Amplifiers – With control of power supply or bias voltage – With control of input electrode or gain control electrode bias
Reexamination Certificate
2000-09-28
2002-12-10
Pascal, Robert (Department: 2817)
Amplifiers
With control of power supply or bias voltage
With control of input electrode or gain control electrode bias
C330S134000, C330S288000, C330S296000, C330S310000
Reexamination Certificate
active
06492869
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese patent application No. 11-280010, filed Sep. 30, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
This invention relates to a linear amplifier and a radio communication apparatus using the linear amplifier, and more particularly to a linear amplifier with a gain varying function using bipolar transistors and a radio communication apparatus using this linear amplifier.
When a modulated wave signal whose amplitude varies greatly is dealt with, a conventional amplifier is used in the range of values far backed off from the saturated output to prevent gain compression from limiting the amplitude. Thus, it is impossible to use the amplifier in its high efficiency region.
As for a method of using such an amplifier as a linear amplifier up to almost the saturated output point, various linearizers (see
FIG. 22
) for canceling the nonlinear characteristics have been designed. Typical linearizers include a system for producing the reverse distortion component in the input signal beforehand and a system for varying the gain of an amplifier according to a variation in the amplitude of the input signal and equalizing the gain in the gain compression region to that in the linear region.
In such linearizers, their added circuits are complex and consume a lot of power. They can be used in the last-stage amplifier in a base station that amplifies high power. They, however, have not been put to practical use in the field of about 1-W-output amplifiers for use with portable telephones, because they have many disadvantages in that the total efficiently hardly improves and the size of the component parts is large.
On the other hand, a high-efficiency amplifier that presents a linear characteristic in a wide dynamic output range is realized by setting the bias condition to class B amplification to reduce the idle current. Actually, however, since the distortion becomes greater due to the nonlinear characteristic of the mutual conductance of elements, it is impossible to set the bias condition to heavy class B amplification by which the idle current is reduced extremely. Therefore, it is desirable that, in a low-output level region where the distortion is small, the bias should be varied in such a manner that the bias current is reduced extremely.
Since in a class-B amplifier using bipolar transistors, the average collector current increases according to the output level, the bias circuit has to supply a sufficient current equivalent to an increase in the average base current accordingly. For this reason, in a current-mirror circuit for supplying the base current via the emitter-follower and others, a bias circuit for supplying a voltage with a reduced impedance shown in
FIG. 20
or
21
is generally used.
In the bias circuit shown in
FIG. 20
, the collector of a transistor Q
21
is connected to one end of a resistance R
21
via a terminal
11
. A control voltage of Vcont is applied to the other end of the resistance R
21
(on a terminal
2
′ side). The base of the transistor Q
21
is connected to the emitter of a transistor Q
3
′. The base of the transistor Q
3
′ is connected to the terminal
11
. A power-supply voltage of vcc is applied to the collector of the transistor Q
3
′. The emitter of the transistor Q
21
is grounded. The emitter of the transistor Q
3
′ is not only rounded via a resistance R
3
′ but also connected to the base of a terminal
4
′ amplification transistor.
In the bias circuit shown in
FIG. 21
, transistors Q
4
′, Q
5
′, are used in place of the transistor Q
2
′. Specifically, the emitter of the transistor Q
4
′ is connected to the collector of the transistor Q
5
′ and the collector of the transistor Q
4
′ is connected to a resistance R
21
. The emitter of the transistor Q
5
′ is grounded. The base and collector of the transistor Q
4
′ are short-circuited. The base and collector of the transistor Q
5
′ are short-circuited. These transistors function as diodes.
With such a circuit, when an attempt is made to reduce the current in proportion to the voltage, fluctuations in the bias current due to temperature changes cannot be compensated for sufficiently unless its control voltage Vcont is made very high. When the control voltage is made high, this becomes a serious problem in a system with a low control voltage, such as a portable telephone. Particularly in a system that has to operate linearly at an output level in a wide dynamic range, such as CDMA (Code Division Multiple Access), both the current and the gain are too large at a low output level at the bias point that satisfies the distortion characteristic at the high output level.
As explained above, when a conventional linear amplifier attempts to realize a linear operation in a high-efficiency operation, it requires a linearizer as shown in FIG.
22
. The system using a linearizer, however, does not produce much effect in a 1-W-class amplifier, such as an amplifier for a portable telephone in terms of compactness and total efficiency. When such an amplifier is operated in the linear region, it is eventually used at 20 to 30% lower efficiency.
Furthermore, when an attempt is made to control the bias current in a wide range to reduce the current during the low output, it is necessary to raise the control voltage or sacrifice temperature compensation. This makes it difficult to lower the voltage or reduce the power consumption in a system that has to operate linearly at the output level in a wide dynamic rage, such as CDMA.
The object of the present invention is to provide a linear amplifier with a bias circuit which is capable of realizing a high-efficiency operation during high output, while maintaining a linear operation, and of reducing the bias voltage with a low control voltage during low output without increasing the number of circuits and the drawn current as compared with a conventional equivalent circuit, and a radio communication apparatus using the linear amplifier.
BRIEF SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a linear amplifier comprising: a first current-mirror circuit including a first transistor whose base and collector are short-circuited for diode connection, whose collector is connected via a first resistance to a power-supply terminal, and whose emitter is grounded; a second current-mirror circuit including a second transistor whose collector and base are connected to power-supply terminals; and an amplification transistor whose emitter is grounded, wherein the base of the first transistor and the emitter of the second transistor are connected to the base of the amplification transistor.
According to a second aspect of the present invention, there is provided a linear amplifier including two or more stages of amplification transistors whose emitters are grounded, the linear amplifier comprising: a first current-mirror circuit including a first transistor whose base and collector are short-circuited for diode connection, whose collector is connected via a first resistance to a power-supply terminal, and whose emitter is grounded; and a second current-mirror circuit including a second transistor whose collector and base are connected to power-supply terminals, wherein the base of the first transistor and the emitter of the second transistor are connected to the base of a transistor at an earlier stage than the last stage of the amplification transistors.
In the linear amplifiers according to the first and second aspects of the present invention, it is desirable that they should meet the following configuration requirements:
(1) The collector of the first transistor and the base of the second transistor are connected to a common power supply.
(2) The base of the second transistor is connected via a second resistance to a power-supply terminal.
(3) The collector of the first
Kabushiki Kaisha Toshiba
Nguyen Khanh Van
Pascal Robert
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