Design And Implementation Of Interface Circuit For Implantable Glucose Sensor

Diabetes complications are the fourth most frequent cause of deaths in developed countries. The implantable glucose senor can realize continous glucose concentration monitoring which is important to the treatment and health care for diabetes patients. The implantable batteryless glucose sensor tags based on radio frequency identification (RFID) possess great potential of continuous glucose monitoring, which obtain energy from external reader through electromagnetic induction as well as receive and transmit signals to communicate with the reader. Interface circuit for implantable glucose sensor is used to amplify and digitize the sensor’s output current, which requires high sensitivity, a wide detection range and low-power for implantable bio-medical application.In this thesis, according to the analysis of RFID tag requirement, sytem specifications of the interface circuit are analyzed. T-switches, source voltage shifting and CDS technique are adopted to reduce the effects of leakage currents, charge injection, dc offset and low-frequency 1/f noise.The architecture and test considerations are presented in this thesis. A CDS integrator with 5 integration sub-ranges is designed to dectect highly sensitive and wide-range current. A current splitter is added for calibration and testing for femtoampere current. An 8-bit 100 kS/s low-power SAR ADC digitizes the output voltage of the S/H circuit.The design and simulation of interface circuit are accomplished. Parasitic effects of critical node and path, mismatch and the substrate coupling are carefully considered during the layout design.The interface circuit is manufactured in SMIC13μm1P8M. The tested results demonstrate that the current splitter and integrator have good linearity in either one single range or among all the ranges. The ENOB of SAR ADC is about 7.8 bit, and the DNL is in the range of-0.15/+0.15 LSB whereas the INL is within-0.4/+0.3 LSB. The smallest actual current is 4 fA with covering the interface circuit by tinfoil. The whole chip consumes 7.2μW power.