SAW recursive filter for mobile telecommunications - has two transducers forming delay line with loop with amplifier and additional transducer connected to filter output

摘要

The recursive filter has an independent numerator and demoninator in its transfer direction and a wide latitude in component choice, and allows electronic timing. The filter has one or more delay lines formed by two elastic surface wave transducers (t1,t2) on a substrate (10) such as lithium niobate. Each line is also coupled by an amplifier (12) with one transducer being connected to receive the electrical input signal to be filtered for conversion to an elastic surface wave. The wave may be introduced by a third transducer which is coupled to the delay line by the substrate. A third transducer (t3) in the form of a transversal filter is coupled to the delay line and serves as an output of the filter. An auxiliary dephaser (11) may be connected to the amplifier input. Additional delay lines may be incorporated and the amplifiers inverted.