High-output amplifier

Amplifiers – With semiconductor amplifying device – Including particular biasing arrangement

Reexamination Certificate

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Details

C330S302000, C330S303000, C327S560000

Reexamination Certificate

active

06549076

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-290801, filed on Sep. 25, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a high-output amplifier using a transistor amplifier.
2. Background of the Invention
In the field of wireless communication systems, digital communication such as CDMA (code division multiple access) is currently the major system, there is a demand for a high-output amplifier (1) having a high gain, (2) having a high efficiency, (3) less influenced by temperature changes, and (4) linearly operative in output levels of a wide dynamic range. In addition to those, in systems like portable telephones using low source voltages, such a high-output amplifier is additionally required to be (5) operative with a low control voltage.
As a conventional high-output amplifier, there is a method using an emitter-grounded bipolar transistor for class AB operation to supply a bias current/voltage by means of a base bias circuit. The principle and characteristics of this method are explained below.
To obtain a high-output amplifier with a high gain, an emitter-grounded bipolar transistor is used as the transistor amplifier of the high-output amplifier. The high-output amplifier is made up of a control circuit and the transistor amplifier, and a bipolar transistor is typically used as the transistor amplifier. For connection of the bipolar transistor, although there are emitter-grounded circuits, base-grounded circuits, collector-grounded circuits (emitter follower circuits), and so on, because of a high gain, emitter-grounded circuits are used in an overwhelmingly majority of amplifier circuits. Emitter-grounded circuits are configured to use the emitter as a common terminal for both the input and the output, apply an input signal to the base and extract the output from the collector.
In order to obtain a high-efficiency high-output amplifier, the bias condition of the above-mentioned emitter-grounded transistor amplifier is adjusted for class AB to perform class AB operation. That is, a high-efficiency amplifier will be obtained by adjusting the bias condition for class B (in which power consumption is essentially zero when the input is zero) instead of class A (in which a considerable amount of current is always supplied to the transistor). Actually, however, since class B operation will increase the distortion by fluctuation of the gain because of the non-linearity of the mutual conductance of devices, by a way of use as class AB (in which a small d.c. current=idling current flows into the transistor even when the input is zero), a high-efficiency high-output amplifier can be obtained.
Next, for the purpose of obtaining a high-output amplifier less affected by temperature fluctuation, a bias is supplied to the control terminal (base) of the transistor amplifier through a bias circuit. That is, in high-output amplifiers using bipolar transistors, major circuits are those using the base/emitter voltage as the reference. However, temperature coefficient of the output current is fairly large, a base bias circuit is used as one of control circuits to prevent the base voltage/current from largely changing with temperature. Such high-output amplifiers include a first conventional high-output amplifier using a bias circuit shown in FIG.
13
. The bias circuit of
FIG. 13
includes a bipolar transistor Q
1
and a resistor R
1
, and uses a diode-connection current mirror circuit made by short-circuiting the base and the collector to supply a bias voltage and a bias current Ib.
As reviewed above, by using a class AB emitter-grounded bipolar transistor, a high-output amplifier having (1) a high gain and (2) a high efficiency can be obtained, and by using the method of supplying the bias current/voltage by using the first conventional bias circuit shown in
FIG. 13
, a high-output amplifier (3) less affected by temperature fluctuations. Further, since the bias circuit of
FIG. 13
uses a single stage transistor, (5) the control voltage may be low.
The first conventional high-output amplifier using the bias circuit of
FIG. 13
, however, cannot satisfies the requirement of (5) linear operation in output levels over a wide dynamic range. That is, in emitter-grounded bipolar transistor for class AB operation, since the average collector current increases in response to the output level, the bias circuit has to supply a sufficient additional amount corresponding to the increase of the average base current responsively; however, the bias circuit as shown in
FIG. 13
cannot supply a sufficient amount of current because a voltage drop by the resistor R
1
occurs.
A second conventional high-output amplifier using a bias circuit of
FIG. 14
linearly operates in output levels over a wide dynamic range. The circuit of
FIG. 14
is a current mirror circuit that supplies the base current through the emitter follower, etc., in which Q is a bipolar transistor, R is a resistor, Vcc is the source voltage, and a current can be supplied by decreasing the output impedance.
The second conventional high-output amplifier using the bias circuit of
FIG. 14
, however, involves the problem that (5) the control voltage of the bias circuit inevitably increases. That is, in the bias circuit of
FIG. 14
, using two-stage transistors, the bias current Ib fluctuates largely with temperature unless the control voltage V
cont
is much higher than twice as large as the ON voltage of the transistors. For example, in the circuit of
FIG. 14
, let the operation voltage of the bipolar transistor Q be 1.2V, then the control voltage V
cont
must be much higher than 2.4V. So, if a control voltage around 2.7V is used for operation, the bias current will be seriously affected by temperature changes. If, however, the control voltage is raised, it invites a serious problem in systems like portable telephones that use low source voltages.
As discussed above, with conventional emitter-grounded transistor amplifiers biased for class AB, although it has been possible to obtain a high-output amplifier having (1) a high gain and (2) a high efficiency, but because of insufficient characteristics of base bias circuits of transistor amplifiers, it has been difficult to obtain a high-output amplifier (3) less affected by temperature changes, (4) linearly operative in output levels over a wide dynamic range and (5) controllable with a low control voltage.
BRIEF SUMMARY OF THE INVENTION
According to an embodiment of the invention, there is provided a high-output amplifier comprising:
a bias circuit (BC) having a first bias circuit and a second bias circuit, said first bias circuit including a first transistor (Q
1
) having one end connected to a first high-voltage-side source (Vcont) and the other end connected to a low-voltage-side source (Vss), said one end being connected to the control terminal of the first transistor, said second bias circuit including a second transistor (Q
2
) having one end connected to a second high-voltage-side source (Vcc), the other end connected to said one end of said first transistor (Q
1
), and a control terminal connected to said first high-voltage-side source (Vcont); and
a transistor amplifier (RF
1
) having a control terminal connected to said one end of said first transistor (Q
1
), one end as an output terminal of said high-output amplifier, and the other end connected to a low-voltage-side source.


REFERENCES:
patent: 5625205 (1997-04-01), Kusama
patent: 5629648 (1997-05-01), Pratt
patent: 6121841 (2000-09-01), Sakuno
patent: 6300837 (2001-10-01), Sowlatti et al.
patent: 6313705 (2001-11-01), Dening et al.
K. Murayama, et al., Proceedings of the 2000 ICICE General Conference, C-10-7, p. 65, “Thermally Stable Power HBT by the Bias Circuit Using Schottky Diode”, 2000.

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