A Multigigahertz Analog Memory with Fast Read-out for the H.E.S.S.-II Front-End Electronics

The H.E.S.S.-I front-end electronics is based on the ARSO chip, a multigigahertz sampler and analog memory used as a level-1 circular buffer. In the future H.E.S.S.-II, the energy threshold will be decreased as low as 10 GeV. This will require a much higher acquisition rate capability and a larger dynamic range incompatible with the electronics developed for HESS-I. These constraints led to the development of the SAM (for Swift Analog Memory) chip to replace the ARSO. The SAM chip includes 2 analog memory channels, with a 256-cell depth each. The sampling frequency is adjustable up to 2GS/s. Thanks to the matrix structure of the analog memory, the readout-time of an event has been decreased by more than two orders of magnitude compared to the one obtain with the ARSO chip. It permits to deal with the high expected rate of H.E.S.S.-II. The SAM input bandwidth and dynamic range are increased up to 250 MHz and more than 11 bits respectively.