Design of front-end circuits for a hip implant IC

Abstract

Modern CMOS technologies enable the design of low power and compact implantable devices for biomedical applications. In this thesis, a design of front-end circuits for a hip implant IC is presented, which combines MEMS and CMOS technologies. The condition of the implant is monitored in terms of its temperature and acoustic properties to detect problems earlier. A temperature sensor for temperature measurements between 30°C and 60°C with 1°C sensitivity is designed by utilizing diodes in 0.18 m CMOS technology with first order sigma-delta modulator based on the PTAT method. A mathematical extrapolation formula is realized by the use of MIM capacitors to obtain an adjustable full-scale temperature range. Smaller full-scale range compared to similar studies results in cost effective design in terms of power and complexity. Dynamic element matching and autozeroing play an important role in minimizing error. An acoustic sensor is designed to detect audio signals up to 1-2kHz by exploiting a MEMS differential capacitive sensor. Second-order sigma-delta modulators based on the method in the temperature sensor are implemented. Discrete and continuous systems are compared in terms of power consumption. Different ADCs are analyzed to obtain the best overall design.