Abstract:
An electronic module including at least one electric motor for driving an analog display, a clock module including a time base delivering a clock signal connected to a divider circuit, the divider circuit delivering a reference signal sent to a control circuit arranged to control the electric motor, the clock module further including a measuring and correction circuit arranged between the time base and the divider circuit and delivering an intermediate compensated signal. The time base, the compensation module, the divider circuit, and the control circuit are arranged in a same case to form the clock module.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention concerns an electronic watch including one or more electric motors for driving an analogue display means, a clock module including a time base delivering a clock signal connected to a divider circuit, said divider circuit delivering a reference signal sent to a control circuit arranged to control the electric motor(s). 
       BACKGROUND OF THE INVENTION 
       [0002]    There is known in the prior art, seen in  FIG. 1 , a time base formed for example by a piezoelectric resonator, such as a quartz resonator  1 , or a silicon MEMS resonator connected to the terminals of an oscillator  2  whose output is connected to a frequency divider circuit  3  to obtain the required operating frequency for the watch to indicate the exact time. The output of frequency divider circuit  3  is connected to a control circuit  4  of an electric motor  5 , for driving the gear trains, not shown here, rotating the analogue display means, such as hands used to provide the time indication, i.e. the hours, minutes and possibly seconds. The resonator, the oscillator, the divider circuit and the control circuit are placed in the same case  6 . 
         [0003]    However, it is not possible with this configuration to have a circuit that is independent of fluctuations in temperature, since no temperature compensation circuit is provided. 
         [0004]    There are known thermally compensated timepiece circuits. These circuits include a timepiece module connected to a quartz and also connected to a temperature measuring and correction circuit. This measuring and correction circuit is thus arranged for measuring the temperature and correcting the operation of the clock circuit. 
         [0005]    One drawback of these circuits is that they occupy space, i.e. they have a large surface area, and calibration is carried out on the assembled calibres. This increases the manufacturing cost of the temperature dependence correction performed on the calibres. Moreover, this configuration is sensitive to any moisture that infiltrates the timepiece case. This moisture sensitivity leads to a deterioration in the accuracy and reliability of the clock circuit. 
         [0006]    Further, for a clock circuit having a chronograph function, there is the added drawback of having an additional module and thus the same problems of surface area and moisture sensitivity. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention concerns an electronic watch which overcomes the aforementioned drawbacks of the prior art by proposing a watch whose time display is reliable and accurate and which is less expensive to manufacture. 
         [0008]    The invention therefore concerns an electronic watch including an electric motor for driving analogue display means, a clock module including a time base delivering a clock signal connected to a divider circuit, said divider circuit delivering a reference signal sent to a control circuit arranged to control said electric motor, characterized in that the clock module further includes a compensation module arranged between the time base and the divider circuit and delivering an intermediate compensated signal and in that the time base, the compensation module, the divider circuit and the control circuit are arranged in the same case to form said clock module, in that said watch further includes a chronograph module connected to the clock module and in that said chronograph module is clocked by the intermediate compensated signal from the clock module. 
         [0009]    In an advantageous embodiment, the time base includes a resonator and an oscillator circuit. 
         [0010]    In an advantageous embodiment, the time base delivers a 32 kHz clock signal. 
         [0011]    In an advantageous embodiment, the chronograph module is arranged to control at least one electric motor. 
         [0012]    In an advantageous embodiment, said clock module case is hermetically sealed. 
         [0013]    In an advantageous embodiment, the clock module case is an integrated circuit incorporating the time base. 
         [0014]    In an advantageous embodiment, the timepiece module case is made of ceramic. 
         [0015]    The advantage of the present invention is that it can produce a watch whose clock module is reliable and not sensitive to external interference such as moisture and the temperature correction is performed on the clock module and not on the watch calibre. 
         [0016]    Further, the present invention easily permits the manufacture of a chronograph clock module using the thermocompensated signal of the clock module which provides a reliable and inexpensive clock module. 
         [0017]    The invention also concerns a method of calibrating at least one clock module including a time base delivering a clock signal connected to a divider circuit, said divider circuit delivering a reference signal sent to a control circuit arranged to control said electric motor, characterized in that the clock module further includes a measuring and correction circuit arranged between the time base and the divider circuit and delivering an intermediate compensated signal, characterized in that the method includes the following steps:
       assembling the time base, the divider circuit, the control circuit and the measuring and correction circuit in a case;   closing the case;   measuring the characteristics of the time base according to temperature;   determining correction parameters;   storing the correction parameters in the measuring and correction circuit.       
 
         [0023]    In an advantageous embodiment, the case is hermetically sealed. 
         [0024]    In an advantageous embodiment, a plurality of clock modules are simultaneously calibrated. 
         [0025]    In an advantageous embodiment, the clock module case is hermetically vacuum sealed. 
         [0026]    In an advantageous embodiment, the method further includes a step consisting in connecting a chronograph module to the clock module, and said chronograph module is clocked by the intermediate compensated signal from the clock module. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    Other advantages and features of the watch according to the present invention will appear more clearly in the following detailed description of embodiments of the invention, given solely by way of non-limiting example and illustrated by the annexed drawings, in which: 
           [0028]      FIG. 1  is a diagram of a prior art electronic watch with analogue display. 
           [0029]      FIG. 2  is a diagram of an electronic watch with analogue display according to the invention. 
           [0030]      FIG. 3  is a diagram of an electronic watch with analogue display according to a variant of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    According to a first embodiment of the invention shown schematically in  FIG. 2 , the invention concerns an electronic timepiece including a clock circuit  10  provided with a clock module  12 . This clock module  12  includes a time base  14  formed by a resonator  14   a  for example a piezoelectric resonator such as a quartz resonator, or a silicon MEMS resonator connected to the terminals of an oscillator  14   b . This oscillator  14   b  is used to deliver a clock signal Sh at a clock frequency. This clock frequency is generally 32768 Hz conventionally referred to as 32 kHz. In the remainder of the description, the term “32 kHz” will be used to refer to this value of 32768 Hz. 
         [0032]    The oscillator output is connected to a frequency divider circuit  16  to obtain the working frequency required for the watch to indicate the exact time. For example, divider circuit  16  will deliver at output a frequency of 1 Hz so that the seconds hand can move at one step per second. The output of frequency divider circuit  16  is connected to control circuit  18 . This control circuit  18  is used to control clock module  12 , i.e. to regulate the rate of the timepiece and to control functions such as the low battery mode. It will be clear that control circuit  18 , time base  14  and frequency divider circuit  16  may be in the form of a single component. 
         [0033]    Clock circuit  10  is also provided with an electric motor M 1  for driving the gear trains (not shown here), rotating the analogue display means, such as hands  22  used to provide the time indication, i.e. hours, minutes and possibly seconds. The electric motor is connected to control circuit  18  which controls the operation of said electric motor M 1 . 
         [0034]    Advantageously according to the invention, control circuit  18 , time base  14  and frequency divider circuit  16  are arranged in the same case  13  and the clock circuit further includes a measuring and correction circuit  26  for thermocompensation. This measuring and correction circuit  26  is placed between oscillator circuit  14   b  and frequency divider circuit  16 . This measuring and correction circuit  26  is used to thermally compensate clock module  12 , i.e. as a function of temperature it will act on the output signal from oscillator  14   b , i.e. clock signal Sh. Measuring and correction circuit  26  acts to ensure that the output signal from said measuring and correction circuit  26  is accurate on average over a defined period. To achieve this, measuring and correction circuit  26  inhibits pulses in clock signal Sh. Consequently, the assembly formed of time base  14  and measuring and correction circuit  26  delivers a signal Si whose frequency is lower than the frequency of clock signal Sh. This is due to the fact that measuring and correction circuit  26  inhibits pulses, i.e. it removes pulses. For example, for a 32 kHz clock signal, a 8192 Hz frequency signal conventionally called a 8 kHz signal, which is thermocompensated i.e. accurate and reliable, will be delivered by the assembly formed of time base  14  and measuring and correction circuit  26 . 
         [0035]    To improve the reliability of clock module  12 , case  13  in which it is arranged is made of ceramic and is hermetically sealed prior to calibration. Case  13  is placed in a vacuum then sealed. This ensures that no moisture will be able to infiltrate said case  13 . Consequently, moisture will have no effect on the accuracy of clock module  12 . 
         [0036]    Indeed, one aspect of the invention consists in providing a calibration method for obtaining a clock circuit  10  which is reliable over the long term. 
         [0037]    To achieve this, the method consists in assembling control circuit  18 , time base  14 , frequency divider circuit  16  and measuring and correction circuit  26  in the same case  13  to form clock module  12 . Next, the calibration is performed in batches, i.e. at the same time. It is thus clear that a plurality of clock modules  12  are calibrated at the same time. This calibration consists in measuring the features of resonator  14   a  and of measuring circuit  26  as a function of temperature and then in determining correction parameters. 
         [0038]    These correction parameters are stored in measuring and correction circuit  26 . Thus, the correction parameters of each resonator  14   a  of a plurality of clock modules  12  are determined simultaneously. 
         [0039]    This method thus has the advantage of permitting a large number of clock modules  12  to be simultaneously calibrated and thus of reducing the costs associated with calibration. 
         [0040]    Advantageously according to the invention, this configuration permits the simple manufacture of a thermocompensated chronograph module  30  as seen in  FIG. 3 . 
         [0041]    Indeed, the present invention uses the clock signal from clock module  12  to clock a chronograph module  30 . This chronograph module  30  includes a control circuit and circuits for operating the hands of the chronograph function. For example, the control circuit of chronograph module  30  is arranged to operate two motors M 2  and M 3 . In that case, it is possible to envisage not having a motor M 1  connected to clock module  12 . 
         [0042]    Preferably, chronograph module  30  is clocked with the thermocompensated signal, i.e. output signal Si from measuring and correction circuit  26  of clock module  12 . In the aforecited example, for a clock signal Sh having a frequency of 32 kHz, a thermocompensated signal Si of frequency 8 kHz is obtained. 
         [0043]    Consequently, chronograph module  30  is a module which does not have its own time base which reduces the cost of the module. 
         [0044]    This thermocompensated signal Si delivered by clock module  12  is used to reconstruct useful signals for chronograph module  30 . For example, the thermocompensated signal may be used to reconstruct a higher frequency signal for clocking a control circuit of the chronograph module. Consequently, the control circuit of the chronograph module can operate motors M 2 , M 3  associated with this chronograph function. 
         [0045]    The reconstructed higher frequency signal can be used for a function of determining the position of the gear trains. 
         [0046]    There are advantages to the possibility of clocking a chronograph module with a thermocompensated clock module signal. 
         [0047]    First of all, this permits the manufacture of a simple thermocompensated chronograph clock module. Indeed, known chronograph clock modules directly use the 32 kHz resonator output signal to operate. Using the signal directly at the resonator output means that the signal cannot be thermocompensated. Consequently, the operation of the chronograph clock module becomes random. Likewise, using an existing thermocompensated signal, means that it is unnecessary to make a chronograph module  30  having its own time base and its own measuring and correction circuit. 
         [0048]    Conversely, with the present invention, it is possible to obtain a clock circuit  10  with an entirely thermocompensated chronograph function at a lower cost. Indeed, the present invention uses only clock module  12  and its thermocompensated signal Si at frequency 8 kHz to thermally compensate chronograph module  30 , ensuring that the thermocompensated signal is used by said chronograph module. Consequently, it is easy to change from a clock module to a chronograph clock module. 
         [0049]    Moreover, this configuration provides a chronograph clock module which is more economical in electrical energy. Indeed, the chronograph module uses a thermocompensated clock signal at a lower frequency than the frequency of time base  14 . The higher the frequency, the greater the losses linked to interconnection capacities. Indeed, the transport of a signal at a certain frequency across a printed circuit board is subject to capacitive and inductive effects, and to any skin effects which may occur. These effects are all frequency connected, involving an increase in losses connected to these effects as a function of frequency. Consequently, to compensate for losses, a higher electrical power must be delivered. 
         [0050]    With the configuration of the invention, a lower frequency is used to clock the chronograph module and thus losses linked to excessive consumption are lower. 
         [0051]    It will be clear that various alterations and/or improvements and/or combinations evident to those skilled in the art may be made to the various embodiments of the invention set out above without departing from the scope of the invention defined by the annexed claims.