Surface wave devices for differential coherent detectors

A surface wave device, for use in a differential coherent detector of a communications system using commutation signaling in which differentially encoded information is communicated using a plurality of N predetermined codewords each comprising a plurality of M bits, the surface wave device comprising:

• at least one input IDT (inter-digital transducer), responsive to an input signal comprising information symbols having a predetermined symbol rate, for propagating a surface wave with a predetermined velocity, the predetermined symbol rate and velocity determining a surface wave propagation distance T corresponding to a duration of one information symbol;
• and, for each of the N codewords:
• a first coded output IDT, responsive to a propagated surface wave which is responsive to the input signal, comprising M taps connected in parallel with one another, the taps having a center-to-center pitch t, in the direction of propagation of the surface wave, equal to T/M, and having phases corresponding to the respective bits of a respective one of the N predetermined codewords;
• and
• a second output IDT responsive to a propagated surface wave which is responsive to the input signal and has a propagation distance which is greater by T than a propagation distance of the surface wave propagated from said at least one input IDT to said first coded output IDT.

A surface wave device comprising:

• at least one input IDT (inter-digital transducer), responsive to an input signal comprising differentially encoded information symbols having a predetermined symbol rate, each symbol comprising a predetermined codeword comprising a plurality of M bits, for propagating a surface wave with a predetermined velocity, the predetermined symbol rate and velocity determining a surface wave propagation distance T corresponding to a duration of one information symbol;
• a first coded output IDT comprising M taps connected in parallel with one another, the taps having a center-to-center pitch t, in the direction of propagation of the surface wave, equal to T/M, and having phases corresponding to the respective bits of the predetermined codeword;
• and
• a second coded output IDT comprising M taps connected in parallel with one another, the taps having a center-to-center pitch t, in the direction of propagation of the surface wave, equal to T/M, and having phases corresponding to the respective bits of the predetermined codeword;
• the fist and second coded output IDTs being responsive to surface waves propagated from said at least one input IDT through a propagation distance for the second coded output IDT which is greater by T than a propagation distance for the first coded output IDT, for providing a first output signal from the first coded output IDT and a second output signal, delayed by the duration of one information symbol relative to the first output signal, from the second coded output IDT.

A surface wave device comprising:

• an input IDT (inter-digital transducer), responsive to an input signal comprising differentially encoded information symbols having a predetermined symbol rate, each symbol comprising a predetermined codeword comprising a plurality of M bits, for propagating a surface wave with a predetermined velocity, the predetermined symbol rate and velocity determining a surface wave propagation distance T corresponding to a duration of one information symbol;
• a first, coded output IDT comprising M taps connected in parallel with one another, the taps having a center-to-center pitch t, in the direction of propagation of the surface wave, equal to T/M, and having phases corresponding to the respective bits of the predetermined codeword responsive to the surface wave propagated from the input IDT to provide a first output signal;
• and
• a second, uncoded output IDT arranged to be responsive to the surface wave propagated by the input IDT via the first, coded output IDT, the second, uncoded output IDT having a center-to-center distance from the first, coded output IDT of T whereby the second, uncoded output IDT provides a second output signal delayed by the duration of one information symbol relative to the first output signal.