A New Capacitance-to-Frequency Converter for On-Chip Capacitance Measurement and Calibration in CMOS Technology

In this paper, a new capacitance-to-frequency converter using a charge-based capacitance measurement (CBCM) circuit is proposed for on-chip capacitance measurement and calibration. As compared to conventional capacitor measurement circuits, the proposed technique is able to represent the capacitance in term of the frequency so that the variations can be easily handled in measurement or calibration circuits. Due to its simplicity, the proposed technique is able to achieve high accuracy and flexibility with small silicon area. Designed using standard 180 nm CMOS technology, the core circuit occupies less than 50 mu m x 50 mu m while consuming less than 60 mu W at an input frequency of 10 MHz. Post-layout simulation shows that the circuit exhibits less than 3 % measurement errors for fF to pF capacitances while the functionality has been significantly improved.