Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
2000-10-20
2004-08-03
Mottola, Steven J. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S133000
Reexamination Certificate
active
06771128
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a power amplifier module, particularly to a technology that is effectively applied to a power amplifier module for a cellular phone system with the capability of output power control to be used on portable terminal equipment used in a mobile communication system.
BACKGROUND OF THE INVENTION
Significant growth has lately been found in the market of cellular phone systems, typically, such as a Global System for Mobile Communication (GSM) and a Personal Communication Network (PCN) and this tendency is anticipated to continue in the future. One of the requirements of such systems as GSM and PCN is that the output power of portable terminal equipment can be controlled, dependent on the distance from a base station to the equipment. This can be fulfilled by controlling the gain of the power amplifier module installed on the equipment.
FIG. 9
shows an example of a typical conventionally used power amplifier module with three stages of output power control. In this power amplifier module, a signal input through a pin
062
is amplified by first-stage, second-stage, third-stage amplifiers
601
,
602
,
603
, and output through a pin
064
. Power source voltage is applied to a pin
063
. At this time, an output power control circuit
607
controls the gains of the amplifiers
601
,
602
, and
603
by changing an idling current that determines a DC bias of transistors
604
,
605
, and
606
. Hetero-Bipolar Transistors (GaAsHBTs) are used as the transistors
604
,
605
, and
606
.
Using the above third-stage amplifier
603
and its output power control circuit
607
, the output power control function will be explained below. The amplifier
603
comprises a transistor
606
, a resistor
611
, coupling capacitance
612
, and an output adjustment circuit
613
. The output power control circuit
607
comprises transistors
608
,
609
, and
610
and resistors
614
,
615
, and
616
. Here, the diode-connected transistors
609
and
610
and the diode-connected transistors
608
and
606
form a current mirror circuit. Current that is as large as mirror ratio times the current flowing across the transistors
609
and
610
flows through the transistor
606
as the idling current.
The voltage across the transistors
609
and
610
becomes substantially constant when an output power control voltage applied to a pin
061
becomes higher than the boot voltage of these transistors. In the voltage region higher than the boot voltage, the idling current increases or decreases in proportion to the control voltage. Because the gain depends on this idling current, the gain can be made variable by controlling the idling current. In fact, the output power control uses this characteristic. In the conventional module example shown in
FIG. 9
, the idling current to flow in the first-stage amplifier
601
is generated by applying a voltage produced by dividing the control voltage by resistance to the base of the amplifier. This means taken is different from the means of idling current supply for the second-stage amplifier
602
and the third-stage amplifier
603
.
SUMMARY OF THE INVENTION
Output power control characteristic requirements are that output power shall change as a monotone function relative to the control voltage in a wide dynamic range of 70 to 80 dB (the output power typically ranges between −40 and 35 dBm for GSM) and that its change factor, or in other words, control sensitivity shall fall within a predetermined value (which is, typically, 150 dB/V or below). In the conventional module example shown in FIG.
9
, however, the idling current changes in proportion to the control voltage.
For the circuit shown in
FIG. 9
, control sensitivity ∂P
21
/∂ Vapc becomes greater as the signal level decreases. This is expressed as:
P
21
=a constant+20log
I
d
(
dB
),
I
d
=(
Vapc−
2Vb)/
Rapc
(1)
∂
P
21
/∂Vapc
=20/(
Vapc−
2Vb )(
dB/V
)where
Vapc
>2Vb (2)
∂P
21
/∂Vapc
=0 where
Vapc ≦
2Vb (3)
The above equations (1) and (2), where P
21
is gain, I
d
is idling current, Vapc is control voltage, Vb is base-emitter voltage of the transistors
609
and
610
, and Rapc is the resistance of the resistor
614
, indicate the following. When the control voltage exceeds the sum of the boot voltages of the transistors
609
and
610
, the idling current starts to flow, resulting in the greatest control sensitivity. The control sensitivity becomes theoretically infinity, but there are many cases where the input signal power level is actually 0 dBm or higher and the DC current generated by a self-bias effect causes the control sensitivity to be around 300 dB/V. For equation (3), idling current I
d
is generated if Vapc ≦2 Vb, but there is no input of the required control voltage Vapc, causing that ∂P
21
/
1
Vapc 0.
For the above conventional module example, the first-stage amplifier
601
, the second-stage amplifier
602
, and the third-stage amplifier
603
operate in different states. Due to this, a kink is liable to take place in the control characteristic, which made it difficult to satisfy the output power control characteristic requirements of the power amplifier module. As apparent from a characteristic chart shown in
FIG. 10
, the control characteristic greatly changes, depending on the power at the input signal pin, and a control voltage Vapc level section representing extremely high sensitivity appears. When the sensitivity becomes extremely high as the characteristic chart shows, the output power Pout greatly changes with even small change of the control voltage Vapc. When a feedback to return such excessive change of the output power Pout to normal is applied, the characteristic also responds to the feedback and such a oscillation state appears that the output power Pout cyclically changes for a period corresponding to the feedback loop.
An object of the present invention is to provide a power amplifier module featuring that its output power characteristic smoothly changes as the input control voltage changes and that its control sensitivity is stable over a wide dynamic range. Another object of the present invention is to provide a power amplifier module of convenient service. The above and other objects as well as noticeable features of the present invention would be elucidated from the whole text of the present specification and the related drawings.
A typical power amplifier module embodied by the invention disclosed herein will be summarized below. The power amplifier module accomplishes output power control in such a manner that: upon the reception of control input voltage, idling current is generated and adjusted such that it exponentially changes, relative to the control input voltage and the idling current is supplied to a power amplifier element.
REFERENCES:
patent: 5841320 (1998-11-01), Ichihara
patent: 6084471 (2000-07-01), Ruth et al.
Kondo Shizuo
Tanoue Tomonori
Yamashita Kiichi
Miles & Stockbridge P.C.
Mottola Steven J.
Renesas Technology Corp.
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