U.S. Philips Corporation

Philip D White

Richard F Mitchell

Richard Stevens

Paul A Moore

Martin Redwood

Christopher S Barnes

In communications systems, such as cordless telephone systems, in which synchronizing signals are transmitted at predetermined intervals on a signalling channel by base stations to say portable, battery-powered receivers, the need to send separate station identification signals is avoided by the synchronizing signals being transmitted from a base station in accordance with a predetermined signalling sequence, for example a pseudo-random sequence, and the receivers using the sequence as a base station identification signal.

System identification in communications system

A duplex speech transmission method is disclosed wherein a limited bandwidth transmission channel is divided in a plurality of successive time slots, alternate time slots being available for each of two parties to call in Speech signals from either of the parties are divided into time segments with the time segments associated with one of said two parties being offset in time with the time segments associated with the other of said two parties. Segments of speech when present are digitised and stored in digital form. A higher rate of quantization is used when speech is present in the segments of one party and not in those of the other party, said higher rate quantized signal being transmitted in the other party's time slot and the immediately following time slot of said one party. A lower rate of quantization is used if both parties have speech in their respective segments, the lower rate quantized signals being time compressed and transmitted in their associated time slots. By the method being digited throughout the end of a segment coincides substantially with the end of the time slot associated with said segment and thus a delay not exceeding half a segment is incurred. By making the segments have a duration of 2 ms then the method complies with PSTN requirements.

Duplex speech transmission method and a system therefor

N.sup.2 acoustic wave devices (A,B,S,T; where N is an integer greater than unity) with substantially the same electrical impedance and transfer characteristics at a given operating frequency are electrically connected in a parallel-series arrangement which has substantially the same electrical impedance and transfer characteristics as any one of the individual N.sup.2 devices, but an increased active device area. The increased active area reduces stress and alleviates acoustically-induced migration in the metal of, for example, transducer electrode fingers (6,7) of resonators at high power levels. The parallel-series arrangement consists of N groups, each of which comprises N devices (A,B or S,T), the corresponding pairs of terminals (4,54 and 54,55) of which are connected in series. Some terminals (54 or 55) may be common to two or more devices and some devices may have merged transducers in which the electrode fingers (6 or 7) of one transducer are a longitudinal extension of the fingers of a parallel transducer. In the case of multi-port devices the input and output terminal pairs may be differently grouped as regards the individual devices to which they belong.

High power acoustic wave arrangement with N.sup.2 parallel-series

In an acoustic wave device having a pair of spaced apart reflectors forming a resonant cavity, each reflector consists of an array of parallel reflective elements. At least one of the reflectors is weighted not by simple withdrawal of reflecting elements from a nominal uniform array but instead by substituting reflective elements of the uniform array with elements providing both net-zero reflection at required positions and also at least partial compensation for the velocity perturbation which would be produced by such simple withdrawal. Such weighting may be used to suppress the side lobes of the reflector response and hence improve the stopband performance of the acoustic wave device and, for example, a coupled resonator filter in which that device is incorporated.

Acoustic wave devices

An acoustic wave resonator device comprises a substrate carrying a pair of spaced apart reflectors forming a resonant cavity that supports only three adjacent distinct resonant mode frequencies. An interdigital transducer is disposed on the substrate between the reflectors and includes an array of electrodes symmetrically arranged relative to a central point of the cavity to form a plurality of electrode pairs with the electrodes of each pair equally spaced on opposite sides of the central point. The central point of the cavity coincides with a node or an anti-node of the standing wave. If the two electrodes of each electrode pair are connected to the same terminal then the transducer has zero net coupling with one set of alternate modes of the cavity, whereas if said two electrodes are connected to opposite terminals then the transducer has zero net coupling with the other set of alternate modes.

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Chessington, United Kingdom

Philip D White