A sixth-order low-pass $g_m$-C filter with a very wide tuning range ($f_c$ = 100 Hz to 10 MHz) is presented. The wide tuning range has been achieved without using switchable components or programmable building blocks. A single stage folded-cascode transconductor is employed to implement the proposed filter. A modified biquadratic topology is introduced to improve the linearity performance of the filter over its tuning range. The power consumption of the filter scales linearly with the cutoff frequency (60 pW/Hz/pole). Implemented in 0.18 $\mu$m CMOS technology, the filter exhibits a relatively constant noise and linearity performance over its entire tuning range and occupies 0.16 mm$^2$ (0.027 mm$^2$/pole) silicon area.