Patent ID: 9110113
Filing Date: 2015-08-18
Classification: G01D,G01R

Abstract:
1. A method of measuring a physical parameter by means of an electronic interface circuit connected to a capacitive sensor, which includes at least first and second differential-connected capacitors, whose common electrode is capable of moving relative to each fixed electrode of the two capacitors to modify the capacitive value of each capacitor when the physical parameter is measured, said electronic circuit including a charge transfer amplifier, which is connected to the common electrode, a logic unit connected to the amplifier output for digital processing of the data supplied by the amplifier and for supplying at least one digital measuring signal, a digital-analogue converter for supplying a measuring voltage, which is defined on the basis of conversion of at least a first binary word or a second binary word relating to the digital measuring signal, a switching unit for alternately supplying each fixed electrode of the two capacitors with the measuring voltage and a regulated voltage or a low voltage from a supply voltage source, the method including, in each successive measuring cycle, steps consisting in: a) in a first phase, biasing the fixed electrode of the first capacitor via the switching unit with a first measuring voltage supplied by the digital-analogue converter, and the fixed electrode of the second capacitor with the low voltage for defined positive biasing of the electrodes, or the regulated voltage for defined negative biasing of the electrodes, the first measuring voltage being defined on the basis of the first binary word relating to the digital measuring signal from a preceding cycle or an initial binary reference word supplied by the logic unit, and according to a reference voltage generated in the digital-analogue converter for positive biasing, or according to an inverted reference voltage generated in the digital-analogue converter for negative biasing, the inverted reference voltage corresponding to the difference between the regulated voltage and the reference voltage, which is set at a value higher than half of the regulated voltage, b) in a second phase, biasing the fixed electrode of the second capacitor via the switching unit with a second measuring voltage supplied by the digital-analogue converter and the fixed electrode of the first capacitor with the low voltage or the regulated voltage, the second measuring voltage being defined on the basis of the second binary word relating to the digital measuring signal or the initial reference binary signal supplied by the logic unit, and according to the reference voltage, if positive biasing is selected in the first phase, or according to the inverted reference voltage, if negative biasing is selected in the first phase, the second binary word being defined in the logic unit as the reverse of the first binary word relative to the reference binary word, and c) incrementing or decrementing by a determined step in the logic unit, the digital measuring signal according to the increase or decrease in charge injection quantity across the moving electrode on the basis of the voltage variation across the fixed electrode of the first capacitor and the voltage variation across the fixed electrode of the second capacitor at the change from the first phase to the second phase.