In the IoT era, numerous sensors need to be deployed at the edge with a constrain on energy consumption. The capacitive sensors-based nodes are promising candidates for low-power operation as they do not consume static power. These sensors mostly require a high-resolution capacitance-to-digital (CDC) converter. These sensor nodes must withstand to harsh environment, the sensor interface circuits must adapt to large parasitic (or base capacitance) variations without significant degradation in resolution. The parasitic capacitance at the input node of the CDCs lowers the system bandwidth as well as degrades the noise performance of the system. Thus, a high-resolution CDC which can sustain large input parasitic capacitance is needed. A 12-bit calibration DAC is used for offset cancellation of the base capacitance of the sensor. A very high-gain (~140dB) low-noise OTA is designed to obtain high settling accuracy in the charge transfer phase. An oversampling SAR ADC is used which employs, data-weighted averaging (DWA), mismatch error shaping (MES), and quantization noise shaping to achieve high accuracy. The CDC has a dynamic range of 8pF and base capacitance compensation of up to 200pF. The CDS is fabricated in UMC 180nm technology and achieves an SNR of 104 dB with an OSR of 32.