Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Reexamination Certificate
2001-01-19
2004-06-08
Chin, Vivian (Department: 2682)
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
C455S075000, C455S076000, C455S192100, C455S256000
Reexamination Certificate
active
06748199
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a portable telephone apparatus, and particularly to a portable telephone apparatus of a mobile communication system, in which a frequency transmitted and received on a radio channel is determined based on a changeable reference frequency, and information such as voice is modulated and demodulated, and is transmitted and received between a plurality of base stations via the above-described radio channel.
As shown in
FIG. 12
, this kind of conventional digital portable telephone apparatus is constructed of a common use section
101
, a reception section
102
, a transmission section
103
, a frequency generating section
104
, a reference frequency generating section
105
, an AFC section
106
, a modulation and demodulation section
107
, a control section
108
, an operation section
109
, a display section
110
, and a transceiver
111
.
A signal (carrier wave signal) on a radio channel, which was received by the common use section
101
via an antenna, is delivered to the reception section
102
, and is mixed with a station issue signal, and is replaced by an intermediate frequency signal, and further, is supplied to the modulation and demodulation section
107
and the AFC section
106
. The intermediate frequency signal supplied from the reception section
102
is demodulated in the modulation and demodulation section
107
, and is output as a voice signal from the transceiver
111
through the control section
108
.
On the other hand, the voice that was input to the transceiver
111
passes the control section
108
, and is digitally modulated in the modulation and demodulation section
107
, and is converted into a signal (carrier wave signal) on a radio channel in the transmission section
103
, and after amplified, is supplied to the common use section
101
and is transmitted.
Further, the operation section
109
and the display section
110
, which provide convenience for conducting a call, are connected to the control section
108
.
A reference frequency signal from the reference frequency generating section
105
is supplied to the frequency generating section
104
, and it generates a station issue signal with accuracy equivalent to frequency accuracy of the reference frequency signal by means of a PLL, and supplies it to the reception section
102
and the transmission section
103
.
It is required that the reference frequency generating section
105
outputs a frequency that is stable within a certain range. However, since it is also required that the portable telephone apparatus becomes to be small-sized, light and cheap, it is not possible to increase accuracy and stability of an output frequency from the reference frequency generating section
105
so much. Accordingly, a frequency of the station issue signal can be also changed easily, and transmission and reception cannot be sometimes conducted at a desired frequency on the radio channel.
On the other hand, since output frequency accuracy and stability of the reference frequency generating means in each base station of a digital mobile communication system are extremely high, with regard to a carrier wave signal transmitted and received on a radio channel, a frequency deviation from a prescribed frequency can be extremely reduced. In addition, quantities of the deviation are slightly different from each other for every base station. Therefore, on a side of the digital portable telephone apparatus, it is necessary to make a frequency deviation in transmission and reception of the apparatus coincide with a frequency deviation of a carrier wave signal of a base station to be connected, that is to say, a frequency deviation of an intermediate frequency signal corresponding thereto, and AFC (Automatic Frequency Control) is conducted for a reference frequency of the apparatus.
In the AFC control in a prior art, first, the AFC section
106
sends one determined initial control signal to the reference frequency generating section
105
, and the reference frequency generating section
105
generates a frequency for a value of the provided initial control signal. The AFC section
106
changes a value of the control signal so as to coincide with a frequency deviation of the intermediate frequency signal supplied from the reception section
102
, and controls the reference frequency generating section
105
.
However, if the above-mentioned AFC control is conducted in a state where reception electric field condition is not good, there is a case in which a frequency of the reference frequency generating section does not exactly coincide with a frequency deviation of a base station. The reason thereof is because, in condition where a reception electric field is low, due to an effect of phasing, an intermediate frequency signal supplied to the AFC section has a lot of phase noises and frequency counting cannot be exactly conducted, and frequency comparison is mistaken. Similarly, if the AFC control is conducted in a state where reception quality condition is not good, there is a case in which a frequency of the reference frequency generating section does not exactly coincide with a frequency deviation of a base station. The reason thereof is because, in condition where reception quality is bad due to an interference disturbance wave and so forth, the disturbance wave is superimposed on an intermediate frequency signal supplied to the AFC section, and thereby, frequency counting cannot be exactly conducted, and frequency comparison is mistaken.
Although there is means for always operating the AFC control as means for solving these tasks, since a consumption electric current becomes to be large, it is not preferable for a digital portable telephone apparatus in which a battery is used for a power supply.
Also, it is known that control of the reference frequency generating section is significantly influenced by heat. In the portable telephone apparatus, since external environment temperature changes suddenly with movement, and the transmission section generates extreme heat during calling, a temperature changing range becomes to be broad. Accordingly, high stability is required for the reference frequency generating section over a wide range even for a temperature change.
Although, as a method for solving this task, to use a reference frequency generating device is considered, which has high stability over a wide range even for a temperature change, and can conduct voltage control, a frequency generating section that meets both conditions is not general one.
SUMMARY OF THE INVENTION
The present invention is made to solve the above-mentioned problems.
Moreover, the objective of the invention is to provide a portable telephone apparatus capable of preventing increase of a consumption electric current without continuously conducting AFC control and keeping communication condition good even though heat influence exists.
The present invention for accomplishing the above-described objective is a portable telephone apparatus characterized in that the apparatus comprises:
reference frequency generating means capable of changing an output frequency for communication with a base station by means of a voltage control signal;
high-accurate reference frequency generating means in which frequency accuracy always meets a prescribed value;
determination means for determining whether or not frequency accuracy of an output signal from the above-described reference frequency generating means meets a predetermined prescribed value; and
selection means for selecting an output signal from the above-described reference frequency generating means in case that a determination result of the above-described determination means meets the above-described prescribed value, and for selecting an output signal from the above-described high-accurate reference frequency generating means in case that a determination result of the above-described determination means does not meet the above-described prescribed value.
In addition, it is preferable that an output signal from the above-described referen
Chin Vivian
McGinn & Gibb PLLC
NEC Corporation
Tran Tuan
LandOfFree
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