A 50-to 300-MHz CMOS Gm-C Tracking Filter Based on Parallel Operation of Saturation and Triode Transconductors for Digital TV Tuner ICs

In this brief, a 50- to 300-MHz CMOS Gm-C tracking low-pass filter has been presented to resolve a LO harmonic-mixing problem for Advanced Television Systems Committee terrestrial and cable digital TV tuner integrated circuits. A Gm-C filter based on parallel operation of a transconductor biased in the saturation region with source degeneration and a transconductor biased in the triode region is chosen to achieve high linearity performance at the very high frequency/ultrahigh frequency bands. The cutoff frequency of the proposed filter is tunable from 50 to 300 MHz. The filter is implemented in a 0.18-mu m CMOS technology and achieves a minimum input-referred noise density of 3 nV/root Hz and maximum in-band output-referred third-order intercept point of 20.7 dBm. It operates at a nominal supply voltage of 1.8 V with bias currents of 114 mA. The active die area is 1.1 mm(2).