Status of the digital pixel array detector for protein crystallography

A two-dimensional photon counting digital pixel array detector is being designed for static and time resolved protein crystallography. The room temperature detector will significantly enhance monochromatic and polychromatic protein crystallographic through-put data rates by more than three orders of magnitude. The detector has an almost infinite photon counting dynamic range and exhibits superior spatial resolution when compared to present crystallographic phosphor imaging plates or phosphor coupled CCD detectors. The detector is a high resistivity N-type Si with a pixel pitch of 150×150 μm, and a thickness of 300 μm, and is bump bonded to an application specific integrated circuit. The event driven readout of the detector is based on the column architecture and allows an independent pixel hit rate above 1 million photons/s/pixel. The device provides energy discrimination and sparse data readout which yields minimal dead-time. This type of architecture allows a continuous (frameless) data acquisition, a feature not found in any current detector being used for protein crystallographic applications. For the targeted detector size of 1000×1000 pixels, average hit rates greater than 8 billion photons/s for the complete detector appears achievable. This paper will present a review of the 8×8 detector array pixel performance which includes the analog amplifier response and the photon counting capabilities. In addition, operational results of a 16×16 detector array prototype, that includes both the analog amplifier and digital readout circuitry functioning together on one integrated circuit.