Imaging sensor with in-pixel amplification
A pixel architecture having an in-pixel amplifier comprising an NMOS transistor and a depletion-mode NMOS load is disclosed. In one aspect, the pixel architecture comprises a pixel core including a pixel photodiode for generating an output signal in accordance with incident light. Further, the in-pixel amplifier is connected to a pixel core to amplify the output signal before it is stored in a column buffer before being read out at output of the pixel architecture. By having an in-pixel amplifier that can be used for amplification of the output signal inside the pixel architecture, a larger output value is obtained which may be stored inside the pixel architecture on a small capacitor with improved signal-to-noise performance. This in-pixel amplification can also improve the quality of stored signals for global shutter operation.
1. A pixel architecture comprising:
a photodiode element operable for generating a signal;
an in-pixel amplifier configured to amplify the generated signal and having a gain greater than one, the in-pixel amplifier comprising an NMOS amplifier with a depletion-mode NMOS load transistor, wherein the depletion-mode NMOS load transistor functions as a load of the NMOS amplifier;
an output for outputting the amplified signal.
2. The pixel architecture according to claim 1 , further comprising at least one storage element connected to the in-pixel amplifier for storing the amplified signal.
3. The pixel architecture according to claim 1 , further comprising a plurality of storage elements connected to the in-pixel amplifier for storing the amplified signal, wherein one of the storage elements is provided for storing the amplified signal for each frame of a plurality of imaging frames, the storage elements being connected in parallel to the in-pixel amplifier and to the output.
4. The pixel architecture according to claim 1 , further comprising a column buffer connected to the output, the column buffer including at least one transistor for reading out signals for the output.
5. The pixel architecture according to claim 1 , wherein the photodiode element forms part of a pixel core, the pixel core including a floating diffusion region, a conversion capacitor, and at least one control transistor, the output from the pixel core forming an input for the in-pixel amplifier.
6. The pixel architecture according to claim 5 , wherein the in-pixel amplifier comprises an active amplifier forming part of a double sampling arrangement.
7. The pixel architecture according to claim 6 , wherein the double sampling arrangement comprises an input sampling capacitor connected to the pixel core and to the active amplifier, and a feedback capacitor connected between an input and an output of the active amplifier.
8. The pixel architecture according to claim 5 , wherein the at least one control transistor comprises a reset gate for resetting the photodiode element.
9. The pixel architecture according to claim 5 , wherein the at least one control transistor comprises a transfer gate for transferring the charge from the photodiode element to the floating diffusion region and a reset gate for resetting the photodiode element.
10. An imaging sensor comprising a plurality of pixels having a pixel architecture according to claim 1 .
11. The imaging sensor according to claim 10 , comprising a global shutter imaging sensor.