Implantable electronic circuits are required to operate with low power dissipation due to the difficulties in supplying power transcutaneously and removing heat from the implant site without dangerous temperature elevation. In chip-scale implants, the circuit design is further restricted by the small implant volume and resulting requirement for a fully on-chip circuit implementation. In this paper we present low-power circuit structures for key functions in chip-scale stimulating implants: power transfer circuits, power supply circuits, communications circuits, stimulating circuits, and leakage monitoring circuits.