Imaging systems having dual storage gate overflow capabilities
An image sensor pixel may include a photodiode that generates first charge for a first frame and second charge for a second frame, first and second storage gates coupled to the photodiode, a floating diffusion coupled to the first storage gate through a first transistor, a second transistor coupled to the second storage gate, and a capacitor coupled to the floating diffusion through a third transistor. The image sensor pixel may output image signals associated with the first charge generated by the photodiode for the first image frame while the photodiode concurrently generates the second charge for the second image frame. The second storage gate may be used to store overflow charge. Overflow charge for the second frame may be stored at the second storage gate while image signals associated with the first image frame are read out from capacitor and the floating diffusion.
1. An image sensor pixel comprising:
a photosensitive element;
a floating diffusion region;
first and second charge storage regions coupled respectively to first and second parallel paths between the photosensitive element and the floating diffusion region;
a transistor having first and second terminals, the floating diffusion region being coupled to the first terminal;
a charge storage structure coupled to the transistor;
a first additional transistor coupling the first charge storage region to the first terminal of the transistor; and
a second additional transistor coupling the second charge storage region to the second terminal of the transistor.
2. The image sensor pixel defined in claim 1 , wherein the charge storage structure is coupled to the second terminal of the transistor.
3. The image sensor pixel defined in claim 2 , further comprising:
a third additional transistor coupled in series with the transistor between the floating diffusion region and a voltage source.
4. The image sensor pixel defined in claim 3 , wherein the charge storage structure comprises a capacitor that has a first terminal coupled to the second terminal of the transistor and a second terminal coupled to the voltage source.
5. The image sensor pixel defined in claim 3 , further comprising:
a fourth additional transistor coupling the photosensitive element to the voltage source.
6. The image sensor pixel defined in claim 2 , wherein the first terminal of the transistor is coupled to a gate terminal of a source follower transistor.
7. The image sensor pixel defined in claim 1 , wherein the first charge storage region is associated with a first storage gate and the second charge storage region is associated with a second storage gate.
8. The image sensor pixel defined in claim 1 , wherein the first charge storage region is associated with a first diode and the second charge storage region is associated with a second diode.
9. An image sensor pixel comprising:
a photodiode;
a floating diffusion region;
first and second charge storage regions coupled along first and second separate paths between the photodiode and the floating diffusion region, respectively;
a first transistor coupled to the floating diffusion region;
a capacitor having a first terminal coupled to a voltage source and a second terminal coupled to the first transistor; and
a second transistor that couples the voltage source to the floating diffusion region, wherein the capacitor is coupled to the floating diffusion region along a third path that is separate from the first path and that is separate from the second path, and wherein the second transistor couples the voltage source to the floating diffusion region along a reset path, along which the first transistor is coupled.
10. The image sensor pixel defined in claim 9 , further comprising:
a third transistor directly coupling the first charge storage region to the floating diffusion region; and
a fourth transistor directly coupling the second charge storage region to the floating diffusion region.
11. The image sensor pixel defined in claim 10 , wherein the third transistor is coupled along the first path and the fourth transistor is coupled along the second path.
12. An image sensor pixel comprising:
a photosensitive element;
a floating diffusion region;
first and second charge storage regions coupled in parallel between the photosensitive element and the floating diffusion region;
a transistor having first and second terminals, wherein the floating diffusion region and the first charge storage region are coupled to the first terminal of the transistor, and the second charge storage region is coupled to the second terminal of the transistor; and
a capacitor coupled to the second terminal of the transistor, wherein the first charge storage region, the second charge storage region, and the capacitor are separated from one another.
13. The image sensor pixel defined in claim 12 , further comprising:
a reset transistor coupling a voltage source to the floating diffusion region, the capacitor having a terminal coupled to the voltage source.
14. The image sensor pixel defined in claim 13 , wherein the reset transistor is coupled to the second terminal of the transistor.