A current summing FIR filter can be implemented with multiple differential input stages and variable tail currents. The variable tail currents can be used to appropriately weight the present and previous digital input signals. The weighted outputs of the differential transistor pairs can be summed to...http://www.google.com.hk/patents/US7301391?utm_source=gb-gplus-share專利 US7301391 - Filtering variable offset amplifier
