A switched-capacitor digital capacitance meter

A digital capacitance meter has been developed based on the switched-capacitor cyclic analog-to-digital (A/D) converter. It consists of the analog arithmetic and sample/hold (S/H) circuits. The arithmetic circuit first samples the capacitance to be measured in a form of its proportional voltage. This voltage is then converted into a binary number by the A/D converter. The whole operation is insensitive to parasitic capacitances, offset voltages of op amps, and the capacitance mismatch involved in the circuit. Therefore, the proposed meter permits an accurate capacitance measurement. Error analysis shows that 12-bit accuracy can be expected by realizing the meter in an IC form. A prototype meter built using discrete components and examples of measurement are also given.