IC design is a core activity at SELEX Galileo's Infrared Centre of Excellence and is central to infrared detector design and development. Not only does the silicon provide a substrate for the infrared sensitive MCT detector diodes, it also provides the electronic readout function for the signals generated by the detector diodes.
The design of readout ICs (ROICs) becomes increasingly complex with larger array format sizes, with dual waveband capability or with additional signal processing functions. Die sizes are large primarily to accommodate the optical imaging area. Transistor counts are high and increasing. For example, our Merlin detector ROIC (1024 x 768 / 16um pixel) has in excess of 5 million transistors.
SELEX Galileo is equipped with powerful world class IC design tools to enhance the quality and integrity of design, simulation, physical layout and other verification tasks. Following requirements capture and robust design review, the design flow translates the requirements to a full chip schematic that are rigorously simulated to verify the user interfaces, signal path and all circuit functions.
Following design release, physical layout translates the electrical or schematic design to physical circuit instances using a combination of existing and new or application specific circuit cells to realise the design. This is a complex task supported by comprehensive in house design rules to achieve both the electrical circuit design and the active imaging area. The active imaging area has to be compatible with other semiconductor technologies to allow the infrared sensitive detector elements to be hybridised with the silicon ROIC.
ROIC designs are mixed signal in that they comprise both analogue and digital circuit elements. These technologies are demanding in themselves and present the design team with often conflicting requirements when combined. Space is at a premium and power must be minimised. ROICs have to be cooled to cryogenic temperatures to enable the IR detector technology to operate. Pixel circuit design must accommodate barely detectable laser return signal pulses to extremely high flux signals in other passive wavebands. The drive for increased circuit integration and functions increases chip complexity yet the user interface must remain easy to use. There is a drive for increased circuit performance and increases in imaging array size and pixel resolution.
SELEX Galileo have a track record going back many years delivering many ROIC types for a range of user applications and platforms, from single element to megapixel array devices. Recent development has culminated in HAWK, OSPREY, HARRIER, MERLIN, CONDOR, SWIFT and SWAN devices. Recent circuit innovation includes multifunction pixels for dual waveband, active and dual mode imaging applications including the topomorphic pixel design concept, as recognised by the Finmeccanica award for innovation in 2007.
