Cellular mobile telephone terminal

Details Cellular mobile telephone terminal Cellular mobile telephone terminal

2000-05-26

2002-01-08

To, Doris H. (Department: 2682)

Telecommunications

Transmitter

With feedback of modulated output signal

C455S069000, C455S552100, C327S308000, C330S278000

Reexamination Certificate

active

06337974

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cellular mobile telephone terminal, and more particularly to the configuration of an attenuator for use in a radio frequency section in a radio transceiver section of a cellular mobile telephone terminal.
2. Description of the Related Art
In CDMA systems (for example, IS-95), signal power arriving at a base station from any cellular mobile telephone terminal must be controlled to a constant value regardless of the distance between the cellular mobile telephone terminal and the base station. To achieve this, gain control is performed in the transmitter section of each cellular mobile telephone terminal.
FIG. 13
schematically shows the relationship of the locations of cellular mobile telephone terminals relative to a base station. In
FIG. 13
, the cell range CL of one base station BS is several tens of kilometers in radius, for example, about 30 km in radius. Within the cell range CL of the base station BS are located many cellular mobile telephone terminals TH
1
, TH
2
operating in different communication conditions, for example, at different distances from the base station BS or under different geographical or terrestrial conditions. These many cellular mobile telephone terminals TH
1
, TH
2
are simultaneously performing communications with the base station BS while moving toward or away from the base station BS and under communication conditions changing from moment to moment.
In this case, if control is to be performed so that the signal power arriving at the base station BS from any cellular mobile telephone terminal will be the same whether the terminal is located farthest away from the base station or nearest to it, then considering the size of the cell range CL, the transmitter section of each cellular mobile telephone terminal is required to have a gain control width of 70 dB or greater and a high linearity of ±1 dB. This situation is known as the near-far problem.
If the gain control at the transmitter section of the cellular mobile telephone terminal is not performed properly, the signal power arriving at the base station becomes greater as the distance between the cellular mobile telephone terminal and the base station decreases; as a result, leakage power to adjacent channels increases, increasing the bit error rate and degrading the communication quality. In
FIG. 14
, solid lines A
1
to A
6
indicate the received signal power levels at the base station from various channels, and dashed line B
4
shows the intermodulation distortion characteristic of the channel A
4
.
FIG. 14
shows the case where the received signal power levels from the channels A
3
and A
5
are masked by the distortion component of the channel A
4
indicated by the dashed line B
4
, so that correct data cannot be recovered from the channels A
3
and A
5
adjacent to the channel A
4
.
To maintain a high carrier-to-noise ratio (C/N), it is desirable that the gain control in the transmitter section of each cellular mobile telephone terminal be performed, as much as possible, in the radio frequency range where the carrier signal level is high. The reason is that, at radio frequencies, the carrier signal level is far higher than the background noise level and, if the gain is lowered in the radio frequency section, a high carrier-to-noise ratio can be maintained. On the other hand, at intermediate frequencies, the carrier signal level is low and, if the gain is lowered in the intermediate frequency section, the difference between the carrier signal level and the ground noise level becomes very small, and this difference between the carrier signal level and the noise level in the intermediate frequency section is carried over directly into the radio frequency section.
However, there has not been available an attenuator, for use in a radio frequency section, that can by itself accomplish gain control with a linearity of ±1 dB over a wide range of 70 dB or greater. In the prior art, to accomplish gain control with a linearity of ±1 dB over a wide range of 70 dB or greater in the radio transmitter section of a cellular mobile telephone terminal, it has been practiced to control the gain in step-like manner in the radio frequency section while continuously controlling the gain in the intermediate frequency section. When the amount of gain control accomplished in the radio frequency section and that accomplished in the intermediate frequency section are used in combination as described above, gain control with a linearity of ±1 dB can be achieved over a wide range of 70 dB or greater.
The gain control at the cellular mobile telephone terminal is performed in the following manner.
At the cellular mobile telephone terminal, a target value for the transmit power necessary to keep the received signal strength at the base station at a constant value is set based on the received signal strength at the cellular mobile telephone terminal, and control is performed so that the transmit power matches the target value by forming a feedback control loop in which the actual transmit power is constantly compared with the target value to cause the transmit power to follow the target value.
Next, the configuration and operation of a prior art cellular mobile telephone terminal will be described with reference to FIG.
15
. As shown in
FIG. 15
, the cellular mobile telephone terminal is constructed with microcomputer logic blocks, etc. and comprises a baseband section
100
which processes voice signals and a radio transceiver section
200
which takes as an input the voice signal processed by the baseband section
100
and performs communications with a base station.
The radio transceiver section
200
comprises a transmitter section
210
which generates signals for transmission to the base station and a receiver section
220
which receives signals transmitted from the base station.
The transmitter section
210
comprises an intermediate frequency section
230
which performs heterodyning for modulation and frequency conversion of the voice signal supplied from the baseband section
100
, and a radio frequency section
240
which amplifies the radio frequency signal output from the intermediate frequency section
230
and supplies it to an antenna
300
via a duplexer
310
.
The intermediate frequency section
230
comprises a modulator
231
, a variable gain intermediate frequency amplifier
232
for amplifying the output signal of the modulator
231
with a variable gain, and a mixer
233
for converting the output of the variable gain intermediate frequency amplifier
232
into a radio frequency signal. The variable gain intermediate frequency amplifier
232
is usually constructed using a bipolar transistor. The variable gain intermediate frequency amplifier
232
is capable of varying its gain with a linearity of ±1 dB over a range of about 40 dB. In this case, the gain is controlled in a continuous manner over a range of about 40 dB using a continuously varying gain control voltage.
The radio frequency section
240
comprises a variable gain radio frequency amplifier
241
for amplifying the radio frequency signal output from the intermediate frequency section
230
and a power amplifier
242
for amplifying the power of the output signal of the variable gain radio frequency amplifier
241
. The variable gain radio frequency amplifier
241
is capable of varying its gain with a linearity of ±3 dB over a range of about 30 dB. In this case, the gain is controlled in several steps, for example, in three steps, using a gain control voltage that takes discrete values.
The variable gain radio frequency amplifier
241
comprises a front-end amplifier (medium power amplifier)
243
and an attenuator
244
for varying the gain of the radio frequency signal to be input to the power amplifier (high power amplifier)
242
cascaded with the front-end amplifier
243
. The attenuator
244
has the function of varying the amount of attenuation with a linearity of ±3 dB over a range of ab

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