Ultra-low frequency bio-medical active-RC lowpass filters

摘要

Active-RC low-pass filters based on R-0.5R ladders are implemented to provide high linear and low power design solutions for integrated biomedical applications. Among various R-αR ladders family, R-0.5R ladders provide the best low frequency selectivity characteristics. The filters exhibit ultra-low pole frequencies and occupy relatively compact silicon areas by using the R-0.5R ladders.

主权项

1. A R-0.5R ladder active-RC low pass filter with reduced pole frequencies and chip area for a high linear and low power bio-medical applications, comprising:
a first inverting input terminal; a second non-inverting input terminal; a first inverting output terminal; a second non-inverting output terminal; first and second operational amplifiers connected together in a Tow-Thomas biquadratic filter circuit; a first R-0.5R ladder circuit connected between the first non-inverting input terminal of the low-pass filter and a third inverting input terminal of the first operational amplifier; a second R-0.5R ladder circuit connected between the second inverting input terminal of the low-pass filter and a fourth non-inverting input terminal of first operational amplifier; a third R-0.5R ladder circuit connected in parallel with a first capacitor, wherein the third R-0.5R ladder circuit is connected between the third inverting input terminal and a third non-inverting output terminal of the first operational amplifier; a fourth R-0.5R ladder circuit connected in parallel with a second capacitor, wherein the fourth R-0.5R ladder is connected between the fourth non-inverting input terminal and a fourth inverting output terminal of the first operational amplifier; a fifth R-0.5R ladder circuit connected between the third non-inverting output terminal of the first operational amplifier and a fifth inverting input terminal of a second operational amplifier; a sixth R-0.5R ladder circuit connected between the fourth inverting output terminal of the first operational amplifier and a sixth non-inverting input terminal of the second operational amplifier; a seventh R-0.5R ladder circuit connected between the third inverting input terminal of the first operational amplifier and a sixth inverting output terminal of the second operational amplifier, wherein the sixth inverting output terminal is connected to the second inverting output terminal of the low-pass filter; and an eighth R-0.5R ladder circuit connected between the fourth non-inverting input terminal of the first and a fifth non-inverting input terminal of the second operational amplifier, wherein the fifth non-inverting output terminal is connected to the first non-inverting output terminal of the low-pass filter.