A lawsuit of HSM Portfolio LLC and Technology Properties Limited LLC against Micron shows how easy image sensor company can be accused in patent infringement. Some of Micron image sensor products allegedly infringe on some of 3 patents:
US5001367 "High speed complementary field effect transistor logic circuits" filed in 1989 and describing an inverter chain with a sequential size scaling.
US5030853 "High speed logic and memory family using ring segment buffer" filed in 1990, describing an inverter chain with a positive feedback.
US5391949 "Differential latching inverter circuit" filed in 1995, describing a latched logic buffer.
Neither patent has a direct relation to the image sensor technology.