Telecommunications – Transmitter and receiver at same station – With frequency stabilization
Reexamination Certificate
1995-08-16
2002-02-05
Urban, Edward F. (Department: 2683)
Telecommunications
Transmitter and receiver at same station
With frequency stabilization
C455S077000, C455S114100, C455S310000
Reexamination Certificate
active
06345172
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a radio system of the type typically represented by a portable telephone system which tunes in the transmitting channel and the receiving channel at desired frequencies. More specifically, the present invention is concerned with elimination of deterioration in radio characteristics which is due to radiation of a fundamental wave and N-th harmonic of a reference clock generated by a clock oscillation circuit built in the radio system.
In recent years, such a small-sized portable radio system as typically represented by a portable telephone system which tunes in the transmitting frequency or the receiving frequency at a desired frequency has been widely exemplified as using a microprocessor which has one chip incorporating many functions in order to realize a reduction in size and weight, a reduction in power consumption, a reduction in cost and a high-class function. When using the microprocessor, there is need for a clock oscillation means operative to generate a reference clock for synchronization. However, the clock oscillation means sometimes radiates the fundamental wave and N-th harmonic of the reference clock in the form of electromagnetic waves into a free space and when the frequencies of the electromagnetic waves coincide with, or are very close to, that of the transmitting channel or the receiving channel, the electromagnetic waves representative of the fundamental wave and N-th harmonic interfere with an electromagnetic wave representative of the transmitting or receiving channel to deteriorate radio characteristics such as a transmitting characteristic and a receiving characteristic.
Methods for elimination of a deterioration in radio characteristics have hitherto been employed including: a method of isolating all portions liable to radiate the fundamental wave and N-th harmonic of a reference clock, for example, isolating wiring conductors associated with the reference clock from the other wiring conductors by shielding the former wiring conductors with a ground line or isolating parts associated with the reference clock from radio means by enclosing these parts with a shield case made of metal; and a method of suppressing the radiation level by confirming portions liable to radiate the fundamental wave and N-th harmonic of the reference clock through, for example, trial production and adding capacitors to these portions.
JP-A-4-150230 discloses a conventional construction which can systematically achieve such elimination. In the conventional construction, there are provided as shown in
FIG. 8
a receiving circuit
5100
for tuning in the receiving frequency at a desired frequency, a control circuit
6000
for performing control of the whole of a radio system, a clock oscillation circuit
1000
adapted to generate a reference clock signal
1200
for the control circuit
6000
, a measuring reference oscillation circuit
1100
for generating a highly accurate oscillation frequency which serves as a reference of measurement of the oscillation frequency of the reference clock
1200
, a measuring circuit
7000
for measuring the frequency of the reference clock
1200
generated by the clock oscillation circuit
1000
in relation to the reference of the oscillation frequency of the measuring reference oscillation circuit
1100
, a comparative arithmetic circuit
3000
for comparing a receiving frequency
5200
tuned in by the receiving circuit
5100
with a result of measurement by the measuring circuit
7000
, and a frequency switching circuit
4000
for switching the oscillation frequency of the reference clock
1200
generated by the clock oscillation circuit
1000
on the basis of a result of comparison by the comparative arithmetic circuit
3000
.
Next, the operation of the aforementioned prior art example will be described. In the prior art example, when the radio system is started, the control circuit
6000
begins to initialize the individual circuits. At that time, the frequency switching circuit
4000
delivers a switching signal
4001
for setting the oscillation frequency of the reference clock
1200
to be generated by the clock oscillation circuit
1000
to a first oscillation frequency. The clock oscillation circuit
1000
applied with the switching signal
4001
sets the oscillation frequency of the reference clock
1200
to the first oscillation frequency. The measuring circuit
7000
then begins to accurately measure the oscillation frequency of the reference clock
1200
to be generated by the clock oscillation circuit
1000
in relation to the reference of the oscillation frequency of the measuring reference oscillation circuit
1100
. When the initialization ends, the control circuit
6000
controls the receiving circuit
5100
to cause it to sequentially scan receiving frequencies, tune in a desired frequency and begin to receive the desired frequency. At that time, the comparative arithmetic circuit
3000
compares the receiving frequency tuned in by the receiving circuit
5100
, the oscillation frequency of the reference clock
1200
measured by the measuring circuit
7000
, whereby when radiation of the fundamental wave and N-th harmonic of the reference clock
1200
is decided to be of frequencies which interfere with the receiving frequency tuned in by the receiving circuit
5100
, the frequency switching circuit
4000
delivers a switching signal
4001
for setting the oscillation frequency of the reference clock
1200
to be generated by the clock oscillation circuit
1000
to a second oscillation frequency. The clock oscillation circuit
1000
applied with the switching signal
4001
sets the oscillation frequency of the reference clock
1200
to the second oscillation frequency. The comparative arithmetic circuit
3000
then compares the receiving frequency tuned in by the receiving circuit
5100
with the oscillation frequency of the reference clock
1200
measured by the measuring circuit
7000
, whereby when radiation of the fundamental wave and N-th harmonic of the reference clock
1200
is decided to be of frequencies which do not interfere with the receiving frequency tuned in by the receiving circuit
5100
, the frequency switching circuit
4000
delivers a switching signal
4001
for setting the oscillation frequency of the reference clock
1200
to be generated by the clock oscillation circuit
1000
to the first oscillation frequency. The clock oscillation circuit
1000
applied with the switching signal
4001
sets the oscillation frequency of the reference clock
1200
to the first oscillation frequency.
Thus, by alternately switching the oscillation frequency of the reference clock
1200
to be generated by the clock oscillation circuit
1000
to the first and second frequencies in accordance with a receiving frequency tuned in by the receiving circuit
5100
, radiation of electromagnetic waves of the fundamental wave and N-th harmonic of the reference clock generated by the clock oscillation circuit
1000
can be prevented from interfering with that receiving frequency tuned in by the receiving circuit
5100
, thereby eliminating a deterioration in radio characteristics.
However, in the conventional radio system described as above, a shield case made of metal, for example, is needed which prevents the influence of electromagnetic waves of the fundamental wave and N-th harmonic of the reference clock signal radiated from portions associated with the clock oscillation circuit, in order to eliminate a deterioration in radio characteristics, raising a problem that a reduction in size and weight is difficult to achieve, and when suppressing the radiation level of electromagnetic waves of the fundamental wave and N-th harmonic of the reference clock signal by adding capacitors, it is very difficult to predict, during the design procedure, portions to which capacitors are added and hence radiating portions must be confirmed once by using a trial product of the radio system, raising a problem that the period for design and development of the radio system is considerably p
Hirai Koutarou
Hoshino Masaki
Stevens Davis Miller & Mosher LLP
Urban Edward F.
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