A modular transconductance reduction technique for very low-frequency Gm-C filters

This paper presents a modular technique for transconductance reduction of a sub-threshold transconductor. This technique employs an ordinary differential pair circuit as a module to build a linear attenuator and to be the main transconductor. By applying the linear attenuation, the input linear range expansion and transconductance reduction are simultaneously achieved by sacrificing around 33% of its dynamic range compared to the ordinary differential pair transconductor. A 2^nd-order Gm-C low-pass as an application of the proposed transconductor has been designed and simulated using 0.18-µm AMS technology. Compared to existing designs, post-layout simulation results show that, with a smaller active area (including bias circuitry, transconductors and capacitors), this design provides greater dynamic range, wider tuning range and lower power consumption.