Design of a CDS ASIC for Multireadout X-Ray CCDs With a 0.032% INL

Design, analysis, and experimental results of a four-channel correlated double sampling (CDS) application specific integrated circuit (ASIC), named CDS4C, are presented. It aims to interface a type of multi-readout swept charge device for applications in the fields of X-ray spectroscopy, imaging as well as timing. Compared with the conventional CDS architectures based on clamping technique, the innovation of the CDS4C ASIC is that it not only moves the clamping switch out of the signal path but also omits the sampling switch, eliminating the nonlinearity and thermal noise introduced by these switches. Besides, it is implemented in a fully differential architecture which suppresses the second-order harmonic distortion and common-mode interferences, improving the linearity furthermore. A theoretical noise analysis that takes into account the limited bandwidth of the opamp highly coincides with the simulation results. A prototype of the CDS4C ASIC is fabricated with GlobalFoundries 0.35-μm CMOS process. The experimental results show, within the effective input dynamic range of 0~20 mV which is equivalent to an X-ray energy band from 0 to 18.25 keV, its integral nonlinearity is 0.032% and equivalent noise charge (ENC) is 8.6 e
^-
under 100 kHz pixel rate, whilst the total power consumption is only 8.5 mW from a single 3.3-V supply voltage. When tested with the target X-ray charge-coupled device (CCD)-CCD236 using a 1 μm Ci
⁵⁵
Fe radioisotope, the ASIC achieves together with the CCD an overall energy resolution characterized by full-width-half-magnitude as 165 ± 4.5 eV at 5.9 keV and a total ENC as 10.3 e
^-
where CCD236 is cooled down to in the vicinity of 190-K.