Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Reexamination Certificate
1998-06-30
2001-05-22
Legree, Tracy (Department: 2681)
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
C455S264000, C455S262000, C455S255000, C331S017000
Reexamination Certificate
active
06236843
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio terminal equipment such as a portable telephone or the like that is provided with an oscillator for use, for example, in semiconductor integrated circuits, more particularly, an oscillator used in fields in which accurate frequencies are needed and, in some cases, certain frequency shifts need to be dealt with.
2. Description of the Prior Art
Conventionally, an oscillator for use in radio terminal equipment of this kind is made up of an oscillation inverter built in a semiconductor integrated circuit, an external or built-in resistor and an external capacitance and crystal oscillator; and its oscillation frequency is fixed.
FIG. 1
is a circuit diagram depicting the configuration of the oscillator used in the traditional radio terminal equipment. Reference numeral
101
denotes an oscillation inverter built in a semiconductor integrated circuit forming radio terminal equipment
104
; reference numeral
102
denotes an output pin of the semiconductor integrated circuit to which an output terminal of the inverter
101
is connected; and reference numeral
103
denotes an input pin of the semiconductor integrated circuit to which an input terminal of the inverter
101
is connected.
Reference numeral
105
denotes a feedback resistor that forms part of an oscillator identified generally by
160
, the feedback resistor
105
being connected to the output and input pins
102
and
103
; reference numeral
106
denotes a crystal oscillator connected in parallel to the feedback resistor
105
; and reference numerals
107
and
108
denotes capacitors (capacitances), which are connected between the output pin
102
and a ground level position
109
and between the input pin
103
and the ground level position
109
, respectively.
Turning next to
FIGS. 2
,
3
and
4
, the operation of the radio terminal equipment will be described.
FIG. 2
is an explanatory diagram showing the mode of communication of the radio terminal equipment, and
FIGS. 3 and 4
are frame timing diagrams of the radio system. A base station
111
has an oscillator that oscillates at a fixed frequency fO (Hz), and radio terminal equipment
112
that is a mobile station has the oscillator
160
.
Since the oscillator of the radio terminal equipment
112
as a mobile station has such a configuration as mentioned above, it oscillates at a frequency independent of the fixed oscillation frequency of the base station
111
. It is desirable that the base station and the mobile station use a system clock of exactly the same oscillation frequency; in practice, however, such various factors as listed below cause a frequency shift in their oscillation.
a. Variations in the performance of crystal oscillators used in the oscillators of the base and mobile stations lead to the variations in oscillation frequency.
b. The oscillation frequency has temperature dependence; the oscillation frequency decreases with an increase in temperature and vice versa. Hence, if the base and mobile stations are in different temperature environments, a considerable difference may sometimes arise between their oscillation frequencies.
c. When the mobile station is moving at high speed, its oscillation frequency as observed from the base station is high or low due to the Doppler effect, depending on whether the mobile station is approaching or going away from the base station.
The oscillation frequencies of the base and mobile stations are caused to differ by various other factors as well.
Let it be assumed that the oscillator
160
of radio terminal equipment
112
, used as a first mobile station, is oscillating at a frequency f
1
(Hz) a little lower than the oscillation frequency f
0
(Hz) of the base station
111
and that the oscillator of radio terminal equipment
112
, used as a second mobile station, is oscillating at a frequency f
2
(Hz) a little higher than the oscillation frequency f
0
(Hz) of the base station
111
. When the oscillation frequencies of the base and mobile stations differ as mentioned above, frame timing based on the frequency difference will differ as depicted in FIG.
3
. That is, the frame timing of the radio terminal equipment
112
as the first mobile station lags behind the frame timing of the base station
111
, whereas the frame timing of the second mobile station
112
leads the frame timing of the base station
111
. On this account, the difference in frame timing, even if very small, will accumulate as indicated by W
1
and W
2
during a long period of time of use; hence, the frame timing of the first and second mobile stations keeps on deviating from the frame timing of the base station
111
, resulting in frame-matched, correct transmission and reception becoming impossible.
As a solution to such a problem as referred to above, there has been proposed a method that uses DPLL (Digital Phase-Locked Loop) techniques to correct for the timing deviation by a very small amount of time on a frame-wise basis. In this instance, when the frame-by-frame timing deviations of the first and second mobile stations
112
are smaller in absolute value than a correction value Dt that is a small amount of time, their frame timing follows that of the base station
111
. When the absolute values of the timing deviations for each frame exceeds the correction value Dt, the timing deviations will accumulate to such relatively large amounts of time t
1
and t
2
as shown in FIG.
4
. Accordingly, the frame timing of the first and second mobile stations
112
goes on departing from the frame timing of the base station
111
; as is the case with the above, no frame-matched, correct transmission and reception are possible and no correct data reception can be expected, either. Another problem is the generation of psychoacoustically uncomfortable noise.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide radio terminal equipment that includes an oscillator which detects from the received frequency the deviation therefrom of the oscillation frequency of the receiving station and controls its own oscillation frequency according to the detected frequency deviation even in a range over which a DPLL is ineffective in correcting the frequency deviation, thereby permitting minimization of the difference between the received frequency from the transmitting station and the oscillation frequency of the receiving station.
To attain the above objective, according to a first aspect of the present invention, there is provided radio terminal equipment that has a switch for connecting therethrough a capacitor to or disconnecting it from the oscillator and control means for effecting ON-OFF control of the switch according to the DPLL output signal. With this arrangement, the difference in oscillation frequency between a base station and the radio terminal equipment as a mobile station can automatically be corrected even in the range over which the frequency difference cannot be corrected by the DPLL—this brings about the effect of preventing a reception error.
According to a second aspect of the present invention, there is provided radio terminal equipment that has control means for effecting selective ON-OFF control of switches each connected to one of a plurality of capacitors according to the DPLL output signal. This ensures avoidance of abrupt capacitance variations, and hence permits control of its oscillation frequency while keeping the oscillator stable in operation.
According to a third aspect of the present invention, there is provided radio terminal equipment that has a plurality of capacitors whose capacitance values differ in steps of C/2n (where n is an integer). This arrangement allows for close capacitance value control, and hence permits control of its oscillation frequency while keeping the oscillator stable in operation.
According to a fourth aspect of the present invention, there is provided radio terminal equipment in which a capacitor has connected thereto a semiconductor switching element whose conducti
Legree Tracy
Leydig Voit & Mayer Ltd
Mitsubishi Denki & Kabushiki Kaisha
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