A 16 X 16 PIXEL ARRAY DETECTOR FOR PROTEIN CRYSTALLOGRAPHY

A 2D pixel array detector prototype is being designed for static and t ime resolved protein crystallography. This pixel detector will signifi cantly enhance time resolved Laue protein crystallography by two or th ree orders of magnitude compared to existing sensors such as films or phosphor screens coupled to CCDs. The resolution in time and dynamic r ange of this type of detector will allow to study structural changes t hat occur within the protein as a function of time (concurrent readout and acquisition). The prototype consists of an array of 16 X 16 pixel s of 150 x 150 mu m(2) size. The individual pixel processor consists o f a low-noise amplifier shaper followed by a differential threshold co mparator which provides the counting of individual photons with energi es above a programmable threshold. To accommodate the very high rates, above 5 X 10(8)/cm(2)/s, each pixel processor has a 3 bit pre-scaler which divides the event rate by 8. Overflow from the divider which def ines a pseudo fourth bit will generate a readout sequence providing th e pixel address. Addresses, generated locally as quantified analog sig nals, will be used to increment a location in an histogramming memory from which the computerized image of the Laue diagram will be generate d.