Development of x-ray CCD camera system with high readout rate using ASIC

Abstract

We report on the development of high-speed and low-noise readout system of X-ray CCD camera with ASIC and the Camera Link standard. The ASIC is characterized by AD-conversion capability and it processes CCD output signals with a high pixel rate of 600 kHz, which is ten times quicker than conventional frame transfer type X-ray CCD cameras in orbit. There are four identical circuits inside the chip and all of them process CCD signals simultaneously. &Delta;&Sigma; modulator is adopted to achieve effective noise shaping and obtain a high resolution decimal values with relatively simple circuits. The results of the unit test shows that it works properly with moderately low input noise of ~70 &mu;V at pixel rate of 625 kHz, and ~40 &mu;V @ 40 kHz. Power consumption is sufficiently low of <120 &mu;uV @ 1.25 MHz. We have also developed the rest of readout and driving circuits. As a data acquisition scheme we adopt the Camera Link standard in order to support the high readout rate of the ASIC. In the initial test of the CCD camera system, we used the P-channel CCD developed for Soft X-ray Imager onboard next Japanese X-ray astronomical satellite. The thickness of its depletion layer reaches up to 220 &mu;m and therefore we can detect the X-rays from ¹⁰⁹Cd with high sensitivity rather than N-channel CCDs. The energy resolution by our system is 379 (&plusmn;7)eV (FWHM) @ 22.1 keV, that is, &Delta;E/E=1.8% was achieved with a readout rate of 44 kHz.