Amplifiers – With semiconductor amplifying device – Including particular power supply circuitry
Reexamination Certificate
2003-04-30
2004-10-19
Choe, Henry (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including particular power supply circuitry
C330S296000
Reexamination Certificate
active
06806775
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power amplifier circuit which amplifies an inputted input signal and outputs it as an output signal.
2. Description of the Related Art
FIG. 11
is a diagram showing the configuration of a related power amplifier circuit
5
using bipolar transistors and its peripheral circuit, and
FIG. 12
is a diagram showing the static characteristic of an amplifying part transistor Q in FIG.
11
.
As shown in
FIG. 11
, a voltage of 3.6 V, for example, is supplied from a power supply
10
to a DC/DC converter
20
. The DC/DC converter
20
converts the supplied voltage into, for example, 1.5 V and supplies it to a collector of the amplifying part transistor Q in the power amplifier circuit
5
. The amplifying part transistor Q is composed of an NPN bipolar transistor. The voltage which is supplied by the DC/DC converter
20
is variable, and in some cases a high voltage (3.6 V, for example) is supplied, while in other cases a low voltage (1.5 V, for example) is supplied.
A high-frequency signal current Isg is supplied to a base of the amplifying part transistor Q from a signal generating circuit
30
via a capacitive element C
1
, and a bias current Ibias from a bias circuit
40
is also supplied thereto. Namely, a base current Ib=Ibias+Isg is supplied to the base. An emitter of the amplifying part transistor Q is grounded.
The bias circuit
40
includes NPN bipolar transistors Q
1
to Q
4
and a resistance R
1
. The bipolar transistors Q
1
and Q
2
and the resistance R
1
constitute a switching control circuit
50
, and the bipolar transistors Q
3
and Q
4
constitute a bias current generating circuit
60
.
As concerns a control voltage Vcon to be supplied to the switching control circuit
50
, a voltage (3.6 V, for example) is supplied when the power amplifier circuit
5
is on, and no voltage (namely, 0 V) is supplied when it is off. In the bias current generating circuit
60
, the bipolar transistor Q
3
is turned on/off according to the on/off of the control voltage Vcon, and when it is on, the bias current Ibias is supplied from a reference voltage Vref to the base of the amplifying part transistor Q, and when it is off, the bias current Ibias is not supplied.
The switching control circuit
50
changes the amount of the bias current Ibias flowing through the bipolar transistor Q
3
by changing the amount of a control current Icon to be supplied to a base of the bipolar transistor Q
3
according to its ambient temperature (ambient temperature of the bipolar transistors Q
1
and Q
2
). Hence, the switching control circuit
50
prevents thermal runaway of the power amplifier circuit. In addition, the bipolar transistors Q
1
and Q
2
also monitor the ambient temperature of the amplifying part transistor Q.
An output node N
0
of this power amplifier circuit is provided on the collector side of amplifying part transistor Q and outputs a voltage output OUT. A load impedance ZL is connected to the output node N
0
.
As shown in
FIG. 12
, the amount of a current Ic flowing through the amplifying part transistor Q is determined by the base current Ib (Ib
1
<Ib
2
<Ib
3
<Ib
4
<Ib
5
<Ib
6
) which flows into the base of the amplifying part transistor Q. As stated above, the base current Ib is the sum of the bias current Ibias from the bias circuit
40
and the signal current Isg from the signal generating circuit
30
. The bias current Ibias is constant unless temperature changes, and hence the voltage of the voltage output OUT is determined by the high-frequency signal current Isg from the signal generating circuit
30
.
Incidentally, as shown in
FIG. 12
, from the characteristics of the bipolar transistor, an amplitude of the voltage output OUT can be widely at high output levels at which the voltage Vc is high, while the amplitude of the voltage output OUT can be only narrowly at low out levels at which the voltage Vc is low.
However, as can be seen from FIG.
11
and
FIG. 12
, even if the voltage Vc is reduced at low output levels, the amount of the current Ic flowing through the amplifying part transistor Q is unchanged. Since power consumption (DC loss) is determined by voltage Vc×current Ic, power consumption is reduced only through a fall in the voltage Vc.
When the voltage Vc is at low output levels, however, it does not matter if the amplitude of the voltage output OUT is small, and hence if it is possible to decrease the amount of the current Ic and thereby reduce power consumption, it is more desirable.
SUMMARY OF THE INVENTION
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, a power amplifier circuit, comprises:
an amplifying part transistor including a bipolar transistor to which a first supply voltage is supplied as a driving voltage and which amplifies an input signal inputted to a base of the amplifying part transistor so as to output the input signal;
a bias current generating circuit which generates a bias current for biasing the base of the amplifying part transistor and supplies the bias current to the base of the amplifying part transistor when the amplifying part transistor performs an amplification operation; and
an additional bias current generating circuit which supplies an additional bias current to the base of the amplifying part transistor in addition to the bias current according to the first supply voltage.
REFERENCES:
patent: 5986509 (1999-11-01), Lohninger
patent: 6052032 (2000-04-01), Jarvinen
patent: 6373329 (2002-04-01), Hosoi et al.
patent: 6492875 (2002-12-01), Luo et al.
patent: 6690237 (2004-02-01), Miyazawa
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