This paper presents a method to evaluate the interactions between a radio-frequency power transfer link and biological tissues. First we analyze the propagation of a plane wave model at the skin interface to evaluate the frequency that optimize the transfer ratio. We then use the Finite-Difference Time-Domain method to calculate the exact electromagnetic fields propagation in a discrete 3D space and time for a box brain model with an inductive emitting antenna. The results exhibit the electric field pattern in the antenna axis plane and ip the back of the head. They show for an optimize frequency carrier (2OMHz) that the attenuation of electric field strength is 15dB and that most of the energy is reflected at the air-tissue interface.This paper presents a general method to perform the power transfer link investigation. First, the section I1 describes the global visual stimulation system. Section 111 explains the power supply problematic for implanted electronic devices. In section IV, we expose the method to evaluate the optimal power transfer frequency (A) and the Finite-Difference Time-Domain method to calculate the exact electromagnetic propagation in space (B) then the subsection C contains the simulation parameters for a box brain model. Finally, the preliminary results are presented in section V and discussed in section VI.

In this paper, we describe the architecture of a new CMOS fully integrated frequency-locked loop (FLL). The proposed FLL contains a frequency-to-voltage converter (FVC), an operational amplifier (opamp) and a differential voltage-controlled oscillator (VCO). The operation of the proposed circuit is based on frequency comparison of a reference and feedback signals. The architecture of the FVC is built upon capacitors charge redistribution principle, whereas the architecture of the VCO is based on differential delay cells in order to minimize the effect of the power supply and the substrate noise. Simulation carried out with Hspice using the CMOS 0.35-m process shows that the FLL is very fast and operates over a wide frequency range. Two versions of the FLL are reported; the basic architecture could show a static offset due to the two employed FVCs. To alleviate this effect, a second version is proposed to completely eliminate the offset. The area of the proposed FLL is very small, and the design could be easily integrated in the same die together with other analog, digital and mixed-signal blocks. A functional test of five samples of a first version of this FLL proved that the proposed FLL works as expected from simulation results. Examples of the application of the proposed FLL are a high-precision VCO and a frequency synthesizer with true-fractional multiplication and division that does not require binary frequency dividers. Index Terms-Differential-delay cell, frequency-locked loop, frequency-to-voltage converter, phase-locked loop, voltage-controlled oscillator. I. INTRODUCTION A PHASE-LOCKED loop (PLL) circuit is an interesting electronic building block widely used in many integrated applications. It is generally used in systems involving automatic control of frequency or phase, such as communications, frequency synthesis, radar, telemetry, and instrumentation systems. The PLL circuit generates an output signal that tracks an input reference signal. The output signal is synchronized with the input reference signal in frequency as well as in phase. Typically, a PLL is built around a phase detector or phase frequency detector (PFD), a charge pump, a low-pass filter, Manuscript

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We present in this paper, a new technique that improves the performance of a radio-frequency(RF) link used, usually, to transfer power and data to implantable electronic devices (sensors and stimulators). The proposed technique, is based on a a negative feedback circuit that includes a new duty-cycle controller to regulate the output of the power amplifier of the link. The technique is simple and reduces greatly the complexity of the RF link. A circuit based on this technique was simulated and the results show that the circuit operates correctly which demonstrates the effectiveness of our technique.