Telecommunications – Transmitter – Power control – power supply – or bias voltage supply
Reexamination Certificate
1999-12-17
2003-06-17
Legree, Tracy (Department: 2681)
Telecommunications
Transmitter
Power control, power supply, or bias voltage supply
C455S126000
Reexamination Certificate
active
06580901
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a burst-type transmission power control apparatus of a radio transmitter, more particularly, to a burst-type transmission power control apparatus suitable for use in a radio transmitter in a time division multiple access (TDMA) system.
2. Description of the Related Art
Technological developments in the field of mobile communication terminals in recent years have been remarkable, Particularly in terms of cellular telephone mobile communication systems which may typically be referred to as special mobile (GSM) systems designed for moving subscribers to utilize telephones. The transmission systems used by such mobile communication systems are shifting or have shifted from analog radio transmission systems to digital radio transmission systems in order to be compatible with networks based on digital exchange technologies, improve the sound quality, maintain the confidentiality of coded signals and raising the communication capacity.
In addition, low-and medium-altitude orbit mobile satellite communication systems have become commercially feasible in recent years as global digital mobile communication systems are connected to each other in a seamless fashion along with portable terminal technologies. As a result, the demand for such systems and such terminals is rapidly increasing.
In such mobile communication systems, the TDMA radio system is used for portable terminals for the purpose of simple communication in order to reduce the load of the hardware on the portable terminal.
Additionally, high speed automatic power control (APC) systems adapted to control the power output including a ramping waveform added thereto before and after a steady-state burst for controlling the transmission burst output level and preventing diffusion into adjacent channels of the transmission spectrum on a frequency base at the time of turning on/off the burst, has been used in order to maintain the quality of transmission/reception lines which can handle a certain level of traffic intensity and allow high density multiple access within the same communication cell.
A first prior art burst-type power control apparatus is of a closed loop type which detects a part of transmission power by a detector and feeds it back tot he gate of a high power amplifier formed by a GaAs field effect transistor (FET) or a Si bipolar transistor (see: FIG. 9 of JP-A-5-152977). This will be explained in detail later.
In the above-described first prior art burst-type transmission power control apparatus, however, since the dynamic range of the detector is narrow, it is difficult both to increase the speed of the rising and falling characteristics of a transmission burst signal, and to increase the power level of a transmission burst signal.
A second prior art burst-type transmission control apparatus further includes a variable attenuator in the closed loop of the first prior art burst-type transmission control apparatus (see: FIG. 10 of JP-A-5-152977). The attenuation degree of the variable attenuator is controlled so as to cause the maximum input level of the detector to be constant, thus broadening the dynamic range o the closed loop, so that the operation of the detector is stabilized on a reproducible basis. This also will be explained in detail later.
In the above-described second prior art burst-type transmission control apparatus, however, the control sensitivity of the high power amplifier is not improved, thus exhibiting a high damping coefficient and giving rise to an overshoot or undershoot during the rising burst period.
A third prior art burst-type transmission control apparatus further includes a variable power driver amplifier at a prestige of the high power amplifier of the second prior art burst-type transmission control apparatus, so as to suppress fluctuation of the control sensitivity of the high power amplifier depending on the output power level (see: FIG. 1 of JP-A-5-152977 & JP-A-10-172380). This also will be explained in detail later.
In the above-described third prior art burst-type transmission control apparatus, however, phase fluctuations occur in the high power amplifier because abrupt fluctuations in the amplitude envelope which occur inside the high power amplifier at and near the burst rising and falling time periods intersects the above phase fluctuation region.
In
FIG. 1
, which illustrates a first prior art burst-type transmission control apparatus (see: FIG. 9 of JP-A-5-152977), a modulated signal S
in
generated from a modulated wave generator
1
which is, in this case, a voltage controlled oscillator (VCO) is transmitted to a high power amplifier
2
. As a result, the high power amplifier
2
is driven by the modulated signal S
in
to generate a transmission burst signal S
out
via a directional coupler
3
. The transmission burst signal S
out
is radiated from an antenna
4
.
The directional coupler
3
takes out a part of the transmission burst signal S
out
, and a detector
5
formed by a diode detects the output signal of the directional coupler
3
. A relative error amplifier
6
compares a reference voltage V
ref
as shown in
FIG. 2A
with the detection voltage V
det
Of the detector
5
as shown in
FIG. 2B
to generate an error voltage V
error
in accordance with the difference between the reference voltage V
ref
and the detection voltage V
det
.
The high power amplifier
2
is constructed by a GaAs field effect transistor (FET) having a gate for receiving the error voltage V
error
, a grounded source and a drain for receiving a power supply voltage V
p
from a power supply battery
7
.
Thus, the transmission burst signal S
out
is fed back by a closed loop of the detector
5
and the relative error amplifier
6
to the high power amplifier
2
, so that the transmission burst signal S
out
as shown in
FIG. 2C
is brought close to the reference voltage V
ref
as shown in FIG.
2
A. In other words, when V
ref
where the level of the transmission burst signal S
out
is higher than a desired level, the relative error amplifier
6
decreases the error voltage V
error
, thus decreasing the level of the transmission burst signal S
out
. On the other hand, when V
det
<V
ref
where the level of the transmission burst signal S
out
is lower than the desired level, the relative error amplifier
6
increases the error voltage V
error
) thus increasing the level of the transmission burst signal S
out
.
The reference voltage V
ref
is generated from a control unit
8
which receives a control signal S
cont
from a base station or the like. The control unit
8
convolutes a rectangular envelope waveform at a steady-state time period defined by time t
2
and time U, a rising ramping envelope wave form at a rising time period defined by time t
1
and time t
2
, and a falling ramping envelope waveform at a falling time period defined by time U and time t
4
on a time basis. The rising and falling ramping envelope waveforms are helpful in removing the spurious spectrum of the transmission burst signal S
out
due to the switching of the GaAs FET of the high power amplifier
2
.
Note that waveforms of the reference voltage V
ref
depending on the control signal S
cont
are stored in a read-only memory (ROM) or a random-access memory (RAM) of the control unit
8
in advance.
In the case of fixed envelope modulation such as Gaussion filtered minimum shift keying (GMSK) modulation which is a angular modulation intrinsically free from amplitude fluctuations unlike &pgr;/4 shift quadrature phase shift keying (QPSK) modulation for personal digital cellular (PDC), there is no need for relative error control to select a relatively large time constant for the loop amplifier including the relative error amplifier
6
for smoothing the detection voltage V
det
including the amplitude fluctuations after detecting the envelope of the transmission burst signal S
out
, taking the averaged power into consideration. In other words, it is possible to select a relatively small time constant in advance and specify only des
Dickstein Shapiro Morin & Oshinsky LLP.
Legree Tracy
NEC Corporation
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