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Session: Poster session II
Session starts: Thursday 24 January, 16:00

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Alessandro Urso (Delft University of Technology)
Marijn Van Dongen ()
Wouter Serdijn (Delft University of Technology)

Abstract:
In order to recruit neurons in the targeted tissue, constant-current neural stimulators are usually used. Recently, Ultra High-Frequency (UHF) stimulation has been proposed and proved to have the same efficacy of constant current stimulation [1]. The total number of external components is reduced, while the power efficiency is increased. This leads to a smaller stimulator device with an increased battery life. The core circuit of the UHF neurostimulator is a DC-DC converter, which generates current pulses. Each stimulation phase is made of a burst of current pulses injected into the tissue at a determined frequency. The amplitude of the pulses is controlled by means of a duty cycle signal. Here, we present the design guidelines and the IC measurement results of a power-efficient UHF neural stimulator. An overall peak power efficiency of 68% is achieved when 8 independent channels with 16 fully configurable electrodes are used. The only external component is an inductor. It is operated in a time-interleaved fashion across all the activated channels. A novel zero-current detection scheme is proposed. It does not require the freewheel diode usually used in DC-DC converters to prevent current flow from the load back to the inductor. A gate-driver circuit is implemented. It allows to use thin gate oxide transistors as high voltage switches. By doing so, the external high voltage supply, usually used in neural stimulators, is avoided and the neurostimulator is powered from a 3.5 V input voltage. Both the current-detection technique and the gate-driving circuit allow to boost the power efficiency by 200% when compared to previous implementations of high-frequency neural stimulators [1], [2]. The circuit is implemented in a 0.18 μm HV CMOS process, and the total chip area is 3.65 mm 2 .