Feedforward notch filter

Details Feedforward notch filter Feedforward notch filter

2001-12-13

2003-04-29

Choe, Henry (Department: 2817)

Amplifiers

With amplifier bypass means

C330S306000

Reexamination Certificate

active

06556080

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to the field of electronic filters. More particularly, in certain embodiments this invention relates to a feed forward method and apparatus for providing a notch filter in an RF amplifier.
BACKGROUND OF THE INVENTION
Radio transceivers, by definition, have both a transmitter and a receiver—often in the same physical package and using a common power supply, antenna and other circuitry. Due to nonlinearities in the amplification process and leakage signals from the receiver, amplifiers such as radio frequency (RF) power amplifiers can produce undesirable spectral components at the output, often including substantial energy at the receiver's receive frequency. These undesired spectral components can create interference at a receive frequency of the associated receiver (i.e., in a transceiver) and may violate federal regulations. Feed forward compensation has been used in amplifiers to help linearize the amplifiers to compensate for such nonlinearities.
A conventional arrangement of a feedforward amplifier is depicted in
FIG. 1
as amplifier
50
. The power amplifier
54
in this case amplifies the RF input signal applied to its input to produce an output signal which passes through delay
58
. The output of amplifier
54
is also passed through a pad
62
to reduce its magnitude. The input signal is also passed through a delay
66
and is subtracted from the output of the pad
62
to produce an error signal that represents the signal that should be removed from the output of amplifier
54
in order to linearize the amplifier
54
's amplification. This error signal is then amplified by error amplifier
72
and subtracted at element
76
from the output signal from delay element
58
. The error amplifier provides enough gain so that the amount of signal subtracted at
76
approximately matches the output level of the corresponding frequency content emerging from the delay
58
. In this manner, the RF output signal from the feedforward amplifier
50
is linearized and the spurious content of the RF output is reduced substantially.


REFERENCES:
patent: 4447790 (1984-05-01), Fukuda et al.
patent: 5119040 (1992-06-01), Long et al.
patent: 5491454 (1996-02-01), Matz
patent: 5977826 (1999-11-01), Behan et al.
patent: 6236272 (2001-05-01), Takei et al.
patent: 6316983 (2001-11-01), Kitamura
patent: 6400226 (2002-06-01), Sato

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