Method for measuring ambient light and corresponding integrated device
In an embodiment a method for measuring ambient light includes successively synchronizing optical signal acquisition phases with extinction phases of a disruptive light source, wherein the disruptive light source periodically provides illumination phases and the extinction phases, accumulating, in each acquisition phase, photo-generated charges by at least one photosensitive pixel comprising a pinned photodiode, wherein an area of the pinned photodiode is less than or equal to 1/10 of an area of the at least one photosensitive pixel, transferring, for each pixel, the accumulated photo-generated charges to a sensing node, converting, for each pixel, the transferred charges to a voltage at a voltage node and converting, for each pixel, the transferred charges to a digital number.
1. A method for measuring ambient light, the method comprising:
successively synchronizing optical signal acquisition phases with extinction phases of a disruptive light source, wherein the disruptive light source periodically provides illumination phases and the extinction phases;
accumulating, in each acquisition phase, photo-generated charges by at least one photosensitive pixel comprising a pinned photodiode, wherein an area of the pinned photodiode is less than or equal to 1/10 of an area of the at least one photosensitive pixel;
transferring, for each pixel, the accumulated photo-generated charges to a sensing node;
converting, for each pixel, the transferred charges to a voltage at a voltage node; and
converting, for each pixel, the transferred charges to a digital number.
2. The method according to claim 1 , further comprising discharging the at least one pixel of parasitic charges accumulated outside the acquisition phase during a reset at a beginning of each acquisition phase.
3. The method according to claim 2 , wherein the reset comprises lowering an electrostatic potential barrier at a transfer gate and connecting the sensing node to a first reference voltage thereby enabling diffusion of the parasitic charges to the first reference voltage.
4. The method according to claim 1 , wherein transferring the accumulated photo-generated charges to the sensing node comprises lowering an electrostatic potential barrier of a transfer gate thereby enabling diffusion of the photo-generated charges to the sensing node.
5. The method according to claim 1 , wherein transferring the accumulated photo-generated charges further comprising transferring it from the sensing node to an input of a transimpedance amplifier and a capacitive element.
6. An integrated ambient light sensing device comprising:
at least one photosensitive pixel comprising a pinned photodiode, wherein an area of the pinned photodiode is less than or equal to 1/10 of an area of the at least one photosensitive pixel;
a conversion circuit electrically connected to the photosensitive pixel via a sensing node; and
a controller configured to:
successively synchronize optical signal acquisition phases with extinction phases of a disruptive light source, wherein the disruptive light source periodically provides illumination phases and the extinction phases;
accumulate, in each acquisition phase, photo-generated charges by the at least one photosensitive pixel; and
transfer the accumulated photo-generated charges to the sensing node,
wherein the conversion circuit is configured to convert the transferred charges to a digital number.
7. The device according to claim 6 , wherein the area of the pinned photodiode is less than or equal to 1/100 of the area of the at least one photosensitive pixel.
8. The device according to claim 6 , wherein each pixel includes a transfer gate between the pinned photodiode and the sensing node, and wherein the controller is configured to control the transfer of the photo-generated charges by generating a potential on the transfer gate adapted to lower an electrostatic potential barrier and enable diffusion of the photo-generated charges to the sensing node and then to the conversion circuit.
9. The device according to claim 8 , wherein the transfer gate is part of a transistor.
10. The device according to claim 8 , wherein the controller is further configured to discharge the at least one pixel of parasitic charges accumulated outside the acquisition phase during a reset at a beginning of each acquisition phase.
11. The device according to claim 6 , wherein the conversion circuit comprises a transimpedance amplifier connected to an analog to digital converter, and wherein the transimpedance amplifier is loop around via a loop comprising a capacitive element.
12. The device according to claim 11 , wherein the conversion circuit comprises a single transimpedance amplifier with a single capacitive element.
13. The device according to claim 6 , wherein the at least one pixel comprises a plurality of pixels arranged in rows and columns.
14. The device according to claim 13 , wherein the controller is configured to activate or de-active a transfer gate of each of the pixels.
15. A system comprising:
a light-emitting display screen;
the device according to claim 6 ; and
a camera,
wherein the light-emitting display screen is the disruptive light source.
16. An integrated ambient light sensing device comprising:
an array of photosensitive pixels, each pixel comprising a pinned photodiode;
a conversion circuit electrically connected to the photosensitive pixels via sensing nodes; and
a controller configured to:
successively synchronize optical signal acquisition phases with extinction phases of a disruptive light source, wherein the disruptive light source periodically provides illumination phases and the extinction phases;
accumulate, in each acquisition phase, photo-generated charges by at least one photosensitive pixel; and
transfer the accumulated photo-generated charges to the sensing node,
wherein the conversion circuit comprises a single transimpedance amplifier looped around by a loop, the loop comprising a single capacitive element, and an analog to digital converter.
17. The device according to claim 16 , wherein the controller is configured to activate or de-active a transfer gate of each of the pixels.
18. The device according to claim 16 , wherein an area of the pinned photodiode is less than or equal to 1/10 of an area of the at least one photosensitive pixel.
19. The device according to claim 16 , wherein an area of the pinned photodiode is less than or equal to 1/100 of an area of the at least one photosensitive pixel.
20. A method for measuring ambient light, the method comprising:
successively synchronizing optical signal acquisition phases with extinction phases of a disruptive light source, wherein the disruptive light source periodically provides illumination phases and the extinction phases;
accumulating, in each acquisition phase, photo-generated charges by at least one photosensitive pixel comprising a pinned photodiode;
transferring the accumulated photo-generated charges to an integration node; and
integrating, for each pixel, the transferred charges on the integration node during a series of the successive acquisition phases.
21. An integrated ambient light sensing device comprising:
at least one photosensitive pixel comprising a pinned photodiode;
an integrator circuit electrically connected to the photosensitive pixel via an integration node; and
a controller configured to:
successively synchronize optical signal acquisition phases with extinction phases of a disruptive light source, wherein the disruptive light source periodically provides illumination phases and the extinction phases;
accumulate, in each acquisition phase, photo-generated charges by the at least one photosensitive pixel; and
transfer the accumulated photo-generated charges to the integration node,
wherein the integration node is configured to integrate the transferred charges during a series of the successive acquisition phases.