Timepiece receptive of a broadcast time-signal for correcting a time error
BACKGROUND OF THE INVENTION 
     The present invention pertains to a timepiece which is receptive of a broadcast time signal for correcting a time error on the basis of the received time signal. More particularly, the present invention pertains to a timepiece receptive of a broadcast time signal for correcting a time error and having circuitry for reducing the consumption of power. 
     Japan has recently begun broadcasting, on a trial basis, a time code signal which is superposed on a standard frequency long radio wave. This time code signal is being broadcast under the control of the Ministry of Posts and Telecommunications, and is effective for correcting a time error in timepieces that are receptive of the time signal. The broadcast time signal includes correct time data indicative of hours and minutes of the days accumulated since January 1 , and the data are transmitted in series in the form of a binary code having one frame per minute. 
     More specifically, the time signal is broadcast having one bit formed by a 1-Hz square pulse. The binary values of &#34;1&#34; and &#34;0&#34; are represented by pulse widths of 500 ms and 800 ms, respectively. Position markers are represented by 200 ms pulses, and the carrier wave has a frequency of 40 KHz. 
     In order to make use of the broadcast time signal for correcting a time error, timepieces are being provided with a receiving circuit. The receiving circuit is supplied power each day at a predetermined time and for a constant time interval. Thus, the receiving circuit can receive the broadcast time signal having correct time data so as to adjust for discrepancies of time in the timepiece. 
     However, since the time signal is received by the timepiece every day at a predetermined time, the timepiece is adjusted every day. The timepiece is adjusted in spite of the fact that daily time adjustment may be unnecessary if the precision of the particular timepiece is high. Therefore, a problem exists in that power may be unnecessarily consumed each time the timepiece receives the time code signal. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a timepiece that selectively receives a time code signal only when reception is determined to be necessary. 
     Another object of the present invention is to provide a timepiece which can save power consumption by receiving the time code signal only when necessary. 
     In accordance with the present invention, a timepiece has receiving means for receiving a broadcast time signal containing correct time data. Reception control means controls the reception of the broadcast time signal by the receiving means. Time counting means counts a current time. Adjusting means determines a time error dependent on the correct time data and the current time. The adjusting means also adjusts the current time counted by the time counting means dependent on the time error. A control circuit controls the reception control means dependent on the time error. In this manner, the control circuit conserves the power consumed by the timepiece by controlling the reception of the broadcast time signal only to times when reception is determined to be necessary. 
     The control circuit controls the adjusting means and includes means for determining whether the correct time data is sufficiently received when the receiving means is receiving the broadcast time signal data, or in other words, when the received broadcast time signal is useful for its intended purpose. Counting means counts a number of times the time data is not sufficiently received, and comparing means compares the number of times the time data is not sufficiently received with a predetermined number. If, however, the number of times the time data is not sufficiently received exceeds the predetermined number, the control circuit controls the adjusting means to determine the time error on the basis of a predetermined value. If the time data is correctly received, the control circuit controls the adjusting means to determine the time error and adjust the current time on the basis of the received time data. 
     Time error storing means is provided for storing the time error and reception time storing means is provided for storing a predetermined reception time. The control circuit includes determining means for determining whether the time error exceeds a predetermined value at the predetermined reception time. If the time error exceeds the predetermined value, then the control circuit controls the reception control means to receive the broadcast signal. However, if the time error does not exceed the predetermined value, then the time error is incremented. 
     The control circuit also includes means for deciding a next reception date and time depending on the time error. The control circuit controls the reception control means to receive the broadcast signal at the next reception date and time. Also, reception date and time storing means may be provided for storing the next reception date and time, which has a value depending on the time error. 
     An elapsed time counting circuit is provided for counting a predetermined elapsed time. The control circuit operates at the predetermined elapsed time for controlling the reception control means to receive the broadcast time signal. The control circuit includes means for resetting the predetermined elapsed time depending on the time error. 
     Thus, in accordance with the present invention, a timepiece receives the broadcast time signal for adjusting the time of the timepiece only when it is determined that such reception is necessary thereby conserving power. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing an embodiment of a timepiece according to the present invention; 
     FIG. 2 is a flowchart for explaining the operation of the embodiment shown in FIG. 1; 
     FIG. 3 is a block diagram showing another embodiment of a timepiece according to the present invention; 
     FIG. 4 is a flowchart for explaining the operation of the embodiment shown in FIG. 3; 
     FIG. 5 is a block diagram showing a third embodiment of a timepiece according to the present invention; 
     FIG. 6 is a flowchart for explaining the operation of the embodiment shown in FIG. 5; 
     FIG. 7 is a block diagram showing a fourth embodiment of a timepiece according to the present invention; and 
     FIG. 8 is a flowchart for explaining the operation of the embodiment shown in FIG. 7. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, an embodiment of the present invention will be described in more detail. A receiving circuit 1 having an antenna, a tuning circuit and an amplifier, is provided for receiving a broadcast time signal containing correct time data. For example, in Japan the receiving circuit 1 is effective to receive the time code signal superposed on a standard frequency long radio wave which is transmitted under control of the Ministry of Posts and Telecommunications. A radio wave detecting circuit 2 shapes the signal wave form received by the receiving circuit 1. 
     A data detecting circuit 3 detects the time data output from the radio wave detecting circuit 2. A time counting circuit 4 is provided for counting a current time. An adjusting circuit 5 is provided for determining a time error which is dependent on the correct time data received by the receiving circuit 1. A memory circuit 6, composed of a RAM or the like, stores data which is indicative of a time error occurring before or after adjustment. A counter 7 is provided for counting a number of times that time data is not sufficiently received (as described in detail below). 
     A control circuit 8 is provided for controlling, among other things, the receiving circuit 1 dependent on the time error. The control circuit 8 may comprise a CPU, ROM, etc. A reception control circuit 9 supplies power to the receiving circuit 1 at a desired time. In accordance with the embodiment shown in FIG. 1, a predetermined reception time storing circuit 10 is provided for storing a predetermined reception time. 
     The operation of the embodiment shown in FIG. 1 will be described hereinbelow with reference to FIG. 2. A power-on signal or a reset signal is generated whenever power (for example, from a battery or external source) is turned on. This power-on signal is inputted into the control circuit 8 (step 2a). In response to this signal, the control circuit 8 activates the reception control circuit 9. The reception control circuit 9 supplies power to the receiving circuit 1 to start the reception of the time code signal (step 2b). At this time, the signal received by the receiving circuit 1 is wave form shaped by the radio wave detecting circuit 2. The data detecting circuit 3 detects the time data included in this signal and transmits the detected time data to the control circuit 8. 
     The control circuit 8 judges whether the time data is correctly detected and received (step 2c). If the time data is not correctly detected because of reception failure due to, for example, noise or a weak signal, the control circuit 8 outputs a signal to the counter 7. The counter 7 counts the number A of reception failures (step 2d). The reception failure is checked by comparing the received time data with the several received data. If the number A has not reached a predetermined number of times (for example, ten times as shown in step 2e), the time data is received again. The above-mentioned operations are repeated until accurate time data can be received, or the number A of reception failures reaches a predetermined number (in this case, ten times). 
     By way of example, the reception control circuit 9 supplies power to the receiving circuit 1 to enable the same to receive the time code signal for 5 minutes. If one frame of the time code signal has a duration of one minute, 4 or 5 frames can be received during the 5-minute period. A reception failure is judged by comparing each received time data in the 4 or 5 frames so that if the received time data does not advance one minute per one frame, the control circuit 8 judges a reception failure. 
     If the time data is correctly detected during the above-mentioned operation step 2c), the control circuit 8 activates the adjusting circuit 5, so that the adjusting circuit 5 can adjust the time of the time counting circuit 4 on the basis of the received time data (step 2f). The time error data B is stored in the memory circuit 6 and is indicative of the time error occurring before and after adjustment (step 2g). In this embodiment, the time error data B is an absolute value of the time which has been adjusted, so that the time error B is an absolute value of a time difference between a time value determined from the correct time data and the current time before adjustment. 
     In summary, the control circuit 8 controls the adjusting circuit 5 and includes means for determining whether the correct time data is sufficiently received when the receiving circuit 1 is receiving the broadcast time signal, or when the received broadcast time signal is useful for its intended purpose. The counter 7 counts a number A of times the time data is not sufficiently received. The control circuit 8 includes comparing means for comparing the number A of times the time data is not sufficiently received with a predetermined number. If the time data is correctly received, the control circuit 8 controls the adjusting circuit to determine the time error B and adjust the current time on the basis of the received data. However, if the number A of times the time data is not sufficiently received exceeds the predetermined number, the control circuit 8 controls the adjusting circuit 5 to determine the time error on the basis of a predetermined value (i.e., B=5). 
     Furthermore, when the current time reaches the predetermined reception time (for example, 00:00 as shown in step 2h) which is stored in the predetermined reception time storing circuit 10, the control circuit 8 judges whether the time error data B stored in the memory circuit 6 is above a predetermined value (for example, 5 seconds or more as shown in step 2i). If the time error data B is 5 seconds or more, the process returns to step 2b and again executes the reception and adjustment operations. On the other hand, if the time error data B is less than 5 seconds, a predetermined value, such as 1 second, is added to the stored time error B and a new value of the time error data B is stored in the memory circuit 6 (step 2j). Then, the process returns to step 2h. Therefore, when the error to be adjusted is small, no time data reception and adjustment operations are executed. Thus, the power consumption is reduced by not requiring the time data reception and adjustment operations. Furthermore, if the time data cannot be detected correctly after the above-mentioned operations (steps 2b, 2c, 2d and 2e) have been repeated ten times, a value of 5 seconds is stored in the memory circuit 6 as the time error data B (step 2k). The process proceeds on to step 2h. In other words, the time data is compulsorily received by the receiving circuit 1 at the next predetermined reception time. 
     In summary, the memory circuit 6 stores the time error B and the predetermined reception storing circuit 10 stores a predetermined reception time. The control circuit 8 includes determining means for determining whether the time error B exceeds a predetermined value at the predetermined reception time. If the time error exceeds the predetermined value, then the control circuit 8 controls the receiving circuit 1 to receive the broadcast signal. If the time error B does not exceed the predetermined value, then the time error B is incremented. 
     In the above embodiment, the time data reception time is previously determined. However, other embodiments in which the next reception date and time are decided according to the time error data B will be described hereinbelow. 
     Referring to FIG. 3, the predetermined reception time storing circuit 10 of the embodiment shown in FIG. 1 is replaced by a reception date and time storing circuit 11. The reception date and time storing circuit 11 may include a RAM or the like and stores the next reception date and time. In FIG. 3, the same numerals denote the same circuits which have the same functions as described with reference to FIG. 1. 
     The operation of the embodiment of the timepiece shown in FIG. 3 will be explained with reference to FIG. 4. In similar manner as described with reference to the embodiment shown in FIGS. 1 and 2, in response to an output signal obtained when a power source is turned on, reception of the time data is started (steps 4a and 4b) When the correct time data is detected (steps 4c, 4d, 4e), the time of the time counting circuit 4 is adjusted (step 4f), and the control circuit 8 decides the date and time for time data reception according to the time error data B. The decided next reception date and time are stored in the reception date and time storing circuit 11 (step 4g). Thereafter, the time data reception is executed and the adjusting operation is executed in the same way as described with reference to the embodiment shown in FIGS. 1 and 2 at the decided date and time (step 4h). 
     For example, when the time error data B is less than 1 second, a date 7 days after the current reception date is decided. When the time error data B is between 1 second and 3 seconds, a date 4 days after the current reception date is decided. When the time error data B is between 3 seconds and 5 seconds, a date two days after the current reception date is decided, and when the time error data B is greater than 5 seconds, a date 1 day after the current reception date is decided. The decided date is read from a ROM table within the control circuit 8 and then stored in the reception date and time storing circuit 11. 
     When the time error is small, since no reception and adjustment operations are executed, it is possible to reduce the power consumption. Further, when the next reception date and time is determined, since the number of accumulated days since January 1 is also included in the received time information, it is possible to determine the decided date by storing the number of accumulated days and adding the above-mentioned number of decided correction days to the accumulated day information. 
     In summary, the control circuit 8 includes deciding means for deciding a next reception date and time depending on the time error data B. The control circuit 8 controls the reception controlling means to receive the broadcast signal at the next reception date and time. The reception date and time storing circuit 11 stores the next reception date and time. The deciding means includes means for determining a number of accumulated days since January 1 from the correct time data, means for deciding a number of correction days dependent on the time error, and means for adding the accumulated days to the correction days to decide the next reception date and time. 
     In the second embodiment, the operation intervals of the receiving circuit 1 are determined on the basis of the reception time. However, it is also possible to determine the operation intervals on the basis of any required time interval. FIG. 5 shows an example of such an embodiment. 
     Referring to FIG. 5, the predetermined reception time storing circuit 10 of the embodiment shown in FIG. 1 is replaced by a time counter 12. In FIG. 5, the same reference numerals denote the same circuits which have the same functions as shown in FIG. 1. 
     The operation of this embodiment will be described hereinbelow with reference to FIG. 6. In a similar manner as in the afore-mentioned embodiments, in response to an output signal generated when the power is turned on, the reception operation starts (steps 6a, 6b). When correct time data is received (steps 6c, 6d, 6e), the time of the time counting circuit 4 is adjusted (step 6f), and the time error data B is stored in the memory circuit 6 (step 6g). At the same time, the time counter 12 is reset (step 6h), and when the time counter 12 counts 20 hours (step 6i), the control circuit 8 executes the same operation as in the afore-mentioned embodiments according to the time error data B (steps 6j, 6k). 
     In summary, an elapsed time counting circuit comprised of the time counter 12 counts a predetermined elapsed time. The control circuit 8 operates at the predetermined elapsed time for controlling the receiving circuit 1 to control reception of the broadcast signal. 
     In the embodiment described with reference to FIG. 6, the desired time interval is 20 hours. However, it is possible to freely determine this time interval. 
     Another embodiment in which the count time of the time counter can be modified according to the time error data B will be described hereinbelow with reference to FIGS. 7 and 8. In FIG. 7, the same numerals denote the same circuits which have the same functions as shown in FIG. 5. 
     As shown in FIG. 8, in the same way as in the aforementioned embodiments, in response to an output signal generated when the power is turned on, the reception operation starts (steps 8a, 8b). When correct time data is received (steps 8c, 8d, 8e), the time of the time counting circuit 4 is adjusted (step 8f). The control circuit 8 presets the time counter 12 by a desired time according to the time error data B (step 8g). When the time counter 12 counts the desired time (step 8h), the data reception and time adjustment operations are executed. 
     For example, when the time error data B is less than 1 second, the count time of the time counter 12 is preset to 100 hours. When the time error data B is between 1 second and 3 seconds, the count time of the time counter 12 is preset to 70 hours. When the time error data B is between 3 seconds and 5 seconds, the count time of the time counter 12 is preset to 40 hours, and when the time error data is greater than 5, the count time of the time counter 12 is preset to 24 hours. Thus, when the time error is small, since the reception and adjustment operations are not executed, it is possible to reduce the power consumption. Furthermore, the above mentioned respective preset times are previously written in a ROM table of the control circuit 8, and prescribed ones of the count times are read out according to the time error data B. 
     In summary, an elapsed time counting circuit comprised of the time counter 12 counts a predetermined elapsed time (desired time). The control circuit 8 operates at the predetermined elapsed time for controlling the reception control means to receive the broadcast signal. The control circuit 8 includes means for resetting the predetermined elapsed time with a count time depending on the time error. 
     In the above-mentioned embodiments, although the upper limit of the number of reception failures is determined to be 10 times, it is possible to set this upper limit value to any appropriate value. Furthermore, the operation intervals of the reception circuit 1 determined according to the time error B can be modified under due consideration of the precision of the time counting circuit 4. 
     Thus, in accordance with the present invention, as described above, since the time signal is received at intervals or times dependent on the time error obtained at the preceding adjustment operation, the reception operation is executed only when necessary so that it is possible to economize the power consumption of the timepiece.