A programmable energy efficient readout chip for a multiparameter highly integrated implantable biosensor system

[摘要] In this work an Application Specific Integrated Circuit (ASIC) for animplantable electrochemical biosensor system (SMART implant, Stett et al., 2014) ispresented. The ASIC drives the measurement electrodes and performsamperometric measurements for determining the oxygen concentration,potentiometric measurements for evaluating the pH-level as well astemperature measurements. A 10-bit pipeline analog to digital (ADC) is usedto digitize the acquired analog samples and is implemented as a single stageto reduce power consumption and chip area. For pH measurements, an offsetsubtraction technique is employed to raise the resolution to 12-bits. Chargeintegration is utilized for oxygen and temperature measurements with thecapability to cover current ranges between 30 nA and 1 μA. In order toachieve good performance over a wide range of supply and process variations,internal reference voltages are generated from a programmable band-gapregulated circuit and biasing currents are supplied from a wide-rangebootstrap current reference. To accommodate the limited available electricalpower, all components are designed for low power operation. Also asequential operation approach is applied, in which essential circuitbuilding blocks are time multiplexed between different measurement types.All measurement sequences and parameters are programmable and can beadjusted for different tissues and media. The chip communicates withexternal unites through a full duplex two-wire Serial Peripheral Interface(SPI), which receives operational instructions and at the same time outputsthe internally stored measurement data. The circuit has been fabricated in a standard0.5-μm CMOS process and operates on a supply as low as 2.7 V.Measurement results show good performance and agree with circuit simulation.It consumes a maximum of 500 μA DC current and is clocked between500 kHz and 4 MHz according to the measurement parameters. Measurement resultsof the on-chip ADC show a Differential Non Linearity (DNL) lower than 0.5 LSB,an Integral Non Linearity (INL) lower than 1 LSB and a Figure of Merit(FOM) of 6 pJ/conversion.

[学科分类] 电子、光学、磁材料