Voltage-to-frequency converter with high sensitivity using all-MOS voltage window comparator

A high-sensitivity voltage-to-frequency converter (VFC) using an all-MOS voltage window comparator is presented in this work. The circuit is composed of one voltage-to-current converter, one charge and discharge circuit, and one all-MOS voltage window comparator. The input voltage is converted into a current which in turn triggers the charge and discharge circuit, where a built-in capacitor is driven. The voltage window comparator monitors the variated voltage on the capacitor and generate an oscillated output of which the vibration frequency is linearly dependent to the input voltage. In this way, the worst-case linear range of the output frequency of the proposed VFC is 0-55.40 MHz verified by simulations given a 0-0.9 V input range. The physical measurement of the proposed VFC shows a 0-52.95 MHz output frequency given a 0-0.9 V input range. The error in linearity is better than 8.5% while the power dissipation is merely 0.218 mW.