High dynamic range imaging systems having differential photodiode exposures

Patent metadata

Field	Value
Publication number	US-2016255289-A1
Application number	US-201514633837-A
Country	US
Kind code	A1
Filing date	Feb 27, 2015
Priority date	Feb 27, 2015
Publication date	Sep 1, 2016
Grant date	—

Abstract

Image sensors may include an array of photodiodes arranged in groups of adjacent photodiodes that generate charge in response to same-colored light. The image sensor may generate high-dynamic-range (HDR) images. To establish an effective exposure ratio between sets of photodiodes on the array for generating HDR images, microlenses may be formed over some photodiodes in a checkerboard pattern and may have portions that extend over other photodiodes in the array. Control circuitry may control photodiodes in each group to perform pulsed integration in which charge transfer control signals are intermittently pulsed for those photodiodes. A substantially opaque element may be formed over photodiodes in each of the groups such that the corresponding photodiodes generate signals in response to crosstalk. In this way, different effective exposures may be established across the array, allowing for HDR images to be generated without motion artifacts and with super-pixel resolution.

First claim

1 . An imaging system, comprising:
an array of photodiodes arranged in rows and columns, wherein the array includes a group of photodiodes and wherein the group of photodiodes comprises first, second, third, and fourth adjacent photodiodes in the array; at least one color filter element formed over the group of photodiodes, wherein the at least one color filter element is configured to pass light of a common color to each photodiode in the group of photodiodes; a first microlens that is optically aligned with the first photodiode and that has portions that extend over the second and third photodiodes; and a second microlens that is optically aligned with the fourth photodiode and that has portions that extend over the second and third photodiodes.

2 . The imaging system defined in claim 1 , wherein the array further comprises an additional group of photodiodes that is adjacent to the group of photodiodes and wherein the additional group of photodiodes comprises fifth, sixth, seventh, and eighth photodiodes, the imaging system further comprising:
at least one additional color filter element formed over the additional group of photodiodes, wherein the at least one additional color filter element is configured to pass light of an additional common color that is different from the common color to each photodiode in the additional group of photodiodes; a third microlens that is optically aligned with the fifth photodiode and that has portions that extend over the second photodiode, the sixth photodiode, and the seventh photodiode; and a fourth microlens that is optically aligned with the eighth photodiode and that has portions that extend over the sixth and seventh photodiodes.

3 . The imaging system defined in claim 1 , wherein the first and fourth photodiodes have a first sensitivity, the second and third photodiodes have a second sensitivity, and the first sensitivity is greater than the second sensitivity.

4 . The imaging system defined in claim 1 , wherein the first and fourth photodiodes have a first sensitivity and the second photodiode has a second sensitivity, and wherein the first sensitivity is greater than the second sensitivity, the imaging system further comprising:
row control circuitry, wherein the row control circuitry is configured to perform pulsed integration operations on the third photodiode so that the third photodiode has a third sensitivity that is less than the second sensitivity.

5 . The imaging system defined in claim 1 , wherein the second and third photodiodes are formed without any corresponding microlenses centered above the second and third photodiodes.

6 . The imaging system defined in claim 5 , wherein the first microlens is deposited using a first reticle, the second microlens is deposited using a second reticle, and the second microlens is deposited over the first microlens so that the second microlens at least partially overlaps the first microlens.

7 . The imaging system defined in claim 5 , further comprising:
a top conformal coating layer formed over the first and second microlenses.

8 . The imaging system defined in claim 1 , further comprising:
a third microlens formed over the second photodiode; and a fourth microlens formed over the third photodiode, wherein the first and second microlenses have a first light collecting area and the third and fourth microlenses have a second light collecting area that is less than the first light collecting area.

9 . The imaging system defined in claim 1 , further comprising:
a camera lens that focuses image light onto the array of photodiodes, wherein the camera lens has a chief ray angle; and a plurality of microlenses, wherein the plurality of microlenses comprises the first and second microlenses, and wherein the each of microlenses of the plurality of microlenses are optically aligned with a portion of a respective corresponding photodiode to account for the chief ray angle of the camera lens.

10 . An image sensor, comprising:
an array of photodiodes arranged in rows and columns, wherein the array comprises a plurality of photodiode clusters, wherein each photodiode cluster includes at least four adjacent photodiodes that capture light of a common color and that are coupled to a common charge storage node via respective charge transfer gates; and row control circuitry, wherein the row control circuitry is configured to:
control at least a first photodiode in each cluster to capture an image using a first integration time;
control at least a second photodiode in each cluster to capture the image using a second integration time that is approximately equal to the first integration time; and
control a third photodiode in each cluster to perform pulsed integration operations to capture the image, wherein performing the pulsed integration operations comprises transferring charges from the third photodiode to the common charge storage node during at least first and second intervals, and wherein the first and second intervals overlap with the first integration time of the first photodiode.

11 . The image sensor defined in claim 10 , wherein the third photodiode is coupled to the common charge storage node via a first transistor and to a voltage source by a second transistor and wherein the row control circuitry is configured to control the third photodiode in each of the photodiode clusters to perform the pulsed integration operations by repeatedly pulsing control signals provided to at least one of the first and second transistors.

12 . The image sensor defined in claim 11 , wherein the row control circuitry is configured to repeatedly pulse the control signals provided to the at least one of the first and second transistors by providing a sequence of control signal pulses having non-uniform spacing in time to the at least one of the first and second transistors.

13 . (canceled)

14 . The image sensor defined in claim 10 , further comprising:
processing circuitry, wherein the processing circuitry is configured to generate a high-dynamic-range image based on image signals captured by the first, second, and third photodiodes in each of the clusters.

15 . A system, comprising:
a central processing unit; memory; input-output circuitry; and an imaging device, wherein the imaging device comprises:
an array of photosensitive regions arranged in rows and columns, wherein the array comprises a plurality of groups of photosensitive regions, wherein each group includes at least first, second, third, and fourth adjacent photosensitive regions on the array that share a common floating diffusion node;
a camera lens that focuses image light onto the array; and
a substantially opaque element formed over the first photosensitive region in each of the groups of photosensitive regions, wherein the first photosensitive region in each of the groups of photosensitive regions is configured to generate charge in response to crosstalk from the second, third, and fourth photosensitive regions of that group without generating charge in response to the image light.

16 . The system defined in claim 15 , wherein the substantially opaque element comprises a metal layer.

17 . The system defined in claim 15 , wherein the substantially opaque element comprises a dark color filter element.

18 . The system defined in claim 15 , further comprising:
a dominant microlens in each group, wherein the dominant microlens in each group is optically aligned with a portion of the third photosensitive region in that group accounting for a chief ray angle of the camera lens.

Assignees

• Semiconductor Components Ind Llc

Inventors

• Johnson Richard Scott
• Gravelle Jr Robert M
• Keelan Brian W
• Silsby Christopher D

Classifications

• H04N25/57 Primary

  Control of the dynamic range · CPC title

• H04N23/843

  Demosaicing, e.g. interpolating colour pixel values · CPC title

• H04N25/59

  by controlling the amount of charge storable in the pixel, e.g. modification of the charge conversion ratio of the floating node capacitance · CPC title

• H04N25/134

  based on three different wavelength filter elements · CPC title

• H04N25/778

  comprising amplifiers shared between a plurality of pixels, i.e. at least one part of the amplifier must be on the sensor array itself · CPC title