A Fully Integrated Stimulator With High Stimulation Voltage Compliance Using Dynamic Bulk Biasing Technique in a Bulk CMOS Technology

This paper presents a fully integrated stimulator using a dynamic bulk biasing technique and a dynamic control scheme in a 180-nm bulk CMOS technology. Unlike the conventional bulk biasing method, the bulk bias voltage is dynamically set according to the different stimulation phases. It avoids the underlying leakage current paths, and improves the maximum stimulation voltage compliance (MSVC). Together with dynamic bulk biasing scheme, a high voltage interface is designed to overcome the limitation of the breakdown voltage of the substrate diode ( V $_{\mathbf{BD}}$ ) between the high and low voltage domains. An all-NMOS dynamic charge pump is also proposed as a dynamic power supply above V $_{\mathbf{BD}}$ and provides dynamic bulk-biasing voltages. Fabricated in a 180-nm standard CMOS technology, the stimulator achieves an MSVC of $\pm$ 16.5 V under a 3.3-V supply, and the achieved MSVC is $\sim$ 1.11 times higher than the V $_{\mathbf{BD}}$ ( $\sim$ 14.8 V) of the substrate diode. The stimulator is also measured in a continuous output test mode for over 10 million cycles, the variation of $\vert$ MSVC $\vert$ is less than 200 mV.