This work focuses on the improvement of a capacitance-to-digital converter (CDC) based on iterative discharging. Time-domain interpolation is applied on the CDC. With such technology, a high-resolution CDC can be achieved while its fully digital feature can be kept. The proposed CDC achieves a resolution of 2.8fF and a FoM of 1.32pJ/step at 5.5pF capacitance. A MEMS capacitive pressure sensor has been bonded to the chip and the output with varying capacitance has been checked.