Amplifiers – With amplifier bypass means
Reexamination Certificate
1999-11-30
2002-05-21
Pascal, Robert (Department: 2817)
Amplifiers
With amplifier bypass means
C330S149000, C455S063300
Reexamination Certificate
active
06392481
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to electrical amplification, and more particularly to feed forward amplification.
2. Description of the Related Art
A feed-forward amplifier system was proposed by Harold S. Black in the 1920's as illustrated by his United States patent, U. S. Pat. No. 1,686,792, which is hereby incorporated by reference for all purposes. The feed-forward amplifier system design was intended to reduce amplifier distortion, e.g., inter-modulation distortion (IMD) of carrier signals (carriers) to thereby suppress cross-talk between multiple carriers. Since then various feed-forward amplifier system designs have been proposed for reducing amplifier distortion and noise. A number of examples of the various feed-forward amplifier designs is provided in U.S. Pat. No. 5,051,704 issued to Chapman et al., hereby incorporated by reference for all purposes. The feed-forward amplifier system is now well established and particularly useful in wideband and multi-carrier systems.
One particular example of a feed-forward amplifier system used for reducing distortion and noise is provided in FIG.
1
. There is shown a feed-forward amplifier system having two different carrier signals, carrier signal
101
and carrier signal
102
having two different frequencies that are input into to node
110
where they produce combined signal
103
. Combined signal
103
is provided through node
111
to an amplifier
112
and an adjuster
113
. The output of amplifier
112
is provided through node
115
to a delay element
117
and to node
116
. The output of adjuster
113
is input to delay element
114
and output therefrom to node
116
. Node
111
, amplifier
112
, node
115
, node
116
, adjuster
113
, and delay element
114
make up a signal cancellation loop
140
. As such, ideally the output of the signal cancellation loop
140
from node
116
has had the signal of the combined carrier signals, signal
103
, removed and contains only the distortion and noise produced as a result of imperfect amplification and inter-modulation products of amplifier
112
. However, in some applications, for example wideband and multi-carrier amplifier systems, the carrier signals are not completely cancelled in the signal cancellation loop
140
, because of non-ideal frequency response of the amplifier
112
.
The output of node
115
is input to delay element
117
and the output of delay element
117
is input to node
120
. The output of node
116
is input to adjuster
118
. The output of adjuster
118
is input to amplifier
119
which amplifies the adjusted distortion and noise component, introduced to the signal by amplifier
112
. The output of amplifier
119
is input to node
120
. Node
115
, node
116
, adjuster
118
, amplifier
119
, delay element
117
, and node
120
make up distortion cancellation loop
150
which operates to remove the distortion and noise component from the output signal of amplifier
112
to thereby produce amplified signal
104
reasonably free of noise and distortion introduced by amplifier
112
.
In operation, the feed-forward amplifier system of
FIG. 1
operates to remove the distortion, e.g., IMD, and noise that would normally occur as a result of the non-ideal characteristics and inter-modulation products of amplifier
112
. First, the distortion and noise generated by amplifier
112
is isolated in the signal cancellation loop by, for example, subtracting the source signal
103
from the amplified output of amplifier
112
. This signal is output from node
116
and is often referred to as the error signal. Next, the error signal is adjusted by adjuster
118
, amplified by amplifier
119
, and then, for example, subtracted at node
120
from the delayed (via delay element
117
) amplified output signal of amplifier
112
which contains distortion and noise introduced by amplifier
112
. As a result, the signal
104
output from the feed-forward amplifier system is intended to have reduced distortion and noise.
However, for some applications amplifier designs are required to be very robust to achieve the distortion and noise reduction required. This is particularly true for wideband and multi-carrier applications such as cellular telephone communications.
SUMMARY OF THE INVENTION
The present invention is directed to improving the quality of the signal output from a feed-forward amplifier system and/or allowing for reduction of the distortion and noise that results from the electrical characteristics of the amplifiers used in a feed-forward amplifier system. The present invention uses multiple adjusters in the signal cancellation loop of a feed-forward amplifier system so as to more accurately adjust the different frequencies within a frequency band. For example, in a multi-carrier feed-forward amplifier system two or more adjusters are provided in the signal cancellation loop so as to provide more accurate adjustment for the various carriers rather than relying on a single adjuster to adjust for all carriers.
According to one variation of the invention, two adjusters are provided in the signal cancellation loop of a two carrier multi-carrier feed-forward amplifier system. Each of the two adjusters is directed to adjusting a respective one of the two carriers. The outputs of the adjusters are combined and input to a delay element in the signal cancellation loop. According to another variation of the invention, the outputs of the adjusters are combined and input to the amplifier in the signal cancellation loop.
As a result of using two or more separate adjuster devices, one (or more) for each carrier, all of the carriers may be adjusted to be cancelled as precisely as one carrier can be cancelled in a single carrier amplifier with a single adjuster. This eases the amplitude and phase response requirements of the main amplifier and reduces the maximum output power of the auxiliary amplifier. As a result, the design and manufacture of the main amplifier becomes easier and lowers its cost. Further, the auxiliary amplifier can be made smaller and efficiency of the feed forward amplifier increases.
Other features and advantages of the invention will become apparent through the following description, the figures, and the claims.
REFERENCES:
patent: 1686792 (1928-10-01), Black
patent: 5051704 (1991-09-01), Chapman et al.
patent: 5334946 (1994-08-01), Kenington et al.
patent: 5444418 (1995-08-01), Mitzlaff
patent: 5594385 (1997-01-01), Anvari
patent: 5926067 (1999-07-01), Myer et al.
patent: 6078216 (2000-06-01), Proctor, Jr.
patent: 6166601 (2000-12-01), Shalom et al.
patent: 0 675 594 (1995-04-01), None
patent: 0 768 752 (1997-04-01), None
patent: 0 774 833 (1997-05-01), None
Meyer, Eschenback, and Edgerley: “A Wide-Band Feedforward Amplifier” IEEE Journal Of Sold-State Circuits, Dec. 1974, vol. 8c-9, No. 6, pp. 422-428.
Narahashi and Nojima: “Extremely Low-Distortion Multi-Carrier Amplifier—Self Adjusting Feed-Forward (SAFF) Amplifier-” IEEE, 1991, pp. 1485-1490.
Myer: “A Multicarrier Feed-forward Amplifier Design” Microwave Journal, Oct. 1994, pp. 78, 83-84, 86, and 88.
Parsons, Kenington, and McGeehan: “Efficient Linearisation of RF Power Amplifiers For Wideband Applications” The Institution of Electrical Engineers, Published by IEE, London, 1994, 7 pages.
Konstantinou and Paul: “Analysis And Design Of Broadband, High Efficiency Feedforward Amplifiers” Department of Electrical Engineering & Electronics, University of Manchester Institute of Science & Technology, IEEE MTT-s Digest, 1996, pp. 867-870.
Banner & Witcoff , Ltd.
Choe Henry
Nokia Networks Oy
Pascal Robert
LandOfFree
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