Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
2000-09-07
2002-12-10
Nguyen, Patricia (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S133000, C330S134000
Reexamination Certificate
active
06492872
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a high frequency power amplifier module in a multi-stage configuration having a plurality of cascaded semiconductor amplifiers (variable power amplifier) and a wireless communication apparatus incorporating this high frequency power amplifier module, and particularly, to the technology which is effectively applied to improve the controllability for the output power by a control voltage.
More specifically, the present invention relates to a high frequency power amplifier module of a type which changes the transconductance by a gate bias for changing the output power of the high frequency amplifier module without a significant increase in power consumption, wherein the high frequency power amplifier module comprises a gate bias control circuit for controlling the gate bias, i.e., a drain current, for use in improving the control lability for the output power by a control voltage.
Mobile communication devices, for example, wireless communication apparatus for use in automobile telephones, portable telephones and so on typically have a built-in high frequency power amplifier module, i.e., a high frequency power amplifier circuit in a transmission output stage thereof. The high frequency power amplifier module is configured to automatically control the output (transmission power) by an APC (Automatic Power Control) circuit.
For example, a high frequency power amplifier module having a plurality of cascaded MOSFETs (Metal Oxide Semiconductor Field-Effect-Transistor) as semiconductor amplifier devices has been widely employed up to now because of its convenience in handling, resulting from the fact that the output can be readily controlled by a positive voltage (for n-channel MOSFETs) biased to the gate.
JP-A-7-94975 discloses a three-stage high frequency HIC (Hybrid IC) module, i.e., a high frequency power amplifier module, which has MOSFETs cascaded in the first, middle and last stages.
This high frequency HIC (hybrid IC) module comprises a first bias circuit configured to bias a gate of a predetermined MOSFET out of MOSFETs in a plurality of stages, based on an output control voltage; a second bias circuit for biasing gates of the remaining MOSFETs other than the predetermined MOSFET based on a fixed power supply; and a switching means for switching a path associated with the fixed power supply and a path associated with the second bias circuit in accordance with the output control voltage. This configuration is intended to improve the controllability of the output and the efficiency.
Each of the bias circuits is composed of three resistors and a capacitor.
The above-cited literature, however, does not describe any technique for controlling the gate bias, which changes in response to a control voltage vapc, in accordance with the output power.
Generally, a setting for the gate bias which changes in response to the control voltage Vapc is determined by the value of a resistor forming part of the bias circuit, for example, in such a manner that the efficiency is improved as the output power is larger.
SUMMARY OF THE INVENTION
The conventional high frequency HIC module changes the transconductance by applying appropriate voltages to the gates of the MOSFETs in the respective stages. This module is advantageous in that a variable output power can be provided in a small circuit configuration without adversely affecting the output power or efficiency.
However, since the gate bias changes at a constant rate in response the control voltage, the bias in each stage for the control voltage cannot be controlled on account of the fluctuating output power of the high frequency power amplifier module, resulting in poor controllability for the output power and inconvenience in utilization. Stated another way, although this high frequency HIC module produces the bias which merely results in good characteristics as a module, it cannot prevent the output power from abruptly changing in response to the control voltage Vapc.
The above cited literature discloses a diagram showing the correlation of the output control voltage Vapc to the output Po.
FIG. 16
is a graph which shows the characteristic of an output power Pout versus a control voltage Vapc, similar to the above. This graph was derived from a test conducted by the present inventors.
As can be seen in the characteristic graph, the output power exhibits abrupt rising for a portion of the control voltage, for example, in a range of 1.1 to 1.5 volts, from which it can be understood that there is a problem in controlling the output for practical use.
This abruptly rising region is present when a gate voltage applied to a MOSFET for amplification which lastly operates (turns on) is close to a threshold voltage Vth. This is because, in this region of the gate voltage, the gain of the MOSFET largely varies, and simultaneously the impedance also largely varies, so that a matching loss of a matching circuit largely varies as well.
Further, as the transconductance g, is improved due to improved performances of recent devices, MOSFETs used in respective stages present larger gain fluctuations with gate bias, resulting in a tendency to more abrupt output power fluctuations and lower output controllability.
It should be noted that the foregoing problem of poor controllability for the output is not limited to the MOSFET but is common to other semiconductor amplifier devices which have a variable gain in response to a control bias applied to a control terminal.
It is an object of the present invention to provide a high frequency power amplifier module which has good output controllability.
It is another object of the present invention to provide a wireless communication apparatus which comprises the high frequency power amplifier module having the good output controllability.
The above and other objects and novel characteristics of the present invention will become apparent from the description in the specification and the accompanying drawings.
Within various embodiments of the invention disclosed in this application, typical aspects will be described below in brief.
A high frequency power amplifier module (power module) using MOSFETs as semiconductor amplifier devices in accordance with one aspect of the present invention comprises a bias circuit for generating a gate voltage in response to a control voltage Vapc generated based on a power control signal of a wireless communication apparatus to reduce fluctuations in output power in response to the control voltage Vpac in a region near a threshold voltage Vth of MOSFETS in respective amplification stages. This provides a power module which facilitates handling in consideration of the controllability for the output power.
Specifically, the power module controls the output power Pout outputted from an output terminal by controlling a gate voltage which is generated in accordance with a division of the control voltage vapc supplied to a bias supply terminal. The gate bias circuit has a circuit for setting the gate voltage supplied to a control terminal, which is responsive to the control voltage Vapc, so as to change largely in a region where the gate voltage Vg is lower than the threshold voltage Vth of the respective MOSFETs; to change slightly near the threshold voltage Vth; and to present desired power amplification characteristics from the vicinity of the threshold voltage Vth to a high Vapc voltage region.
When the gate bias circuit is applied to a multi-stage power module, the control voltage Vapc serves as an optimal gate bias for each MOSFET through the gate bias circuit. The timing at which the MOSFET in each stage turns on in response to the control voltage Vapc is also set in accordance with fluctuations in the gate bias of each stage with respect to the control voltage Vapc.
Next, a bias circuit for a multi-stage power module will be described particularly in terms of the timing at which the MOSFET in each stage turns on, with reference to
FIG. 12
which shows changes in the gate voltages Vg of the MOSFETs in the respective
Adachi Tetsuaki
Fujioka Toru
Hotta Masao
Matsunaga Yoshikuni
Morikawa Masatoshi
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Nguyen Patricia
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