Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
2002-02-25
2004-05-04
Nguyen, Khanh Van (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S289000
Reexamination Certificate
active
06731171
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power amplifier module. More specifically, the present invention relates to technology effectively applicable to power amplifier modules for, e.g., cellular phones which need to keep high linearity under environmental changes such as changes of ambient temperature and control voltage.
2. Description of the Related Art
Portable telephones used in CDMA (Code Division Multiple Access), PDC (Personal Digital Cellular), TDMA (Time Division Multiple Access), and other systems are required to have high linearity and efficiency under environmental changes such as changes of ambient temperature and control voltage. To meet this requirement without allowing the performance of the telephone to drop, it is essential to maintain a stable operating point (idling current) of the power amplifier, which, among other components of the telephone has the greatest influence on the linearity and efficiency of the telephone, under environmental changes such as changes of ambient temperature and control voltage.
FIGS. 11A and 11B
show examples of power amplifiers using GaAs-HBTs (Heterojunction Bipolar Transistors) presented in the C-10-7 of the 2000 General Conference of the Institute of Electronics, Information and Communication Engineers.
FIG. 11A
shows one of the unit amplifiers of a power amplifier. Reference numeral
1
is a power terminal;
14
, a grounding terminal;
2
, a control terminal;
8
, an input terminal;
11
, an output terminal;
22
to
24
and
28
, GaAs-HBTs (hereinafter simply referred to as “transistors”);
21
,
25
, and
26
, resistors;
27
, a coupling capacitance;
29
, an RF choke inductor; and
15
, a bias circuit comprised of some of the above parts.
In the circuit of
FIG. 11A
, the transistors
24
and
28
connected by a Darlington connection and the transistors
22
and
23
connected by a diode connection constitute a current mirror circuit. If the ratio of the current mirror is set to “n” by setting the emitter area of the transistor
28
“n” times as large as the emitter area of the transistors
22
and
23
, a current Iq, which is “n” times as large as a current Ib passing through the transistors
22
and
23
in the diode configuration, passes through the amplifying transistor
28
as an idling current. Keeping the current Ib constant is, therefore, important to stabilize the idling current Iq.
An input signal is input through the input terminal
8
, amplified by the amplifying transistor
28
, and output through the output terminal
11
. A matching circuit (not shown) is connected to the input terminal
8
; another matching circuit (not shown), to the output terminal
11
. The resistor
26
and the RF choke inductor
29
are used to isolate signal components from the bias circuit
15
and the power line of low impedance.
In the circuit of
FIG. 11B
, an idling current Iq is stabilized by offsetting the temperature characteristics of base-emitter voltage of transistors
24
and
28
by the temperature characteristics of Schottky diodes
30
to
33
connected in series in bias circuit
15
. Although the threshold voltage of the Schottky diode is about a half of that of the GaAs-HBT, the former's temperature characteristics are almost the same as the temperature characteristics of base-emitter voltage of the latter. It is therefore possible to connect in series twice as many Schottky diodes as GaAs-HBTs, and any desired temperature compensation effect can be accomplished by changing the ratio of the resistance of resistor
21
to the resistance of resistor
36
. In this unit amplifier, four Schottky diodes are connected in series to obtain temperature characteristics of the idling current Iq of a practical level. Reference numerals
34
and
35
also indicate Schottky diodes, which are dispensable from the point of view of the basic function of the unit amplifier.
SUMMARY OF THE INVENTION
The power amplifier of
FIG. 11A
is simple in configuration and has an advantage that all active elements can be formed by a transistor process. However, because a current Ireg passing through the resistor
21
is governed by: (i) the difference between the voltage at the control terminal
2
and the sum of the base-emitter voltage of the transistor
22
and that of the transistor
23
; and (ii) the resistance of the resistor
21
, the current Ireg varies in accordance with changes of ambient temperature and control voltage. The current Ib changes in proportion to the current Ireg. In other words, no means is provided for stabilizing the idling current Iq when changes of ambient temperature and control voltage occur. Therefore, the dependency of the idling current Iq on the ambient temperature and the control voltage is large. In addition, it is difficult to achieve a high yield because the performance of the unit amplifier is liable to be affected by the deviation in manufacture of resistors
21
. When the control voltage is 2.8 V and the ambient temperature varies within a range of 30±60° C., the idling current varies within a range larger than ±40%. When the ambient temperature is 30° C. and the control voltage lowers from 2.8 V to 2.7 V, the idling current Iq is reduced by 30% or so.
The idling current of the unit amplifier of
FIG. 11B
is stabilized by using Schottky diodes. This method, however, requires a Schottky diode process which is different from the GaAs-HBT process. Because it is difficult to stably control Schottky barriers and electrode contact in a Schottky diode process, it is difficult to manufacture power amplifiers at high repeatability and a high yield. As in the case of the unit amplifier of
FIG. 11A
, the unit amplifier of
FIG. 11B
has no means for stabilizing the idling current when a variation of the control voltage occurs. Accordingly, the idling current is reduced by 50% or so when the control voltage lowers from 2.8 V to 2.7 V.
In accordance with the above, an object of the present invention is to provide a power amplifier module with a bias circuit capable of feeding stable idling currents to power amplifier units. Another object of the present invention is to provide a power amplifier module which can be manufactured at low cost and a high yield by forming a bias circuit and power amplifier units in a stable transistor process.
A representative example of the invention disclosed in this application is as follows. A differential circuit provides error amplification with a first arrangement to detect changes of the control voltage and a second arrangement to detect changes of ambient temperature as mutual standard voltage inputs to produce an idling current. As a result, the effects of the changes of the control voltage and the ambient temperature are removed. The idling current controls the gain of a power-amplifying transistor. Input signals are fed to the power-amplifying transistor through a first matching circuit, and output signals from the power-amplifying transistor are fed to a load circuit through a second matching circuit.
Other and further objects, features and advantages of the invention will appear more fully from the following description.
REFERENCES:
patent: 5724004 (1998-03-01), Reif et al.
patent: 5990746 (1999-11-01), Samuels
patent: 6052032 (2000-04-01), Jarvinen
patent: 6215358 (2001-04-01), Hon et al.
patent: 6359948 (2002-03-01), Turudic et al.
patent: 6472937 (2002-10-01), Gerard et al.
“Thermally stable power HBT by the bias circuit using Schottky diode” Keiichi Murayama et al., Semiconductor Device Research Center, Matsushita Electronics Corporation, pp. 1-4 and p. 65.
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Nguyen Khanh Van
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