A 10.7-MHz CMOS SC radio IF filter using orthogonal hardware modulation

FM radio receivers require an IF filter for channel selection, customarily set at an IF center frequency of 10.7 MHz. Up until now, the limitations of integrated radio selectivity filters in terms of power dissipation, dynamic range, and cost are such that it is still required to use an external ceramic 10.7-MHz bandpass filter. This paper demonstrates a CMOS switched-capacitor IF filter that can be integrated with most of the rest of the FM receiver, eliminating external components and printed circuit board area. This is made possible through a combination of two techniques: orthogonal hardware modulation, and delta-charge redistribution. It exhibits a tightly controlled center frequency with a Q of 55 and also contains a programmable gain. The filter occupies an area of 0.7 mm/sup 2/ in a 0.6 /spl mu/m CMOS process with poly-poly capacitors. The new filter requires only 16 mW of power, and this is offset by elimination of the power needed in current designs to drive off-chip filters.