Methods and systems for detecting a capacitance using sigma-delta measurement techniques

A system for determining a capacitance value of a measurable capacitance, the system comprising:

• an integrating capacitance configured to store charge received from the measurable capacitance;
• a charge changing circuit coupled to the integrating capacitance, the charge changing circuit including an array of delta capacitances;
• and
• a controller configured to determine the capacitance value by repeatedly applying a predetermined voltage to the measurable capacitance, repeatedly sharing charge between the measurable capacitance and the integrating capacitance to accumulate charge on the integrating capacitance, repeatedly measuring a voltage on the integrating capacitance using a quantizer of the controller and generating quantized values responsive to the repeated measurings, repeatedly changing charge on the integrating capacitance by a quantized amount of charge using a selected portion of the array of delta capacitance in the charge changing circuit, the selected portion of the array based on the quantized values, and determining the capacitance value of the measurable capacitance by digitally filtering the quantized values.

A method for measuring a measurable capacitance, the method comprising the steps of:

• applying a voltage to the measurable capacitance using a first switch;
• allowing the measurable capacitance to share charge with an integrating capacitance;
• changing a charge on the integrating capacitance by a quantized amount of charge if the voltage on the integrating capacitance is past a threshold of a quantizer, the quantized amount of charge determined at least in part as a function of a quantized value outputted by the quantizer;
• repeating each of the applying step, the allowing step, and the changing step at least once, wherein the repeating maintains the voltage on the integrating capacitance near the threshold of the quantizer;
• and
• filtering the quantized values outputted by the quantizer to provide a measure of the measurable capacitance.