Patent Publication Number: US-7583565-B2

Title: Electronic timepiece

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electronic timepiece for displaying time by carrying out a time counting operation based on an output signal of an oscillation circuit. 
   2. Description of the Prior Art 
   In a background art, there is utilized an electronic timepiece for displaying time by carrying out a time counting operation based on an output signal of an oscillation circuit. 
   According to the electronic timepiece of the background art, in normal operation, the oscillation circuit is operated by a predetermined constant voltage supplied from a constant voltage circuit for carrying out a sampling operation in order to achieve low power consumption formation. Further, as a countermeasure against a case in which a terminal of a crystal oscillator constituting the oscillation circuit is leaked by stain or the like of a substrate pattern, a direct current cutting capacitor for protecting from leakage is inserted into an oscillation circuit loop to stabilize an oscillation characteristic. 
   However, an oscillation start characteristic of the oscillation circuit is deteriorated by the low power consumption formation, and further, a noise constituting a trigger of oscillation is difficult to be inputted by the capacitor and, therefore, a problem arises that the oscillation tart characteristic is further deteriorated. 
   In order to promote the oscillation start characteristic, there are proposed inventions for promoting the oscillation start characteristic of the oscillation circuit by separately providing an inverter for oscillation having a high drive function (refer to JP-A-10-206568) and providing an auxiliary amplifier portion having a high amplification factor (refer to JP-A-2002-280834). 
   However, since the inverter for oscillation having the high drive function or the auxiliary amplifier portion having the high amplification factor is separately provided, there poses a problem that power consumption is increased, or the constitution becomes complicated. 
   It is an object of the invention to be able to promote an oscillation start characteristic while having a simple constitution and maintaining low power consumption. 
   SUMMARY OF THE INVENTION 
   According to the invention, there is provided an electronic timepiece characterized in an electronic timepiece comprising oscillating means having a capacitor for protecting from a leakage at inside of an oscillation circuit loop for outputting a signal of a predetermined frequency, dividing means for outputting a timepiece signal constituting a reference of a time counting operation by dividing an output signal of the oscillating means, driving means for outputting a drive signal based on the timepiece signal outputted from the dividing means, displaying means for displaying current time by being driven by the driving means, drive power supplying means for supplying a drive power at least to the oscillating means, and controlling means for controlling the drive voltage outputted from the drive power supplying means, wherein the oscillating means includes switching means, and the controlling means controls the switching means to shortcircuit the capacitor in starting to oscillate the oscillating means and insert the capacitor to inside of the oscillation circuit loop after an elapse of a predetermined time period. 
   The controlling means controls the switching means to shortcircuit the capacitor in starting to oscillate the oscillating means and insert the capacitor to inside of the oscillation circuit loop after an elapse of a predetermined time period. 
   Here, there may be constructed a constitution in which the controlling means controls the drive power supplying means to supply a power source voltage to the oscillating means as the drive voltage in starting to oscillate the oscillating means. 
   Further, there may be constructed a constitution in which the controlling means supplies a voltage within a predetermined range lower than the power source voltage and a voltage pulsating by a predetermined period from the drive power supplying means to the oscillating means by intermittently controlling to drive the drive power supplying means by the predetermined period after an elapse of a predetermined time period from starting to oscillate the oscillating means. 
   Further, there may be constructed a constitution in which the controlling means controls the drive power supplying means to supply the power source voltage in starting to oscillate the oscillating means, thereafter, controls the drive power supplying means to supply a constant voltage lower than the power source voltage by a predetermined voltage to the oscillating means during a predetermined time period until intermittently driving the drive power supplying means. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     A preferred form of the present invention is illustrated in the accompanying drawings in which: 
       FIG. 1  is a block diagram of an electronic timepiece according to an embodiment of the invention; 
       FIG. 2  is a circuit diagram of a portion of the electronic timepiece according to the embodiment of the invention; and 
       FIG. 3  is a timing chart of the electronic timepiece according to the embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a block diagram of an electronic timepiece according to an embodiment of the invention. 
   In  FIG. 1 , an electronic timepiece includes an oscillation circuit  10  for generating a time base signal having a predetermined frequency, a dividing circuit  12  for generating a timepiece signal constituting a reference of time counting by dividing the time base signal of the oscillation circuit  10 , a drive circuit  15  for driving a display portion  16  for displaying time based on the timepiece signal, a control circuit  14  for controlling the oscillation circuit  10  and a constant voltage circuit  13  in synchronism with a signal from the dividing circuit  12 , and the display portion  16  for displaying current time or the like by being driven by the drive circuit  15 . 
   The oscillation circuit  10  includes an oscillation stabilizing circuit  11  for continuing an oscillation operation even when current leakage is brought about in the oscillation circuit  10 . The oscillation stabilizing circuit  11  includes a capacitor for protecting from current leakage and an opening/closing switch connected in parallel with the capacitor arranged inside of an oscillation circuit loop as described later. 
   The display portion  16  includes a motor, a train wheel, an indicating hand for displaying time and the like when the electronic timepiece is an analog electronic timepiece, and includes a digital display of a liquid crystal display or the like for displaying time or the like when the electronic timepiece is a digital electronic timepiece. 
   Further, although in  FIG. 2 , it is indicated to supply a drive power only to the oscillation circuit  10  from the constant voltage circuit  13 , and drive power supply paths to other constituent elements  12 ,  14  through  16  are omitted, the drive power may be supplied also to the other constituent elements  12 ,  14  through  16  from the constant voltage circuit  13 , or the drive power may be supplied thereto from another path. That is, the drive power is supplied at least to the oscillation circuit  10  from the constant voltage circuit  13 . 
     FIG. 2  is a circuit diagram showing details of the oscillation circuit  10  shown in  FIG. 1  and portions the same as those of  FIG. 1  are attached with the same notations. 
   In  FIG. 2 , the oscillation circuit  10  includes a crystal oscillator  21 , capacitors  22 ,  23 , an inverter  24 , a resistor  25  and the oscillation stabilizing circuit  11 . The crystal oscillator  21 , the capacitors  22 ,  23 , the inverter  24  and the resistor  25  constitute the oscillation circuit loop. 
   The oscillation stabilizing circuit  11  is a circuit for continuing an oscillation operation even when current leakage is brought about in the oscillation circuit  10 , and includes a capacitor  26  for protecting from current leakage and an opening/closing switch  27  connected in parallel with the capacitor  26  inside of the oscillation circuit loop. The opening/closing switch  27  is switchable between open and closed states and is controlled to open and close by an opening/closing control signal COFF supplied from the control circuit  14 . 
   The oscillation circuit  10  is constituted by a semiconductor integrated circuit including also the switch  27  other than the crystal oscillator  21 , and the crystal oscillator  21  is outwardly attached to a circuit substrate. 
   A power source terminal of the constant voltage circuit  13  is connected with a power source voltage VDD constituting an output voltage of a battery for the power source (not illustrated). A control input portion of the constant voltage circuit  13  is inputted with an output voltage control signal VREGUP and is inputted with an output timing control signal VREGSP. The constant voltage circuit  13  supplies a drive voltage VREG in accordance with the control signals VREGUP, VREGSP from the control circuit  14  to the oscillation circuit  10 . 
   Further, the oscillation circuit  10  constitutes oscillating means, the dividing circuit  12  constitutes dividing means, the constant voltage circuit  13  constitutes drive power supplying means, the control circuit  14  constitutes controlling means, the drive circuit  15  constitutes driving means, the display portion  16  constitutes displaying means, and the switch  27  constitutes switching means. 
     FIG. 3  is a timing chart of the electronic timepiece according to the embodiment of the invention, portions the same as those of  FIG. 2  are attached with the same notations. 
   The operation of the electronic timepiece according to the embodiment will be explained in details in reference to  FIG. 1  through  FIG. 3  as follows. 
   In  FIG. 1 , at time T 0 , when the power source of the electronic timepiece is inputted, the control circuit  14  outputs the opening/closing control signal COFF to the oscillation stabilizing circuit  11  to bring the switch  27  into a closed (ON) state. Thereby, the capacitor  26  is shortcircuited by the switch  27  in the closed state. 
   Simultaneously therewith, the control circuit  14  outputs the output voltage control signal VREGUP at high level and the output timing control signal VREGSP at high level to the constant voltage circuit  13 . 
   The constant voltage circuit  13  continuously supplies an output voltage of a voltage of the power source voltage VDD in response to the output voltage control signal VREGUP at high level and the voltage in response to the output timing control signal VREGSP at high level to the oscillation circuit  10  as a drive voltage. 
   The oscillation circuit  10  is continuously supplied with the drive voltage of the power source voltage VDD from the constant voltage circuit  13  and therefore, the oscillation circuit  10  easily starts the oscillation operation. Further, since the capacitor  26  is shortcircuited by the switch  27 , the oscillation operation is triggered by noise in starting and the oscillation operation can easily be started. 
   Next, at time T 1  after an elapse of a predetermined time period from time T 0 , the control circuit  14  brings the switch  27  into an open (OFF) state. Thereby, the capacitor  26  for protecting from leakage is inserted into the oscillation circuit loop and therefore, even when leakage is brought about, the oscillation operation is continuously carried out without being hampered by the capacitor  26 . 
   Next, at time T 2  after an elapse of a predetermined time period from time T 1 , the control circuit  14  brings the output voltage control signal VREGUP to low level. The constant voltage circuit  13  supplies a drive voltage of a predetermined constant voltage lower than the power source voltage VDD by a predetermined voltage to the oscillation circuit  10  as the output voltage in response to the output voltage control signal VREGUP at low level. Thereby, the oscillation circuit  10  is driven by low power consumption. 
   Next, at time T 3  after an elapse of a predetermined time period from time T 2 , the control circuit  14  constitutes the output timing control signal VREGSP by a pulse signal having a predetermined period and a predetermined duty cycle. The constant voltage circuit  13  is driven intermittently in response to the output timing control signal VREGSP, and a terminal voltage of a capacitor (not illustrated) charged by the constant voltage during a high level time period of the pulse signal and discharged during a low level time period of the pulse signal is supplied to the oscillation circuit  10  as the drive voltage. 
   That is, the constant voltage circuit  13  supplies the drive voltage of a voltage pulsating between the constant voltage and the voltage lower than the constant voltage by the predetermined voltage by a period the same as that of the pulse signal to the oscillation circuit  10 . Thereby, the oscillation circuit  10  can be driven by lower power consumption. 
   The dividing circuit  12  divides a signal generated by the oscillation circuit  10  as described above to generate a timepiece signal constituting a reference of time counting. The drive circuit  15  drives the display portion  16  based on the timepiece signal. The display portion  16  displays current time or the like by being driven by the drive circuit  15 . 
   As described above, the electronic timepiece according to the embodiment shortcircuits the capacitor  26  for protecting from current leakage by bringing the switch  27  of the oscillation stabilizing circuit  11  into the closed state at the time of starting oscillation. Further, the constant voltage circuit  13  starts to oscillate the oscillation circuit  10  by supplying the drive voltage of the power source voltage VDD. Thereby, the oscillation circuit  10  is easily started to oscillate. Further, after an elapse of a predetermined time period from starting oscillation, the continuous constant voltage lower than the power source voltage VDD is supplied as the drive voltage supplied to the oscillation circuit  10 . Thereby, the oscillation circuit  10  continues the oscillation operation stably. Further, after an elapse of a predetermined time period, the capacitor  26  is inserted (switched) into the oscillation circuit loop by bringing the switch  27  into the open state and oscillation is prevented from being stopped by current leakage, and by intermittently driving the constant voltage circuit  13 , the voltage lower than the constant voltage and varying in a predetermined voltage range by the intermittent drive period is supplied to the oscillation circuit  10  to continue the oscillation operation. 
   Therefore, since the capacitor  26  is constituted to shortcircuit in starting oscillation and therefore, the oscillation is easily started, and since the capacitor  26  is inserted into the oscillation circuit loop after starting oscillation, the oscillation operation can be restrained from being stopped by leakage. 
   Further, in starting oscillation, the oscillation circuit is driven by the high voltage and therefore, the oscillation is easily carried out, and after carrying out the oscillation, the oscillation circuit is driven by a low voltage or driven intermittently and therefore, power saving formation can be achieved. 
   Further, it is not necessary to separately provide an inverter for oscillation having a high drive function and an auxiliary amplifying portion having a high amplification factor and therefore, low power consumption can be constituted and the constitution can be simplified. 
   According to the electronic timepiece of the invention, oscillation start characteristic can be promoted while having a simple constitution and maintaining low power consumption. 
   Further, the electronic timepiece of the invention is applicable to various electronic timepieces of an electronic wristwatch, an electronic clock, an electronic timepiece having a calendar function and the like, and is particularly suitable for an electronic timepiece constituting a power source by a battery.