The use of resonant circuits as gain boots in capacitive sensors

The historical development of mankind has continued with the emergence of industrial revolutions and the development of technology. These developments are still sustainable with the development of technology. While these new technologies take place in every aspect of human life, they have helped the development of sensor technology. As a result of the inclusion of this technology in human life, the efficiency and reliability of the sensors are also extremely important. This situation causes smart sensors to take place in quite different areas of our lives. Capacitive sensors are used extensively in industrial, medical, automotive and many other application areas. The reason why they are used at this density is that the capacitive sensors are related to the signal processing technique. In the case of signal processing technique, resonance circuits have an important place to increase the measuring range and sensitivity of capacitive sensors. As a result of the use of resonant circuits that connect the output signal of a capacitive sensor to a coil, the signal is strengthened and the sensitivity of the signal is increased. Increasing the measuring range of the sensors is also provided by resonant circuits. The measuring range of the sensors depends on the sensor capacitance and is limited. Thus, gain can be achieved by expanding the measuring range by using resonant circuits. Since the resonant frequency is dependent on the capacitance value of the sensor, the circuit must be readjusted in case the capacitance value of the sensor or sensor is changed. Circuits behave like short-circuit in series resonance and open-circuit in parallel resonance. Since the coil and capacitor circuit connected in series act as a short circuit, the active circuit cannot produce gain. There are several problems in using very low capacitors to read capacitive electrodes with low capacitance values. These problems are usually caused by the printed circuit board, soldering and component. In this thesis; A circuit design has been made that will increase the gain in the capacitive sensor of the resonant circuit that can be used in the industry. The purpose of this design is to gain gain by using different capacitors in resonant circuits. In the circuit designed for this situation, a low value capacitor is used and the capacitor located at the opamp input is used as the electrode capacitor. In order to obtain resonance gain from the designed circuit, other capacitors used in the circuit were chosen ten times the size of the capacitor at the circuit input. Four types of circuits are designed for gain. While the first two designs are not preferred because they are not useful for gain increase, the third type circuit is not preferred because it oscillates. The fourth type circuit has been studied since it gives the expected gain increase at the desired level in all tests. The designed circuit is a mixed circuit filter and includes capacitor, coil, resistor and opanmp. High frequency pass LF351 opamp is used for opamp.