Amplifiers – With control of power supply or bias voltage – With control of input electrode or gain control electrode bias
Reexamination Certificate
2001-10-31
2003-06-10
Mottola, Steven J. (Department: 2817)
Amplifiers
With control of power supply or bias voltage
With control of input electrode or gain control electrode bias
C330S134000
Reexamination Certificate
active
06577190
ABSTRACT:
RELATED APPLICATION
The present application claims the benefit of Korean Patent Application No. 64273/2000 filed Oct. 31, 2000, which is herein fully incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a linear gain control amplifier, and more particularly, to a wide band linear gain control amplifier for a mobile communications system.
2. Description of the Background Art
FIG. 1
is a block diagram illustrating the construction of a conventional linear gain control amplifier. As illustrated therein, the linear gain control amplifier includes: a compensating circuit unit
10
for converting a control signal CTL inputted for linear gain control into a control voltage V
CTRL
having an exponential form; a first amplifier
20
for gain-controlling an input signal RF_IN according to the control voltage V
CTRL
to output an amplification signal AMP_OUT; a surface acoustic wave filter
30
for filtering any distortions in the amplification signal AMP_OUT and any noise present therein; and a second amplifier
40
for gain-controlling an output of the filter
30
according to the control voltage V
CTRL
to output a compensating signal RF_OUT.
Here, as illustrated in
FIG. 2
, the first amplifier
20
includes: a low-pass filter unit
21
for filtering a low frequency of a control voltage V
CTRL
to output a DC component; a high-pass filter unit
22
for filtering a high frequency of an input signal RF_IN; a capacitor C
3
and inductor L
1
for matching the input signal RF_IN inputted via the high-pass filter unit
22
and an input impedance; an amplification control transistor
23
for amplifying a high-pass filtered input signal to a predetermined level and controlling the gain of an amplification signal AMP OUT by the DC component from the control voltage V
CTRL
; a tank circuit unit
24
for applying a predetermined DC level voltage to the amplification signal AMP_OUT and matching the amplification signal AMP_OUT and a predetermined output impedance; and a bypass circuit unit
25
for removing an AC component applied to the amplification control transistor
23
. The second amplifier
40
can be constructed to be the same as the first amplifier
20
, while the filter
30
can be a surface acoustic wave filter.
The operation of the conventional gain control amplifier will now be described.
First, the compensating circuit unit
10
compensates an externally inputted control signal CTL so that the control signal output characteristics are exponentially approximated for thereby outputting a predetermined control voltage V
CTRL
. This is to linearize the gain characteristics of each amplifier
20
and
40
for the control voltage V
CTRL
by making the previously gain-compensated control voltage V
CTRL
have exponential characteristics, since the gain characteristics of each amplifier
20
and
40
for the control voltage are logarithmic.
The first amplifier
20
gain-controls an input signal RF_IN according to a control voltage V
CTRL
applied from the compensating circuit unit
10
, to thus output an amplification signal AMP_OUT to the filter
30
. The filter
30
filters any distortions in the amplification signal AMP_OUT and any noise present therein, to thereby output a filtered signal to the second amplifier
40
. Then, the second amplifier
40
gain-controls the filtered signal again for thereby outputting a compensating signal RF_OUT.
Here, with the respect to the operation of each amplifier
20
and
40
, when an input signal RF_IN is applied to the first amplifier
20
, the high-pass filter unit
22
filters a high frequency of the applied input signal RF_IN, and the capacitor C
3
and inductor L
1
matches the input impedance of the filtered input signal RF_IN, thus minimizing a loss generated during inputting of a signal.
The amplification control transistor
23
is controlled by an output RF_IN of the high-pass filter unit
22
applied to an input gate G
2
, for thereby amplifying the output RF_IN to a predetermined level according to a set gain and thereafter outputting an amplification signal AMP_OUT. The above amplification control transistor
23
can be a transistor device having a dual-gate structure G
1
, G
2
as shown in FIG.
2
.
At this time, the low-pass filter unit
21
receives the compensated control voltage V
CTRL
output from the compensating circuit unit
10
and filters a low frequency thereof, for thereby applying a DC component to a control gate G
1
of the amplification control transistor
23
. As such, the gain of the amplification control transistor
23
is controlled according to the voltage applied to the control gate G
1
for thereby outputting the compensated amplification signal AMP_OUT to the filter
30
.
Here, since the amplification signal AMP_OUT has a high output level, the tank circuit unit
24
is added to an output terminal in order to use the source voltage VCC as a bias voltage. The tank circuit unit
24
employs a resistor R
4
, a capacitor C
5
, and an inductor L
2
having particular values so that the first amplifier
20
has a desired output impedance in order to match an impedance of the filter
30
.
In addition, the bypass circuit unit
25
serves to remove an AC component applied to the amplification control transistor
23
. Input and output impedance are controlled to a predetermined level by making each capacitor C
3
, C
4
, and C
5
to have variable characteristics.
As described above, the conventional linear gain control amplifier is allowed to have a wide gain variable range by using the first and second amplifiers
20
and
40
, and allowed to have the linearity of the first and second amplifiers
20
and
40
with gain characteristics for a control voltage by exponentially compensating a control signal CTL by the gain compensating unit
10
.
However, since the above-described conventional linear control amplifier includes a surface acoustic wave filter (filter
30
), as well as an inductor and variable capacitors, it is difficult to make the conventional linear control amplifier into an integrated circuit (IC). Also, the necessary inductor cannot be easily formed by standard CMOS processes. Furthermore, an additional process is required to implement the necessary variable capacitors. These drawbacks result in undesirably increased fabrication costs incurred in semiconductor chip manufacturing.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a linear gain control amplifier, which can be easily implemented and formed by standard CMOS processes and can be made into an integrated circuit (IC).
The linear gain control amplifier according to an embodiment of the present invention includes a compensating circuit unit for generating a first compensation control voltage having an exponential relation to a received basic control signal, and also for generating a second control voltage associated with the first control voltage; a variable gain amplification unit for varying a gain by the compensated control voltage; and a driving amplification unit for amplifying a signal inputted from the variable gain amplification unit to an output signal of a desired size.
Advantages of the present invention will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 5099204 (1992-03-01), Wheatley, III
patent: 5757230 (1998-05-01), Mangelsdorf
patent: 5867063 (1999-02-01), Snider et al.
Hynix / Semiconductor Inc.
Mottola Steven J.
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