Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
2002-06-14
2004-07-06
Mottola, Steven J. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S133000
Reexamination Certificate
active
06759906
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a technique employable effectively for multistage high frequency power amplifier circuit devices, each having a plurality of semiconductor amplification elements connected in a cascade, as well as for such radio communication apparatuses as portable telephones, etc. in which such a high frequency power amplifier circuit device is built respectively. More particularly, the present invention relates to a technique for improving the controllability of an output power (gain) with use of a power control signal voltage of the high frequency power amplifier circuit device and the efficiency of the device at a low power output.
In such radio communication apparatuses (mobile communication apparatuses) as mobile telephones, portable telephones, etc., a multistage high frequency power amplifier circuit device is built in the transmission side output stage respectively. The high frequency power amplifier circuit device includes semiconductor amplification elements such as MOSFETs (Metal Oxide Semiconductor Field-Effect-Transistors) and FaAs-MESFETs, etc., which are connected in a cascade. In the high frequency power amplifier circuit device, the semiconductor amplification element in the last stage is usually composed of discrete parts (an output power MOSFET, etc.) and the semiconductor amplification element in the preceding stage and the bias circuit are often integrated into a semiconductor integrated circuit formed on one semiconductor chip. Hereinafter, a component in which a semiconductor integrated circuit that includes semiconductor amplification element parts, the bias circuits, capacity elements, etc. are integrated will be referred to as a high frequency power amplifier module or simply as a module.
And, a portable telephone system is generally configured so as to change the output (transmission power) according to the ambient conditions with use of a power level command signal received from a base station so as not to cause radio interference in the communications with another portable telephone. For example, in the case of the cellular portable telephone such as the 900 MHz band standard method employed in the United States of America, the GSM (Global System for Mobile Communication) method employed in Europe, etc., the high frequency power amplifier module in the transmission side output stage is configured so that the gate bias voltage of each output power element is controlled so as to output a power required for talking with use of the output voltage Vapc of the APC (Automatic Power Control) circuit.
In addition, for a portable telephone, employment of a high efficiency high frequency power amplifier module is a very important factor for deciding a talking time and a waiting time, that is, an operating life of the battery. This is why the performance of the mutual conductance, etc. among the semiconductor amplification elements of a module has been improved to achieve such the high efficiency.
Japanese Patent Application No. Hei 11(1999)-275465 discloses a radio communication apparatus in which a multistage high frequency power amplifier module is built. The module includes a plurality of MOSFETs that are connected in a cascade. This radio communication apparatus improves the controllability of the output power Pout (to suppress an increase of the Pout with respect to an increase of the Vapc, that is, &Dgr;Pout/&Dgr;Vapc) with use of bias means provided to generate a gate bias voltage Vg so as to minimize the variation of the output power Pout with respect to the Vapc around the threshold voltage Vth of the MOSFET in each amplification stage according to the power control signal voltage Vapc generated on the basis of its body power control signal.
SUMMARY OF THE INVENTION
FIG. 23
shows a bias circuit that controls the gate bias voltage in each stage in the three-stage high frequency power amplifier module disclosed in the above official gazette non-linearly with respect to the power control signal voltage Vapc. As shown in
FIG. 23
, the bias means (bias circuit) of the three-stage high frequency power amplifier module is composed of a plurality of resistors R
01
to R
04
connected serially and a transistor Q
01
connected to those resistors R
01
to R
04
through a diode respectively. The resistor's voltage dividing ratio is set so as to obtain the maximum power at a position where the Vapc becomes as large as about 2 V, thereby the gate bias in each stage is decided. The diode-connected transistor is usually transformed into an MMIC (Microwave Monolithic IC) with use of the same semiconductor process technology as that of the amplification MOSFET.
FIGS. 24 and 25
are graphs for denoting a relationship between the power control signal voltage Vapc in the bias means shown in FIG.
23
and the gate bias voltage Vg in each stage and a relationship between the power control signal voltage Vapc obtained by the present inventor through a test of a module composed as shown in FIG.
23
and the output voltage Pout. The amplification MOSFETs used in the above test have a threshold voltage Vth of about 0.8 V respectively.
In the bias circuit disclosed in the above gazette, the gate bias voltage Vg in each stage is varied linearly (Vg=Vapc), since the control voltage Vapc is output as Vg1 to Vg3 with no change. This is because the Q
01
is off until the control voltage Vapc reaches the threshold voltage of the diode-connected transistor Q
01
as to be understood from the graph shown in
FIG. 24
that shows a relationship between the control voltage Vapc of this circuit and the gate bias voltage Vg in each stage. The gate bias voltage Vg is then varied non-linearly.
In the module shown in
FIG. 23
, however, the threshold voltage Vth of the amplification MOSFET becomes almost the same as the threshold voltage of the diode-connected transistor formed in the same process, so that the amplification MOSFETs in all the stages are driven almost concurrently, thereby the output power Pout changes suddenly. In other words, as to be understood from the graph shown in
FIG. 25
, the output power curve that denotes the characteristics of the output power is inclined sharply around 0 dBm and the output power Pout changes significantly due to a slight change of the voltage Vapc. This is why the controllability of the output power has not been improved to the required level. In addition, the output power Pout also comes to change more sharply depending on a variation of the threshold voltage Vth of the amplification MOSFETs.
In prior to the present invention, the inventor has examined a bias circuit composed of a plurality of resistors R
01
to R
04
connected serially as shown in FIG.
20
. The bias circuit is used to linearly control the gate bias voltage in each stage in the three-stage high frequency power amplifier module with respect to the power control signal voltage Vapc.
FIGS. 21 and 22
are graphs for denoting a relationship between the power control signal voltage Vapc and the gate bias voltage Vg in each stage in the bias circuit shown in
FIG. 20 and a
relationship between the power control signal voltage Vapc obtained by the inventor through a test of the module composed as shown in FIG.
20
and the output power Pout. The threshold voltage Vth of the amplification MOSFETs used in the above test is about 0.8 V.
As shown in
FIG. 20
, a resistance ladder circuit is generally used as a bias circuit for linearly controlling an object voltage. The voltage dividing ratio of the resistor decides an inclination of the gate bias voltage Vg. As to be understood from the graph shown in
FIG. 22
, the curve that denotes the characteristics of the output power inclines sharply around an output power of 0 dBm. The output power Pout changes significantly at a slight change of the voltage Vapc even when the bias circuit as shown in
FIG. 20
is used. This means that the output controllability is not so good.
Under such circumstances, it is an object of the present invention to provide a high frequency power amplifier
Furuya Tomio
Matsudaira Nobuhiro
Matsunaga Yoshikuni
Matsushita Koichi
Shimizu Toshihiko
Mattingly Stanger & Malur, P.C.
Mottola Steven J.
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