A digital-to-analog converter for a cortical microelectrode stimulator

This paper describes an integrated digital-to-analog converter (DAC) for a intra-cortical microelectrode stimulator. The circuit has a special feature that consists on charging and discharging the same current to prevent electric charge accumulation that might harm the brain. The DAC has 5 bits of resolution supplying a maximum current of 100 µA to one electrode of the cortical stimulator. The circuit is sized to operate at a maximum sampling frequency of 1 MHz, has an active area of 0.077 mm², and the biasing part consumes only 19.2 µA, from a 3.3 V supply voltage. The circuit has low area to reduce its impact inside the brain and is low power to allow using wireless energy harvesting circuits preventing the use of batteries or wires, to reduce the risk of infections. A circuit prototype was implemented in AMS 0.35um CMOS technology, and tested.