Different technologies offer advantages and disadvantages for the design of vision chips. The dominant technologies available to date are CMOS, BiCMOS, CCD, and GaAs (MESFET and HEMT). CMOS has been exhaustively used in many designs. The additional bipolar transistor in BiCMOS processes, though advantageous in achieving better matching properties and higher speeds, is not easily justifiable when comparing other factors in the design. While commercial grade CMOS processes are accessible through fabrication brokers, such as MOSIS and CMP, the CCD processes available for prototyping are of a low quality. GaAs processes have been used only to a very limited extent because there are no readily available photodetector structures in such processes, and more importantly, analog circuit design is severely limited by gate leakage in MESFET and HEMT transistors. In the following sections advantages and disadvantages of each process are highlighted.