Polaroid CCD Camera - Manual (Page 10)

Section 2 - Introduction to CCD Cameras
Page 6
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
X=1 X=M
Y=1
Y=N
Output
Readout Register
Amplifier
Figure 2.1 - CCD Structure
2.2.1. Full Frame and Frame Transfer CCDs
In the ST-7E, ST-8E, ST-9E, ST-10E and ST-1001E, 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, ST-9E, ST-10E and ST-1001E 2 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.
2 The ST-1001E does not have a second CCD for tracking.