A 99.5dB-SNR Self-Timed Highly-Flexible Capacitance-to-Digital Converter With Fast Zoom Technique

This work presents the first reported high-precision self-timed capacitance-to-digital converter (CDC) based on a Floating-Inverter Amplifier (FIA), operating without the need for an external oversampling clock. An adjustable multi-bit quantizer enables switching between two quantization noise modes, supporting accurate conversion across a wide range of input capacitances. A zoom-based coarse quantization using a floating ring oscillator (FRO) provides a fast, low-power estimate of the input capacitance. To improve energy efficiency, a power-aware FIA array is employed in the first integrator, with the number of active FIAs dynamically configured based on the coarse quantization result. Fabricated in 65-nm CMOS and operating at 1.2 V, the prototype achieves 94.8 aF resolution under 25.3 pF input with 10.4 μW power, yielding a Schreier FoM of 174.9 dB.