Amplifiers – With amplifier bypass means
Reexamination Certificate
2000-10-31
2002-12-17
Lee, Benny (Department: 2817)
Amplifiers
With amplifier bypass means
C330S149000, C330S306000
Reexamination Certificate
active
06496065
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a linear amplifier, and more particularly, to a linear amplifier using a low frequency 2
nd
order intermodulation feed-forwarding method.
2. Description of the Related Art
When a mobile terminal or a mobile base station power-amplifies and transmits a signal, the receiving sensitivity of a receiving side is degraded by distortion due to the interference between a fundamental signal to be transmitted and its intermodulation component.
In order to solve the above problem, conventional linear amplifiers shown in
FIGS. 1A
,
1
B and
2
are used. Each of the conventional linear amplifiers roughly includes an input impedance matching unit (Z
s
)
20
for matching the output impedance of a signal source Vs with the input impedance of the input port of a transistor
12
,
14
or
24
, and an output impedance matching unit (Z
L
)
29
impedance-matching the output port of the transistor
12
,
14
or
24
with an output load. An amplifier shown in
FIG. 1A
tunes to a distortion component signal using a source harmonic tuning method and reflects an intermodulation signal reflected by the gate of the transistor
12
back to the gate using a reflection coefficient control unit
17
having a variable capacitor or a stub at the gate port of the transistor
12
, thereby offsetting a distortion component. In
FIG. 1B
, a reflection coefficient control unit
16
is installed to the rear of the transistor
14
, and tunes a harmonic output from the rear of the transistor
14
and reflects the harmonic back to the gate using a load harmonic tuning method, thereby offsetting a 3
rd
order harmonic component.
FIG. 2
shows a linear amplifier using an intermodulation signal feed-backwarding method. The linear amplifier of
FIG. 2
includes an amplification transistor
24
, filters
25
and
28
for filtering a 2
nd
order harmonic component from an input signal, a phase shifting unit
26
for shifting the phase of the 2
nd
order harmonic component, and an amplifier
27
for amplifying the phase-shifted 2
nd
order harmonic component to a predetermined value. The phase-shifted 2
nd
order intermodulation signal is fed backward to the input port of the amplification transistor
24
, thereby offsetting a 3
rd
order intermodulation component.
However, these conventional intermodulation signal tuning methods can offset only several dB of 3
rd
order harmonic component. In the intermodulation signal feed-backwarding method, 10 dB to 15 dB of intermodulation component can be offset, but the characteristics is unstable and the band is narrowed.
SUMMARY OF THE INVENTION
An objective of the present invention is to provide a linear amplifier using a low frequency 2
nd
order intermodulation feed-forwarding method for offsetting a 3
rd
intermodulation component while maintaining the stable characteristics of a linear amplification circuit obtained by feed-forwarding.
To achieve the above objective, the present invention provides a linear amplifier using a low frequency 2
nd
intermodulation feed-forwarding method to offset the 3
rd
intermodulation component of a fundamental signal, the device including: a transistor for amplifying the power of the fundamental signal; an input impedance matching unit connected to the gate of the transistor for impedance-matching a source of the received fundamental signal with the gate of the transistor; a first filter unit, one end of which is connected to the gate of the transistor, for filtering a 2
nd
order intermodulation signal from the fundamental signal; a low frequency amplifier connected to the other end of the first filter unit, for amplifying the 2
nd
order intermodulation signal with a predetermined voltage gain; a second filter unit connected in series between the output port of the low frequency amplifier and the drain output port of the transistor, for filtering the amplified 2
nd
intermodulation signal and feeding the same to the output port of the transistor; and an output impedance matching unit connected to the output port of the transistor for impedance-matching the output port of the transistor with an external load.
The voltage gain (&bgr;) of the low frequency amplifier
-
gm
3
·
C
0
gmd
·
C
1
.
The gm
3
and gmd are the coefficients of terms v
gs
(t)
3
and V
gs
(t)v
ds
(t), respectively, of Equation:
i
ds
[v
gs
,v
ds
]=gm·v
gs
(
t
)+
gd·v
gs(t)
+gm
2
·
v
gs
(
t
)
2
+gmd·v
gs
(
t
)
v
ds
(
t
)+
gd
2
·v
ds
(
t
)
2
+gm
3
·v
gs
(
t
)
3
+gm
2
d·
v
gs
(
t
)
2
·v
ds
(
t
)+
gmd
2
·v
gs
(
t
)·
v
ds
(
t
)
2
+gd
3
·v
ds
(
t
)
3
+. . .
which is a Taylor series extension formula of the drain-source non-linear current i
ds
[v
gs
,v
ds
] of the transistor.
Also, C0 and C1 in the voltage gain are the coefficients of the constant term and term v
gs
(t) in Equation C
gs
[v
gs
(t)]=C
0
+C
1
·v
gs
(t)+C
2
·v
gs
(t)
2
+ . . . , which is a power series of a gate source capacitor of the transistor.
REFERENCES:
patent: 5276406 (1994-01-01), Samay et al.
patent: 5406226 (1995-04-01), Cioffi et al.
patent: 6052029 (2000-04-01), Uda et al.
patent: 6163221 (2000-12-01), Matsuno
patent: 6-214416 (1996-03-01), None
patent: 7-062070 (1996-09-01), None
Yang et al.; A New Linear Amplifier Using low-frequency second order intermodulation Component Feedforwarding; IEEE Microwave and Guided Wave Letters, vol. 4, No. 10, Oct., 1999.*
Yang et al.; “A New Linear Amplifier Using Low-Frequency Second-Order Intermodulation Component Feedforwarding”,IEEE Microwave and Guided Wave Letters, vol. 4, No. 10, Oct. 1999, pp. 419-421.
Kang Sang-hoon
Kim Bum-man
Yang Youn-goo
Choe Henry
Lee Benny
Leydig , Voit & Mayer, Ltd.
Pohang University of Science and Technology Foundation
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