We present the first demonstration of a continuous-time, fifth-order, elliptic, gm-C low-pass active filter in 0.25 mum complementary (npn + pnp) silicon-germanium (C-SiGe) heterojunction bipolar transistor (HBT) technology. This C-SiGe technology features npn SiGe HBTs with peak fT and fmax of 170 GHz and 170 GHz, respectively, as well as pnp SiGe HBTs having fT and fmax of 90 GHz and 120 GHz, respectively. This C-SiGe active filter was implemented with Voorman transconductors (Voorman, 2000) to fully exploit the complementary high-speed npn and pnp SiGe HBTs. The circuit occupies an area of 0.82 mm2, and exhibits a filter cut-off frequency of 4.1 GHz. This C-SiGe active filter achieves a record continuous tuning range between 70 MHz and 4.1 GHz, attains an output noise power spectrum density (PSD) of -143 dBm/Hz, and operates off a 3.5 V supply, with a total power consumption of 100 mW at the maximum bandwidth of 4.1 GHz