Signal conditioning for capacitive sensors with field programmable analog arrays

The applicability of FPAAs to the signal conditioning involved in interfacing elementary sensors may be non-trivial since FPAAs are generally targeted at processing voltage-mode signals only. Here, we consider the usage of a popular switched-time FPAA to capacitive sensing, with particular regard to the problem of annihilating the influence of parasitic reactance which may easily exceed the capacitance variations to be detected. It is shown that a proper exploitation of the FPAA signal conditioning primitives can make them up to the task of detecting capacitance variations below the hundred fF threshold. A sample application is illustrated as a proof of concept.