A 1 V CMOS switched-opamp switched-capacitor pseudo-2-path filter

Switched-opamp (SO) techniques are explored to operate switched capacitor (SC) circuits in 1 V supply without on-chip voltage multiplier or low V/sub T/ devices. However, the existing SO techniques require isolating the opamp from the signal path by turning off completely either the entire opamp or its output stages after the integration phase. As a result, these SO techniques cannot be applied to realize the useful SC pseudo-N-path filters, which require an idle phase in the system for further signal processing. A modified SO technique implements an additional switchable opamp in parallel with the original switchable opamp but working in an alternative clock phase. As such, for every clock phase, there exists an opamp that is fully functional in the SC system. With the two switchable opamps both realized in a two-stage approach, it is sufficient to turn off only the output stages to isolate the signal path. The two switchable opamps are further combined to realize a single two-switchable-output-pair opamp to save power and area and to minimize the mismatch. To demonstrate the idea, a 1 V fully differential two-switchable-output-pair opamp is realized in a 0.5 /spl mu/m CMOS process with nMOS and nMOS threshold voltages 0.66 V and /spl sim/0.85 V respectively.