Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Reexamination Certificate
2001-10-11
2004-05-04
Appiah, Charles (Department: 2686)
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
C455S208000, C455S318000, C331S066000, C331S176000, C331S041000
Reexamination Certificate
active
06731919
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an amplifier apparatus that is used as a high-frequency amplifier apparatus for use in, for example, a wireless apparatus. More particularly, the invention concerns an amplifier apparatus that even when the ambient temperature changes can maintain the performance of sharply attenuating a frequency band adjoining to a frequency band serving as an object to be amplified.
2. Description of the Related Art
For example, a high-frequency amplifier apparatus that is used in a conventional wireless apparatus is constructed in multiple stages. As a method of limiting the pass frequency band, a band pass filter is connected to an input or output of the high-frequency amplifier apparatus. Or, a bandpass filter is connected to between two adjoining stages of the high-frequency amplifier apparatus. By doing so, there is generally made up a construction of limiting the frequency pass band and thereby attenuating a frequency band the amplification of that is unnecessary.
In
FIG. 2
, there is illustrated a construction of the above-described conventional high-frequency amplifier apparatus. A reference numeral
1
denotes a band pass filter that causes a signal having a frequency band (a peculiar-to-apparatus band, i.e., an original band), an object to be amplified, to be passed therethrough and that causes the other frequency bands to be attenuated down to a required level. A reference numeral
2
denotes a low-noise amplifier that low-noise-amplifies the original band signal that has passed through the band pass filter
1
. A reference numeral
3
denotes a power amplifier that amplifies the low-noise-amplified signal up to a required high-frequency power. A reference numeral
4
denotes a bandpass filter that attenuates an unneeded frequency band.
In the above-described high-frequency amplifier apparatus, it is effective in case its required performance is seen in the circumstances where the attenuation characteristics of frequencies other than the pass band frequency are gentle and the attenuation at an adjoining frequency band is relatively small. In
FIG. 3
there is illustrated a filter transmission characteristic. Assume that the characteristic indicated surrounded by each mark A in the figure be the required filter transmission characteristic. Then, a characteristic
5
shows that a transmission characteristic further sharpening the gradient of the filter transmission characteristic is required, while a characteristic
6
shows that the gradient of the transmission characteristic meets the required gradient. However, in the latter case, because the characteristic
6
is made to be the one wherein the pass bandwidth B is narrowed, a transmission characteristic making the pass bandwidth wider is required.
In order to realize the filter transmission characteristic meeting the above-described required transmission characteristic, it becomes necessary to make up the following construction. Namely, wherein the gradient of the transmission characteristic is made sharp by increasing the number of the filter stages; or the transmission loss is made small and the end of the pass band is made acute by enlarging the volume of the filter per se.
However, this construction is inevitably followed by an increase in the volume and weight of the high-frequency amplifier apparatus, as well as by an increase in the cost that occurs due to the increase in the cost for adjustment.
On this account, as a high-frequency amplifier apparatus that can solve the increase in the stages number and volume of the pass band filter, which are the above-described points in problem, to thereby enable miniaturization and economization of it, the following construction has hitherto been proposed. Namely, wherein an original signal is converted by a frequency converter to a frequency falling within an intermediate-frequency band (IF band) the frequency of that is lower than the original frequency. Then, the IF band is connected to a filter of a required transmission characteristic. Then, this IF band is again converted to the original frequency by a frequency converter.
In
FIG. 4
there is illustrated the construction of a high-frequency amplifier apparatus in which to convert the signal into the IF band for processing thereof. A reference numeral
11
denotes a band pass filter that permits the passage therethrough of a signal having a frequency band (an original band: fr) to be amplified. A reference numeral
12
denotes a low-noise amplifier that low-noise-amplifies the signal the frequency of that is the original band. A reference numeral
13
denotes a frequency converter that converts the signal having the original band to an IF band (fi). A reference numeral
14
denotes an IF frequency band pass filter that permits the passage therethrough of the signal having the IF frequency band (fi). A reference numeral
15
denotes an IF frequency band amplifier that amplifies the signal having the IF band. A reference numeral
16
denotes an IF frequency band pass filter that permits the passage therethrough of the signal having the IF frequency band (fi). A reference numeral
17
denotes a frequency converter that converts the signal having the IF frequency band (fr) to the original band (fr). A reference numeral
18
denotes a power amplifier that amplifies the converted signal having the original band up to a high-frequency power. And a reference numeral
19
denotes a band pass filter that attenuates an unneeded frequency band.
And, in this high-frequency amplifier apparatus, an oscillation frequency signal from a local oscillator
20
is distributed by a distributor
21
into the converters
13
,
17
. And, by multiplying the original band by a local oscillation frequency, frequency conversion is performed between the original band and the IF band.
Here, in
FIG. 5
, there are illustrated a transmission characteristic
22
of a filter the center frequency of that is a frequency fr
0
and a transmission characteristic
23
of a filter the center frequency of that is a frequency fi
0
lower than the frequency fr
0
. As illustrated in the figure, assuming that the pass bandwidth &Dgr;f be the same in the bandwidth in terms of either filter, it is known that the following can be said. Namely, in case the number of stages is the same, the transmission characteristic that is lower in the center frequency becomes sharper in gradient of attenuation. Namely, in
FIG. 5
, the following is known in terms of the relationship that when the frequency displacements &Dgr;f from the both center frequencies are the same in value holds true between the amounts &agr;
1
, &agr;
2
of attenuation of the respective filters. Namely, the &agr;
1
is greater than the &agr;
2
.
Accordingly, in the case of constructing a multi-stage amplifier apparatus for limiting the pass band of frequency, when making great the amount of attenuation of an adjoining frequency, there has hitherto been used the amplifier apparatus such as in FIG.
4
. Namely, the amplifier apparatus for converting the original frequency to the IF band.
However, in case the amplifier apparatus has been made to have such a construction as illustrated in
FIG. 4
, the band pass filter
14
or
16
for passing the IF frequency band has a center frequency of its pass band shifted due to a change in the ambient temperature. Resultantly, a shift of the frequency occurs in the transmission characteristic of the filter, with the result that the filter has the inherent drawback incapable of filtering its required band of frequency.
In
FIG. 6
there is illustrated a change in the transmission characteristic due to a change in the ambient temperature of the band pass filter. The characteristic
24
indicated by a solid line represents the filter transmission characteristic at normal temperature while the characteristic
25
indicated by a broken line represents the filter transmission characteristic at the time of a change in the temperature.
In case having used the above-described filter whose characteri
Fujimoto Shoji
Ito Hidefumi
Suto Masaki
Uchida Takashi
Urata Junetsu
Appiah Charles
Hitachi Kokusai Electric Inc.
Perez-Gutierrez Rafael
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