Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1998-06-04
2000-01-04
LaBalle, Clayton
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
310313R, 333150, 333154, H01L 4104, H03H 900
Patent
active
060113448
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a surface acoustic wave transducer, especially a surface acoustic wave distributed acoustic reflection transducer known as a DART, driven in differential mode and having low-impedance inputs/outputs. There is a growing demand for this type of drive, especially in view of the advances in integrated circuits.
The basic structure of a DART being assumed to be known, it will therefore not be described in detail in the present description.
To drive a transducer in differential mode it is necessary to use a structure having symmetrical differential inputs. The basic structure of DARTs does not allow them to be used directly in differential mode. This is because the reflector of the DART constitutes an asymmetry between the connection pads linked respectively to the differential inputs.
Transducers and filters using these transducers can be applied in many fields such as radars or mobile radiocommunication systems, in particular for filtering the intermediate frequencies.
A DART structure with differential inputs is known, described in particular in patent No. 92 10966 entitled "Transducteur d'ondes unidirectionnel [Unidirectional wave transducer]", filed by the Applicant on Sep. 15, 1992 and published as U.S. Pat. No. 2,695,771. This structure allows differential feed between a positive and negative source, referenced with respect to earth, and includes two emitter cells which are linked to the positive source and flank a third emitter cell linked to the negative source, and these three cells are separated by a first and a second reflective cell and possibly linked to earth, these cells naturally being taken to earth potential by symmetry. This configuration uses a maze structure in which the earthed electrodes are interposed between those linked to the positive source and those linked to the negative source. This maze poses a problem of sampling and of high impedance as seen by the inputs/outputs of the structure.
The objective of the present invention is to overcome the aforementioned drawbacks.
To this end, the subject of the invention is a surface acoustic wave transducer driven in differential mode, characterized in that it consists of at least a first transducer and a second transducer which are connected in parallel so as to obtain the symmetry of the differential inputs, respectively forming a first and a second acoustic channel; the two transducers exhibiting a specified longitudinal offset with respect to one another.
The advantage of the structure of the transducer according to the invention is that it presents low impedances to the inputs/outputs of this structure in respect of a structure with two parallel acoustic channels driven in differential mode.
Other characteristics and advantages of the present invention will be clearly understood on reading the description which follows and the appended figures which represent:
FIGS. 1a and 1b, a known example of a structure of a transducer of DART type with non-differential inputs viewed from above and in section respectively,
FIGS. 2a, 2b and 2c, an embodiment of a transducer comprising two transducers connected in series to form a transducer with differential inputs viewed from above and in section respectively,
FIG. 3, a first structure of a transducer according to the invention with two transducers in parallel, driven in differential mode and longitudinally offset,
FIGS. 4a, 4b and 4c, a second structure of a transducer according to the invention comprising two transducers connected in parallel, driven in differential mode and offset by .lambda./2, and their respective sectional view,
FIGS. 5a, 5b and 5c, a third structure of a transducer according to the invention comprising two transducers connected in parallel, driven in differential mode and offset by .lambda./2, and their respective sectional view,
FIGS. 6a, 6b and 6c, a fourth structure of a transducer according to the invention comprising two transducers connected in parallel, driven in differential mode and offset by .lambda./2, and their respective sectional v
REFERENCES:
patent: 4081769 (1978-03-01), Shreve
patent: 4405874 (1983-09-01), Suthers
patent: 4491757 (1985-01-01), Hartmann
patent: 5020034 (1991-05-01), Solal et al.
patent: 5475348 (1995-12-01), Hode et al.
patent: 5663696 (1997-09-01), Morgan
patent: 5703427 (1997-12-01), Solal et al.
Dufilie Pierre
Solal Marc
"Thomson-CSF"
LaBalle Clayton
Medley Peter
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