A 177 ppm RMS Error-Integrated Interface for Time-Based Impedance Spectroscopy of Sensors

This paper presents an integrated circuit for time-based electrical impedance spectroscopy (EIS) of sensors. The circuit exploits maximum-length sequences (MLS) in order to perform a broadband excitation of the sensors under test. Therefore, the measured time-domain EIS is obtained by cross-correlating the input with the output of the analog front end (AFE). Unlike the conventional digital approach, the cross-correlation operation is performed in the analog domain. This leads to a lower RMS error in the measured time-domain EIS since the signal processing is not affected by the quantization noise of the analog-to-digital converter (ADC). It also relaxes the sampling frequency of the ADC leading, along with the lack of random access memory (RAM) usage, to a reduced circuit complexity. Theoretical concepts about the circuit’s design and operation are presented, with an emphasis on the thermal noise phenomenon. The simulated performances are shown by testing a sensor’s equivalent model composed of a 50 kΩ resistor in parallel with a 100 (Formula presented.) (Formula presented.) capacitor. A time-based EIS output of 255 points was obtained with a maximum tested frequency of 500 (Formula presented.) (Formula presented.) and a simulated RMS error of 0.0177% (or 177 ppm)

Imepdance Sensing Techniques for Integrated Circuits Sensor Applications

Impedance measurements are increasingly demanded in modern CMOS sensing systems as impedance is the most common electrical signal obtained from sensors, delivering physical, chemical and biomedical quantity changes. Impedance sensing for wide interested frequency, broad dynamic range, and various sensor interfaces has numerous challenges, especially targeted in CMOS miniaturization with power and area limitation. In this thesis, first, a low power impedance-based cytometer architecture for cell analysis applications is presented. Fabricated in 0.18μm CMOS process with 6pArms input-referred noise over 200Hz bandwidth at 0.5 MHz modulation frequency, the impedance sensor demonstrates in detecting 3μm diameter particles. Secondly, using impedance sensing technique, a low-power RC oscillator based on IQ-balanced impedance sensing FLL is designed and demonstrated, achieving 25.4ppm/°C across temperature variation and 0.27%/V across supply variation at 650kHz output frequency

Advances in High-Resolution Microscale Impedance Sensors

Sensors based on impedance transduction have been well consolidated in the industry for decades. Today, the downscaling of the size of sensing elements to micrometric and submicrometric dimensions is enabled by the diffusion of lithographic processes and fostered by the convergence of complementary disciplines such as microelectronics, photonics, biology, electrochemistry, and material science, all focusing on energy and information manipulation at the micro- and nanoscale. Although such a miniaturization trend is pivotal in supporting the pervasiveness of sensors (in the context of mass deployment paradigms such as smart city, home and body monitoring networks, and Internet of Things), it also presents new challenges for the detection electronics, reaching the zeptoFarad domain. In this tutorial review, a selection of examples is illustrated with the purpose of distilling key indications and guidelines for the design of high-resolution impedance readout circuits and sensors. The applications span from biological cells to inertial and ultrasonic MEMS sensors, environmental monitoring, and integrated photonics