Hybrid CMOS image sensor with event driven sensing

An image sensor, comprising:

• a pixel cell, comprising:
• a photodiode configured to photogenerate charge in response to incident light;
• a source follower transistor coupled to the photodiode to generate an image signal in response to the charge photogenerated by the photodiode, wherein the image signal is coupled to be received by image readout circuitry through a row select transistor of the pixel cell;
• and
• a reset transistor coupled to reset the charge photogenerated by the photodiode;
• a mode select circuit having a first node coupled to the reset transistor and a second node coupled to a pixel supply voltage;
• and
• an event driven circuit coupled to a third node of the mode select circuit,
• wherein the mode select circuit is configured to couple the first node to the second node during an imaging mode to supply the pixel supply voltage to the reset transistor to reset the photodiode, and
• wherein the mode select circuit is further configured to couple the first node to the third node during an event driven mode to couple a photocurrent of the photodiode responsive to the incident light to drive the event driven circuit through the reset transistor to detect changes in the photocurrent of the photodiode, wherein the event driven circuit comprises:
• a current to voltage converter coupled to the third node of the mode select circuit, wherein the current to voltage converter is coupled to convert the photocurrent of the photodiode to an output voltage signal responsive to the photocurrent of the photodiode, and
• an asynchronous delta modulation circuit coupled to the current to voltage converter, and
• a comparator stage coupled to the asynchronous delta modulation circuit, wherein the asynchronous delta modulation circuit and comparator stage are coupled to generate asynchronously a first event signal modulated in response to a positive slope in the output voltage signal from the current to voltage converter, and wherein the asynchronous delta modulation circuit and comparator stage are further coupled to generate asynchronously a second event signal modulated in response to a negative slope in the output voltage signal from the current to voltage converter.