An 8025-MHz 7th-order Bessel filter built with single-amplifier biquadratic MOSFET-C filters

摘要

This paper is a practical guide to building higher-order filters with single-amplifier biquadratic MOSFET-C sections Theory, design guidelines, and measurement electronics are discussed by example of a 7th-order current-mode filter built to the specifications of a 1 × DVD read channel filter. The 7th-order filter was fabricated with the double-poly 0.6-micron CMOS process by AMS. It is continuously tunable from 4.5 MHz up to 10 MHz, covers a chip area of only 0.24 mm{sup}2, and consumes 49 mW from a 3.3-V supply. The SNR at -40 dB of harmonic distortion is between 48 dB and 50 dB over the whole tuning range. The comparatively low power consumption and chip area could be achieved by using single-amplifier biquadratic building blocks implemented as MOSFET-C filters and generating the control voltage of the MOSFET resistors with an on-chip charge pump. The technique is, with a small loss of SNR, also applicable on fabrication processes where only gate-oxide capacitors are available.