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

A modified switched-opamp technique is proposed to enable switched-capacitor (SC) circuits to operate at 1 V with the opamp fully functional in all phases. A 1-V fully differential two-switchable-output-pair operational amplifier has been designed for the proposed technique, which is then employed in a 1-V fully differential SC pseudo-2-path filter. Implemented in a standard single-poly triple-metal 0.5-μm CMOS process, the filter achieves a sixth-order bandpass response centered at 75 kHz with a quality factor of 45. Capacitors formed with polysilicon and highly doped n-well (cap-well option) regions are used to achieve both good linearity and small chip area. At 1-V supply, the filter obtains an output swing of 1.2 V_pp and a dynamic range of 54 dB while dissipating 310 μW and occupying a chip area of 0.8 mm².