A High-Power CMOS Class-D Amplifier for Inductive-Link Medical Transmitters

Powering of medical implants by inductive coupling is an effective technique, which avoids the use of bulky implanted batteries or transcutaneous wires. On the external unit side, class-D and class-E power amplifiers (PAs) are conventionally used, thanks to their high efficiency at high frequencies. The initial specifications driving this study require the use of multiple independent stimulators, which imposes serious constraints on the area and functionality of the external unit. An integrated circuit class-D PA has been designed to provide both small area and enhanced functionality, the latter achieved by the addition of an on-chip (PLL) a dead-time generator and a phase detector. The PA was designed in a 0.18-μm CMOS high-voltage process technology and occupies an area of 9.86 mm2. It works at frequencies up to 14 MHz and 30-V supply and efficiencies higher than 80% are obtained at 14 MHz. The PA is intended for a closed-loop transmitter system that optimizes power delivery to medical implants.