Output stage of a dynamic current steering deep brain stimulator

Clinical deep brain stimulation (DBS) uses 4 cylindrical electrodes driven in monopolar or bipolar configurations. This yields a spherical stimulation field around the electrode modulating both targeted and untargeted areas. This paper presents an approach in which activation field spread beyond targeted areas can be mitigated using dynamic current steering. Dynamic current steering uses segmented electrodes together with dynamic current sources in order to accurately stimulate intended neural tissue. This paper will focus on the output stage of the dynamic current steering system. The output stage uses dynamic current sources (DCS) in implementing 8 push-pull current sources that are interfaced to 16 electrodes so as to enable current steering. The dynamic current sources operate in two phases - programming and stimulation. This technique was adopted because it reduces power consumption and output current mismatch. The 16 electrodes can be driven both as anodes and cathodes. As a proof of concept the stimulator uses a supply of 3.3 V to drive biphasic current pulses of up to 0.5 mA through its electrodes. The circuit was implemented in a 0.18 μm CMOS technology.