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An eighth order active-RC filter for low-IF and zero-IF DVB tuner applications is presented,which is implemented in Butterworth biquad structure.An automatic frequency tuning circuit is introduced to compensate the cut-off frequency variation using a 6-bit switched-capacitor array.Switched-resistor arrays are adopted to cover different cut-off frequencies in low-IF and zero-IF modes.Measurement results show that precise cut-off frequencies at 2.5,3,3.5 and 4 MHz in zero-IF mode,5,6,7 and 8 MHz in low-IF mode can be achieved,60 dB frequency attenuation can be obtained at 20 MHz,and the in-band group delay agrees well with the simulation.Two-tone testing shows the in-band IM3 achieves-52 dB and the out-band IM3 achieves-55 dB with-11 dBm input power.This proposed filter circuit,fabricated in a SMIC 0.18μm CMOS process,consumes 4 mA current with 1.8 V power supply.
An eighth order active-RC filter for low-IF and zero-IF DVB tuner applications is presented, which is implemented in Butterworth biquad structure. An automatic frequency tuning circuit is introduced to compensate the cut-off frequency variation using a 6-bit switched -capacitor array.Switched-resistor arrays are adopted to cover different cut-off frequencies in low-IF and zero-IF modes.Measurement results show that precise cut-off frequencies at 2.5, 3, 3.5 and 4 MHz in zero-IF mode , 5,6,7 and 8 MHz in low-IF mode can be achieved, 60 dB frequency attenuation can be obtained at 20 MHz, and the in-band group delay agrees well with the simulation. Two-tone testing shows the in- band IM3 achieves -52 dB and the out-band IM3 achieves -55 dB with -11 dBm input power. This proposed filter circuit, fabricated in a SMIC 0.18 μm CMOS process, consumes 4 mA current with 1.8 V power supply.