Digital technique for precise measurement of variable capacitance

A sensor system comprising a sensor capacitor, the capacitance of which varies with a parameter to be sensed, the system further comprising:

• means for isolating a definite amount of charge on a node electrically connected to the sensing capacitor;
• means for modifying the distribution of said definite charge on the node by modifying at least a voltage applied to the sensing capacitor;
• a detector for determining change in voltage on the node;
• and
• calibration means connected to the detector for storing a calibration signal indicative of a change in voltage on the node, which change results from other than change in capacitance of the sensing capacitor, and for correcting the determined change in voltage based on the calibration signal.

A sensor system comprising a sensing capacitor, the capacitance of which varies with a parameter to be sensed, the system further comprising:

• a node electrically connected to the sensing capacitor;
• a reference capacitor connected to the node;
• a comparator for sensing the voltage on the node;
• a switch in parallel with the comparator for isolating a definite amount of charge on the node;
• means for modifying the distribution of said definite charge on the node by modifying voltages applied to the sensing capacitor and reference capacitor;
• a coupling capacitor connected to the node;
• digital successive approximation means for receiving an output from the comparator and applying a feedback signal through the coupling capacitor to null and thus determine a change in voltage on the node resulting from the modified distribution of charge;
• and
• calibration means connected to the successive approximation means for storing a calibration signal indicative of a change in voltage on the node, which change results from other than change in capacitance of the sensing capacitor, to correct the determined change in voltage.

The method of sensing a parameter which results in change in capacitance of at least one sensing capacitor comprising:

• isolating a charge on a node electrically connected to the sensing capacitor;
• modifying the distribution of said charge on the node by modifying at least a voltage applied to the sensing capacitor;
• and
• determining change in voltage resulting from the modified distribution of charge by comparing in a comparator the voltage on the node to a reference and, responsive to an output from the comparator, performing successive approximations to generate a feedback signal applied to an input to the comparator.

A method of sensing a parameter which results in change in capacitance of at least one sensing capacitor comprising:

• isolating a charge, on a node electrically connected to the sensing capacitor;
• modifying the distribution of said charge on the node by modifying at least a voltage applied to the sensing capacitors;
• determining the change in voltage on the node;
• and
• correcting the determined change in voltage based on a calibration signal indicative of a change in the voltage on the anode which results from other than change in capacitance of the sensing capacitor.