A 0.026mm2 capacitance-to-digital converter for biotelemetry applications using a charge redistribution technique

This paper proposes a direct capacitance-to-digital converter (CDC) for biotelemetry applications. The proposed circuit is based on a charge redistribution technique using a capacitive sensor and a ranging capacitor array. The circuit does not require accurate reference voltages, so it is robust for fluctuation of supply voltage. Output-code range can be dynamically zoomed in arbitrary capacitance range of sensor output by using the ranging capacitor array. An 8-bit converter with an active area of 0.026 mm2, consuming 0.9 nJ per sample, is demonstrated. The proposed circuit maintains its performance even in the condition of 28% fluctuations in supply voltage. Measurement results of the readout circuit are also demonstrated, which shows that the proposed circuit can work well in the presence of large parasitic capacitances.