A dual-link coil arrangement and a novel digital frequency-shift keying (FSK) demodulator are presented. The primary application of this system is for inductively powered biomedical implants. The implant is provided with data and power via two separate links. Two sets of coils are used in an arrangement such that the magnetic interference between the two pairs is minimized. The demodulator circuitry presented relies solely on delaying elements, utilizing a delayed digital FSK signal to sample the original digital FSK signal. A synchronized clock can be derived from the FSK signals alone, however, by utilizing the power signal to obtain a synchronized clock, a higher data rate and a decrease in complexity of the receiver circuitry can be achieved. The system was implemented on the bench and experimentally tested at a data rate of 2.083 Mbps with zero bit error rate while receiving a 4.17/6.25 MHz FSK carrier signal synchronized with 2.083 MHz clock derived from the power carrier. The power link was set to provide 58mW.
With more clinical trials proving viability of visual prosthesis follows the demand for higher resolution devices. As the number of electrodes increases, due to surgical difficulties, it is preferred to keep their length short by placing the implant close to the stimulation site, where there are considerable constraints on device size. On the contrary, the physical volume of the implant generally increases with increasing number of electrodes. Splitting the implant into two modules and placing only the essential circuits near the site of stimulation solves the aforementioned problem. However now the problem is redirected to the robustness and the safety of the interface joining these modules. A novel two-wire interface driving a 98 channel neurostimulator incorporating the split-architecture is presented. The stimulator is provided with both power and data by sending square current waveforms via the two-wire interface. The stimulator itself is fabricated using 0.35 μm HVCMOS technology and occupies 4.9 × 4.9 mm(2) and requires no external decoupling capacitor.
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