In a CCD imaging system, the signal charge is stored in which component before readout?

• A. Capacitors
• B. Diodes
• C. Transistors
• D. Wires

Answer: (A)

In a CCD, the light-generated signal is stored in the potential wells created under the gate electrodes of each pixel. These wells act like tiny capacitors, holding a packet of electrons until the charge is clocked out. The amount of charge in a well represents the light level for that pixel, and later the charge is shifted through the serial readout and converted to a voltage at the output.

Diodes aren’t used to store the signal in a CCD pixel, transistors are used to move the charge around but not to hold it for the entire exposure, and wires don’t provide the storage function either. The key idea is that the pixel’s charge sits in a capacitive well before readout.