Image sensing pixels with lateral overflow storage
An image sensor includes sensing pixels, each comprising a photodetector in electrical communication with a floating diffusion capacitor via a transfer gate, and a lateral overflow storage capacitor coupled to the floating diffusion capacitor via a lateral overflow control gate. A first readout circuit circuitry located between the transfer gate and the lateral overflow control gate comprises a first amplifier. A second readout circuitry, located opposite the lateral overflow control gate from the first readout circuitry, comprises a second amplifier. Following image integration, charge stored on the floating diffusion capacitor is readout using the first readout circuitry and charge stored on the lateral overflow storage capacitor is readout using the second readout circuitry. In a second readout, charge stored on the photodetector is readout using the first readout circuitry with a first amplification applied and charge stored on the photodetector is readout with a second, different amplification applied.
1. A method of operating an image sensor to compensate for spatial noise, the image sensor comprising a plurality of sensing pixels, each sensing pixel comprising a photodiode, a floating diffusion capacitor, and a transfer gate to control transfer of charge between the photodiode and the floating diffusion capacitor, the method comprising:
for each of the sensing pixels,
integrate charge at the photodiode during an image integration;
following the image integration, transfer charge from the photodiode to the floating diffusion capacitor by applying a first energization to the transfer gate, thereby adding a first amount of gate-induced source leakage (GISL) charge to the floating diffusion capacitor;
read a first voltage across the floating diffusion capacitor;
apply a second energization to the transfer gate while the charge from the photodiode and the first amount of GISL charge is stored on the floating diffusion capacitor;
read a second voltage across floating diffusion capacitor; and
determine a pixel signal intensity based upon the first voltage and the second voltage.
2. The method of claim 1 , wherein charge is not integrated at the photodiode between the first energization of the transfer gate and the second energization of the transfer gate.
3. The method of claim 1 , wherein the image sensor generates an image frame based on determined pixel signal intensities from the plurality of sensing pixels without applying additional spatial noise compensation to the determined pixel signal intensities.
4. The method of claim 1 , wherein the image integration occurs during conditions wherein the photodiode is not saturated during the image integration.
5. The method of claim 1 , wherein each sensing pixel includes multiple conversion gain stages, and wherein the second voltage is subtracted from signal readout from a high conversion gain stage and not from another conversion gain stage.
6. The method of claim 1 , wherein determining the pixel signal intensity based upon the first voltage and the second voltage includes subtracting the second voltage from the first voltage.