A 1.8–65 fJ/Conv.-Step 64-dB SNDR Continuous-Time Level Crossing ADC Exploiting Dynamic Self-Biasing Comparators

This work presents a power-efficient level crossing (LC) ADC designed to digitize sparse signals. It uses dynamically self-biased comparators, which require minimal current when the input voltage is far from a decision threshold. It also uses a DAC architecture which avoids the signal attenuation commonly present in prior LC ADC works, improving the achievable SNDR. The prototype is designed and implemented in a 65-nm CMOS technology, and occupies an area of 0.0045 mm $^{2}$ . In a 20 kHz bandwidth, the LC-ADC achieves a 64 dB SNDR. Thanks to the proposed techniques a power efficiency of up to 1.8 fJ/conv.-step is achieved for sinusoidal inputs. For sparse biopotential signals, a FoM $_{\text{W}}$ as low as 0.9 fJ/conv.-step was measured. This makes the prototype interesting for e.g., biomedical applications that make use of spike-based processing.