Bottom-plate sampling is a technique used in sampling switches to mitigate which effect?

• A. Bottom-plate sampling increases sampling frequency.
• B. Bottom-plate sampling helps mitigate charge injection by sampling on the bottom plate of the capacitor to minimize feedthrough.
• C. Bottom-plate sampling reduces thermal noise by cooling the plate.
• D. Bottom-plate sampling is unrelated to sampling switches.

Answer: (B)

Bottom-plate sampling focuses on reducing charge injection from the switching action into the stored value. When a sampling switch turns off, the channel charge in the transistor can couple into the hold capacitor, creating a small error called charge injection or feedthrough. By driving the bottom plate of the capacitor during sampling, the injected charge is largely contained on that plate, while the top (hold) plate remains effectively stable. This minimizes the change in the held voltage caused by the switch, so the output more accurately reflects the true input. The other options don’t address this switching-related disturbance: it’s not about increasing speed, cooling the plate, or being unrelated to sampling switches.