Development of a high-rate, high-resolution detector for EXAFS experiments

A new detector for EXAFS experiments is being developed. It is based on a multi-element Si sensor and dedicated readout ASICs. The sensor is composed of 384 pixels, each having 1mm² area, arranged in four quadrants of 12 × 8 elements, and wire-bonded to 32-channel front-end ASICs. Each channel implements low noise preamplification with self-adaptive continuous reset, high order shaper, band-gap referenced baseline stabilizer, one threshold comparator and two DAC adjustable window comparators, each followed by a 24-bit counter. Fabricated in 0.35μm CMOS dissipates about 8mW per channel. First measurements show at room temperature a resolution of 14 rms electrons without the detector and of 40 rms electrons (340eV) with the detector connected and biased. Cooling at -35C a FWHM of 205eV (167eV from electronics) was measured at the Mn-Kα line. A resolution of about 300eV was measured for rates approaching 100kcps/cm² per channel, corresponding to an overall rate in excess of 10MHz/cm². A channel-to-channel threshold dispersion after DACs adjustment of 2.5 rms electrons was also measured.