Patent ID: 7304483
Filing Date: 2007-12-04
Classification: G01D,G01P,H03M

Abstract:
1. A differential capacitor one terminal capacitor interface circuit for sensing the capacitance of first and second capacitors comprising: a differential integrating amplifier having first and second summing nodes and an input common mode voltage; and a switching circuit for charging a first capacitor of said differential one terminal capacitor to a first voltage level and a second capacitor of said differential one terminal capacitor to a second voltage level in a first phase, in a second phase connecting said first capacitor to said first summing node and said second capacitor to said second summing node of said amplifier to provide first and second output changes substantially representative of the difference between said first and second voltage levels and said input common mode voltage, in a third phase charging said first capacitor to said second voltage level and said second capacitor to said first voltage level, and in a fourth phase connecting said first capacitor to said second summing node and said second capacitor to said first summing node of said amplifier to provide third and fourth output changes substantially representative of the difference between said first and second voltage levels and said input common mode voltage, the combined first, second, third and fourth changes representing the capacitance of said first and second capacitors substantially independent of said input common mode voltage.