A tunable, video-frequency, low-power, single-amplifier biquadratic filter in CMOS

IIn this paper, a tunable single-amplifier biquadratic lowpass filter is presented. It consists of one balanced low-gain current amplifier and a second-order MOSFET-C feedback network. The filter was integrated in a double-poly 0.6 pm CMOS process and operates from a 3.3 V power supply. The pole frequency is tunable from 15.2 to 17.2 MHz, the pole Q is 3, the spurious-free dynamic range is at least 60dB, and the filter consumes only 2.4mW per pole. Furthermore, the active area used per pole is only 0.06 mm’. The filter is well suited for low-power video-frequency applications, and demonstrates that the MOSFET-C filter technique can be applied successfully to filters other than those based on integrator-connected topologies. When desi gning a video-frequency fi lter for minimum power consumption, it seems reasonable to use as few active components as possible. Good candidates for low-power filters are therefore single-amplifier active RC filters, which produce two or more poles with an RC network in the feedback path of an amplifier. Using a single-amplifier biquadratic lowpass filter (lowpass SAB) as an illustrative example, we demonstrate how such filters can be implemented in CMOS, and also give qualitative design rules for minimizing the power consumption of such filters. ;