Circuits de transmission sans fil a faible puissance pour dispositifs implantables

The aim of the Polystim Laboratory is to develop new electronic devices to assist subjects affected by neurological pathologies. This work takes part of the "UroStim" project which consists of developing a stimulation implant to allow paraplegic people to recover controls of their bladder system. Feedback is essential in this implant since it permits to be aware of some parameters connected to the state of the nerve-electrode connections and the volume of the bladder. A wireless link is therefore necessary to transmit the information and avoid possible risks of infections related to wires.; In this work, we propose a new approach for data transmission previously achieved through the inductive link by modulating the load in the receiver circuit. The implementation of this solution have revealed its limits since depending on the modulation index, there is a tradeoff between transmission with a good signal to noise ratio, data rate and power transfer efficiency. Moreover, transmissions suffer from fading which lead to a poor reliability. The alternative approach of a radiofrequency wireless link permits to transmit the information over tens of meters without having to bring the controller close to the implant.; The proposed system works in an autonomous way powered by a rechargeable battery. It is composed of three main blocks which are respectively the oscillator with an external resonator, the power amplifier and the output matching network which maximizes the transferred power. The frequency modulation is achieved by switching equal extra capacitances on each side of the SAW resonator. It shifts the reactance of the loop and thus the resonance frequency. The chosen frequency band is between 402 MHz and 405MHz and corresponds to the band allocated to medical communication devices. The aim is to have a transmitter consuming less than 5mW.; Two versions of the oscillator have been implemented in CMOS 0.18 mum technology, 1.8V supply voltage from TSMC. The area consumed by the design is 620x920 mum2. The tests have been realized with a specific test board to measure the open loaded loop gain, the equivalent load presented by the matching network and the output power at the antenna. A particular care has been spent to the high frequencies involved with a wide ground plane and decoupling capacitors on the power supply.; During the tests, the oscillation did not start at power up. A start-up circuit and larger margins for loss compensation are needed so that the oscillator could appear. The measured open loop gain with a 50 Ohms load is--2.7dB which shows that the conditions are almost fulfilled for oscillation start-up.