CMOS

 

CMOS has been and will remain the dominant technology is almos all VLSI design areas, including vision chips. This is a direct result of the following advantages offered by CMOS processes.

• Mature technology: CMOS processes are well established and continue to become more mature. The powerful trust by leading edge digital memory and processors has led to continuous improvement and down scaling of CMOS processes.
• Design resources: Circuit and system design in CMOS is supported by a vast number resources. Many design techniques and design libraries for analog and digital design are available.
• Availability: CMOS processes are now readily available for prototype designs through fabrication brokers, at low prices. This has boosted the design knowledge by real implementations, rather than pure theoretical treatments.
• Price: CMOS is the cheapest process available, when compared against other technologies with the same minimum feature size.

The major disadvantages of CMOS technology for implementing vision chips are:

• Analog circuit design: Leading edge processes are not characterized and tuned for analog circuit design.
• Photodetectors: The photodetector structures are not characterized in any of the processes. It is the designer's responsibility to assure that the photodetectors function as desired.
• Second order effects: In the scaling process some second order device characteristics, such as subthreshold operation, are usually ignored or paid less attention, and their cancellation is more desired than their improvement.
• Mismatch: Mismatch in CMOS devices is relatively high. This is specially hindering the reliability of analog processing in vision chips.