Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
2002-11-26
2004-06-15
Choe, Henry (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S296000
Reexamination Certificate
active
06750718
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio-frequency amplifier. In particular, the invention relates to a radio-frequency amplifier in a transmission power amplifier for a CDMA modulation type portable terminal.
2. Background Art
In recent years, small information terminals (hereinafter referred to as “portable terminals”) such as cellular phones and PDAs have spread. In portable terminals, amplifiers having high power consumption efficiency are now required. Among multiple access schemes employed by cellular phones is a code division multiple access (CDMA) modulation scheme that is based on a spread spectrum technique. In transmission power amplifiers for CDMA modulation type portable terminals, not only the power load efficiency at the time of high output power but also the efficiency at the time of low output power is important because a power control is performed during a communication. Therefore, conventionally, in such amplifiers, switching is made between bias settings for high output power and low output power.
FIG. 4
shows a conventional power amplifier
60
with a bias circuit having a bias setting switching function. In
FIG. 4
, reference numeral
1
denotes a radio-frequency (RF) transistor;
7
, a terminal of a collector voltage source for the RF transistor
1
;
3
, a bias circuit unit for supplying a base bias to the RF transistor
1
; and
2
, a bias switching circuit unit for switching between bias settings. In the bias circuit unit
3
, reference numeral
10
denotes a transistor Q
1
;
6
, a terminal of a bias circuit voltage source Vcb that is connected to the collector of the transistor Q
1
(
10
);
8
, a resistor R
1
that is provided between the emitter of the transistor Q
1
(
10
) and the ground GND;
5
, a terminal of a reference voltage Vref;
9
, a resistor R
2
that is provided between the terminal
5
of the reference voltage Vref and the base of the transistor Q
1
(
10
); and
23
and
24
, transistors that are provided between the base of the transistor Q
1
(
10
) and the ground GND. In the bias switching circuit unit
2
, reference numeral
11
denotes a transistor Q
2
;
21
, a resistor that is provided between the collector of the transistor Q
2
(
11
) and the base of the RF transistor
1
;
4
, a bias switching MOD terminal; and
22
, a resistor that is provided between the base of the transistor Q
2
(
11
) and the bias switching MOD terminal
4
.
Next, an operation of the conventional amplifier
60
will be described with reference to FIG.
4
. When the amplifier
60
is in high output power operation, the bias switching MOD terminal
4
receives an off-voltage (0 V) and hence the transistor Q
2
(
11
) of the bias switching circuit unit
2
is turned off. As a result, the voltage that is output from the bias circuit unit
3
is supplied to the RF transistor
1
without modification. The base bias that is supplied to the RF transistor
1
at this time is set so that an output power distortion characteristic that is required for the amplifier
60
in high output power operation is satisfied with a sufficient margin.
On the other hand, when the amplifier
60
is in low output power operation, the bias switching MOD terminal
4
is given an on-voltage (3 V) and hence the transistor Q
2
(
11
) of the bias switching circuit unit
2
is turned on. As a result, a current flows through the bias switching circuit unit
2
and the base bias of the RF transistor
1
is lowered. When the amplifier
60
is in low output power operation, even if the base bias of the RF transistor
1
is lowered, the amplifier
60
operates in a linear range and hence its distortion characteristic should be satisfactory. The above-described bias switching function can increase efficiency at the time of low output power when the amplifier
60
operates in a linear range.
As described above, in the conventional bias circuit having the function of switching the base bias of the RF transistor
1
, the base bias that is set by the bias circuit unit
3
is subjected to switching of the bias switching circuit unit
2
. This causes a problem that a variation in the idle current of the RF transistor
1
strongly depends on a variation in the bias voltage that is output from the bias circuit unit
3
. When the amplifier
60
is in low output power operation, its efficiency strongly depends on the idle current of the RF transistor
1
, to increase the efficiency of the amplifier
60
and thereby it is necessary to accurately set the bias that is output from the bias circuit unit
3
. When the amplifier
60
is in low output power operation, a current of about 100 mA flows through it and hence a current of about 5 mA is consumed in the bias circuit unit
3
. There is a problem that this current greatly influences the efficiency of the amplifier
60
.
SUMMARY OF THE INVENTION
The present invention has been achieved to solve the above problems and an object of the invention is therefore to provide a radio-frequency amplifier capable of increasing its efficiency by decreasing a variation in the idle current of an RF transistor.
According to one aspect of the present invention, a radio-frequency amplifier is provided for amplifying a radio-frequency signal. The radio-frequency amplifier comprises a radio-frequency transistor, a reference voltage supply unit for supplying a first base bias from a reference voltage source to a base of the radio-frequency transistor via a first resistor, and a bias circuit unit for outputting a second base bias to the base of the radio-frequency transistor. The bias circuit unit comprises a switching terminal that provides a signal that serves to switch outputting the second base bias or not. The radio-frequency transistor performs a constant voltage operation and the radio-frequency amplifier produces a high output power when the bias circuit unit outputs the second base bias. The radio-frequency transistor performs a constant current operation and the radio-frequency amplifier produces a low output power when the bias circuit unit does not output the second base bias.
Other and further objects, features and advantages of the invention will appear more fully from the following description.
REFERENCES:
patent: 6313705 (2001-11-01), Dening et al.
patent: 6333677 (2001-12-01), Dening
patent: 6369657 (2002-04-01), Dening et al.
patent: 5-145349 (1993-06-01), None
Maemura Kousei
Moriwaki Takao
Choe Henry
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
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