Amplifiers – With pilot frequency control means
Patent
1994-04-22
1995-12-19
Mullins, James B.
Amplifiers
With pilot frequency control means
330151, H03F 126
Patent
active
054771870
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention generally relates to radio telecommunication systems and more particularly to a feed forward amplifier suitable for a broadband RF amplifier used in base stations of mobile telephone systems as well as to a control of such a feed forward amplifier.
BACKGROUND ART
With the deployment of digital mobile telephone systems, there is a demand for compact, low-power consumption base stations that can be constructed at a reduced cost. In order to achieve this object, a common amplification construction is employed for the RF amplifiers of the base stations, wherein a plurality of carriers of different frequencies are amplified by a common, single amplifier. In order to amplify a plurality of signals of different frequencies simultaneously, such amplifiers generally employ the feed forward construction which is suitable for eliminating cross modulation distortion.
In the conventional feed forward amplifiers, however, there has been a problem that the equilibrium of the feed forward loop tend to be lost due to a change in the operational environment such as ambient temperature. Such a deviation of the feed forward loop results in a degradation in the compensation of distortions. In order to avoid such a deviation of the feed forward loop, therefore, the conventional feed forward amplifier generally has a control function for detecting the operational state of the loop and for controlling the loop automatically in response to the detected state of the loop.
FIG. 1 shows the fundamental construction of a well known feed forward amplifier. Referring to FIG. 1, it will be noted that the feed forward amplifier is generally formed of a distortion extraction loop 1 and a distortion elimination loop 2.
In the distortion extraction loop 1, an input RF signal including therein a main signal component is supplied to an input terminal 3, wherein the RF signal is branched by a hybrid circuit 4 into a first branch signal and a second branch signal. The first branch signal is amplified in a main amplifier 5 and branched further in a directional coupler 6. One of the signals thus branched in the directional coupler 6 is then supplied to a power synthesizer 8 via an attenuator 7. On the other hand, the signal of the second branch is supplied to a variable attenuator 10 and a variable phase shifter 11 via a delay line 9, and the signal thus passed through the attenuator 10 and the phase shifter 11 is supplied to the power synthesizer 8. Thereby, the variable attenuator 10 and the variable phase shifter 11 are set such that both main signal components, supplied to the power synthesizer 8 along the first and second paths, have an equal amplitude and delay time as well as a mutually opposite phase difference of 180.degree. (inverse phase relationship). As a result, the main signal components are suppressed in the output of the power synthesizer 8, and the output of the power synthesizer 8 contains only the non-linear distortion components that are formed in the main amplifier 5.
In the distortion elimination loop 2, on the other hand, the other output of the directional coupler 6 is supplied to the power synthesizer 13 via a delay line 12. Further, the non-linear distortion components extracted by the power synthesizer 8 are supplied to a secondary amplifier 16 for amplification via a variable attenuator 14 and a variable phase shifter 15. After amplification in the secondary amplifier 16, the signal is supplied to the power synthesizer 13. In this case, too, the variable attenuator 14 and the variable phase shifter 15 are set such that both of the distortion components supplied to the power synthesizer 13 via respective paths have the same amplitude and delay time as well as a mutually opposite phase difference of 180.degree. and thereby the distortion components are suppressed effectively from the output RF signal of the directional coupler 6 and, hence, in the output RF signal of the main amplifier 5. As a result, the distortion of the main signal is minimized.
As described above, the feed fo
REFERENCES:
patent: 4389618 (1983-06-01), Bauman
patent: 5157345 (1992-10-01), Kenington et al.
Seidel, "A Microwave Feed-Forward Experiment", The Bell System Technical Journal, Nov. 1971, pp. 2879-2916.
Hanaka Mitsunori
Hasegawa Junichi
Kitazawa Teruhiko
Kobayashi Fumihiko
Nakamura Tomohiro
Fujitsu Limited
Mullins James B.
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