Charge sharing: definition · Chip Field Guide

Beginner

When a tiny bucket of charge is joined to a much bigger wire, the charge spreads out and changes the wire only a little.

Novice

What happens when a DRAM cell’s capacitor is connected to its bit line: the charge spreads over both capacitances, so the bit line moves only a small fraction of the cell’s voltage.

Expert

$\Delta V = (V_{\mathrm{cell}} - V_{\mathrm{pre}}) \cdot C_{\mathrm{S}}/(C_{\mathrm{S}} + C_{\mathrm{BL}})$ . With $C_{\mathrm{BL}}$ several to tens of times $C_{\mathrm{S}}$ , the transfer ratio is a few percent, so the signal is a small fraction of the cell voltage, and the sense amplifier must resolve it against its own offset and coupling noise.