Amplifiers – With amplifier bypass means
Reexamination Certificate
2000-06-12
2002-06-04
Mottola, Steven J. (Department: 2817)
Amplifiers
With amplifier bypass means
C330S149000
Reexamination Certificate
active
06400223
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 are 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 educing 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 (and matching) of the amplifier
112
(and other passive components).
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. The known feed-forward amplifier system described above suffers from poor carrier cancellation in wide-band adaptive feed-forward amplifiers for multi-carrier operation. There are several ways to attempt to overcome this problem. First, an unnecessarily large error amplifier can be used to compensate for the poor carrier cancellation. The problem with this approach is that it leads to poor system efficiency. Another approach to alleviate this problem is to specify the required performance of active and passive components from manufacturers to fit within tight phase and gain flatness tolerances and that have very good matching. This approach, however, increases the unit price of the components and has limitations in terms of what can be achieved in practice. Finally, complex and more elaborate digital control circuitry can be used in order to provide high phase and gain control accuracy and resolution, but this approach also leads to increased costs with only marginal performance improvements.
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 over wide bandwidths. The present invention uses multiple signal cancellation loops in a feed-forward amplifier system. The double carrier cancellation method and apparatus disclosed herein improve carrier cancellation levels and at the same time avoid the disadvantages described above. In addition, the double carrier cancellation method and apparatus leads to a reduction in the size of the error amplifier needed in the distortion cancellation loop thus leading to improved system efficiency.
According to one variation of the invention, two signal cancellation loops of a two carrier multi-carrier feed-forward amplifier system are provided, wherein each loop shares the same amplifier and each loop has a separate adjuster. The separate adjusters can be used to adjust different portions of a frequency band.
Other features and advantages of the invention will become apparent through the following description, the figures, and the claims.
REFERENCES:
patent: 6066984 (2000-05-01), Tomaru et al.
patent: 6133791 (2000-10-01), Horiguchi et al.
Banner & Witcoff , Ltd.
Mottola Steven J.
Nokia Networks OY
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