Amplifiers – With semiconductor amplifying device – Including particular power supply circuitry
Reexamination Certificate
1998-12-10
2001-01-09
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including particular power supply circuitry
C330S127000
Reexamination Certificate
active
06172568
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to power amplifiers, and more particularly to a power amplifier that amplifies power of an input signal by using an output signal fed back.
2. Description of the Background Art
A conventional power amplifier disclosed in Japanese Patent Publication No. 61-23687 will now be described while referring to the block diagram of FIG.
7
. In
FIG. 7
, the power amplifier includes an input terminal
1
, a voltage amplifier stage
2
, a power amplifier stage
3
, including transistors Q
1
to Q
4
, a feedback circuit
4
, a DC power source
5
, and an output terminal
6
. Such a power amplifier operates as follows. An input signal of this power amplifier is provided to the voltage amplifier stage
2
through the input terminal
1
. The voltage amplifier stage
2
amplifies the voltage of the input signal up to a given value on the basis of the feedback voltage described later and provides the output to the power amplifier stage
3
. Since the power amplifier stage
3
is generally formed of a complementary circuit (SEPP circuit), its voltage amplification is one. Accordingly, when receiving the output signal from the voltage amplifier stage
2
, the power amplifier stage
3
amplifies the current of the input signal up to a given value, without amplifying the voltage value of the input signal. The signal amplified by the power amplifier stage
3
is supplied to a load (not shown) through the output terminal
6
, and is also supplied to the feedback circuit
4
. The feedback circuit
4
, having two internal resistors, attenuates the voltage of the supplied signal and feeds the feedback voltage back to the voltage amplifier stage
2
.
As described above, with the combination of the voltage amplifier stage
2
and the power amplifier stage
3
, the power amplifier amplifies power of the input signal and supplies it to the load.
The DC power source
5
supplies DC power-supply voltages + Vcc
2
and −Vcc
2
to the voltage amplifier stage
2
and the power amplifier stage
3
. It is required to greatly vary the load voltage for supplying large power to the load since the power amplifier stage
3
has a voltage amplification equal to one. According to the power amplifier of
FIG. 7
, while the voltage supplied to the load must be varied up to the DC power-supply voltages ±Vcc
2
, the output voltage of the voltage amplifier stage
2
must also be varied up to the DC power-supply voltages ±Vcc
2
, since the voltage amplification of the power amplifier stage
3
is one. This requires the voltage amplifier stage
2
to be able to withstand the same voltage as the power amplifier stage
3
. That is to say, in order for the power, amplifier to provide high power requires the use of transistors capable of withstanding high voltages in the voltage amplifier stage
2
. However, transistors with high withstand voltages are expensive, which will result in an increased price of the power amplifier.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a high power amplifier at a low price. The invention achieves this object with the following characteristic structure.
According to a first aspect, a power amplifier for amplifying power of an input signal by using an output signal fed back comprises: a voltage amplifier stage for amplifying voltage of the input signal to provide an output signal; a power amplifier stage for amplifying power of the output signal from the voltage amplifier stage to provide an output signal; a voltage divider for dividing the output signal from the power amplifier stage to output a divided voltage; and a constant voltage circuit for regulating a supplied DC voltage to a constant voltage, with a voltage at an internal reference point being varied by the divided voltage outputted from the voltage divider, and then supplying the regulated DC voltage to the voltage amplifier stage.
According to the first aspect above, the voltage divider divides the output signal from the power amplifier stage and applies a divided voltage to the reference point in the constant voltage circuit. The constant voltage circuit regulates the supplied DC voltage to a constant voltage with the voltage at the reference point being varied by the applied divided voltage and then supplies the regulated DC voltage to the voltage amplifier stage. Since the voltage amplifier stage operates with the regulated DC voltage, it can strengthen the voltage of its own output signal and the withstand voltage of the voltage amplifier stage can be lower than the withstand voltage of the power amplifier stage. This results in a high power amplifier that has a low price.
A second aspect depends on the first aspect, in which the power amplifier further comprises a DC power source for supplying the DC voltage to the constant voltage circuit, wherein the DC power source also supplies the DC voltage to the power amplifier stage.
According to the second aspect above, the DC power source supplies DC voltage to both the power amplifier stage and the constant voltage circuit. According to the second aspect, the power-supply structure of the power amplifier can be simplified. This results in a power amplifier that has a still lower price.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4333059 (1982-06-01), Yamaguchi et al.
patent: 4435846 (1984-03-01), Weise
patent: 5182527 (1993-01-01), Nakanishi et al.
patent: 5604924 (1997-02-01), Yokoya
patent: 5892404 (1999-04-01), Tang
patent: 61-23687 (1986-06-01), None
Matsushita Electric - Industrial Co., Ltd.
Nguyen Khanh Van
Pascal Robert
Wenderoth , Lind & Ponack, L.L.P.
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