Changeset 40441

Timestamp:

May 21, 2018, 5:57:52 PM (8 years ago)

Author:

watersc1

Message:

Update on CTE issue

File:

• trunk/doc/release.2015/ps1.detrend/detrend.tex (modified) (1 diff)

trunk/doc/release.2015/ps1.detrend/detrend.tex

@@ -643 +643 @@
 compared to the rest of the detector are identified.  Twenty-five of
 the sixty OTAs in GPC1 show some evidence of poor CTE, with this
-pattern appearing (to varying degrees) in roughly triangular patches
-on the OTA due to defects in the semiconductor manufacturing
-\czw{check this fact with Peter}.  To generate the mask for these
-regions, a sample set of 26 evenly-illuminated flat-field images were
-measured to produce a map of the image variance in 20x20 pixel bins.
-As the flat screen is expected to illuminate the image uniformly on
-this scale, the expected variances in each bin should be Poissonian
-distributed with the flux level.  However, in regions with poor CTE,
-adjacent pixels are not independent, as the charge in those pixels is
-more free to spread along the image columns.  This reduces the
-pixel-to-pixel differences, resulting in a lower than expected
+pattern appearing (to varying degrees) in roughly triangular patches.
+During the manufacture of the devices, an improperly tuned
+semiconductor process step resulted in a radial pattern of poor
+performance on some silicon wafers.  When the OTAs were cut from these
+wafers, the outer corners exhibited the issue.  To generate the mask
+for these regions, a sample set of 26 evenly-illuminated flat-field
+images were measured to produce a map of the image variance in 20x20
+pixel bins.  As the flat screen is expected to illuminate the image
+uniformly on this scale, the expected variances in each bin should be
+Poissonian distributed with the flux level.  However, in regions with
+poor CTE, adjacent pixels are not independent, as the charge in those
+pixels is more free to spread along the image columns.  This reduces
+the pixel-to-pixel differences, resulting in a lower than expected
 variance.  All regions with variance less than half the average image
 level are added to the static mask.