Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
2000-09-21
2004-01-27
Summons, Barbara (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S150000, C333S153000, C333S133000, C455S272000, C455S276100
Reexamination Certificate
active
06683515
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface-acoustic-wave filter using a transversal SAW filter used for a high-frequency circuit of a radio communication unit.
2. Related Art of the Invention
A surface-acoustic-wave filter has been frequently used so far as a RF- or IF-stage filter of a transceiving circuit of a communication unit. Particularly recently, a portable telephone according to a mode referred to as CDMA (Code Division Multiple Access) has been positively developed as a next-generation mobile communication system.
The CDMA communication mode allows the so-called RAKE reception for improving the sensitivity by synthesizing delay waves of a multipath.
A CDMA receiving circuit is described below by referring to the accompanying drawings.
FIG. 9
is an illustration showing the outline of a CDMA receiving circuit. In
FIG. 9
, symbol
702
denotes a demodulating section,
703
a
and
703
b
denote antennas,
704
a
and
704
b
denote filters,
705
a
and
705
b
denote amplifiers,
706
a
and
706
b
denote mixers,
707
a
and
707
b
denote transversal SAW filters, and
708
denotes a delay unit. In this case, the transversal SAW filters
707
a
and
707
b
are assumed as the same device.
Operations of the CDMA receiving circuit having the above configuration according to the prior art are described below. That is, a signal received by the antenna
703
a
passes through the filter
704
a
and amplifier
705
a
and is converted into an IF signal by the mixer
706
a
. When assuming the signal as an IF signal “a,” the IF signal “a” passes through the transversal SAW filter
707
a
and is output to the demodulating section
702
.
Similarly, a signal received by the antenna
703
b
passes through the filter
704
b
and amplifier
705
b
and is converted into an IF signal by the mixer
706
b
. When assuming the signal as an IF signal “b,” the IF signal “b” passes through the transversal SAW filter
707
b
and delay unit
708
and is output to the demodulating section
702
.
The demodulating section
702
performs RAKE reception by synthesizing the IF signal “a” and the IF signal “b” input by being delayed by the delay unit
708
.
Operations of the CDMA receiving circuit are described above.
However, the above configuration has problems that a single delay unit is required for RAKE reception and thereby, the circuit size increases. Therefore, the CDMA receiving circuit cannot be applied to a compact portable terminal unit.
SUMMARY OF THE INVENTION
The present invention is made to solve the above problems and its object is to provide a surface-acoustic-wave filter capable of reducing the number of parts for signal delay and downsizing a receiving circuit, and a communication unit using the surface-acoustic-wave filter.
One aspect of the present invention is a surface-acoustic-wave filter, comprising:
a piezoelectric substrate; and
a plurality of transversal surface-acoustic-wave (SAW) filters set on the piezoelectric substrate and respectively having at least two inter-digital transducer (IDT) electrodes for transceiving surface acoustic waves,
characterized in that periods for surface acoustic waves to propagate from inputs to outputs of the SAW filters differ in the SAW filters and thereby, timings of outputs from the SAW filters are different from each other.
Another aspect of the present invention is a surface-acoustic-wave filter, comprising:
a piezoelectric substrate;
a plurality of filters set on the piezoelectric substrate and respectively having at least two inter-digital transducer (IDT) electrodes for transceiving surface acoustic waves; and
a plurality of impedance-matching circuits connected to input sides and output sides of the filters,
characterized in that output timings of output-side impedance-matching circuits of the filters are different from each other.
Still another aspect of the present invention is a communication unit using a CDMA mode, comprising:
receiving means provided with;
a plurality of antennas,
a plurality of mixers for converting signals sent from the antennas into IF signals,
a plurality of surface-acoustic-wave (SAW) filters for passing the IF signals, and
a demodulating section for demodulating the IF signals,
wherein said surface-acoustic-wave filter is used for the SAW filters.
According to the above configuration, a surface-acoustic-wave filter of the present invention is characterized by having transversal SAW filters corresponding to a plurality of reception signals, making group delay times of the transversal SAW filters different from each other, and thereby providing a group delay time difference for IF signals output from the SAW filters and makes it possible to downsize a CDMA receiving circuit by including a delay-unit function in the surface-acoustic-wave filter and reducing the number of parts of the CDMA receiving circuit in accordance with the above configuration.
REFERENCES:
patent: 3845420 (1974-10-01), Holland et al.
patent: 3908137 (1975-09-01), Hunsinger et al.
patent: 3952269 (1976-04-01), Bristol
patent: 4583047 (1986-04-01), Le Goff épouse Hénaff et al.
patent: 4682174 (1987-07-01), Richmond et al.
patent: 5434893 (1995-07-01), Le Roy et al.
patent: 5563610 (1996-10-01), Reudink
patent: 6229840 (2001-05-01), Ichihara
patent: 6275482 (2001-08-01), Jevremovic et al.
patent: 50-17951 (1975-02-01), None
Japanese Office Action for JP 2000-285859 mailed Apr. 1, 2003 (w/ partial English translation).
Monma Kenji
Nakamura Hiroyuki
Nishimura Kazunori
Yamada Toru
RatnerPrestia
Summons Barbara
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