranging, e.g. using interferometry; from the projection of structured light · CPC title