Global shutter image sensor

An apparatus comprising:

• a photodiode;
• a charge sensing unit including a first charge storage device and a second charge storage device;
• an analog-to-digital converter (ADC);
• and
• a controller configured to:
• within an exposure period:
• enable the photodiode to, in response to incident light, accumulate residual charge and transfer overflow charge to the first charge storage device and the second charge storage device when the photodiode saturates;
• after the exposure period ends:
• disconnect the second charge storage device from the first charge storage device;
• transfer the residual charge to the first charge storage device to cause the charge sensing unit to generate a first voltage;
• control the ADC to quantize the first voltage to generate a first digital value to measure the residual charge;
• connect the first charge storage device with the second charge storage device to cause the charge sensing unit to generate a second voltage;
• quantize the second voltage to generate a second digital value to measure the overflow charge;
• and
• generate a digital representation of an intensity of the incident light based on the first digital value, the second digital value, and based on whether the photodiode saturates.