Amplifiers – With semiconductor amplifying device – Including frequency-responsive means in the signal...
Patent
1998-03-02
2000-11-07
Mottola, Steven J.
Amplifiers
With semiconductor amplifying device
Including frequency-responsive means in the signal...
330 68, H03F 3191
Patent
active
061442607
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an amplifier for use in wireless communication equipment such as a transmitter of portable telephone, for example.
BACKGROUND ARTS
In general, an amplifier for communication equipment is required to have high efficiency and it is known that a matching circuit is used to achieve high efficiencies of an amplifier as disclosed in a Japanese Published Unexamined Patent Application of No. 32335/95. When signals are amplified by an amplifier, such undesired signal components as noise and the like that exist outside the frequencies intended for Amplification are also amplified at the same time. Because of this, a filter is connected to the output side of an amplifier to attenuate undesired signal components such as noise and the like.
One of the problems involved with the foregoing system has been that attenuation of the noise amplified by an amplifier and additional noises has to be achieved by a filter alone situated behind the amplifier in the system, thereby requiring the filter to have large attenuation by using many resonators resulting in a bulky filter. In addition, the loss in a pass-band of the filter connected behind the amplifier tends to increase, thus requiring the amplifier to output more power with resultant hindrance to the efficiency improvement of the amplifier.
More specifically, the relations involved with band-pass filter attenuation vs. frequency characteristics, frequency spacings in transmitting signals and receiving signals, and the like will be explained with reference to FIG. 14. FIG. 14 shows a case wherein a receiving signal band is located in a higher frequency band than a transmitting signal band. In general, with portable telephones, a plurality of both transmitting signal frequencies and receiving signal frequencies are prepared within a given frequency band, thereby communications being performed between transmitting signals and receiving signals through a step of selecting a pair of frequencies, the frequency spacing of which maintains a constant value. Also, signals that have passed a filter behind an amplifier are needed to suppress undesired signal components such as noise and the like existing in the receiving signal frequencies in order to prevent a reduction in receiving sensitivity caused by an infiltration of undesired signals into a receiving section. The general characteristics required of a filter that satisfies the foregoing requirement are to have a small amount of attenuation in the transmitting frequency band and a large amount of attenuation in the receiving frequency band, and to make the attenuation in the transmitting frequency band stay lower than the tolerated attenuation level of the transmitting signal at the highest frequency and the attenuation in the receiving frequency band maintain the needed attenuation of the receiving signal at the lowest frequency. As a result, the filter characteristics are required to have a large amount of attenuation change for frequency changes, thereby causing, in general, the filter characteristics to show large attenuation in transmitting signals and reduced amplification efficiencies.
DISCLOSURE OF THE INVENTION
The object of the present invention is to reduce noises outputted from an amplifier, thereby allowing a filter connected behind the amplifier to have less steep attenuation characteristics and at the same time improving efficiencies of the amplifier.
In order to achieve the foregoing object, an amplifier of the present invention comprises a first filter, which is connected between the output section of a first amplification circuit and the input section of a second amplification circuit, has specified pass band and a specified attenuation band and show different values between input impedance and output impedance.
According to the structure as described in the above, the signals intended for amplification and outputted from the first amplification circuit are inputted to the second amplification circuit almost without any attenuation while the noises outputt
REFERENCES:
patent: 5805023 (1998-09-01), Fukuden
Fujihashi Yoshikuni
Hashimoto Koji
Takahashi Hiroshi
Yahata Kazuhiro
Matsushita Electric - Industrial Co., Ltd.
Mottola Steven J.
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