Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
2001-06-04
2003-05-20
Lam, Tuan T. (Department: 2816)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S296000
Reexamination Certificate
active
06566954
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high frequency amplifier bias circuit which uses a hetero junction bipolar transistor (“HBT”) such as InGaP/GaAs type or the like, a high frequency power amplifier which uses the bias circuit, and a communication device which uses the high frequency power amplifier. More particularly, this invention relates to a high frequency power amplifier which carries out output power control such as in CDMA (code division multiple access) system.
BACKGROUND OF THE INVENTION
High frequency power amplifiers used in cellular phones or the like require even higher efficiency in order to simultaneously achieve the objects of making the battery more compact and more lightweight and enabling long duration of calls. Therefore, in a high frequency power amplifier which corresponds to a digital modulation system, high linearity is needed. In order to realize, at a low cost, a high frequency power amplifier which satisfies this demand, development of a small module which contains a transistor and passive components, and an MMIC (Microwave Monolithic IC) in which a transistor and passive components are provided on the same semiconductor substrate, has been carried out actively. Moreover, in order to reduce the number of components, integration, such as incorporating a bias circuit for supplying voltage or electric current to a transistor for amplification in an MMIC, has advanced.
FIG. 1
is a circuit diagram which illustrates a high frequency power amplifier using therein a conventional emitter-follower-transistor type constant voltage source bias circuit. As shown in
FIG. 1
, in this high frequency power amplifier that uses a bipolar transistor, emitter-follower-transistor
12
is used as a voltage source for supplying a base electric current to the transistor
11
for amplification (“transistor
11
”). Further, transistors
13
and
14
are provided in order to eliminate fluctuations, due to temperature, of voltage between base and emitter of the transistor
11
(“VBE voltage”) and the VBE voltage of the emitter-follower-transistor
12
. The transistors
13
and
14
are provided in two stages.
Collector of the emitter-follower-transistor
12
is connected to the power source terminal
15
. Emitter of the emitter-follower-transistor
12
is grounded via the resistor
16
. Base of the emitter-follower-transistor
12
is connected, via the resistor
17
, to the control input terminal
18
to which a control signal is supplied from the outside. Base of the transistor
11
is connected, via the resistor
10
, to the node of the emitter of the emitter-follower-transistor
12
and the resistor
16
.
The resistor
16
provides an electric current, which has an amplitude equal to about 1.3 V (VBE voltage of the transistor) divided by the resistance of the resistor
16
, to the emitter-follower-transistor
12
. Thus, the electric current which provided by the resistor
16
to the emitter-follower-transistor
12
is hardly dependent on the control signal. The emitter of the transistor
11
is grounded, the base is connected to an input terminal
111
, and the collector is connected to an output terminal
112
of the high frequency power amplifier via a not shown matching circuit.
The collector of the transistor
14
for temperature compensation for the emitter-follower-transistor
12
is connected to the power source terminal
15
. The emitter of the transistor
14
is grounded via the resistor
19
, and is also connected to the base of the transistor
13
for temperature compensation for the transistor
11
. Further, the base of the transistor
14
is, together with the collector of the transistor
13
for temperature compensation for the transistor
11
, connected to the control input terminal
18
via the resistor
17
. The emitter of the transistor
13
is grounded.
In general, in an amplifier which uses an HBT, in order to simultaneously realize both, high efficiency and high linearity, a bias point of the transistor must be set near Class B. Also, a bias point which fluctuates little must be provided. The inventor/s of this invention studied the relation between the bias electric current and the control input voltage into the control input terminal
18
for the bias circuit which is used in the conventional high frequency power amplifier shown in FIG.
1
. The result of this study is shown as “conventional example” in FIG.
3
.
As shown in
FIG. 3
, in the conventional bias circuit, the bias electric current changes substantially rectilinearly from 4 mA to 125 mA corresponding to the control input voltage between 2.5 V to 3.5 V. Therefore, for example, in order to make a bias electric current of 40 mA ±10% (i.e., 36 mA to 44 mA) flow, the control input voltage must be controlled to the extremely narrow range of 2.7 V ±0.03 V. In order to achieve this, a highly precise external circuit is needed. A highly precise external circuit is costly, therefore, there is a problem in that the cost of the entire device increases.
In the conventional bias circuit shown in
FIG. 1
, as shown in
FIG. 3
, if due to some reason the control input voltage increases from the reference voltage 2.7 V to 3.5 V which is the power source voltage, the bias electric current exceeds 120 mA. Therefore, generation of heat is promoted, and breaking due to the overcurrent caused thereby occurs. A technology for preventing such a breakage due to thermorunaway is known. A protection circuit such as an electric current cutoff circuit may be provided at the collector side of the transistor
11
(for example, see Japanese Patent Application Laid-Open (JP-A) No. 6-95751 or Japanese Patent Application Laid-Open (JP-A) No. 5-37256).
In such a protection circuit, a resistor is connected to the collector of the transistor
11
, and the output electric current of the transistor
11
is controlled on the basis of the output electric current value of the transistor
11
which is sensed by the resistor or a bias electric current value which is supplied to the transistor
11
.
However, if the protection circuit is provided, voltage drop occurs at the resistor connected to the collector of the transistor
11
or at the electric current cutoff circuit. Therefore, there is a problem in that the value of the power source voltage which is applied to the transistor
11
effectively decreases. Moreover, there is a problem in that a part of the RF power is consumed due to a loss component of the electric current cutoff circuit or the resistor for electric current detection, and the power added efficiency of the amplifier deteriorates.
In addition, in order to prevent the power source circuit side from being unstable and oscillating due to leakage of the RF output, a capacitor of an order of several &mgr;F for bypassing the leakage of the RF output is applied to the electric current cutoff circuit. The response speed of the cutoff circuit is limited by a time constant of the capacitor. Therefore, it is difficult to make the response speed of the cutoff circuit sufficiently fast with respect to the speed of progression of the thermorunaway, and a problem arises in that the thermorunaway cannot be prevented effectively.
Moreover, in the conventional bias circuit shown in
FIG. 1
, there is a problem in that it is difficult to completely suppress fluctuations in the bias electric current when the temperature changes. Results obtained by studies of the present inventor on the relation between the temperature and the bias electric current, for the bias circuit which is used in the conventional high frequency power amplifier shown in
FIG. 1
, are shown as a conventional example in FIG.
4
. In the high frequency power amplifier which is shown in
FIG. 1
, the temperature change of the bias electric current of the transistor
11
is expressed by following equation (1).
&Dgr;J
11
/&Dgr;
Tj=&Dgr;J
14
/&Dgr;
Tj+&Dgr;J
13
/&Dgr;
Tj−&Dgr;J
12
/&Dgr;
Tj
(1)
In equation (1), &Dgr;J
14
/&Dgr;Tj, &Dgr;J
13
/&Dgr;Tj, &Dgr;J
12
/&Dgr;Tj, and &Dgr;J
11
/&Dgr;Tj are the t
Fujitsu Quantum Devices Limited
Lam Tuan T.
Staas & Halsey , LLP
LandOfFree
High frequency amplifier bias circuit, high frequency power... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High frequency amplifier bias circuit, high frequency power..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High frequency amplifier bias circuit, high frequency power... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3059909