A new charge balancing scheme for electrical microstimulators based on modulated anodic stimulation pulse width

Circuit Design Considerations for Power-Efficient and Safe Implantable Electrical Neurostimulators

“…This control error is used in a negative-feedback loop to automatically adjust the cathodic and anodic charge. The control offset voltage is usually chosen as 0 V. In order to balance the charge, the negative-feedback loop can control either the amplitude [17] or the duration of the cathodic and anodic phases [18].…”

“…In this case, the circuit is not used to match the charge between the two phases of the biphasic stimulation pulse, but, instead, it is used to match the charge between the activation phases of subsequent biphasic pulses. As explained in [18], the charge-metering circuitry consists of two parallel branches. Each branch uses a unit capacitor to measure the charge being delivered to the tissue.…”

Analysis of passive charge balancing for safe current-mode neural stimulation

“…The water window depends largely on electrode material, e.g., [−0.6 V, 0.8 V] (with respect to a Ag-AgCl reference electrode) for Pt and IrOx, and [−0.9 V, 0.9 V] for TiN [3]. However, much smaller windows are often considered for safety (e.g., ±100 mV [7], or ±50 mV [14]). Though some implementations that aim at controlling the electrode potential already exist [7], [15], this approach is not as common as those that try to limit the DC current.…”