A liquid voltage is applied to a first side of a lipid bilayer. The liquid voltage comprises a tag-reading period with a tag-reading voltage that tends to capture a tag into a nanopore in the lipid bilayer and an open-channel period with an open-channel voltage that tends to repel the tag. A pre-charging voltage source is connected to an integrating capacitor and a working electrode on a second side of the lipid bilayer during a pre-charging time period, such that the integrating capacitor and the working electrode are charged to a pre-charging voltage. The pre-charging voltage source is disconnected from the integrating capacitor and the working electrode during an integrating time period, such that a voltage of the integrating capacitor and a voltage of the working electrode may vary as a current flows through the nanopore. The pre-charging time period overlaps with a beginning portion of the tag-reading period.