Amplifiers – With semiconductor amplifying device – Including particular power supply circuitry
Reexamination Certificate
2002-08-23
2003-07-29
Choe, Henry (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including particular power supply circuitry
C330S010000, C330S127000, C363S041000
Reexamination Certificate
active
06600376
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a power amplifier, and more particularly to a high efficiency power amplifier.
2. Description of Related Art
As is well known, an amplifier is a device that receives an input and applies a defined gain in order to produce an output that is greater than the input. For example, a voltage amplifier may receive a 10V input and produce an output of 20V, if the voltage amplifier has a gain of two. Amplifiers are able to apply the gain to produce an output up to a certain value. For example, a voltage amplifier can produce an output up to a value of the operational voltage applied to the amplifier. That is, a voltage amplifier with an operational voltage of 15V and a gain of three can produce the desired output as long as the input does not exceed 5V. If the voltage amplifier receives an input voltage of 6V it attempts to produce an output of 18V, which is above the maximum that this voltage amplifier can produce. Therefore, the voltage amplifier does not have the potential to drive the load to the desired voltage.
Amplifiers work best if they produce outputs near the maximum output of the amplifier. That is, an amplifier with an operational voltage of 15V works most efficiently when producing outputs around 15V. However, the typical outputs of a 15V amplifier are probably much lower since the 15V operating voltage (i.e., maximum output) is selected to handle peak input voltages. For example, the maximum input voltage (peak voltage) for a 15V amplifier with a gain of three is 5V, and a typical input voltage may be in the range of 1-3V.
FIG. 1
illustrates a schematic diagram of a conventional sine wave amplifier system. The power circuit
101
transfers the received AC power or DC power to a required operation voltage supplied to the amplifier circuit
102
. The amplifier circuit
102
receives the sine wave signal supplied from the small signal producer
103
and produces an output according the defined gain of the amplifier circuit
102
.
FIG. 2
is a schematic diagram illustrating a conventional Class B amplifier circuit
102
. Other amplifier circuits, such as Class A, Class AB or other types of amplifier circuits, may use the same method described in the following for analysis. First, this amplifier circuit
102
is powered by a pair of operation voltages (+V and −V) supplied from the power circuit
101
. The transistor Q
1
is responsible for amplifying the received signal during period T
1
, and the transistor Q
2
is responsible for amplifying the received signal during period T
2
. Both Q
1
and Q
2
transistors operate in a linear region.
FIG. 3
is a waveform diagram further illustrating the operation of the conventional sine wave amplifier system. The amplifier circuit
102
receives a small signal supplied from the small signal producer
103
and produces a sine wave output according to the defined gain. The amplifier circuit
102
is powered by a pair of operation voltage sources (+V and −V) supplied from the power circuit
101
. As the chart depicts, the typical maximum output voltage V
p
is required to be between +V and −V. The sine wave output signal V
R
is represented by the following equation:
V
R
=V
P
×sin(2
&pgr;ft
)
Therefore, the output efficiency varies with the output signal waveform. Typically, the amplifier circuit
102
runs at peak efficiency periodically when peak output voltage V
p
appears. Therefore, the sine wave amplifier system as shown in
FIG. 1
is very inefficient. On the other hand, the voltage difference (V
ce
) between the collector electrode and the emitter electrode of the transistors Q
1
and Q
2
is changed when the output signal changes. The power dissipation is as follows:
powerdissipation=
V
ce
×I
c
(1)
V
ce
is the voltage difference between the collector electrode and the emitter electrode of the transistor. I
c
is the current of the collector electrode. The equations shown in the following describe the voltage V
ce
and the current I
c
of the transistors Q
1
and Q
2
, respectively:
V
ce
(
Q
1
)
=
V
-
V
p
×
sin
(
2
π
f
t
)
V
ce
(
Q
2
)
=
V
+
V
p
×
sin
(
2
π
f
t
)
I
c
(
Q
1
)
=
V
p
×
sin
(
2
π
f
t
)
/
R
sin
(
2
π
f
t
)
>
0
I
c
(
Q
1
)
=
0
sin
(
2
π
f
t
)
<
0
I
c
(
Q
2
)
=
V
p
×
sin
(
2
π
f
t
)
/
R
sin
(
2
π
f
t
)
<
0
I
c
(
Q
2
)
=
0
sin
(
2
π
f
t
)
>
0
In accordance with equation (1), the power dissipation of the transistors is as follows:
powerdissipation=
V
ce
(
Q
1
)
×I
c
(
Q
1
)+
V
ce
(
Q
2
)×
I
c
(
Q
2
)
In accordance with the above equation, the power dissipation is about 30% to 70%.
Thus, an inherent problem associated with standard amplifiers is the conflict between the desirability of providing large output potentials and the undesirability of providing lower potentials through a large potential drop. One solution is provided in FIG.
4
.
FIG. 4
illustrates a schematic diagram of an amplifier system in accordance with the conventional analog to digital amplifier system. The power circuit
401
transfers the received AC power or DC power to the required operation voltage supplied to the analog to digital amplifier circuit
402
. The analog to digital amplifier circuit
402
receives the sine wave signal supplied from the small signal producer
403
and produces a pulse-width-modulation (PWM) wave, in which the analog to digital amplifier circuit
402
is controlled by a PWM signal that is provided by the PWM signal producer
404
. Then, the PWM wave passes through the semiconductor switch
405
and is provided to the wave filter, which comprises an inductor L and a capacitor C, to produce an output wave that is enlarged and in the same phase with the input sine wave signal. Although such an analog to digital amplifier system may obtain a high output efficiency, the wave filter requires a high-value inductor and thus occupies a large area and raises the power dissipation.
SUMMARY OF THE INVENTION
According to the above descriptions, because the conventional amplifier system needs to handle the peak outputs, the output efficiency cannot attain an optimal state. Even though the output efficiency may be raised by such an analog to digital amplifier system, this analog to digital amplifier system requires a wave filter that is composed of an inductor L and a capacitor C to produce an enlarged output wave in the same phase with the input sine wave signal. Although such an analog to digital amplifier system may obtain high output efficiency, the wave filter requires a high-value inductor and thus occupies a large area and raises the power dissipation. Therefore, this present invention provides a new amplifier system structure to overcome the above drawbacks, such as low output efficiency and large area occupation.
Typically, the efficiency of an amplifier circuit can be improved by dynamically changing the level of the supply voltages. That is, the level of the supply voltages is changed in response to changes in the level of the input analog signal. The goal of this strategy is to minimize the voltages supplied to the amplifier circuit to avoid extra power dissipation. In other words, the level of the supply voltages is changed in response to changes in the level of the input analog signal. Therefore, when a peak signal must be transmitted, the supply voltages supply at their respective high levels. When a lower level signal
Choe Henry
Dickinson Wright PLLC
Entrust Power Co., Ltd.
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