The preferred detector for the guider camera is an E2V CCD47-20 frame transfer CCD. The array is made up of two sections of 1024×1024 pixels, each independently clocked. One section is covered with an opaque aluminum mask. The detector has a split serial register with two output amplifiers, so it can be read using either output (or both). The device is backside illuminated, with 13 µm square pixels, 80% broadband quantum efficiency, and less than 3 e- rms readout noise (at 20 kpix/s). The recommended parallel transfer time for the back-illuminated E2V CCD47 chip is 10 µs, so the frame transfer time is close to 10 ms.

Another candidate detector is the E2V CCD67, a 256×256 pixel frame transfer device with 26 µm pixels, and an on-chip mask. The smaller format (ie smaller field-of-view) of this device can be traded-off for a faster frame rate.

And, there is also the SITe 1024×1024 pixel, back-illuminated SI-003A device. With an off-chip mask attached to the CCD package, it could be used in frame transfer mode, with a 512×1024 pixel imaging area. The principal limitation of this device is the parallel transfer time (180 µs) which limits the frame rate.The guider camera electronics will support various detector choices without modification. Each different detector is mounted on a custom header board. The characteristics of the three detectors are shown in the table.

CCD Detector Properties

Device Specifications	E2V CCD47	E2V CCD67	SITe SI-003A	Units
Readout Noise	3	3	5	e-
Peak Quantum Efficiency	>80	>80	>80	%
Array size	2048 × 1024	512 × 256	1024 × 1024	pixels
Pixel size	13	26	24	µm
Amplifiers	2	2	2
Dark current	250	1000	700	e-/pix/s