Temperature stabilised tunable Gm-C filter for very low frequencies

In this work, a continuous time low pass filter, with sub-Hz upper band limit, is presented. The circuit is based on a Gm-C approach, where the transconductance is stabilised against temperature variations over a wide temperature range (0-80°C) using a DC feedback loop applied to a dummy transconductor (master). The very low transconductance values required to obtain low frequency singularities are achieved by means of multistage current division. A first order low pass prototype filter has been fabricated by means of the 1-μm BCD3S process of STMicroelectronics