Investigation of electronic circuit designs for capacitance measurements

Capacitive sensors with many uses such as measurements of flow, pressure, liquid level, distance, thickness, shaft angle, linear position, acceleration, inclination are preferred because they can measure different materials, work contactless and are resistant to wear. Besides the structure of the sensor itself, one of the most important factors that determine the working performance and effectiveness of capacitive sensors is the design of the electronic circuits that process the information from the sensor. The subject of this thesis is the investigation of these electronic circuit structures, which generally consist of the front-end circuit that accepts the signal from capacitive measurement and a signal processing circuit unit. As the front-end circuit topology, the transimpedance amplifiers, which are mostly preferred in practice, were chosen. Transimpedance amplifiers based on the principle of converting current data coming from the capacitance to voltage and outputting it to the next signal processing circuit unit have been analyzed for many performance aspects. In addition, an investigation including simulation studies and numerical calculations in the computer environment is presented in this thesis to help design more optimized, stable, and low noise front-end circuits. Both analog and digital demodulation methods, which are the parts of signal processing circuits in the general structure of capacitive measurement, are examined in this thesis. With the hybrid system designed for lossy capacitance measurements, a drive signal and reference signals are generated by digital methods; demodulation process was performed with analog lock-in amplifiers. Theoretical, analytical, and numerical analyzes were performed for a digital signal processing platform using digital lock-in amplifiers. Also, capacitance measurement performance implemented in the digital platform was examined.