Applicability of Field Programmable Analog Arrays to Capacitive Sensing in the Sub-pF Range

Abstract

FPAAs have recently been introduced to reduce analog design costs and bridge the gap between ASICs and circuits made of standard-parts. Here, their applicability to capacitive sensing is investigated. Switched-mode FPAAs were not originally introduced for the readout of elementary sensors or their desensitization from parasitics. Nonetheless, we show that specific techniques can make them up to the task of reading capacitance variations in the tens fF range. We also show that FPAA sensor interfaces can achieve automatic, trimmer-free calibration by FPAA reconfiguration. We conclude by illustrating a sample application as a proof-of-concept of the proposed techniques.

Low noise accelerometer microsystem with highly configurable capacitive interface

“…The capacitive sensing method, however, suffers from severe parasitic capacitance problems [3,4]. For example, in surface micromachined polysilicon microsensors, the nominal sensing capacitance is typically on the order of several pF.…”