J. Millaud

ASIC-based event-driven 2D digital electron counter for TEM imaging

A two-dimensional application specific integrated circuit (ASIC) based detector, designed for X-ray protein crystallography, has been tested to determine its suitability as a direct electron detector for TEM imaging in the voltage range of 20-400 keV. Several markedly different properties of this device distinguish it from the charge coupled device (CCD) detectors: (1) the ASIC detector can be used directly under electron bombardment in the voltage range stated above, therefore requiring no scintillator screen; (2) each active pixel of the device is an electron counter and generates digital output independently; (3) the readout of the device is frameless and event driven; (4) the device can be operated at the room temperature and is nearly noise free; and (5) the counting dynamic range of the device is virtually unlimited. It appears that an imaging system based on this type of device would be ideal for low-dose TEM imaging and online diffraction observation and recording, as well as more conventional imaging, providing the many advantages of direct digital readout for almost all applications.

STATUS OF THE DIGITAL PIXEL ARRAY DETECTOR FOR PROTEIN CRYSTALLOGRAPHY

Abstract 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 150×150xa0μm, and a thickness of 300xa0μm, 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.

The column architecture-a novel architecture for event driven 2D pixel imagers

We describe an electronic architecture for two-dimensional pixel arrays that permits very large increases in rate capability for event- or data-driven applications relative to conventional x-y architectures. The column architecture also permits more efficient use of silicon area in applications requiring local buffering, frameless data acquisition, and it avoids entirely the problem of ambiguities that may arise in conventional approaches. Two examples of active implementation are described: high energy physics and protein crystallography.

A 16 × 16 pixel array detector for protein crystallography

Abstract A 2D pixel array detector prototype is being designed for static and time resolved protein crystallography. This pixel detector will significantly enhance time resolved laue protein crystallography by two or three orders of magnitude compared to existing sensors such as films or phosphor screens coupled to CCDs. The resolution in time and dynamic range of this type of detector will allow to study structural changes that occur within the protein as a function of time (concurrent readout and acquisition). The prototype consists of an array of 16 × 16 pixels of 150 × 150 μ m 2 size. The individual pixel processor consists of a low-noise amplifier shaper followed by a differential threshold comparator which provides the counting of individual photons with energies above a programmable threshold. To accommodate the very high rates, above 5 × 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 defines a pseudo fourth bit will generate a readout sequence providing the pixel address. Addresses, generated locally as quantified analog signals, will be used to increment a location in an histogramming memory from which the computerized image of the Laue diagram will be generated.

A prototype 8 × 8 pixel array X-ray detector for protein crystallography

Abstract An 8 × 8 pixel array X-ray detector prototype ( 1 100 maximum is less than 1 pixel width (150 μm), which is less than ( 1 2 ) that of a CCD and ( 1 7 ) that of an imaging plate detector [1].

Development of a multiframe optical imaging detector for proton radiography at LANL

In this paper we give a brief report on the development of simple direct- and indirect-detection imagers for proton radiography experiments. We outline a conceptual design for a novel, multi-frame 5 mega frames per second (Mfs) hybrid imager. The high-density interconnect is identified as a critical enabling technology. We present a description of a 3D electronics packaging cube, which was completed in a recent feasibility study.

Optimization of signal extraction and front-end design in a fast, multigap ionization chamber

This paper discusses the criteria that have been adopted to optimize the signal processing in a shower detector to be employed as a Large Hadron Collider (LHC) beam luminosity monitor. The original aspect of this instrument is its ability to operate on a bunch-by-bunch basis. This means that it must perform accurate charge measurements at a repetition rate of 40 MHz. The detector must withstand an integrated dose of 100 Grad, that is, two to three orders of magnitude beyond those expected in the experiments. To meet the above requirements, an ionization chamber consisting of several gaps of thickness 0.5 mm, filled with a gas that is expected to be radiation resistant, has been designed. Crucial in the development of the system is the signal processing, as the electronics noise may set the dominant limitation to the accuracy of the measurement. This is related to two aspects. One is the short time available for the charge measurement. The second one is the presence of a few meter cable between the detector and the preamplifier, as this must be located out of the region of highest radiation field. Therefore, the optimization of the signal-to-noise ratio requires that the best configuration of the chamber gaps be determined under the constraint of the presence of a cable of nonnegligible length between and detector and preamplifier. The remote placement of the amplifying electronics will require that the front-end electronics be radiation hard, although to a lesser extent than the detector.

A/D processing system for 64-element pixel detector

A new, 8/spl times/8-element pixel detector array for time resolved protein crystallography has been developed at the Lawrence Berkeley National Laboratory (LBNL). Each element has its own on-chip charge sensitive preamplifier and shaper with a peaking time of 100 ns. A total of 64 parallel analog to digital processing channels are required to support the detector. We describe a low-cost, low-power AD processing system, comprising a fast peak-sensing amplifier/stretcher, followed by a slower 12-bit ADC. Each channel also includes a histogramming memory for a fully stand-alone operation of the system. Circuit performance and test data are also presented.

Overview of the DPAD detector for protein crystallography

A 2D photon counting digital pixel array detector is being designed for static and time resolved protein crystallography. This room temperature detector will significantly enhance monochromatic and polychromatic protein crystallographic throughput data rates by more than two or three orders of magnitude when compared to present data collection systems. The detector has an unbounded 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 X 150) microns, and a thickness of 300 microns that 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 bit rate above 1 million photons/sec. The device provides energy discrimination and sparse data readout that yields minimal dead time. This type of architecture allows an almost continuous (frame-less) data acquisition, a feature not found in any current detector being used for protein crystallographic applications. For the targeted detector size of (1000 X 1000) pixels, average hit rates greater than 1011 photons/sec for the complete detector appears achievable. This paper will present an overview of the hybridized detector performance which includes the analog amplifier response and the photon counting capabilities of the (16 X 16) array operating with both digital and analog circuitry. Also the operation of the serial interface will be described.

3D interconnect architecture for high-bandwidth massively paralleled imager

Abstract The proton radiography group at LANL is developing a fast (5×10 6 xa0frames/s or 5xa0megaframe/s) multi-frame imager for use in dynamic radiographic experiments with high-energy protons. The mega-pixel imager will acquire and process a burst of 32 frames captured at inter-frame time ∼200xa0ns. Real time signal processing and storage requirements for entire frames, of rapidly acquired pixels impose severe demands on the space available for the electronics in a standard monolithic approach. As such, a 3D arrangement of detector and circuit elements is under development. In this scheme, the readout integrated circuits (ROICs) are stacked vertically (like playing cards) into a cube configuration. Another die, a fully depleted pixel photo-diode focal plane array (FPA), is bump bonded to one of the edge surfaces formed by the resulting ROIC cube. Recently, an assembly of the proof-of-principle test cube and sensor has been completed.