Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
1999-11-08
2001-11-06
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S193000
Reexamination Certificate
active
06313715
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a duplexer, more specifically to a surface acoustic wave (SAW) duplexer, which operates with surface acoustic waves.
Such SAW duplexers are known, for example from Published, Non-Prosecuted German Patent Application DE 195 14 798 A1 and from Published, European Patent Application EP 0 422 637 A3.
Duplexers of this generic type are in principle frequency filters, via which different frequency bands can be passed. An exemplary embodiment of such a duplexer is a mobile telephone apparatus, in which a first frequency band, a transmission frequency band, is passed from a circuit configuration which produces it, via a transmission filter, to an antenna, and a reception frequency band which is received via the antenna is passed via a reception filter to a circuit configuration that processes it.
A fundamental problem with the duplexers of this type is the necessity to interconnect two two-port devices to form a three-port device. In the process, the transmission characteristics of the two individual filters, the transmission filter and the reception filter, should be changed as little as possible. Since the filters are normally connected in parallel on the antenna side, it is necessary for the respective other filter to have a high impedance, particularly in the passband of the filters. In the passband, the individual filters are generally matched to 50 W. The impedances of the individual filters in the passband of the respective other filter are considerably different than 50 W.
However, the impedances of the individual filters have to be transformed to the high-impedance area in order that they have a high impedance in the frequency band of the respective other filters, and represent an open circuit in the ideal case. If both individual filters are matched to 50 W, then a specific transformation is required to change the impedance outside the passband without adversely affecting the characteristics in the passband.
Until now, such transformations have been carried out by strip lines. Since SAW filters are generally capacitive outside the passband, the impedance must be shifted through more than 180° until it is large enough and thus has little adverse effect on the other filter. Depending on the dielectric constant of the substrate material, this phase shift can be carried out only by a relatively long strip line. This results in the strip line occupying a large amount of space and having high losses.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a SAW duplexer that overcomes the above-mentioned disadvantages of the prior art devices of this general type, which has a transformation capability of the type under discussion with a smaller space requirement and lower losses.
With the foregoing and other objects in view there is provided, in accordance with the invention, a surface acoustic wave (SAW) duplexer operating with surface acoustic waves, including a chip, containing:
a transmission path containing a transmission SAW filter having an impedance;
a reception path containing a reception SAW filter having an impedance; and
a transformation network having a series capacitance being an interdigital converter disposed in one of the transmission path and the reception path, the transformation network transforming the impedance of one of the transmission SAW filter and the reception SAW filter in a passband of an other of the transmission SAW filter and the reception SAW filter to a high-impedance area.
In accordance with an added feature of the invention, there is an antenna connected to the transmission path and the reception path, and the series capacitance is disposed between the antenna and one of the transmission path and the reception path.
In accordance with an additional feature of the invention, the series capacitance is disposed only in the transmission path.
In accordance with another feature of the invention, the series capacitance is disposed only in the reception path.
In accordance with a further added feature of the invention, the series capacitance is two series capacitances with one of the two series capacitances disposed in the transmission path and the other of the two series capacitances disposed in the reception path.
In accordance with a further additional feature of the invention, the transmission SAW filter has an output side, the series capacitance has a side facing away from the output side of the transmission SAW filter, and including an inductance connected in parallel with the series capacitance on the side facing away from the output side of the transmission SAW filter.
In accordance with yet another feature of the invention, the reception SAW filter has an input side, the series capacitance has a side facing away from the input side of the reception SAW filter, and including an inductance connected in parallel with the series capacitance on the side facing away from the input side of the reception SAW filter.
In accordance with another added feature of the invention, the series capacitance is a chip interdigital converter.
With the foregoing and other objects in view there is further provided, in accordance with the invention, a surface acoustic wave (SAW) duplexer operating with surface acoustic waves including a chip, containing:
a transmission path containing a transmission SAW filter having an impedance;
a reception path containing a reception SAW filter having an impedance;
a first transformation network being an interdigital converter disposed in one of the transmission path and the reception path, the first transformation network transforming the impedance of the one of the transmission SAW filter and the reception SAW filter in a passband of an other of the transmission SAW filter and the reception SAW filter to a high-impedance area; and
a second transformation network being a line impedance disposed in the other of the transmission path and the reception path, the second transformation network transforming the impedance of the other of the transmission SAW filter and the reception SAW filter in a passband of the one of the transmission SAW filter and the reception SAW filter to a high-impedance area.
In accordance with an added feature of the invention, the interdigital converter is disposed in the transmission path, and the line impedance is disposed in the reception path.
In accordance with a concomitant feature of the invention, the line impedance is a stripline.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a SAW duplexer, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
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patent: 5561406 (1996-10-01), Ikata et al.
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patent: 5864260 (1999-01-01), Lee
patent: 6043725 (2000-03-01), Taguchi et al.
patent: 6057744 (2000-05-01), Ikada
patent: 6115592 (2000-09-01), Ueda et al.
patent: 19514798A1 (1996-01-01), None
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patent: 07273597 (1995-10-01), None
Bergmann Andreas
Muller Peter
Greenberg Laurence A.
Lerner Herbert L.
Pascal Robert
Siemens Matsushita Comp. GmbH & Co. KG
Stemer Werner H.
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