What are clock-induced charges?

Clock-induced charges (C⁣I⁣C⁣) are an important source of noise in low imaging with E⁣M⁣C⁣C⁣D⁣ cameras.  These false counts are created when reading a C⁣C⁣D⁣, as the p⁣h⁣o⁣t⁣o⁣e⁣l⁣e⁣c⁣t⁣r⁣o⁣n⁣s⁣ are transferred to the storage area or as they are travelling through the EM register. While these charges are also generated in conventional C⁣C⁣D⁣s⁣, they are negligible since readout noise and t⁣h⁣e⁣r⁣m⁣a⁣l⁣ ⁣n⁣o⁣i⁣s⁣e⁣ are orders of magnitude higher. In contrast, the E⁣M⁣C⁣C⁣D⁣ technology renders the readout noise negligible, thanks to E⁣M⁣ ⁣G⁣a⁣i⁣n⁣, and is deep cooled to significantly reduce t⁣h⁣e⁣r⁣m⁣a⁣l⁣ ⁣n⁣o⁣i⁣s⁣e⁣. This means clock-induced charges are the dominant source of noise in most E⁣M⁣C⁣C⁣D⁣ acquisitions.


In C⁣C⁣D⁣s⁣, the charges must be transferred down to a single component, the output amplifier, where they are read and can be accessed by the user. In order to move the charges, an electronic oscillator, or clock, generates a patterned electric signal that goes from a high voltage to a low voltage. This clock signal oscillation transfers the signal charges, p⁣h⁣o⁣t⁣o⁣e⁣l⁣e⁣c⁣t⁣r⁣o⁣n⁣s⁣, on the sensor down to the readout area.

When these clock signals reach a certain phase, the inversion phase, positive charges (“holes”) are created in the silicon sensor chip. Some of these holes stay trapped on the chip and, once the clock signal ends the inverted phase, they are accelerated. These fast-moving charges can collide with the silicon atoms of the chip with enough force to create an electron.  The electron created is then trapped in a pixel with the p⁣h⁣o⁣t⁣o⁣e⁣l⁣e⁣c⁣t⁣r⁣o⁣n⁣s⁣ where it becomes indistinguishable from the true signal.