Switched-Mode Operational Amplifiers and Their Application to Continuous-Time Filters in Nanoscale CMOS

We introduce a new class of feedback amplifiers, called switched-mode operational amplifiers (SMOAs) that address voltage-swing limitations of classical feedback amplifiers in scaled CMOS technologies. By exploiting the increased timing resolution available in scaled CMOS, SMOAs encode analog signal information in the time domain and provide near-rail-to-rail output-signal swing, high output-stage efficiency and better linearity. A 4th-order, 70 MHz continuous-time active-RC Butterworth filter is presented in 65 nm CMOS to demonstrate the advantages of SMOAs. The filter consumes 25.4 mW from a 0.6 V supply and achieves 55.8 dB peak SNDR while operating at a full-scale of 873 mV
$ _{\rm ppd}$
. Thanks to SMOAs, the full-scale (73% of the 0.6 V supply voltage) and the bandwidth are respectively, a 2.5
$\times $
and 6.2
$\times $
improvement over other state-of-the-art low-voltage filters.