1. An apparatus, comprising: a first capacitor; and a capacitance sensing circuit comprising a second capacitor selectively connectable to the first capacitor, wherein the capacitance sensing circuit is configured to transfer charge linearly from the first capacitor to the second capacitor for a plurality of cycles and to determine a value of the first capacitor; a buffer amplifier comprising an input terminal and an output terminal, wherein the input terminal is coupled to the second capacitor; and an adder to add an offset voltage to an output of the buffer amplifier, the adder comprising a first terminal and a second terminal, wherein the first terminal is coupled to the output terminal of the buffer amplifier and wherein the second terminal is selectively connectable to the first capacitor.