Note: Descriptions are shown in the official language in which they were submitted.
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Description
Cordless telephone
The invention relates to a cordless telephone with a
clock function.
Cordless telephones have been used since the 70s -
initially in the United States and are now in
widespread use. whereas, initially, the elimination of
a line connection to the telephone socket represented
the single most important functional feature in its
use, new functional features and specific applications
have been developed in the meantime. Thus, cordless
telephones having a number of mobile parts have been
offered for some time in which a voice connection
between the individual mobile parts is also possible,
the cordless telephone, at the same time, taking over
the function of a house telephone. Modern cordless
telephones are also equipped with the so-called CLIP
(calling line identification presentation) function of
the indication of the directory number or name of a
caller on the display of the mobile part.
Cordless telephones with clock function are also known
in which the clock time or date and clock time can be
indicated on the display of the mobile part and
possibly the fixed part. This represents a useful
additional function especially when the mobile part is
used outdoors, for example in the garden or in the
playground. The combination with the CLIP function in a
cordless telephone with answering machine for storing
the clock time of a call together with the name and
directory number of the caller is also useful.
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According to the prior art, the mobile part does not
need to have its own time base but the fixed part can
display the clock time generated here directly on the
display of the mobile part.
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The disadvantageous factor in known cordless telephones
with clock functions is that when the supply voltage is
interrupted, for example in the case of disturbances in
the power system or complete depletion of the battery
or a change of battery (in the mobile part), the clock
function fails. To prevent this, it is also known to
back up the clock function by means of a separate power
source (button cell or appropriate battery) or by means
of a capacitor. These solutions, too, have
disadvantages. Thus, the storage capacity of a
capacitor used for this purpose may be insufficient for
securing the clock function in the case of relatively
long interruptions of the power supply. Both the
provision of a capacitor and of an auxiliary power
source represent an additional expenditure on
components which results in an increase in costs.
The invention is, therefore, based on the object of
specifying an improved cordless telephone with clock
function, in which the availability of this function is
secured with very high probability and which manages
without significant additional constructional and cost
expenditure.
This object is achieved by a cordless telephone having
the features of claim 1 and 2, respectively.
The invention includes the fundamental technical
teaching of securing the clock function via the
connection between fixed part and mobile part by
appropriately utilizing oscillator elements existing as
clock generator in the fixed part and the mobile part,
and the associated processing capacity.
Particularly high reliability for ensuring the clock
function is created in an embodiment in which the
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backup is bidirectional, i.e. resynchronization of the
clock function is not only possible via the connection
to the fixed part in the case of a power interruption
at the mobile part but
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in the case of a power interruption of the fixed part,
resynchronization of the clock function established
there is also possible via the connection to the mobile
part.
The interrogation means provided for implementing the
resynchronization function are preferably constructed
in such a manner that they are automatically activated
after the end of the interruption of a power supply. In
principle, the provision of a manual actuating element
is also possible - in any case in the mobile part in
which an interruption of the power supply is, as a
rule, performed by the user himself, for example by
changing the batteries, or is at least noticed.
The effectiveness of the invention essentially depends
on the interrogation or resynchronization means
essentially being implemented as software on the basis
of the existing hardware processing capacity and the
existing transmitting and receiving facilities.
Using a radio clock module in the fixed part increases
the availability of the clock function even further and
simplifies the construction at the fixed part but,
naturally, is associated with increased cost
expenditure. The solution will be appropriate,
therefore, if the use of the radio clock module is
being considered for reasons of precision of the time
information.
Furthermore, advantages and suitabilities of the
invention are obtained from the subclaims and the
following description of preferred embodiments with
reference to the figures, in which:
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Figure 1 shows a functional block diagram of the
components of an embodiment of a cordless
telephone which are essential for carrying
out the invention, and
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Figure 2 shows a functional block diagram of an
embodiment of the fixed part which is
modified compared with figure 1.
Figure 1 shows in a highly diagrammatic sectional
representation the functional components of a cordless
telephone 1 which are essential for the explanation of
the invention, which telephone comprises a fixed part
lA and a mobile part 1B (or a number of mobile parts of
the same structure). The fixed part lA has a mains
power supply 3 via a mains connection 3a which feeds
all components of the fixed part, indicated by a boldly
drawn arrow to the right. A fixed part controller 5
with working memory (RAM) 5a and program memory (ROM)
5b associated in the usual manner controls (apart from
its remaining functions which are not related to the
invention and will not, therefore, be explained here)
the backup of the clock function by the fixed part.
The fixed part has a radio clock receiver 7 followed by
a radio time processing stage 9, the output of which is
connected to a transmitter 13 of the mobile part via a
clock time transmitting switch 11 driven by the
controller 5. The output of a fixed part receiving
stage 15 is connected to (among other things) the
controller 5.
The mobile part 1B has a battery power supply 17 which
supplies the entire mobile part with power which is
again symbolized by a boldly drawn arrow. The battery
power supply 17 is associated with a voltage sensor 19
followed by a threshold discriminator 21 for detecting
voltage interruptions or an inadmissible drop in the
operating voltage. The output of the threshold
discriminator 21 is connected to the input of a flip
flop 23, the output of which is connected to a clock
time interrogation generator 25 and which can be
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in the form of a monostable flip flop or else a
bistable flip flop depending on the actual construction
of the interrogation generator. The output of the
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interrogation generator 25 is connected to a mobile
part transmitting stage 27.
The mobile part, too, has a controller (mobile part
controller) 29 with associated working memory 29a and
program memory 29b. The input of the controller is
connected to an input keypad 31 of the mobile part via
which a clock time indication, for example, can be
called up. The mobile part 1B has a crystal base 33 as
internal clock generator which is followed in the usual
manner by divider and counter stages for obtaining a
time indication, which are combined in a time
generating stage 35 in the figure. The output of the
time generating stage 35 is connected to a display 39
of the mobile part via a clock time display switch 37
driven by the mobile part controller 29. The output of
a mobile part receiving stage 41 is connected to the
mobile part controller 29. The mobile part controller
29, in turn, is connected to a control input of the
time generating stage 35 via a time synchronization
stage 43.
The operation of the arrangement shown is as follows:
in the fixed part lA, a highly accurate real time is
permanently provided by the radio clock receiver 7 and
the radio time processing stage 9, which real time can
be optionally displayed there (which is not part of the
invention) and/or can be used for control purposes.
Should the mains power supply fail at any time,
automatic resynchronization of the real-time generation
is performed in a manner known from radio clocks after
the supply has been restored, so that the radio time is
available again in the fixed part a short time after
the end of the interruption.
In the mobile part 1B, a real time which is independent
of the fixed part and is also less accurate is
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obtained from the clock signals of the crystal base 33
by means of the time generating stage 35 and is
displayed on the display 39 by the mobile part
controller 29 via the clock time display switch 37 with
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the appropriate key input by the user of the control.
When the batteries are exhausted or are changed, the
operating voltage provided by the battery power supply
17 drops below a permissible minimum value which is
detected via the voltage sensor 19 and the threshold
discriminator 21 and leads to the generation of an
activation pulse for the clock time interrogation
generator 25 by the flip flop 23 as soon as the
operating voltage detected rises above the permissible
minimum value again (after the batteries have been
charged up, for example, or changed). The clock time
interrogation generator then outputs a predetermined
interrogation sequence to the mobile part transmitting
stage 27 and, at the same time, activates the mobile
part controller 29 for processing a response signal of
the fixed part 1A which is to be received then via the
mobile part receiving stage 41.
This response signal is generated there in that the
interrogation signal transmitted by the mobile part
transmitting stage 27 via the air interface (symbolized
by a zig-zag arrow) is received by the fixed part
receiving stage 15, processed in the fixed part
controller 5 on the basis of a program stored in the
program memory 5b and then the clock time transmitting
switch 11 of the fixed part is closed. The time signal
present at the output of the radio time processing
stage 9 is then transferred to the fixed part
transmitting stage 13 and transmitted by the latter to
the mobile part receiving stage 41. From the output of
the latter, it reaches the mobile part controller 29
which, on the basis of a program stored in the program
memory 29b, drives the time synchronization stage 43
which, in turn, adjusts the time generating stage 35 to
the radio time transmitted from the fixed part. In this
manner, a correct clock time which can be optionally
displayed is provided in the mobile part lb virtually
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immediately after the end of the interruption of the
power supply in the mobile part lb. In this
arrangement, the receiving connection for clock time
synchronization only exists for a very short time in a
power-saving manner.
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Figure 2 shows an implementation of the fixed part
which is modified compared with the embodiment shown in
figure 1. Components corresponding to one another in
both figures are also designated by the same reference
numbers and will not be explained again in the text
which follows. The most significant difference consists
in replacing the radio clock receiver by an inexpensive
crystal time base 7' which, however, is not self-
resynchronizable. In this embodiment of the fixed part
lA', a voltage discriminator 45 must be provided at the
output of the power supply 3 and a time synchronization
stage 47 which is connected to a control input of the
modified time processing stage (crystal time processing
stage) 9' must be provided in this embodiment of the
fixed part lA' in a similar manner to the mobile part
according to figure 1.
The output of the voltage discriminator 45 is connected
to a flip flop 49 which, in a similar manner to the
flip flop 23 of the mobile part from figure 1, outputs
a trigger pulse as soon as the operating voltage rises
again after an inadmissible drop in the operating
voltage of the mains power supply 3. This trigger pulse
activates a clock time interrogation generator 51 at
the fixed part which outputs a preprogrammed
interrogation signal sequence to the fixed part
transmitting stage 13. Analogously to the sequence of
resynchronization of the mobile part clock time,
described above in connection with figure l, this
interrogation is received in the receiving part of the
partner station (in this case of the mobile part),
processed in its controller 29 and answered with the
output of a clock time information item via its
transmitter 27. This information is received in the
fixed part receiver 15 and supplied via the controller
5 to the time synchronization stage 47 which uses it
for
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resynchronizing the crystal time processing stage 9'
At the mobile part, this function requires the
provision of a connection between the output of the
time generating stage 35 and the input of the mobile
part transmitting stage 27 according to figure 1 which
is enabled via the controller 29 when an interrogation
signal
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is received via the receiving stage 41. Since the
configuration of the mobile part only differs from that
shown in figure 1 in this aspect, the mobile part has
not been pictorially represented again in figure 2.
