A Parasitic-Insensitive Charge Transfer Circuit for Capacitive Sensing using Active Output Voltage Feedback Technique

Abstract This paper introduces a new parasitic-insensitive charge transfer circuit using active output voltage feedback. The proposed parasitic-insensitive charge transfer circuit uses a passive charge transfer circuit for maximum output voltage dynamic range. A feedback loop between the transfer and output nodes is formed using a unity-gain opamp to make the two nodes’ potentials same, which prevents the charges stored at parasitic capacitors from transferring to the output. With those two characteristics, the proposed parasitic-insensitive charge transfer circuit offers full supply output voltage dynamic range for capacitive sensing without degradation of the linearity from the effects of parasitic components. The proposed parasitic-insensitive charge transfer circuit’s performances were simulated with standard 0.35μm CMOS technology and compared with those of a passive charge transfer circuit. It can be concluded from the results that the proposed parasitic-insensitive charge transfer circuit can be effectively used as a capacitive sensor with improved touch sensitivity for wider range of touch devices which include larger parasitic components.