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In this paper, a low power CMOS integrated capacitance-to-frequency converter with on-chip temperature sensor and fully digital output designed for humidity sensor interface is newly proposed, which is manufactured by using a standard 0.35 Â¿m 2P/3M CMOS process. This ROIC (readout IC) consists of on-chip PTAT temperature sensing circuit, low power temperature-to-frequency converter, low power C-F converter, digital compensation circuit, OTP memory, control logic and serial I/O circuits. Capacitance interfacing capability of the circuit is ultra-wide, up to 350 pF, which is higher than previously reported works. At a clock speed of 1 MHz, the average power dissipation is as low as about 150 Â¿W with one humidity measurement per one second, which is lower than ever reported works. And the minimum detectable capacitance is as low as about 4.5 fF.