# Electronic – Charge transfer in CCD

ccdintegrated-circuitoptoelectronicsphotonicspixels

I have a basic doubt about charge transfer between pixels of a CCD. Let's consider this animation (picture taken from wikipedia):

A precise time sequence of applied voltages between gates and bulk allows to move the charge between a pixel (represented by a MOS element) to the next one.

But this picture shows the semplified situation in which only the pixel at left has some charge inside (i.e. only that pixel has been excited from light). What would happen if all three MOS are excited with light? How can we distinguish (in the external circuitry) which pixel has been excited (and how much it has been excited) if their charges are mixed (since the charge of one pixel goes to the next one etc) during the transfer mechanism?

The charges are moved top-to-bottom in the main "Image Section" part of the array, using clocks $$\I\phi 1\$$, $$\I\phi 2\$$ and $$\I\phi 3\$$. Then, at the bottom ("readout" section), they are moved right-to-left toward the output buffer, using clocks $$\R\phi 1\$$, $$\R\phi 2\$$ and $$\R\phi 3\$$.