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A 0.55 V supply voltage fourth-order low-pass continuous-time filter is presented. The low-voltage operating point is achieved by an improved bias circuit that uses different opamp input and output common-mode voltages. The fourth-order filter architecture is composed by two active- Gm-RC biquadratic cells, which use a single opamp per-cell with a unity-gain-bandwidth comparable to the filter cut-off frequency. The - 3 dB filter frequency is 12 MHz and this is higher than any other low-voltage continuous-time filter cut-off frequency. The -3 dB frequency can be adjusted by means of a digitally-controlled capacitance array. In a standard 0.13 mum CMOS technology with VTHN ap 0.25 V and VTHP ap 0.3 V, the filter operates with a supply voltage as low as 0.55 V. The filter (total area=0.47 mm2) consumes 3.4 mW. A 8 dBm-in-band IIP3 and a 13.3 dBm-out-of-band IIP3 demonstrate the validity of the proposal.