Variable resolution pixel
A photosensor having a plurality of light sensitive pixels each of which comprises a light sensitive region and a plurality of storage regions for accumulating photocharge generated in the light sensitive region, a transfer gate for each storage region that is selectively electrifiable to transfer photocharge from the light sensitive region to the storage region, and an array of microlenses that for each storage region directs a different portion of light incident on the pixel to a region of the light sensitive region closer to the storage region than to other storage regions.
1. A photosensor having a plurality of light sensitive pixels having variable spatial resolution formed on a substrate, each pixel comprising:
a light sensitive region in which incident light generates photocharge carriers;
a plurality of storage regions for accumulating photocharge carriers generated in the light sensitive region;
a transfer gate associated with each storage region of the plurality of storage regions that is electrifiable to cause photocharge in different size portions of the light sensitive region to drift to the storage region and vary thereby the spatial resolution of the pixel; and
an array of microlenses comprising at least one microlens for each storage region of the plurality of storage regions that directs light incident on the at least one microlens to a region of the light sensitive region that is closer to the storage region than to other storage regions of the plurality of storage regions.
2. The photosensor according to claim 1 wherein the array of microlenses comprises a single microlens for each storage region.
3. The photosensor according to claim 1 wherein the microlens array exhibits rotational symmetry.
4. The photosensor according to claim 3 wherein the rotational symmetry has an order equal to a number of the plurality of storage regions.
5. The photosensor according to claim 1 wherein the number of the plurality of storage regions is equal to two.
6. The photosensor according to claim 1 wherein the number of the plurality of storage regions is equal to or greater than four.
7. The photosensor according to claim 1 and comprising a controller that electrifies a transfer gate associated with a storage region to cause photocharge generated in the light sensitive region to drift to the storage region.
8. The photosensor according to claim 7 wherein the controller electrifies a transfer gate of only one storage region with a transfer voltage to cause photocharge generated at substantially any location in the light sensitive region to drift to the one storage region.
9. The photosensor according to claim 7 wherein the controller simultaneously electrifies the transfer gate associated with each storage region with a same transfer voltage to cause photocharge generated at locations in the light sensitive region closest to a storage region to drift to the storage region.
10. The photosensor according to claim 7 wherein the controller electrifies the substrate to shutter the photosensor ON and OFF.
11. The photosensor according to claim 1 wherein the light sensitive region comprises a photodiode.
12. A time of flight (TOF) three dimensional (3D) camera that images a scene to determine distances to features in the scene, the TOF-3D camera comprising:
a light source that transmits a train of light pulses to illuminate the scene;
a photosensor according to claim 1 that receives light reflected by the features from the transmitted light pulses; and
a controller that shutters the photosensor ON and OFF following each light pulse to accumulate photocharge generated in the photodiodes of pixels in the photosensor by light from the light pulses reflected by the features during an exposure period chosen from a plurality of different exposure periods;
wherein the controller electrifies transfer gates of different storage regions to accumulate photocharge generated during different exposure periods in different storage regions,
determines amounts of accumulated photocharge in different storage regions from a same frame of the photosensor and uses the amounts to determine distances to features in the scene.
13. The TOF-3D camera according to claim 12 wherein the different exposure periods comprise exposure periods that begin at different times following a time at which a light pulse in the train of light pulses is transmitted.
14. The TOF-3D camera according to claim 12 wherein the different exposure periods comprise exposure periods having different durations.
15. The TOF-3D camera according to claim 12 wherein a number of the plurality of different exposure periods is equal to or greater than two.
16. The TOF-3D camera according to claim 15 wherein a number of the plurality of storage regions is equal to or greater than the number of the plurality of different exposure periods.
17. A camera that images a scene to acquire a picture of the scene, the camera comprising:
a photosensor according to claim 8 that receives light from the scene;
a light meter that determines an intensity of light reaching the camera from the scene; and
a controller that controls electrification of transfer gates responsive to intensity of light measure by the light meter.
18. The camera according to claim 17 wherein the controller controls electrification of the transfer gates responsive to a threshold light intensity.
19. The camera according to claim 18 wherein if the measured intensity is less than the threshold the controller electrifies a transfer gate of only one storage region with a transfer voltage.
20. The camera according to claim 19 wherein if the measured intensity is greater than the threshold the controller simultaneously electrifies the transfer gate associated with each storage region with a same transfer voltage.