A BiCMOS wireless stimulator chip for micromachined stimulating microprobes

This paper describes a 4-channel BiCMOS wireless stimulator chip, (Interestim-2), to be integrated with the University of Michigan micromachined passive stimulating microprobes sharing the. same process. Interestim-2 uses an amplitude modulated 4MHz carrier to receive data and power through inductive coupling. It is designed to generate two regulated 5V and. 10V supplies capable of providing up to 50mW, to regenerate a 4MRz internal clock from the radio-frequency (RF) carrier, and to extract data bit stream up to 100kBit/sec from the ASK modulated RF carrier. Any of the stimulating sites can be connected to V-CC, an individual current sink, a common analog line, or left at high impedance. A 7-bit digital to analog converter (DAC) controls the gate voltage of NMOS transistors' used as current sink, whose output characteristic is nonlinear and gives finer control over smaller stimulating current levels. The circuitry has been designed and fabricated through the University of Michigan's single metal, dual-poly 3-mum BiCMOS process, and consists of 1600 transistors occupying an area of 13mm(2) (Fig. 1). The total power dissipation of the chip is less than 10mW.