Patent ID: 7403020

Claim:
A method for measuring a capacitance, the method comprising: measuring a time for charging or discharging a known reference capacitance C ref and unknown stray capacitances C par based on a comparator running time t comp by t 1 =( C ref +C par )* R+t comp (1); measuring a time for charging or discharging a known capacitance to be measured C meas and unknown stray capacitances C par based on said comparator running t comp by t 2 =( C meas +C par )* R+t comp (2); measuring a time for charging or discharging stray capacitances C par based on said comparator running time t comp by t 12 =C par *R+t comp (3); determining said capacitance to be measured C meas by eliminating said stray capacitances C par as well as the comparator running time t comp according to: ( t 2 - t 12 ) ( t 1 - t 12 ) = ( ( ( C meas + C par ) * R + t comp ) - ( C par * R + t comp ) ) ( ( ( C ref + C par ) * R + t comp ) - ( C par * R + t comp ) ) = ( C meas * R ) ( C ref * R ) and accordingly C meas = C refr * ( t 2 - t 12 ) ( t 1 - t 12 ) ; and determining a sensor parameter based on said measured capacitance C meas .