The CEB replacement (CEB-R) features new CCD controller and signal processing electronics based upon a programmable SIDECAR (system image, digitizing, enhancing, controlling, and retrieving) ASIC (Application-Specific Integrated Circuit) manufactured by Teledyne Scientific & Imaging. The dual-slope integrator within the CEB-R delivers nearly 1 e− lower read noise than was obtained with the old CEB. The CEB-R does, however, induce some low-level (1-2 DN) correlated noise and a spatially variable bias level in the WFC images. The bias level of each pixel also shifts by 0.02-0.3% of the signal. These artifacts are removed in CALACS pipeline processing and have little to no effect on most WFC science programs. Because the bias gradient depends on the timing pattern of the CCD read out, fewer WFC subarray options are supported in this cycle than were supported in previous pre-SM4 observing cycles.
Table 2.1 lists the basic characteristics of the WFC CCDs before the failure of ACS in January 2007 and after the installation of the CEB-R during SM4 in May 2009. The fourth column in the table lists the section in this Handbook where detailed information about each characteristic can be found. Further details on improvements can be found in ACS ISR 2011-04 (Golimowski et al., 2011).
