An implantable low power mixed signal telemetry chip for measurements of the frequency dependent impedance of transplanted kidneys for rejection control

The paper presents a low power mixed signal telemetry chip for measurements of the frequency dependent impedance of transplanted kidneys. The purpose of this chip is to observe in vivo, if there is any correlation between the impedance of the organic tissue and its healing or rejection process. In the case of correlation new diagnostic principles are possible. The chip consists of both a digital and an analog part. The digital part is mainly dedicated to the communication protocol. It includes also the power management with clock switches and power down signals according to the Petri net principle. The analog part generates the stimulating harmonic signal with the help of piecewise linear (PWL) sine functions, PWL is realized by switching four differently sized output transistors at a 16 times oversampling rate. The imaginary and real part of the impedance are measured by the four-probe method. An 8 bit analog to digital converter and a multifunctional digitally controlled sample-and-hold circuit are also implemented