6B-3 Low Loss IF Filters for Multimedia Applications - New Limits in Recursive Filter Technology

Presently IF filters for multimedia applications are mainly high loss transversal filters. For upcoming mobile applications a reduction of insertion loss will be highly welcome. We present a new class of recursive filters with an overall performance comparable to conventional transversal filters but much lower insertion attenuation. To substitute conventional transversal filters we had to realize recursive filters with a bandwidth significantly larger than known up to now. The very low center frequencies and thus large wavelengths usual for multimedia IF filters lead to a low relative filter length. SPUDT cells with very high reflectivity were required to suppress triple transit signal and a much larger set of different cells than usual was necessary to reduce discretization errors in withdrawal weighting. As an example we present a 36 MHz filter with a length of only 69 wavelengths, a bandwidth of 8 MHz and 40 dB selectivity. The insertion attenuation is about 16 dB lower than that of a comparable conventional transversal filter. Group delay ripple is below 80 ns and passband ripple below 0.8 dB