eLine100: A Front End ASIC for LCLS Detectors in Low Noise Applications

eLine100 is a fast-frame 96-channel readout ASIC for SLAC Linac Coherent Light Source (LCLS) detectors. The circuit has been designed to integrate the charge from high-capacitance 2D sensors with rolling shutter and 1D sensors. It has a noise floor of 55 e^- + 8 e^-/pF r.m.s. at room temperature and it is suitable for applications requiring resolutions on the order of 100 e^- r.m.s. and signals up to 120 photons/pixel/pulse at 8 keV ( 260 ke^-). 2D sensors with a rolling shutter like the X-ray Charge Pump Sensor (XCPS), for which the ASIC has been optimized, present many pixels which are bussed on the same readout line. This characteristic, together with the fixed LCLS beam period, impose limitations on the time available for the read out of each pixel. Given the periodic structure of the LCLS beam, the ASIC developed for this application is a time-variant system, providing a two-stage low-noise charge integration, filtering, correlated double sampling and a processing speed of up to 250 k pixel/s on each channel. To cope with the required input range, a charge pump scheme has been implemented using an asynchronous zero-balance measurement method. It provides on-chip 1-bit coarse analog-to-digital conversion of the integrated charge. The residual charge is sampled using correlated double sampling into an analog memory, multiplexed and measured with the required resolution by an external ADC. In this paper, the ASIC architecture and performances are presented.