U.S. Philips Corporation

Robert J Murray

Robert Frederick Milsom

Richard F Mitchell

John M Schofield

Christopher J Collier

Ian Flinn

Ian Flinn, Deceased

A transmission system in which a suitably modulated speech or data signal is combined with a low bit rate (100b/s) spread spectrum signal and transmitted simultaneously on the same channel with the modulated speech lying within the bandwidth of the spread spectrum signal. At a receiver the modulated speech or data signal is demodulated and the modulated speech or data signal together with the spread spectrum signal are applied to a multiplier in which the spread spectrum signal is despread. A code synchronizing signal may be included in the modulated signal prior to transmission and when recovered in the receiver, the synchronizing signal is applied to a pseudo-random code generating means. The transmission system may include a text transmission system in which case the low bit rate signal comprises pages of data. A number of pages may be transmitted simultaneously by spreading the data associated with each page by orthogonal psuedo-random codes.

Transmission system for sending two signals simultaneously on the same

An acoustic surface wave device comprising a piezoelectric substrate provided with an input transducer (2), an output transducer (4) and a compact reflective multistrip coupler (6) in which the strips of each pair of comparatively widely spaced strips (7 or 8)in one array of mutually parallel strips are connected to respective strips of a pair of comparatively narrowly spaced strips (8 or 7) in the other array. The wide and narrow spacings alternate along each array. The improvement provides further electrodes (9) located in the relatively wide spaces in each array and electrically interconnected so as to effect a transfer of signal currents along each array and from one array to the other. The device improves efficiency, reduces insertion loss and improves the shape of the pass band.

Acoustic surface wave device including a reflective multistrip coupler

A surface acoustic wave bandpass electrical filter has double electrode input and output transducers (IP and OP) whose combined amplitude-frequency response has a fundamental passband centered on a frequency f.sub.o and a corresponding third harmonic passband. An interposed multistrip coupler (MSA2) has strips (ST) with a mark-to-space ratio of one-to-one and a center-to-center spacing .lambda..sub.S2 /2 chosen such that f.sub.o /f.sub.S2 is in the range 0.80 to 1.14 but excluding substantially 1.0, whereby a stopband in the amplitude-frequency response of the coupler (MSA2) between 2f.sub.S2 and 4f.sub.S2 suppresses the amplitude-frequency response of the input and output transducers (IP and OP) over a range of frequencies including 3f.sub.o .+-.0.5f.sub.o.

Acoustic wave bandpass electrical filters

Surface acoustic wave bandpass transversal filters, e.g. television intermediate frequency filters, comprising a +.theta..degree. rotated Y-cut X-propagating lithium niobate substrate with .theta. in the range from 121.degree. to 127.degree., preferably 123.degree. to 125.degree.. For a suitable range of filter bandwidths (35 db bandwidth between 0.05 and 0.5) these substrates provide reduced degradation of the filter upper stopband predominantly due to indirect bulk shear waves in the frequency range from the passband up to the frequency where direct bulk longitudinal wave degradation becomes significant. This frequency range is 41.5 MHz to approximately 55 MHz for a U.K. system t.v. i.f. filter and is 60.25 MHz to approximately 90 MHz for a Japanese system t.v. i.f. filter.

Surface acoustic wave filters

A surface acoustic wave bandpass filter consists of input and output interdigital transducers (IP, OP) with an interposed track changing multistrip array (MSA). A conventional broadband array (MSA) is divided into two groups of strips with respect to a center of symmetry (C) separated by different distances along the input track (T1) and the output track (T2) such that the array (MSA) suppresses a predetermined frequency. If the input and output transducers (IP, OP) both have a double electrode configuration, electrode separation .lambda.o/4, providing a fundamental passband at a corresponding frequency f.sub.o and an equal amplitude passband at the third harmonic 3f.sub.o, then a separation difference of .lambda.o/6 between the groups of the array (MSA) in the two tracks (T1, T2) can suppress the third harmonic passband in the filter output. The two groups of the multistrip array may be further sub-divided to suppress more than one frequency (FIG. 5). Also a multistrip array arranged in groups to provide a shaped bandpass response may have each group divided to suppress a selected harmonic passband of the array (FIG. 6).

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Horley, United Kingdom

Robert J Murray