This paper reports a sensing principle and FPGA design of a capacitive touch pad/interface where the sensing pad is connected to the I/O pin via an external resistor. The circuit transforms the change in pad capacitance into voltage amplitude during charging, discharging and sharing phases. By using multiple pins and resistors, a multipad system is achieved. The sensing algorithm is implemented in VHDL code. The read-out cycle is parallel and short, what results in a high noise immunity in low frequency range. The silicon/hardware requirements are minimal. The interface can be easily embedded into a system-on-chip and used for human-machine, bio-chemical and mechanical sensor interfacing.
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