Power efficient output stages for high density implantable stimulators — Review and outlook

In implantable stimulators, a current-controlled stimulation is preferred over a voltage-controlled due to its safety. However, the power efficiency is a major disadvantage. By reducing the headroom voltage needed in the current driver, power efficiency of a constant current stimulation is improved. A promising technique is to bias the transistor in triode region whereas improving output impedance through the regulated cascode structure. This comes with a feature of implicit compliance monitor. This paper presents an overview on recent highly compliance output drivers and proposes a new power efficient high compliance output stage.