| This project seeks to develop wireless circuit interface and associated electronics for an implantable neural stimulating microsystem with a large number of stimulating sites for use in neural prostheses. The implantable microsystem should be inductively powered, button-sized, with 1024 sites, arranged in a 3-D configuration, with 128 simultaneous channels, each capable of sourcing +/-100muA. The major challenges towards this goal are the implant size, microassembly method, large number of sites, effective and safe stimulation, low power consumption, and wideband wireless link between the implant and the external world.; Three approaches were followed in design of this microsystem: (1) Interestim-1, a telemetry interface chip for operating the existing micromachined hardwired active stimulating probes by providing regulated power, serial data bit-stream, clock, and synchronization pulses. (2) Interestim-2, a modular, wireless, microstimulating chip for any kind of microelectrodes, including the passive micromachined silicon probes. (3) Interestim-3, a modular, wireless, active silicon microstimulating probe with all the wireless, stimulation, and site selection circuitry integrated on the probe backend to reduce the total number of interconnects to only 2 per probe.; Research on different blocks of this microsystem resulted in several state-of-the-art circuit designs, which can be used in similar applications such as radio-frequency identification (RFID) and smartcards. Many of these blocks are brought together in Interestim-2B, a 4.6mm x 4.6mm, modular, 32-site, wireless microstimulating SoC (2 modules/chip), fabricated in a 1.5-mum, 2M/2P standard-CMOS foundry process, which can receive power and stimulation data at 2.5Mbps, using a 5/10MHz FSK carrier. An on-chip full-wave rectifier, followed by a series regulator, can supply the chip with up to 50 mW. Eight current drivers per module can generate up to 65,800 stimulus pulses/sec at +/-270muA full-scale, with 5 bits of resolution, ∼100MO of output impedance, and a wide voltage compliance range that extends within 150mV and 250mV of the 5V and ground supply rails for sinking and sourcing currents, respectively. The modular architecture of Interestim-2B allows the operation of up to 64 modules in parallel, while sharing a single receiver LC-tank circuit, in order to support a total of 2048 stimulating sites. Interestim-2B was combined with 1--4, 16-site, passive, chronic, intracortical microelectrode arrays in several prototype implants, and successfully used in various in vitro and acute in vivo experiments. |
