Patent ID: 7323879

Claim:
A method of measuring at least two capacitor pairs, wherein each of the capacitor pairs comprises at least a first capacitor and a second capacitor, the method comprising: providing a first switch to each capacitor pair respectively, each first switch having a first terminal and a second terminal, wherein the first terminal of each first switch is connected to a terminal of the first capacitor of the corresponding capacitor pair, and the second terminal of each first switch is connected to a first pad respectively; providing a second switch to each capacitor pair respectively, each second switch having a first terminal and a second terminal, wherein the first terminal of each second switch is connected to a terminal of the second capacitor of the corresponding capacitor pair, and the second terminal of each second switch is connected to a second pad respectively; providing a third switch to each capacitor pair respectively, each third switch having a first terminal and a second terminal, wherein the first terminal of each third switch is connected to another terminal of the first capacitor and another terminal of the second capacitor of the corresponding capacitor pair; and providing a P-type transistor, the P-type transistor having a gate, a drain and source, wherein the gate of the P-type transistor is connected to the second terminal of each third switch the drain of the P-type transistor is connected to a third pad, and the source of the P-type transistor is connected to a fourth pad; wherein a capacitance of one of the first capacitors, a capacitance of one of the second capacitors, or a ratio of a difference between the capacitance of the one of the first capacitors and the capacitance of the one of the second capacitors to an average of the capacitance of the one of the first capacitors and the capacitance of the one of the second capacitors is measured via the first pad, the second pad, the third pad and the fourth pad.