ULN1C: An Ultra-Low Noise Readout ASIC for X-Ray CCD Adopting ΣΔ-CDS Technique

We present in this work the development of a singlechannel correlated double sampling (CDS) ASIC, named ULN1C, targeting the readout of X-ray CCDs for applications in the fields of both X-ray spectroscopy and imaging. The ASIC adopts two time-interleaved pre-modulated 3-order 1-bit incremental ΣΔ modulators (SDMs) and two 5-order 228-point truncated cascade of integrated comb (TCIC) filters. It features both optimized sampling strategy for the SDM and decimation scheme for the TCIC filter in order to achieve ultra-low noise, high-linear as well as low-power performances. ULN1C ASIC is fabricated with GlobalFoundries 0.35μm 2P4M CMOS process and occupies a chip area of 2992μm×2018μm. When tested standalone, the ASIC achieves a maximum 55ppm integral nonlinearity (INL) and 10.9μV equivalent input-referred noise (EIN) under 100kHz pixel rate (PR) within the maximum effective input dynamic range (DR) of 60mVppand only consumes 18.4mW from a single 3.3V supply voltage; When tested with the target X-ray CCD- CCD236 using a 1μCi ⁵⁵Fe radioisotope, by cooling down the CCD to in the vicinity of 160K, the ASIC achieves an energy resolution (FWHM) as 132.4eV±2.4@5.9keV under 100kHz PR which is very close to the 121eV@5.9keV Fano Limit. The total readout noise of the system is only 5.2e^-.