A widely tunable CMOS Gm-C filter with a negative source degeneration resistor transconductor

Abstract

We propose a new negative source degeneration resistor (NSDR) transconductor to achieve a wide continuous-tuning range gm-C filter applicable for IEEE802.11a/b/g wireless-LANs and W-CDMA. The NSDR-transconductor using a source degeneration resistor and positive feedback differential amplifier that acts as a negative resistor. This configuration enables the equivalent source degeneration resistance to be drastically increased without degrading linearity, thus resulting in a wide gm tuning. A 6th -order elliptic low-pass filter using this NSDR-transconductor exhibits a cutoff frequency (f/sub c/) tuning range of 1.5-12MHz, which is two times wider than that of conventional filters. Additionally, we introduce a new figure of merit (FoM) evaluating the basic filter performance. This filter shows 0.35 fj (FoM) in the IEEE802.11a mode, which is, to our best knowledge, the best value in the CMOS channel-select filters.