Compact Current Reference Circuits with Low Temperature Drift and High Compliance Voltage

Highly accurate and stable current references are especially required for resistive-sensor conditioning. The solutions typically adopted in using resistors and op-amps/transistors display performance mainly limited by resistors accuracy and active components non-linearities. In this work, excellent characteristics of LT199x selectable gain amplifiers are exploited to precisely divide an input current. Supplied with a 100 µA reference IC, the divider is able to exactly source either a ~1 µA or a ~0.1 µA current. Moreover, the proposed solution allows to generate a different value for the output current by modifying only some connections without requiring the use of additional components. Experimental results show that the compliance voltage of the generator is close to the power supply limits, with an equivalent output resistance of about 100 GΩ, while the thermal coefficient is less than 10 ppm/°C between 10 and 40 °C. Circuit architecture also guarantees physical separation of current carrying electrodes from voltage sensing ones, thus simplifying front-end sensor-interface circuitry. Emulating a resistive-sensor in the 10 kΩ–100 MΩ range, an excellent linearity is found with a relative error within ±0.1% after a preliminary calibration procedure. Further advantage is that compliance voltage can be opposite in sign of that obtained with a passive component; therefore, the system is also suitable for conditioning active sensors.

AC and DC Differential Bridge Structure Suitable for Electrochemical Interfacial Capacitance Biosensing Applications

This paper presents a capacitive differential bridge structure with both AC and DC excitation and balancing capability for low cost electrode-solution interfacial capacitance biosensing applications. The proposed series RC balancing structure offers higher sensitivity, lower susceptibility to common-mode interferences, and drift control. To evaluate the bridge performance in practice, possible effects of initial bridge imbalance due to component mismatches are investigated considering the required resolution of the balancing networks, sensitivity, and linearity. This evaluation is also a guideline to designing the balancing networks, balancing algorithm and the proceeding readout interface circuitry. The proposed series RC bridge structure is implemented along with a custom single frequency real-time amplification/filtering readout board with real-time data acquisition and sine fitting. The main specifications for the implemented structure are 8-bit detection resolution if the total expected fractional capacitance change at the interface is roughly 1%. The characterization and measurement results show the effectiveness of the proposed structure in achieving the design target. The implemented structure successfully achieves distinct detection levels for tiny total capacitance change at the electrode-solution interface, utilizing Microcystin-(Leucine-Arginine) toxin dilutions as a proof of concept.

Toward Integrated Pressure Sensors for Temperatures up to 600°C

The main objective of this study is to develop pressure-sensing systems by integrating pressure transducers with the interface circuitry in one package that can withstand harsh environments, particularly high temperatures up to 600°C. To achieve that, both pressure transducer and interface circuitry are individually required to operate and survive up to 600°C with acceptable degrees of reliability. This article reports performance evaluation of fabricated 4H-SiC Junction Field Effect Transistors along with differential pairs for use in the interface circuitry. The test results are very promising and show stable performances from 25°C up to 600°C. Moreover, design, fabrication, and early test (from 25°C up to 100°C) of an SiC-based circular diaphragm-type pressure transducer are also reported.

Towards Integrated Sensors for Environments with Temperatures up to 600 °C

The main objective is to develop sensing systems by integrating transducers such as pressure sensing elements with the interface circuitry in one package that can withstand harsh environments, particularly high temperatures up to 600 °C. To achieve that, both pressure transducer and interface circuitry are individually required to operate and survive up to 600 °C with acceptable degrees of reliability. This paper reports performance evaluation of fabricated 4H-SiC JFETs along with differential pairs for use in the interface circuitry. The test results are very promising and show stable performances from 25 °C up to 600 °C. Moreover, design, fabrication, and early test of a SiC based circular diaphragm type pressure transducer is also reported.