aLFA-C: astronomy large format array controller: design and characterization of an advanced FPA controller

The Large Format Array-Controller (aLFA-C) development is sponsored by the ESA Cosmic Vision Program, resulting in an interfacing ASIC matched to the larger, clearer, lower-temperature focal plane arrays (FPA’s) demanded for future astronomical science missions [1]. The goal of this ASIC is to control and readout detector arrays and address the stringent operation requirements detector in a cryogenic infrared (IR) spacecraft environment [2]. Destined for use in space, the device is designed “radiation hard” throughout, and uses the imec DARE technology in the digital core and Caeleste’s “RH” in the analog part. The ASIC is capable of driving power supplies and bias lines, of delivering timing sequences, of acquiring the output signals of a wide range of FPA technologies, at temperatures even below 30K, with high accuracy; and of interfacing with the warm front-end electronics via a SpaceWire interface. For external use, the chip contains 12 regulators (LDO or normal regulator), 32 accurate voltage sources (VDAC), 8 programmable current sources (IDAC), 36 analog to digital converters(ADC) running at 100 kHz sampling rate, of which 32 can be interleaved to allow higher conversion rates on fewer channels, each input signal can be amplified and conditioned by a low noise programmable gain amplifier, and then digitized by a 16-bit successive approximation analog-to-digital converter (SAR-ADC). The programmable sequencer allows for 8 signal loops with a maximum word depth of 512, capable to work together with the embedded S8 microprocessor for more elaborate schemes. The specified operating range is 35 – 400K, yet the ASIC is found to be fully functional from 25K to room temperature (elevated temperature not yet tested). This paper presents an overview of the aLFA-C ASIC design with descriptions of its analog, mixed-signal and digital circuit blocks, test environment and preliminary test results.