Specifications

88 ST-133/ST-133A Controller Manual Version 2.H
Readout of the Array
In this section, a simple 6 × 4 pixel interline CCD is used to demonstrate how charge is
shifted and digitized. As described below, two different types of readout, overlapped and
non-overlapped can occur. In overlapped operation, each exposure begins while the
readout of the previous one is still in progress. In non-overlapped operation (selected
automatically if the exposure time is shorter than the readout time) each readout goes to
completion before the next exposure begins.
Overlapped Operation Exposure and Readout
Figure 45 illustrates exposure and readout when operating in the overlapped mode.
Figure 45 contains four parts, each depicting a later stage in the exposure-readout cycle.
Eight columns of cells are shown. Columns 1, 3, 5 and 7 contain imaging cells while
columns 2, 4, 6 and 8 contain storage cells. The readout register is shown below the
array.
Part 1 of the figure shows the array early in the exposure. The imaging cells contain
charge proportional to the amount of light integrated on each of them. The storage cells
are empty 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 45 shows the situation early in the readout. 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 new exposure begins immediately.
Part 3 of Figure 45 shows the transfer to the readout register continuing. The uppermost
two cells in each column are shown empty. Each row of charges is moved in turn into the
readout register and from there out of the array for further processing. The process
continues until all charges have been completely transferred out of the array. The
imaging cells continue accumulating charge throughout the readout process. Integrating
in this way while the readout takes place achieves the maximum possible time efficiency.
Part 4 of Figure 45 illustrates the situation at the end of the readout. The storage cells
and readout register are empty, but charge accumulation in the imaging cells continues
until the end of the programmed exposure.