Section 2 - Introduction to CCD Cameras
horizontal register of pixels. This register collects a line at a time and then transports the charge packets in a serial manner to an on-chip amplifier. The final operating step, charge detection, is when individual charge packets are converted to an output voltage. The voltage for each pixel can be amplified off- chip and digitally encoded and stored in a computer to be reconstructed and displayed on a television monitor."1
Readout Register
Output
Y=1
Amplifier
Y=N
X=1X=M
Figure 2.1 - CCD Structure
2.2.1. Full Frame and Frame Transfer CCDs
In the ST-7E, ST-8E and ST-9E, the CCD is read out electronically by shifting each row of pixels into a readout register at the Y=0 position of the CCD (shown in Figure 2.1), and then shifting the row out through an amplifier at the X=0 position. The entire array shifts up one row when a row is shifted into the readout register, and a blank row is inserted at the bottom. The electromechanical shutter built into the camera covers the CCD during the readout to prevent streaking of the image. Without a shutter the image would be streaked due to the fact that the pixels continue to collect light as they are being shifted out towards the readout register. CCDs with a single active area are called Full Frame CCDs.
For reference, the ST-5C, ST-237, STV and ST-6 CCD cameras use a different type of CCD which is known as a Frame Transfer CCD. In these devices all active pixels are shifted very quickly into a pixel array screened from the light by a metal layer, and then read out. This makes it possible to take virtually streak-free images without a shutter. This feature is typically called an electronic shutter.
2.3.Camera Hardware Architecture
This section describes the ST-7E, ST-8E and ST-9E CCD cameras from a systems standpoint. It describes the elements that comprise a CCD camera and the functions they provide. Please refer to Figure 2.2 below as you read through this section.
1"History and Advancements of Large Area Array Scientific CCD Imagers", James Janesick, Tom Elliott. Jet Propulsion Laboratory, California Institute of Technology, CCD Advanced Development Group.
