Space Telescope Science Institute   4.1 Overview  4.2.2 CCD Spectral Response

4.2 The CCDs


4.2.1 Detector Properties


WFC Properties

The WFC/CCD consists of two 4096 x 2048 charge-coupled devices that are sensitive from the near UV to the near IR. They are thinned, backside-illuminated devices manufactured by Scientific Imaging Technologies (SITe). They are butted together along their long dimension to create an effective 4096 × 4096 array with a gap corresponding to approximately 50 pixels between the chips. The CCD camera design incorporates a warm dewar window, designed to prevent buildup of contaminants on the window that cause a loss of UV throughput.

A summary of the ACS CCD performance is given in Table 4.1.

Table 4.1: ACS CCD detector performance characteristics.
Characteristic
WFC performance
HRC performance
Architecture
Thinned, backside illuminated
anti-reflection coated
multi-phase pinned
Thinned, backside illuminated
anti-reflection coated
multi-phase pinned
Wavelength range
3700 Å to 11,000 Å
2000 Å to 11,000 Å
Pixel Format
2 butted 2048 × 4096
1024 × 1024
Field of View
202" × 202"
29" × 26"
Pixel Size
15 µm × 15 µm
21 µm × 21 µm
Pixel Plate Scale
0.05"
0.027"
Quantum Efficiency
~77% @ 4000 Å
~83% @ 6000 Å
~67% @ 8000 Å
~33% @ 2500 Å
~69% @ 6000 Å
~53% @ 8000 Å
Dark Count (as of July'05)
~0.0038 e-/second/pixel
0.0044 e-/second/pixel
Read Noise
~5 e- rms
~4.7 e- rms
Full Well
~ 84,700 e-
~155,000 e-
Gain (max. 65, 535 DN)
1, 2, 4, and 8 electrons/DN
1, 2, 4, and 8 electrons/DN
Operating Temperature*
-77ºC
-81ºC


* Average temperature value for WFC1 and WFC2

HRC

The HRC CCD is a flight-spare STIS 1024 ×1024 CCD, also manufactured by SITe. It is a thinned, backside-illuminated device, but is coated using a process developed by SITe to provide good quantum efficiency in the near-ultraviolet. The performance characteristics and specifications are given in Table 4.1


 4.1 Overview  4.2.2 CCD Spectral Response
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