Differential-mode/common-mode feedforward transconductor for low-voltage Gm-C filters

Low-voltage transconductor circuits suitable for G.-C filter are proposed. The proposed structures were developed from a well-known Nauta's inverter-type class-AB transconductor to improve common-mode rejection without sacrificing extra power consumption. The improvement relies on feed-forwarding both common-mode and differential mode signals, making it power efficient because additionally power has not be wasted only for suppressing common-mode signal. The concept has been confirmed by comparison with simulation on 1-V 5(th)-order Chebyshev lowpass filters constructed from the proposed transconductors in 0.18 mu m CMOS process. The proposed transconductors offer improvement on common-mode rejection by 50dB with 20% less current consumption while still preserving dynamic range.