Post-SM4 ACS/WFC Bias Striping: Characterization And Mitigation
Abstract
The Advanced Camera for Surveys (ACS) CCD Electronics Box Replacement includes a SIDECAR2 Application-Specific Integrated Circuit (ASIC) that exhibits a low frequency noise (1mHz to 1Hz) on the bias and reference voltages it generates for the Wide Field Channel CCDs (Loose 2011). This noise contribution, first seen in thermal-vac testing, does not matter for bias voltages going to the CCD since it is cancelled out by correlated double sampling (CDS). However, there is one reference voltage from the ASIC that is used to offset the signal, applied after the CDS stage. Here, the noise does not cancel out, and manifests as a slow moving variation of the baseline. In practice, we observe a "striping" noise in all post-SM4 Wide Field Channel (WFC) images, virtually uniform across both amplifier readouts (the entire 4096 columns) of each WFC CCD. An example of this phenomenon is shown in Figure 1, where we have taken a post-SM4 bias frame and subtracted the (tripe-free) calibration superbias to remove fixed bias structure and thereby highlight the striping noise.
- Publication:
-
Hubble after SM4. Preparing JWST
- Pub Date:
- July 2010
- Bibcode:
- 2010hstc.workE..54G