Pulse or digital communications – Transmitters – Antinoise or distortion
Reexamination Certificate
1999-12-29
2004-09-07
Tse, Young T. (Department: 2634)
Pulse or digital communications
Transmitters
Antinoise or distortion
C375S146000, C455S127300
Reexamination Certificate
active
06788744
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in an electronic equipment on which is mounted a circuit capable of acquiring desired characteristics for a specific level of an input signal, to a power control circuit for maintaining the level of a signal outputted by a subsequent stage of the circuit, at a specific value, and to a transmitter having the power control circuit mounted thereon.
2. Description of the Related Art
The CDMA (Code Division Multiple Access) system is being applied to various communication systems because it intrinsically has confidentiality and interference-resistivity and is a multiple access system capable of making effective use of radio frequencies.
On the other hand, the CDMA system is being positively applied in recent years to a mobile communication system because it is able to solve the near-far problem by establishing the technique for realizing the transmitting power control of high responsiveness and accuracy.
FIG. 14
is a block diagram showing an example of the configuration of a transmission part of a radio base station of a mobile communication system to which the CDMA system is applied.
In
FIG. 14
, a plurality N of power controlling parts
91
-
1
to
91
-N are fed at their individual base band inputs with different base band signals
1
to N, and their outputs are connected with corresponding inputs of a multiplexing part
92
. The output of the multiplexing part
92
is connected with a feeding point of an antenna
98
through a D/A converter
93
, a modulator
94
, a multiplier
95
, a variable gain amplifier
96
and an amplifier
97
, which are connected in tandem. The output of an oscillator
99
is connected with a carrier input of the modulator
94
, and the output of an oscillator
100
is connected with a spreading code input of the multiplier
95
. Control terminals of the power controlling parts
91
-
1
to
91
-N and the variable gain amplifier
96
are connected with the corresponding input/output ports of a controlling part
101
.
In the transmission part of the configuration, the controlling part
101
forms a wireless zone and a radio channel appropriate for the CDMA system between itself and a mobile station located in the wireless zone, by associating itself with the not-shown receiving part on the basis of a predetermined channel setting procedure. Moreover, the controlling part
101
watches the transmission qualities of the individual radio channels thus formed, by associating itself with the above-described receiving part.
On the other hand, the controlling part
101
varies the gain (FIG.
15
(
1
)) to a value appropriate for the watching result, for such ones of the power controlling parts
91
-
1
to
91
-N as correspond to the individual radio channels of the watching result, to absorb the difference in the transmission loss for each radio channel, as caused by the difference in the relative distances between the individual mobile stations located in the above-described wireless zones and the radio base station and by the change in the distances.
Here, the processing to vary the gain in the base band regions of the power controlling parts
91
-
1
to
91
-N, as described above, will be simply called the “transmitting power control”.
The multiplexing part
92
thus multiplexes the base band signals, having the level set in the base band regions by the power controlling parts
91
-
1
to
91
-N operating under the controlling part
101
, to generate a digital signal indicating the sum of the signals to be transmitted to the above-described plurality of radio channels in the digital region.
The D/A converter
93
converts the digital signal into an analog signal. The modulator
94
generates a primary modulated wave by modulating the carrier signal generated by the oscillator
99
, according to the analog signal.
Here, it is assumed for simplicity that the modulation made by the modulator
94
corresponds to a primary modulation appropriate for the direct sequence type of the CDMA system.
The multiplier
95
generates the transmission wave by performing a secondary modulation to multiply the spreading code generated by the oscillator
100
and the above-described primary modulated wave.
The variable gain amplifier
96
performs power amplification (FIG.
15
(
2
)) together with the amplifier
97
to feed the above-described transmission wave to the feeding point of the antenna
98
. Here, the gain of the variable gain amplifier
96
is adjusted to a constant value at which the level of the transmission wave takes a predetermined value in the course of the running and maintaining routines.
By sharing the variable gain amplifier
96
and the amplifier
97
for the transmissions of the plurality of radio channels, therefore, the hardware of the radio base station is scaled down, and the level of the transmission wave to be transmitted through the antenna
98
is kept for each channel at the level of eliminating or easing the “deterioration in the transmission quality caused by a drastic change or difference of the location of the individual mobile stations located in the wireless zone formed by the radio base station” (as will be shortly called the “near-far problem”).
Here in this example of the prior art, in order to solve the near-far problem, the transmitting power control generally has to be made over a dynamic range wider by
40
decibels to
60
decibels than that of the transmitting part appropriate for the TDMA system or the FDMA system.
In order to achieve the desired characteristics for the analog signal fed under the power control made over such wide dynamic range, therefore, not an active modulator to which an active element is applied but a passive modulator composed of only passive element(s) has/have to be applied as the modulator
94
.
However, the passive modulator has a wider dynamic range than that of the active modulator (FIG.
16
(
b
)), as shown in FIG.
16
(
a
), but it is constructed mostly of discrete parts so that it has a large physical size.
Of the circuits constructing the passive modulator, moreover, a phase shift circuit for converting the carrier signal generated by the oscillator
99
into two carrier signals crossing each other has a far higher changing rate of phase shift with respect to the temperature than that of an equivalent circuit belonging to the active modulator.
In the example of the prior art, therefore, a temperature compensating circuit for compensating the fluctuation of the phase shift with respect to the temperature has to be mounted together with the modulator
94
.
Here, the active modulator has a far lower changing rate of characteristics with respect to the temperature than that of the passive modulator, as illustrated in FIGS.
17
(
a
) and (
b
), so it can be applied when a desired dynamic range is achieved.
However, the active modulator is unable to realize the above-described wide dynamic range due to the characteristics of the active elements to be applied and by the restrictions on the power supply voltage, so that it is practically hard to apply and cannot always realize an integrated circuit.
On the other hand, with the above-described desired dynamic range wider, the level of the analog signal to be actually inputted to the modulator
94
has a higher possibility of exceeding the range of the appropriate input level at which the upper limit and the lower limit are given, for example, by two thin dotted lines as illustrated in
FIG. 15
, and at which the above-described desired characteristics are kept.
SUMMARY OF THE INVENTION
An object of the invention is to provide a power control circuit and a transmitter having performances maintained stable over a wide dynamic range without any drastic changes in the configuration.
Another object of the invention is to keep the desired characteristics and performances maintained even if the level of an input signal may fluctuate.
Still another object of the invention is to avoid the degradation of performances due to the fluctuation or deviation of the characteristics of co
Katten Muchin Zavis & Rosenman
Lugo David B.
Tse Young T.
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