Development of an analog LSI for readout of X-ray CCDs

We integrated analog readout electronics for X-ray CCDs to an LSI. One LSI chip has two channels, each of which consists of an integrated correlated-double-sampling circuit (iCDS) and an analog-to-digital converter (ADC). We designed the LSI using “OPEN IP”, which is a library of reliable circuit blocks open to public developed by ISAS/JAXA. We fabricated the LSI through 0.25μm complimentary metal-oxide semiconductor (CMOS) process provided by Taiwan Semiconductor Manufacturing Company (TSMC). First, We tested the LSI with false signals of X-ray CCDs to check if the circuits function as designed and confirmed the expected function of the LSI. We finally succeeded in processing analog signals from an X-ray CCD using the LSI and confirmed an imaging and photon-counting capabilities. The energy resolution was 710±10eV at 5.9 keV (full-width at half-maximum) and the readout noise was 55e-r.m.s., which is 11 times larger than that processed with the conventional system made of discrete electronic parts. We found by SPICE simulations which part was the main noise source, and concluded that we could redesign an LSI with lower noise developed from this first prototype for the next try.