Wave transmission lines and networks – Automatically controlled systems
Reexamination Certificate
2001-09-28
2003-06-10
Summons, Barbara (Department: 2817)
Wave transmission lines and networks
Automatically controlled systems
C333S132000, C333S205000, C333S134000
Reexamination Certificate
active
06577205
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an adaptive high-frequency filter device to be used primarily in a high-frequency section of wireless apparatuses such as cellular telephones, an adaptive filter device combined to a transmit-receive antenna, and a wireless apparatus using those devices.
2. Prior Art
In recent years, it has been practiced that in simultaneous two-way wireless communication apparatuses such as cellular telephones and car telephones used in cellular wireless communication systems, a filter device is provided between a transceiver and its antenna. In this wireless communications system, available frequency bands are assigned to a transmitting frequency band and a receiving frequency band, and the filter device is equipped with, on the receiver side, a filter device that allows the passing of a receivable frequency band and, on the transmitter side, a filter device that allows the passing of a transmittable frequency. In communications apparatuses for use in this system, in recent years, there have been exploited frequency-shift type filter devices in which each of a frequency band for reception use and a frequency band for transmission use is divided into two so that the filter device is enabled to switch between the divided smaller frequency bands.
Japanese Patent Publication No. 11-243304 discloses an example of filter devices of frequency-shift type. As shown in
FIG. 9
, this filter device comprises a receiving filter device and a transmitting filter device which are combined at a single antenna terminal and connected in series. In the combined filter device, the transmitting filter device has its transmitting terminal
94
connected to a final stage of the transmitter, the receiving filter device has its receiving terminal
95
connected to a high-frequency stage of the receiver, and an antenna terminal
96
is connected to a common-use antenna circuit.
Each filter device of the combined device is formed of two- or three-stage filters, each of which includes a dielectric resonator
91
which is, in common, grounded at one end, where a capacitance
93
is connected in parallel to the dielectric resonator
91
via a PIN diode switch
92
which turns on or off the parallel capacitance
93
to switch the resonance frequency.
The filter device, generally, includes a band pass filter and a band elimination filter. In one of the band elimination filters as shown in
FIG. 9
, an input or output terminal is connected to a notch coupling capacitance
97
and a resonator
91
in series, the resonator being grounded, and also to a loading capacitance
99
being grounded, while the input terminal is connected to an output terminal via an interstage coupling inductor
98
. For the makeup of a filter device including multi-stage filters, these filters are connected in series, each having a different resonating frequency.
In the other band pass filter, input and output ends are made up so that an inter-stage coupling capacitance
910
and an input-output coupling inductor
911
are connected in series, and that the resonator
91
having one end grounded is connected to this capacitance
910
and inductor
911
. A branch coupling capacitance
912
is connected between the input and output ends in a parallel fashion. These filters are connected in series to make up a multi-stage band pass filter.
These two filter devices (i.e., transmitting filter device and receiving filter device) are connected in series at an antenna terminal, sharing the antenna terminal. For connection to a common antenna used in a simultaneous transmit-and-receive apparatus, the filter devices are connected to the antenna terminal via an L-type matching circuit of an inductor
913
and a capacitance
914
for matching purposes, thus forming a filter device for common use of both transmitter and receiver of the above apparatus.
In such a frequency-shift type filter device for common use with a high-frequency antenna, the dielectric resonator
91
is provided with the capacitor
93
in parallel via the PIN diode switch
92
as shown in
FIG. 9
, wherein the resonance frequency of the resonator
91
can be selectively switched between a low frequency f
1
and a high frequency f
2
by electrically turning on and off the PIN diode switch
92
. In the example shown in
FIG. 9
, the receiving filters and the transmitting filters each use a resonator changeable resonance frequency. One filter device generally uses two or more filters for switching their respective resonance frequencies, resulting in switching the center frequency of the filter band.
This filter device has advantages so as not to be necessary to lower the pass loss throughout the whole passband, or to increase the attenuation ratio throughout the whole attenuation band. Therefore, each of the two filter devices are only required to cover a half of the whole band, thereby reducing the burden of the filter device. That is, this can exhibit the same effect, apparently, as the transmit and receive frequency gap of the filter expanded by a half of the entire passband.
Japanese Patent Publication No. 2000-312161 discloses the concept that a wireless apparatus changes the attenuation amount of the filter depending on nations or regions where the apparatus is used by detecting positional information with other communication means such as signals transmitted from a base station or GPS.
In the above filter devices, to decrease the burden of the filter with attenuation characteristics covering the whole bandwidths for transmission and reception in a communication system, the filter characteristics are changed to be applicable to the communication frequency bands that are differently allotted for the country in which the wireless apparatus is used.
Further,
FIG. 10
shows a structure of an actual prior-art wireless apparatus, such as a portable cellular telephone, including filter devices for a transmit-receive antenna. The apparatus includes a semiconductor integrated circuit
103
provided with a wireless circuit, a filter device
101
which is connected to the semiconductor integrated circuit
103
, and an internal antenna
102
which is coupled to a dielectric filter device
101
, these being mounted on, or formed in, a printed circuit board
104
, and an external antenna
106
is also provided which is connected to the filter devices
101
. This wireless apparatus is large in number of parts, difficult to manufacture, and also occupied in great deal by the wireless section.
The prior art filter devices have only been capable of changing the filter band frequency, alternatively and simply, to either one of two frequency passbands, subordinate to frequency selection of transmitting signals and received signals.
The technique of changing the attenuation amount based on detected positional information has not provided sufficient characteristics for the filter.
Further, the wireless apparatuses for simultaneous bi-directional wireless communication have been insufficient to protect against interfering waves other than an under-reception target signal under actual wave environments in which the wireless apparatus is used, as well as to suppress spurious signals issued by the apparatus itself during signal transmission. Thus, the characteristics of antenna-coupled filters are required to be changed adaptively in response to the change of wave environments around, and the operating state of, the wireless apparatus in use.
In order to completely prevent such interfering waves and unnecessarily radiated waves, the conventional filter devices in which passband frequencies are fixed had to involve ultra-high filtering performance characteristics, necessitating multi-stage high-Q resonators, in which case the filter devices would be required to have a large size. Downsizing the resonators to downsize the filter device would cause the high-frequency characteristics to deteriorate, not obtaining practical, required characteristics.
Furthermore, from the viewpoint of the configuration of parts in such actual filte
Ishizaki Toshio
Yamada Toru
Matsushita Electric - Industrial Co., Ltd.
Summons Barbara
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