IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS, VOL. 5, NO. 3, JUNE 2011 283 Integrated High-Voltage Inductive Power and Data-Recovery Front End Dedicated to Implantable Devices Fayçal Mounaïm, Student Member, IEEE, and Mohamad Sawan, Fellow, IEEE Abstract—In near-field electromagnetic links, the inductive voltage is usually much larger than the compliance of low-voltage integrated-circuit (IC) technologies used for the implementation of implantable devices. Thus most integrated power-recovery approaches limit the induced signal to low voltages with inefficient shunt regulation or voltage clipping. In this paper, we propose using high-voltage (HV) complementary metal–oxide semicon- ductor technology to fully integrate the inductive power and data-recovery front end while adopting a step-down approach where the inductive voltage is left free up to 20 or 50 V. The advantage is that excessive inductive power will translate to an additional charge that can be stored in a capacitor, instead of shunting to ground excessive current with voltage limiters. We report the design of two consecutive HV custom ICs—IC1 and IC2—fabricated in DALSA semiconductor C08G and C08E tech- nologies, respectively, with a total silicon area (including pads) of 4 and 9 mm , respectively. Both ICs include HV rectification and regulation; however, IC2 includes two enhanced rectifier designs, a voltage-doubler, and a bridge rectifier, as well as data recovery. Postlayout simulations show that both IC2 rectifiers achieve more than 90% power efficiency at a 1-mA load and provide enough room for 12-V regulation at a 3-mA load and a maximum-available inductive power of 50 mW only. Successful measurement results show that HV regulators provide a stable 3.3- to 12-V supply from an unregulated input up to 50 or 20 V for IC1 and IC2, respectively, with performance that matches simulation results. Index Terms—Bridge circuits, complementary metal–oxide semiconductor (CMOS) integrated circuits, high-voltage tech- niques, implantable biomedical devices, inductive power trans- mission, rectifiers, regulators. I. INTRODUCTION C HRONIC implantation of biomedical power-consuming devices requires wireless power transmission through in- ductive links in order to avoid the limited operation lifetime of batteries. In some applications, such as neurostimulation for bladder rehabilitation, a near-field inductive link may be the only possible solution to provide sufficient power to address Manuscript received June 22, 2010; revised September 27, 2010; accepted December 01, 2010. Date of publication February 10, 2011; date of current ver- sion May 25, 2011. This work was supported in part by NSERC, in part by ReSMiQ, in part by the Canada Research Chair on Smart Medical Devices, and in part by the design and implementation tools from CMC Microsystems. This paper was recommended by Associate Editor R. Rieger. The authors are with the Department of Electrical Engineering, Polystim Neurotechnologies Laboratory, Ecole Polytechnique de Montreal, Mon- treal, QC H3T 1J4, Canada (e-mail: faycal.mounaim@polymtl.ca; mo- hamad.sawan@polymtl.ca). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TBCAS.2010.2103558 Fig. 1. Inductive power recovery with simple shunt regulation. the large electrode-nerve impedance and high-current stimula- tion requirements. However, during low-current consumption periods, the inductively recovered voltage may largely exceed the low-voltage integrated circuits (ICs) compliance. To pro- tect the system from these high voltages, power-recovery cir- cuits use voltage limiters either on-chip using voltage clipping, or off-chip using discrete components, such as Zener diodes or shunt regulators [1], [2]. These approaches are usually not en- ergy efficient and this was the case of the most recently pub- lished system architectures [3]–[5], where a shunt regulator was used to limit the rectified voltage to 3.3 or 5 V as shown in Fig. 1. Using inductively coupled spiral antennas, energy is transmitted to the implant by an external controller. The transmitted energy is recovered as the parallel LC network resonates at a carrier frequency of 13.56 MHz. This frequency is chosen within the industrial-scientific-medical (ISM) radio band so that coupling attenuation through the skin tissues remains acceptable with the use of 4-cm diameter antennas. The inductive voltage is then rectified and filtered with the capacitor which also can be seen as the energy storage for the implant. The shunt reg- ulator was mainly chosen to provide a simple voltage limiting option with small space requirements in a discrete implementa- tion. However, the regulator must be adjusted according to the worst case so that it remains capable of providing the maximum required stimulation current when available inductive energy is minimal. Since the inductive voltage is limited, any excessive inductive power that is not used by the system will be heat-dis- sipated by the shunt regulator because the resulting excessive current will be simply shunted to ground. Moreover, the 5-V supply turned out to be insufficient over time in recent chronic dog experiments as the cuff-electrode/ nerve interface impedance may become higher than 4 k eight months after implantation. Consequently, the stimuli generator supply must be increased to at least 9 or 10 V to provide the 2-mA required stimulation current to these high electrode im- pedances. The rest of the system should still run at 3.3 V or lower to reduce power consumption. Assuming that the rectified voltage is limited by a shunt regu- lator, there are two possible approaches in order to provide dual 1932-4545/$26.00 © 2011 IEEE