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Appendix G Interline CCD Cameras 91
because no charge has been transferred to them. The arrows between adjacent imaging and
storage cells indicate the direction the charge will be shifted when the transfer occurs.
Part 2 of Figure 49 shows the situation early in the readout cycle. The charge in the imaging
cells has been transferred to the adjacent storage cells and down-shifting to the readout
register has started. Note that a second exposure doesn’t begin while the readout is in
progress.
Part 3 of Figure 49 shows the transfer to the readout register continuing. Two cells in each
column are shown empty, indicating the continuing downward movement of charge. The
charges are moved to the readout register and from there out of the array for further
processing. The process continues until the storage cells’ contents have been completely
transferred out of the array. The imaging cells are electronically switched off and do not
accumulate any charge as the readout takes place. Because this scheme is less time efficient
than that used in the overlapped mode, the frame rate may be lower in non-overlapped
operation than it is in overlapped operation with the some exposure time settings.
Part 4 of Figure 49 illustrates the situation at the end of the readout. Both the imaging and
storage cells are empty. In Freerun operation, the imaging cells will be switched back on
immediately, allowing charge accumulation to begin. In Ext Sync operation with no
PreOpen, they are not switched back on until after the External Sync pulse is detected.
43
12
Empty Readout Register. Exposure
has ended and image is being
transferred to storage cells.
Image has been shifted to storage cells and
first line has been shifted to Readout Register.
After first image are read out, storage cells are
empty. Second exposure begins if in Freerun
mode. Otherwise, waits for Ext Sync.
A2
A1
B2
B1
A4
A3
B4
B3
A6
A5
B6
B5
C2
C1
C4
C3
C6
C5
A1 B1
C1
A2 B2
A4
A3
B4
B3
A6
A5
B6
B5
C2
C4
C3
C6
C5
Charge from first cell has been
shifted to the Output Node.
A1 B1
C1
A2 B2
A4
A3
B4
B3
A6
A5
B6
B5
C2
C4
C3
C6
C5
Figure 49. Non-Overlapped Mode Exposure and Readout
A subsection of the CCD can be read out at full resolution, sometimes increasing the
readout rate while retaining the highest resolution in the region of interest (ROI).