Differential Second-Order Lowpass Filter
Original Publication Date: 1985-Apr-01
Included in the Prior Art Database: 2005-Feb-18
An analog differential signal needed a large gain before being limited. The original design amplified each side of the differential signal single endedly, thus amplifying noise and other transients as well as the desired signal. Common mode rejection (CMR) was necessary to eliminate problems caused by the noise amplification. Only two operational amplifiers (op amps) were available to obtain the proper gain and transfer function. A standard second-order lowpass infinite gain multiple-feedback Butterworth filter was required in the design to give adequate gain and proper channel response. A basic instrumentation amplifier was used as a model for the filter, since the amplifier uses two op amps and has a differential input and output and CMR.