A current tuneable fully differential transconductor dedicated for filtering applications

In this paper, a current tuneable fully differential transconductor cell (gm-C) dedicated for filtering applications is proposed. The architecture used for this new cell is based on a cross-coupled differential pairs input stage with folded cascode output stage in order to realise a high DC-gain integrator. This approach is preferred to the use of the negative resistance load (NRL) approach, since it is more stable and does not require another NRL circuit tuning when the overall transconductance of the cell is modified. Realisation techniques for a gm-C high-order continuous-time filter are also discussed which allow full programmability of the centre frequency and the quality factor of the filter. Finally, a design example of a 4th-order bandpass filter is presented with 3.3 V 0.35 μm CMOS technology available through the Canadian Microelectronics Corporation (CMC).