Many industrial applications require high-resolution ADCs whose low-frequency performance is important. CTDSMs are attractive due to their implicit antialiasing and resistive inputs. However, their low-frequency precision is degraded by flicker noise. The loop filter of such modulators is usually realized using active-RC techniques, and the CTDSMs' 1/f noise is mostly due to the input stage of the 1st OTA. Using large input devices to reduce 1/f noise greatly increases area occupied by the input stage, and degrades linearity due to the increased parasitic capacitance at the OTA virtual ground.
['Sujith Billa', 'Amrith Sukumaran', 'Shanthi Pavan']
15.4 A 280µW 24kHz-BW 98.5dB-SNDR chopped single-bit CT ΔΣM achieving <10Hz 1/f noise corner without chopping artifacts