An ultra-low-power, low-voltage frequency synthesizer designed for implantable medical devices is presented. Several design techniques are adopted to address the issues in ultra-low voltage and current design. The charge pump (CP) in the synthesizer utilizes dynamic threshold-voltage and switch-coupled techniques to provide a high driving current with a low standby current. The synthesizer adopts a ring-based voltage controlled oscillator (VCO) that utilizes a dual resistor-varactor tuning technique to compensate for process-voltage-temperature (PVT) variations and the exponential voltage-to-current curve. Implemented in a 0.13-m CMOS technology, the 0.5-V medical-band frequency synthesizer consumes 440 W while exhibiting a phase noise of 91.5 dBc/Hz at 1-MHz frequency offset.Index Terms-Wireless implantable devices, low power, low voltage, PLL, MedRadio, low power electronics.

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In this work, we demonstrate the use of a nontraditional logic for the implementation of a dual-modulus prescaler. The proposed prescaler consumes less power than TSPC designs and is faster than ETSPC designs. The maximum speed reaches up to 96% of that of a single divide-by-2 D-flip-flop, the theoretical limit. Implemented in 130-nm CMOS technology, the maximum input frequency reaches 14.1GHz with a power consumption of 1.2mW.

Intensity-modulated radiation therapy (IMRT) requires precise delivery of the prescribed dose of radiation to the target and surrounding tissue. Irradiation of moving body anatomy is possible only if stable, accurate, and reliable information about the moving body structures are provided in real time. This paper presents a magnetic position tracking system for radiation therapy. The proposed system uses only four transmitting coils and an implantable transponder. The four transmitting coils generate a magnetic field which is sensed and measured by a biaxial magnetoresistive sensor in the transponder in the tumor. The transponder transmits the information back to a computer to determine the position of the transponder allowing it to track the tumor in real time. The transmission of the information from the transponder to the computer can be wired or wireless. Measurements using a biaxial sensor agree well with the field strength calculated from the ideal equations. The translation from the measurement data to the 3-D location and orientation requires a numerical technique because the equations are in nonclosed forms. The algorithm of tracking is implemented using MATLAB. Each calculation of the position along the target trajectory takes 30 ms, which makes the proposed system suitable for real-time tracking of the transponder for radiation assessment and delivery. An error of less than 2 mm is achieved in the demonstration.

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