Video and 3D time-of-flight image sensors
View Patent ↗Electronic devices may include time-of-flight (ToF) image pixels. Each ToF pixel may include a photodiode, a first capacitor coupled to the photodiode via a first transfer gate, a second capacitor coupled to the photodiode via a second transfer gate, and a third capacitor coupled to the photodiode via a third transfer gate. The first transfer gate may be turned on for a given duration to store a first charge in the first capacitor. The second transfer gate may be turned on for the given duration to store a second charge in the second capacitor. The third transfer gate may be turned on for a duration that is longer than the given duration to store a third charge in the third capacitor. Depth information may be computed based on the first, second, and third stored charges and a corresponding pixel constant.
1. An image sensor for imaging a scene having at least some background light, comprising:
a non-visible light emitter that emits non-visible light; and
a time-of-flight (ToF) image pixel, comprising:
a floating diffusion node;
a photosensitive element;
a first storage element coupled between the floating diffusion node and the photosensitive element that receives charge generated at least partially from reflected portions of the non-visible light; and
a second storage element coupled between the floating diffusion node and the photosensitive element that receives charge generated only from the background light.
2. The image sensor defined in claim 1 , wherein the non-visible light emitter comprises an infrared pulse emitter.
3. The image sensor defined in claim 1 , wherein the first and second storage elements comprise capacitors.
4. The image sensor defined in claim 1 , wherein the time-of-flight image pixel further includes:
a third storage element that receives charge generated at least partially from the reflected emitter non-visible light;
a first charge transfer gate coupled between the first storage element and the photosensitive element;
a second charge transfer gate coupled between the second storage element and the photosensitive element; and
a third charge transfer gate coupled between the third storage element and the photosensitive element.
5. The image sensor defined in claim 4 , further comprising:
a first control line on which a first control signal that controls the first charge transfer gate is provided;
a second control line on which, a second control signal that controls the second charge transfer gate is provided; and
a third control line on which a third control signal that controls the third charge transfer gate is provided.
6. The image sensor defined in claim 5 , wherein the second storage element has a storage capacity that is at bigger than that of the first storage element, wherein the first control signal is pulsed high for a first duration, wherein the third control signal is pulsed high for the first duration, and wherein the second control signal is pulsed high for a second duration that is longer than the first duration.
7. The image sensor defined in claim 1 , further comprising:
processing circuitry operable to compute depth information based on charges stored in the first and second storage elements.
8. The image sensor defined in claim 1 , further comprising:
a dual-band filter-formed on top of the time-of-flight image pixel, wherein the dual-band filter passes at least some visible light and at least some non-visible light.
9. A method of operating an image sensor that includes a non-visible light emitter and a time-of-flight (ToF) Image pixel the method comprising:
while the non-visible light emitter is activated, transferring charge to a first memory element in the time-of-flight image pixel;
while the non-visible light emitter is deactivated, transferring charge to a second memory element in the time-of-flight image pixel; and
while the non-visible light emitter is deactivated, transferring charge to a third memory element in the time-of-flight image pixel immediately after transferring charge to the first memory element, wherein transferring charge to the second memory element occurs after a predetermined wait time following the transfer of charge to the third memory element.
10. The method-defined in claim 9 , wherein:
the time-of-flight image pixel further includes a photodiode;
transferring the charge to the first memory element comprises asserting a first control signal for a first duration to turn on a first charge transfer gate coupled between the photodiode and the first memory element;
transferring the charge to the second memory element comprises asserting a second control signal for a second duration that is different than the first duration to turn on a second charge transfer gate coupled between the photodiode and the second memory element; and
transferring the charge to the third memory element comprises asserting a third control signal for the first duration to turn on a third charge transfer gate coupled between the photodiode and the third memory element.
11. The method defined in claim 10 , wherein the second duration is longer than the first duration.
12. The method defined in claim 10 , further comprising:
retrieving a pixel constant associated with the time-of-flight image pixel; and
computing depth information based on the retrieved pixel constant and the charges stored in the first, second, and third memory elements.
13. The method defined in claim 12 , wherein computing the depth information comprises computing a ratio of the first duration to the second duration and computing a-weighted difference between the charges stored in the second and third memory elements and between the charges stored in the first and second memory elements.
14. A system, comprising:
a central processing unit;
memory;
a lens;
input-output circuitry; and
an imaging device for imaging a scene having at least some backlight light, comprising:
an infrared illuminator that emits infrared light;
a time-of-flight (ToF) pixel that includes a first storage element for receiving charge generated while the infrared illuminator is activated, a second storage element for receiving charge generated while the infrared illuminator is deactivated, and a third storage element for receiving charge generated while the infrared illuminator is deactivated, wherein the charge received by the third storage element corresponds only to charge generated by the background light; and
processing circuitry configured to compute depth information based on charges stored in the first, second, and third storage elements and further configured to obtain color video information based only on charge stored in the third storage element.
15. The system defined in claim 14 , wherein the first storage element has a storage capacity that is equal to that of the second storage element and that is smaller than that of the third storage element.
16. The system defined in claim 14 , wherein the time-of-flight pixel further includes:
a photodiode;
a first transistor interposed between the first storage element and the photodiode;
a second transistor interposed between the second storage element and the photodiode; and
a third transistor Interposed between the third storage element and the photodiode, wherein the first and second transistors receive pulse control signals having a given pulse width, and wherein the third transistor receives another pulse control signal having a pulse width that is longer than the given pulse width.
17. The system defined in claim 14 , further comprising:
a dual-band filter formed over the imaging device.