A 14-Bit 30-MS/s 38-mW SAR ADC Using Noise Filter Gear Shifting

We present a successive approximation register analog-to-digital converter (ADC) that employs a comparator with time-varying noise performance, realized by changing the integration time of a G
_m
-C preamplifier. This approach allows us to relax precision and enhance speed during noncritical decisions, leading to an aggregate speed-up of 22% compared to a conventional design. The ADC operates at 30 MS/s, achieves a peak signal-to-noise and distortion ratio of 77.2 dB, and consumes 38 mW from 1.2 V/2.5 V supplies, corresponding to a Schreier FOM of 163.1 dB (161.6 dB at Nyquist). The proof-of-concept converter is implemented in a 40-nm LP complementary metal-oxide semiconductor process and occupies 0.24 mm
²
.