A Switched-Capacitor Low-Pass Filter with Multiple-Channel Double-DSB OP Amplifiers

Wideband filters employing OP Amplifiers (OP Amps) are required in sensing devices. A fourth-order Switched-Capacitor Low-Pass Filter (SC LPF) with multiple-channel Double Dynamic Switching Bias Folded-Cascode OP Amps (DDSB OP Amps) consisting of $1-2 \mu \mathrm{m}$ multiple channel-length MOSFETs and short-channel sampling/CMOS switches capable of processing video signals, which enables a low gain in a passband and a high attenuation in a wide stop-band, was proposed. The DDSB OP Amp enables a high speed filtering operation while keeping a low power dissipation and low distortion. The switches with a $1.5\ \mu \mathrm{m}$ channel length were optimized to greatly reduce their feed-through. Through SPICE simulations, the DDSB SC LPF showed the practically usable attenuation performance of below −41 dB in the stop-band, nearly 9 dB lower than that in the conventional $2.5\ \mu \mathrm{m}$-channel SC LPF, without causing a marked passband gain leap. The simulation results confirmed that the DDSB SC LPF is useful for achieving a wide stop-band with a practically usable attenuation maintaining low distortion and low power consumption due to a high speed settling operation of the DDSB OP Amp and the great decrease of feed-through in the switches.