Digital readout electronics for microcalorimeters

Microcalorimeters are cryogenic radiation detectors that measure the energy of incident photons or particles by the increase of temperature in an absorber. They are capable of achieving ultra-high energy resolution, but only with small active volumes and pulse decay times in the order of milliseconds. Consequently, detection efficiency per detector is very low. A practical detector thus requires a large array of microcalorimeters, and either time-domain or frequency domain multiplexing is used to minimize the number of leads exiting the cryostat to room temperature signal processing. Existing readout electronics generally stream the multiplexed data onto a computer hard drive for offline processing. XIA LLC is developing digital microcalorimeter readout electronics that offer real time signal processing. The electronics consist of two major parts: a set of daughter cards and a standardized core processor board. Each daughter card is designed to interface a specific type of microcalorimeter (individual outputs, time multiplexed, frequency multiplexed, etc.) to the core processor. The combination of the standardized core plus a set of easily designed and modified daughter cards allows the design to not only meet present detector signal processing requirements but also ensure future expandability to as yet unspecified detector systems. In this paper, we first present the general architecture of the daughter cards and the core processor board. Then we describe the detailed hardware implementation of the core processor board and of the daughter card with analog inputs.