A 4–40MHz continuous-time LPF with on chip automatic tuning for a direct conversion DBS Tuner

A continuous-time 7th-order Butterworth Gm-C low pass filter (LPF) with on-chip automatic tuning circuit has been implemented for a direct conversion DBS tuner in a 0.35 um SiGe BiCMOS technology. The filterpsilas -3dB cutoff frequency f0 can be programmed from 4 MHz to 40 MHz. Measurement results show that the filter has 0 dB passband gain, 30 nV/Hzfrac12 input referred noise, -3 dBVrms passband IIP3, 27 dBVrms stopband IIP3. The I/Q LPFs with the tuning circuit draw 13 mA (with f0=20 MHz) from 5 V supply, and occupy an area of 0.5 mm2.