The pn-CCD on-chip electronics

A new pn-CCD with an activa area of 3x1 cm2 was recently fabricated for ESA's X-ray Multi Mirror Mission (XMM). The front-end electronics has been integrated on the same chip as the detector, and its noise behaviour was investigated. X-rays from a 55Fe source have been used for the absolute calibration. The measured electronic Equivalent Noise Charge (ENC) of the on-chip amplifier was 8.8 e- at room temperature and 2.2 e- at the CCD operating temperature of 150 K. The improvements with respect to the last version with noise figures of 4.8 e- (at 150 K) are due to the reduction of the total input capacitance by a factor of 1.6, the improvement of the transistor transconductance by a factor of 2, and the reduction of 1/f noise because of the different p-well implant with a better thermal annealing. (orig.)