Linear transconductor with rail-to-rail input swing for very large time constant applications

A new approach to obtain very-small transconductance systems, i.e. large value equivalent resistors, on standard CMOS technology is proposed. The transconductor is characterised by a compact topology, high current dynamic range and linearity up to rail-to-rail input swing and symmetric operation for positive and negative currents. Experimental results show transconductance values as small as 3 pA/V (equivalent to 330 GΩ) with fA working capability, ideal in various applications such as high sensitivity integrators or lowpass filters with sub-Hz cutoff frequencies.