A characterization method for projected capacitive touch screen panel using 3-port impedance measurement technique

The parasitic components of touch screen panels (TSPs) need to be accurately extracted and reflected in a system design to improve touch sensibility. We propose a simple but accurate method to extract the parasitic resistance (R) and capacitance (C) values of TSP modules. First, three impedance values are extracted from three successive 3-port measurements in which the impedance between two ports are measured while the other remaining port is floating. Using the proposed algorithm and the conversion matrix, the R and C mesh model of the TSP can be constructed. The concept of the proposed method is described with a simple circuit with 3 capacitors and 3 resistors. It is demonstrated that we can use the proposed method to characterize an entire network of a TSP module using the saturation characteristic of R and C below a certain frequency. We achieved the worst accuracy of 88% in resistance and 82.3% in capacitance with a 4×4 emulated TSP sample.