Title: Variable gain amplifier for high frequency band using microstrip hybrid
Abstract: The present invention relates to a variable gain amplifier for a high frequency band, and comprises a divider for dividing a input signal; a fixed variable gain amplifier for amplifying an output signal of the divider; a microstrip ring hybrid for outputting a plurality of signals which have the same or different phases, wherein the microstrip ring hybrid comprises a plurality of input terminals and output terminals having a constant impedance; a switch for selectively inputting an output of the variable gain amplifier to any one of the input terminals of the microstrip ring hybrid; a transmission line for delaying the output signal of the divider; and a combiner for combining each of the output signals of the microstrip ring hybrid and a signal passing through the transmission line and outputting the combined signal, wherein the output power is controlled by selectively inputting the output of the variable gain amplifier to any one of the input terminals of the microstrip ring hybrid by means of the switches, so that its input-output matching may be obtained irrespective of its gain.
Patent Number: 6,977,554 Issued on 12/20/2005 to Sung, et al.
| Inventors:
|
Sung; Jin Bong (Daejon-shi, KR);
Kang; Sung Weon (Daejon-shi, KR);
Kim; Yun Tae (Daejon-shi, KR)
|
| Assignee:
|
Electronic and Telecommunications Research Institute (KR)
|
| Appl. No.:
|
679056 |
| Filed:
|
October 2, 2003 |
Foreign Application Priority Data
| Nov 08, 2002[KR] | 10-2002-0069129 |
| Current U.S. Class: |
330/286; 330/51; 330/124.R |
| Intern'l Class: |
H03F 003/60 |
| Field of Search: |
330/286,51,124.R
|
References Cited [Referenced By]
U.S. Patent Documents
| 5289193 | Feb., 1994 | Lenormand et al.
| |
| 5528245 | Jun., 1996 | Aker et al.
| |
| 6211729 | Apr., 2001 | Morkner et al.
| |
| 6531935 | Mar., 2003 | Russat et al.
| |
| 6806768 | Oct., 2004 | Klaren et al.
| |
| Foreign Patent Documents |
| 2000/-106510 | Apr., 2000 | JP.
| |
| 1020000060736 | Oct., 2000 | KR.
| |
Primary Examiner: Nguyen; Patricia
Attorney, Agent or Firm: Blakely Sokoloff Taylor & Zafman
Claims
1. A variable gain amplifier, comprising:
a divider for dividing a input signal;
a fixed variable gain amplifier for amplifying an output signal of the divider;
a microstrip ring hybrid for outputting a plurality of signals which have the
same or different phases, the microstrip ring hybrid comprising a plurality of
input terminals and output terminals having a constant impedance;
a switch for selectively inputting an output of the variable gain amplifier to
any one of the input terminals of the microstrip ring hybrid;
a transmission line for delaying the output signal of the divider; and
a combiner for combining each of the output signals of the microstrip ring hybrid
and a signal passing through the transmission line and outputting the combined
signal,
wherein the output power is controlled by selectively inputting the output of
the variable gain amplifier to any one of the input terminals of the microstrip
ring hybrid by means of the switches.
2. A variable gain amplifier according to claim 1, wherein an impedance of an
inner diameter line and the distances between the terminals of the microstrip ring
hybrid is controlled, thereby each of the terminals having an impedance Z
0.
3. A variable gain amplifier according to claim 1, wherein the impedance Z
0
is 50Ω, wherein the impedance of the inner diameter line is √2 Z
0,
and wherein the distance between terminals is λ/4 or 3λ/4.
4. A variable gain amplifier according to claim 1, wherein the number of each
of the input and output terminals of the microstrip ring hybrid is two.
5. A variable gain amplifier according to claim 1, wherein the length of the
transmission line is λ/4 or 3λ/4.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a variable gain amplifier for a high frequency
band, and more specifically, to a variable gain amplifier for a high frequency
band using a microstrip ring hybrid so that the constant matching conditions in
input and output may be obtained irrespective of its gain.
2. Description of the Prior Art
Generally, a conventional variable gain amplifier is able to control its
gain by converting transmission paths of signals with a switch or by controlling
a bias current or voltage of the amplifier.
FIG. 1 is a circuit diagram illustrating a conventional variable gain amplifier
with a switch. The conventional variable gain amplifier comprises a fixed variable
gain amplifier
101 and a switch
102 which is connected between a
input terminal IN and an output terminal OUT of the fixed variable gain amplifier
101.
When the switch is turned OFF, the input IN and the output OUT are disconnected,
so that high output power can be obtained by operation of the fixed variable gain
amplifier
101. When the switch is turned ON, the input IN and the output
OUT are connected, so that low output power can be obtained.
In the conventional variable gain amplifier described above, the low and high
output powers can be obtained in accordance with change of the impedance of the
amplifier associated with the switch being turned ON and OFF. Most of the variable
gain amplifiers obtain high output power with the switch being turned OFF. However,
in order to obtain low output power of the variable gain amplifier when the switch
is turned ON, the gain of the variable gain amplifier may be lowered due to the
resistance of the switch itself. Therefore, it is a problem that good condition
of impedance matching can not be obtained with the conventional variable gain amplifiers.
SUMMARY OF THE INVENTION
A object of the present invention is to provide a variable gain amplifier in
which
the output of amplifier to the microstrip ring hybrid having a constant impedance
irrespective of its output power, thereby controlling its gain and thus solving
the aforementioned problems.
In order to accomplish the above object, a variable gain amplifier for a high
frequency band according to the present invention is characterized to comprise
a divider for dividing a input signal; a fixed variable gain amplifier for amplifying
an output signal of the divider; a microstrip ring hybrid for outputting a plurality
of signals which have the same or different phases, wherein the microstrip ring
hybrid comprises a plurality of input terminals and output terminals having a constant
impedance; a switch for selectively inputting an output of the variable gain amplifier
to any one of the input terminals of the microstrip ring hybrid; a transmission
line for delaying the output signal of the divider; and a combiner for combining
each of the output signals of the microstrip ring hybrid and a signal passing through
the transmission line and outputting the combined signal, wherein the output power
is controlled by selectively inputting the output of the variable gain amplifier
to any one of the input terminals of the microstrip ring hybrid by means of the switches.
In addition, a microstrip ring hybrid according to the present invention is characterized
in that the impedance Z
0 is 50 Ω, the impedance of the inner diameter
line is 2 Z
0, and the distance between terminals is λ/4 or 3λ/4.
In addition, a microstrip ring hybrid according to the present invention is characterized
in that the number of each of the input and output terminals of the microstrip
ring hybrid is two and the length of the transmission line is λ/4 or 3λ/4.
BRIEF DESCRIPTION OF THE DRAWINGS
The aforementioned aspects and other features of the present invention will be
explained in the following description, taken in conjunction with the accompanying
drawings, wherein:
FIG. 1 is a circuit diagram illustrating a conventional high frequency band
variable gain amplifier with a switch; and
FIG. 2 is a circuit diagram illustrating a variable gain amplifier according
to the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention will be described in detail by way of a preferred embodiment
with reference to accompanying drawings.
A microstrip ring hybrid has two input ports through which two signals are input
and output ports which output the components of addition and difference of the
two input signals. The microstrip ring hybrid has mainly been adapted to a frequency
combiner, an amplifier or a high frequency band circuit.
When the microstrip ring hybrid is designed to have inner diameter line, of
which impedance is √{square root over (2)} Z
0 and to have distances
between terminals which are λ/4 and 3λ/4, the impedances at the terminals
are equal to Z
0, where the Z
0 is a characteristic impedance
of wave propagation and about 50 Ω.
By using input-output matching characteristics of the microstrip ring hybrid
according
to the present invention, it is possible to obtain good input-output standing wave
ratio irrespective of the output power. Therefore, it is possible to implement
a variable gain amplifier having constant input and output matching characteristics
irrespective of the gain.
Now, the preferred embodiments of the present invention will be described in
details with reference to the accompanying drawings.
FIG. 2 is a circuit diagram illustrating a variable gain amplifier according
to the present invention.
An input signal S
IN is divided into two signals; a signal S
0
and a signal S
5. When the signal S
0 is input to a fixed variable
gain amplifier
202, the signal S
0 is amplified by the fixed variable
gain amplifier
202. Passing through a transmission line
205, the
signal S
5 is delayed by the transmission line
205 for a predetermined time.
The output of the fixed variable gain amplifier
202 is transferred to
one of input terminals P
1, P
2 of a microstrip ring hybrid
204
with the operation of a switch
203. When the microstrip ring hybrid
204
receives the output of the fixed variable gain amplifier
202, the microstrip
ring hybrid
204 converts the output of the fixed variable gain amplifier
202 to two signals having the same amplitudes and the opposite phases (or
two signals having the same amplitudes and the same phases) through two output
terminals Q
1 or Q
2.
Each of the signals from the output terminals Q
1 and Q
2 of the
microstrip ring hybrid
204 and the delayed signal which passes through the
transmission line
206 are combined at the combiner
206. The combined
signal is output through output terminal S
OUT of the combiner
206.
Now, the operation of the variable gain amplifier according to the present invention
will be described in details with reference to Tables 1 and 2 described below.
Table 1 shows a signal component in low power characteristics.
The input signal S
IN is divided by the divider
201 into two
signals S
0 and S
5 which have amplitudes of V/√{square root
over (2)} and phases of φ.
When the signal S
0 is input to the fixed variable gain amplifier
202,
the signal S
0 is amplified by the variable gain amplifier
202, and
then, is transferred to one of input terminal P
1, P
2 of the microstrip
ring hybrid
204 with the operation of the switch
203. When the signal
S
1 having the amplitude of GV/√{square root over (2)} and the phase
of φ due to the amplification of the fixed gain amplifier
202 is input
to the input terminal P
1, the signal S
4 having the amplitude of GV/2
and the phase of φ-90° and the signal S
3 having the amplitude
of GV/2 and the phase of φ+90° are output from the output terminals
Q
1, Q
2 of the microstrip ring hybrid
204, respectively. In
other words, when the signal S
1 having the amplitude of GV/√{square
root over (2)} and the phase of φ is input to the input terminal P
1
and the signal S
2 is not input to the input terminal P
2, the signals
S
3 and S
4 output from the output terminals Q
1 and Q
2,
respectively, of the microstrip ring hybrid
204 have the same amplitudes
and the phase difference of 180°.
After that, the output signals S
3, S
4 of the microstrip ring
hybrid
204 and the signal S
6 having the amplitudes of V/√{square
root over (2)} and the phases of φ90° delayed through the V/√{square
root over (2)} transmission line
205 are input to the combiner
206.
The combiner
206 combines the signals S
3, S
4, and S
6
to output a signal having the amplitude of V/√{square root over (2)} and
the phase of N/A at the output terminal S
out, where N/A denote a phase
which is determined in accordance with the characteristics of the combiner. In
other words, the signal of the output terminal S
out has a low output
power characteristics having a gain of -3 dB.
| |
TABLE 1 |
| |
|
| |
Signal |
Voltage |
Phase (°) |
| |
|
| |
SIN |
V |
N/A |
| |
S0 |
V/√{square root over (2)} |
φ |
| |
S1 |
GV/√{square root over (2)} |
φ |
| |
S2 |
0 |
N/A |
| |
S3 |
GV/2 |
φ + 90° |
| |
S4 |
GV/2 |
φ - 90° |
| |
S5 |
V/√{square root over (2)} |
φ |
| |
S6 |
V/√{square root over (2)} |
φ + 90° |
| |
Sout |
V/√{square root over (2)} |
N/A |
| |
|
Table 2 shows a signal component in high power characteristics.
The input signal S
IN is divided by the divider
201 into two
signals S
0 and S
5 which have amplitudes of V/√{square root
over (2)} and phases of φ.
When the signal S
0 is input to the fixed variable gain amplifier
202,
the signal S
0 is amplified by the variable gain amplifier
202. and
transferred to one of input terminal P
1, P
2 of the microstrip ring
hybrid
204 with the operation of the switch
203. When the signal
S
2 having the amplitude of GV/√{square root over (2)} and the phase
of φ due to the amplification of the fixed gain amplifier
202 is input
to the input terminal P
2, the signals S
4 and S
3 having the
amplitude of GV/2 and the phase of φ+90° are output from the output
terminals Q
1, Q
2 of the microstrip ring hybrid
204. In other
words, when the signal S
2 having the amplitude of GV/√{square root
over (2)} and the phase of φ is input to the input terminal P
1 and
the signal S
2 is not input to the input terminal P
2, the signals
S
3 and S
4 output from the output terminals Q
1 and Q
2,
respectively, of the microstrip ring hybrid
204 have the same amplitudes
and the same phases.
After that, the output signals S
3, S
4 of the microstrip ring
hybrid
204 and the signal S
6 having the amplitudes of V/√{square
root over (2)} and the phases of φ90° delayed through the /4 transmission
line
205 are input to the combiner
206. The combiner
206 combines
the signals S
3, S
4, and S
6 to output a signal having the amplitude
of V/√{square root over (2)} +GV and the phase of N/A at the output terminal
S
out, where N/A denote a phase which is determined in accordance with
the characteristics of the combiner. In other words, the signal of the output terminal
S
out has a high output power characteristics.
| |
TABLE 2 |
| |
|
| |
Signal |
Voltage |
Phase (°) |
| |
|
| |
SIN |
V |
N/A |
| |
S0 |
V/√{square root over (2)} |
φ |
| |
S1 |
0 |
N/A |
| |
S2 |
GV/√{square root over (2)} |
φ |
| |
S3 |
GV/2 |
φ + 90° |
| |
S4 |
GV/2 |
φ + 90° |
| |
S5 |
V/√{square root over (2)} |
φ |
| |
S6 |
V/√{square root over (2)} |
φ + 90° |
| |
Sout |
V/√{square root over (2)} + GV |
N/A |
| |
|
As shown in Tables 1 and 2, when the microstrip ring hybrid is designed to have
inner diameter line, of which impedance is √{square root over (2)}Z
0
and to have distances between terminals of λ/4 and 3λ/4, the impedances
at the terminals are equal to Z
0 Both output terminals Q
1 and
Q
2 of the microstrip ring hybrid have the same impedance of Z
0,
even though a signal is applied to any one of the two input terminals P
1
and P
2 of the microstrip ring hybrid. In addition, the impedances of the
input and output of the transmission line
205 are equal to Z
0.
Therefore, in the variable gain amplifier according to the present invention, there
are no changes of the three input impedances and the output impedance of the combiner
206. And also, the input and output standing wave ratio can be kept constant.
As described above, according to the present invention, the gain is able to controlled
by selectively inputting signals into the microstrip ring hybrid having constant
impedance irrespective of the magnitude of the output power by using the switches.
Therefore, it is possible to keep impedance matching of input and output good irrespective
of the magnitude of the output power. As a result, it is possible to easily implement
a frequency mixer, an amplifier, and a high frequency band circuit, etc., having
good operational characteristics by using the variable gain amplifier.
The present invention has been described with reference to a particular embodiment
in connection with a particular application. Those having ordinary skill in the
art and access to the teachings of the present invention will recognize additional
modifications and applications within the scope thereof.
It is therefore intended by the appended claims to cover any and all such applications,
modifications, and embodiments within the scope of the present invention.
*
