Fig. 2.
A: simplified schematic of the voltage-clamp circuitry in PatchChip. On-chip diodes are used in place of large-valued feedback resistors. Diodes have an exponential relationship between voltage and current, as well as a sensitivity to temperature. Depending on the direction of Icell, either D1 or D2 will conduct, and Vout will be a logarithmic function of the measured current. An on-chip temperature sensor can be used to factor out temperature dependencies. B: detailed schematic of voltage-clamp circuit showing transistors M1–M6 that implement the diode-like feedback elements. See text for definition of variables.