Integrated multipurpose analog frontend for electrochemical ISFET sensors IonSensitiveFieldEffectTransistors (ISFETs) are an alternative to the common glass electrode for pH sensing. They promise higher integration, easier manufacturing and are interesting for biological, medical and environmental applications. However, they require a different and slightly more complex readout circuit. We propose a new circuit based on a standard mixedsignalprocessor with minimal required external components. The operating point of the ISFET is set with a servo loop in software using only the integrated DACs and opamps and an external resistor. With the internal ADC, feedback is provided for the software loop and the result is read. We compare this method with a fully analog ISFET readout circuit and show their equivalence. The new circuit provides some additional features, such as run time configurable operating point and channel type settings. The integrated MCU can also perform calibration and sensor diagnosis functionality and eases the integration in other systems and parallel operation of many units with its digital interfaces.

Current Measurement Transducer Based on CurrenttoVoltagetoFrequency Converting Ring Oscillator with Cascade Bias Circuit We propose a ring oscillator (RO) based currenttovoltagetofrequency (Ixe2x80x93Vxe2x80x93F) converting current transducer with a cascade bias circuit. The Ixe2x80x93Vxe2x80x93F converting scheme guarantees highly stable biasing against RO, with a railtorail output operation. This device was fabricated using National NanoFab Center (NNFC) 180 nm complementary metaloxidesemiconductor (CMOS) technology, which achieves a current resolution of 1 nA in a measurement range up to 200 nA. A noise floor of 11.8 pAxe2x88x9aHz, maximum differential nonlinearity (DNL) of 0.15 in 1 nA steps, and railtorail output with a 1.8 V power supply is achieved. The proposed transducer can be effectively applied to biosensing devices requiring a compact area and low power consumption with a low current output. The fabricated structure can be applied to monolithicthreedimensional integration with a biosensing device.