Patent Publication Number: US-8971155-B2

Title: Radio wave timepiece

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a radio wave timepiece that performs digital display. 
     2. Description of Related Art 
     Heretofore, in electronic timepieces, there have been radio wave timepieces which have a function to receive a standard wave including time information expressed in a predetermined format (time code), to obtain time data, and to correct a time of an internal timepiece thereof. 
     Among the radio wave timepieces having the function as described above, in a digital radio wave timepiece having a digital display function by liquid crystal and the like, electromagnetic noises occur owing to changes of a current and a voltage, which are related to a drive signal for the liquid crystal. The electromagnetic noises are mixed into the standard wave in the event of receiving the standard wave, and deteriorate quality of a demodulated time code signal. 
     Accordingly, heretofore, in the digital radio wave timepiece, there have been developed: a technology for intermitting drive of the liquid crystal during such reception of the standard wave; and a technology for performing operation control so that timing of sampling the time code signal in a discrete manner and drive timing of the liquid crystal can differ from each other (for example, refer to Japanese Unexamined Patent Application Laid-Open Publication No. 2008-215929). 
     However, if such a functional restriction that the drive of a digital display unit is stopped during a period of receiving the standard wave is added, then, during the period concerned, a user is forced to be subjected to such an inconvenience that the time cannot be confirmed. 
     SUMMARY OF THE INVENTION 
     The present invention provides a radio wave timepiece capable of continuing the drive of the digital display unit during the reception of the standard wave. 
     According to an aspect of the present invention, there is provided a radio wave timepiece that includes: a display unit to display a current time in a digital manner; a display drive unit to drive the display unit by a drive signal of a predetermined drive waveform frequency; a receiver unit to receive radio waves of a plurality of different frequencies including time information; and a control unit to set the drive waveform frequency during the reception of a radio wave by the receiver unit so that harmonic frequencies with respect to the drive waveform frequencies can be different from a receiving frequency of the radio wave. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages and features of the present invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein: 
         FIG. 1  is a block diagram showing an entire structure of a radio wave timepiece of an embodiment of the present invention; 
         FIG. 2  is a block diagram showing an internal configuration of a radio wave receiver unit; 
         FIGS. 3A to 3D  are charts showing examples of COM waveforms stored in a display driver,  FIG. 3E  is a chart showing an example of a SEG waveform, and  FIG. 3F  to  FIG. 3I  are charts showing examples of output waveforms in which the COM waveforms and the SEG waveform are combined with each other; 
         FIGS. 4A and 4B  are diagrams showing spectrums of noises which occur in an event where a display unit is driven by the display driver; 
         FIGS. 5A and 5B  are diagrams individually showing waveforms of signals received by the radio wave receiver unit, demodulated signals, and TCOs; 
         FIG. 6  is a flowchart showing a procedure of control operations which a CPU executes in an event of performing standard wave receiving processing; and 
         FIGS. 7A and 7B  show display examples to the display unit during the standard wave receiving processing. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description of an embodiment of the present invention will be made in detail with reference to the drawings. 
       FIG. 1  is a block diagram showing an entire structure of a radio wave timepiece of an embodiment of the present invention. 
     The radio wave timepiece  1  of the embodiment of the present invention is a digital radio wave timepiece capable of digital-displaying a time by liquid crystal display. This radio wave timepiece  1  may be a wrist watch or a table clock. Alternatively, the radio wave timepiece  1  may be a digital display device having a function of a radio wave timepiece. 
     The radio wave timepiece  1  includes: an antenna ANT and a radio wave receiver unit  41 , which are as a receiver unit; a CPU  42  (control unit, display control unit); a random access memory (RAM)  43 ; a read only memory (ROM)  44 ; a display unit  45 ; a display driver  46  (display drive unit); an oscillator circuit  47 ; a frequency divider circuit  48 ; a time counter circuit  49 ; a power supply unit  50 ; an operation unit  51 ; and the like. 
       FIG. 2  is a block diagram showing an internal configuration of the radio wave receiver unit  41 . 
     The radio wave receiver unit  41  includes a receiving circuit that demodulates a time code signal from a standard wave received by using the antenna ANT that receives a radio wave of the long wave band. The standard wave is an amplitude-modulated wave (AM wave) of the long wave band, and in the radio wave receiver unit  41  of this embodiment, the standard wave is demodulated, for example, by a superheterodyne method though a demodulation method is not particularly limited to this. The radio wave receiver unit  41  includes; a low noise amplifier (LNA)  411 ; a local oscillator  412 ; a mixer  413 ; a band pass filter (BPF)  414  (narrow band pass unit); an intermediate frequency (IF) amplifier  415 ; a detector circuit  416 ; and the like. The radio wave receiver unit  41  amplifies, by the LNA  411 , a received signal as a standard wave corresponding to a tuning frequency of the antenna ANT (for example, the standard wave is a wave of 40 kHz or 60 kHz, which comes from JJY as a standard wave transmitting station of Japan), converts the received signal into a signal of an intermediate frequency, and thereafter, in the BPF  414 , allows a signal within a predetermined frequency range (for example, a range of approximately ±10 Hz) to selectively pass therethrough. Then, an output signal of the BPF  414  is amplified by the IF amplifier  415 , and thereafter, the time code signal is demodulated by the detector circuit  416 . This radio wave receiver unit  41  has a configuration in which a power supply is turned on according to an instruction from the CPU  42  only in the event of receiving the standard wave. Moreover, it is made possible to change the tuning frequency of the antenna ANT by finely adjusting a setting of a tuned circuit in the radio wave receiver unit  41 . 
     Moreover, this radio wave receiver unit  41  further includes an analog/digital converter (ADC) (not shown), digital-binarizes the demodulated time code signal at a predetermined sampling frequency, and outputs the time code signal as a time code output (TCO) to the CPU  42 . 
     Note that multiple data may be outputted depending on a method of decoding time data from the time code signal in the CPU  42 . Moreover, an analog signal may be directly binarized by using a comparator. Furthermore, an output as the TCO is not particularly limited; however, the TCO is configured so as to become a low-level voltage signal in the case of being larger than a predetermined threshold voltage set in the ADC, and to become a high-level voltage signal in the case of being smaller than this threshold voltage. 
     The CPU  42  controls and manages the entire operation of the radio wave timepiece  1 . Moreover, upon receiving the TCO from the radio wave receiver unit  41 , the CPU  42  decodes and obtains the time data from this time code. As a decoding method of the time data and an enhancement method of sensitivity at the time of decoding the time data, various conventional technologies are usable. Moreover, the CPU  42  sends a signal to the time counter circuit  49  based on the obtained time data, and corrects current time data held by the time counter circuit  49 . 
     The RAM  43  provides a working memory space to the CPU  42 . Moreover, the RAM  43  stores setting data regarding a reception time of the standard wave and the standard wave transmitting station from which the reception is attempted. 
     In the ROM  44 , there are stored: a variety of programs for allowing the radio wave timepiece  1  to perform various operations; and initial setting data. In the programs stored in the ROM  44 , a program  44   a  for receiving the standard wave and correcting the timepiece is included. When execution of the program  44   a  is instructed based on a set time stored in the RAM  43  or on an operation input from the operation unit  51 , the CPU  42  expands the program  44   a  on the RAM  43 , and executes the same. Moreover, in the ROM  44 , a standard wave reception setting table  44   b  (storage unit) is included, in which, in association with one another, there are stored: transmission frequencies of such standard wave transmitting stations located all over the world, from which the radio wave timepiece  1  is capable of receiving signals; formats of the time code; respective symbol patterns; and frame frequencies at which the display unit  45  is driven during periods while the radio waves from the standard wave transmitting stations are being received. 
     The display unit  45  has a configuration capable of digital-displaying the time data, and for example, is a liquid crystal display (LCD) capable of segment-displaying numbers and letters. The display unit  45  may be a display according to another mode, for example, a display according to a dot matrix mode, or may be an organic electro luminescent (EL) display. 
     The display driver  46  is an LCD driver that outputs a voltage signal for displaying the time and other information on the LCD as the display unit  45  based on a control signal from the CPU  42 . In the display driver  46 , there are stored in advance: a predetermined number (for example, four) of common (COM) voltage signal waveforms; and a predetermined number (for example, eight) of segment (SEG) voltage signal waveforms. The respective segments of the display unit  45  are individually controlled to be turned on and turned off by potential differences between the COM voltages and the SEG voltages in such a manner that the COM voltage signal waveforms and the SEG voltage signal waveform selectively outputted by the display unit  45  are combined with each other. 
     For example, the oscillator circuit  47  outputs an oscillation signal of 32 kHz. The frequency divider circuit  48  frequency-divides this oscillation signal, and creates and outputs frequency signals necessary for operations of the respective units such as the CPU  42  in the radio wave timepiece  1 . Among the frequency signals outputted from the frequency divider circuit  48 , a 1 Hz signal is inputted to the timer counter circuit  49  and is used for counting the current time. Moreover, the frequency divider circuit  48  is made capable of appropriately switching a frequency division ratio and outputting signals of different frequencies in accordance with an instruction from the CPU  42 . 
     The time counter circuit  49  is a counter. The time counter circuit  49  counts signals inputted every second from the frequency divider circuit  48 , and sequentially adds the counted signals to an initially set time, thereby counting the current time. Moreover, it is made possible to correct the current time data, which is stored in this time counter circuit  49 , in accordance with a control command from the CPU  42 . 
     The power supply unit  50  supplies a drive voltage to the CPU  42 , and in addition, supplies the respective voltages, which are necessary to drive the display unit  45 , to the display driver  46 . For example, in order to drive the display unit  45  with a ⅓ bias (B), the power supply unit  50  supplies a ground voltage (V 0 ) and three types of drive voltages (V 3 , V 2 =V 3 ×⅔, V 1 =V 3 ×⅓) to the display driver  46 . 
     The operation unit  51  includes pluralities of keys and buttons. When these keys and buttons are operated, the operation unit  51  converts contents of the operations into electrical signals, and outputs the electrical signals as input signals to the CPU  42 . 
     Next, a description is made of such turn-on control for the respective segments of the display unit  45 . 
       FIGS. 3A to 3D  are charts showing examples of four types of COM voltage signal waveforms set in the display driver  46 . 
       FIG. 3E  is a chart showing an example of a one pattern among the SEG voltage signal waveforms.  FIGS. 3F to 3I  are charts showing examples of output voltage signal waveforms in which these COM voltage signal waveforms and the SEG voltage signal waveform are combined with each other. Numbers 0 to 3 written under the respective charts denote numeric value portions of the voltage values V 0  to V 3  at the respective pieces of timing shown on an axis of abscissas. In a usual state, the display driver  46  of this embodiment outputs the COM voltage signal waveforms and the SEG voltage signal waveform, in each of which a duty (D) is ¼, at a frame frequency f 1 =100 Hz (frame period: 10 ms). In the output voltage signal waveforms, waveforms in this frame period and waveforms in which the waveforms concerned are inverted in polarity appear continuously. Accordingly, as shown in  FIGS. 3F to 3I , the output voltage signal waveforms become periodic signals of 50 Hz as a half of the frame frequency f 1 , and the display unit  45  is driven at this frequency (drive waveform frequency). 
     Here, as shown in the output voltage signal waveforms of  FIGS. 3F to 3H , in the combinations of the COM voltage signal waveforms of  FIGS. 3A to 3C  and the SEG voltage signal waveform, only positive and negative voltages V 1  are outputted, and all of segments to which the voltages concerned are supplied turn to a turn-off state. Meanwhile, as shown in the output voltage signal waveform of  FIG. 3I , in the combination of the COM voltage signal waveform of  FIG. 3D  and the SEG voltage signal waveform of  FIG. 3E , positive and negative voltages V 3  are outputted at predetermined timing in a frame period, and a segment to which the voltages concerned are supplied is turned on. A plurality of the SEG voltage signal waveforms are set and stored in the display driver  46  so that it can become possible to turn on arbitrary zero to four segments by the combinations of the SEG voltage signal waveform with the COM voltage signal waveforms of  FIGS. 3A to 3D  as described above. Then, the SEG voltage signal waveform is selected based on the control signal from the CPU  42 , whereby it becomes possible to control turn-on states and turn-off states of the four segments. Moreover, the plurality of SEG voltage signal waveforms are selected and outputted simultaneously, whereby a larger number of the segments can be controlled to be turned on and turned off. 
     Next, a description is made of electromagnetic noises to be caused by the output of the voltage signal waveform. 
       FIG. 4A  and  FIG. 4B  are diagrams showing spectrums of electromagnetic noise intensities which occur in an event where the display unit  45  is driven by the display driver  46 .  FIG. 4A  shows spectrum intensities of the electromagnetic noises from 0 Hz (direct current component) to 500 Hz. Moreover,  FIG. 4B  shows spectrum intensities of the electromagnetic noises from 39.75 kHz to 40.25 kHz. 
     Electromagnetic noises which occur by a rectangular voltage signal with a frame frequency f 1 =100 Hz, that is, a drive waveform frequency of 50 Hz appear on frequencies integer times 50 Hz. Among such electromagnetic noises at the respective frequencies, those within a receiving frequency range by the antenna ANT are received together with the standard wave. 
     At this time, as shown in  FIG. 4B , in the case where such occurrence frequencies of the electromagnetic noises are included in a pass frequency band R 1  of the BPF  414 , the electromagnetic noises are superimposed on the time code signal, and receiving sensitivity (C/N) ratio is lowered. Meanwhile, 50 Hz as a frequency interval of harmonics of electromagnetic pulses is wide enough in comparison with approximately 10 Hz as the pass frequency band R 1  of the BPF  414 . Hence, a case is possible where the occurrence frequencies of the electromagnetic noises are not included in the pass frequency band R 1  of the BPF  414 . The electromagnetic noises at this time are cut by the BPF  414 , and do not affect the receiver sensitivity for the time code signal. 
     Accordingly, in the radio wave timepiece  1  of this embodiment, the frame frequency is appropriately changed at the time of receiving the standard wave, whereby all of the occurrence frequencies of the electromagnetic noises are made to go out of the pass frequency band R 1  by the BPF  414 . That is to say, in response to the receiving frequency of the standard wave, the frame frequency is set so that the occurrence frequencies of the electromagnetic noises cannot be superimposed on the pass frequency band R 1  of the BPF  414 . 
       FIGS. 5A and 5B  are diagrams individually showing voltage waveforms of output signals of the BPF  414 , the demodulated signals and the TCOs in the event of receiving the standard wave of 40 kHz by the radio wave receiver unit  41 .  FIG. 5A  shows such signals in the case where the electromagnetic noises are included in the pass frequency band R 1  of the BPF  414 . Moreover,  FIG. 5B  shows such signals in the case where the electromagnetic noises are not included in the pass frequency band R 1  of the BPF  414 . 
     In the case where the electromagnetic noises are included in the pass frequency band R 1  of the BPF  414 , noise components are mixed into the output signal (a 2 ) of the BPF  414 , the demodulated signal (a 1 ) and the TCO (a 3 ). Here, in the frame frequency of a liquid crystal drive signal as a generation source of the electromagnetic noises, it is possible that small frequency errors and fractions may be included owing to output accuracy of the oscillation signal of 32 kHz, which is outputted from the oscillation circuit  47 , setting of the frequency divider circuit  48 , and the like. Hence, as shown in  FIG. 5A , the harmonic frequency of the drive waveform frequency and the receiving frequency of the standard wave do not coincide with each other completely, and a shift is present therebetween, whereby a beat occurs in the demodulated signal (a 1 ). During a period while the voltage of the demodulated signal is being lowered owing to variations of the signal intensity, which are caused by this beat, the TCO (a 3 ) is often converted to a high level by mistake, followed by output. 
     Meanwhile, as shown in  FIG. 5B , in the case where the electromagnetic noises are not included in the pass frequency band R 1  of the BPF  414 , the components of the electromagnetic noises are not included in the output signal (b 2 ) of the BPF  414  and the demodulated signal (b 1 ). Hence, the TCO (b 3 ) that is correct is obtained and outputted. 
     Here, in the actual voltage waveform, finite rise time and drop time are included in such a rectangular wave, whereby, as shown in  FIG. 5A  and  FIG. 5B , a pulse width is present at a peak of each of the spectrum intensities. Hence, the frame frequency is set so that a center frequency of the pass frequency band R 1  and an intermediate value between occurrence frequencies of two electromagnetic noises which are adjacent to or side by side with the pass frequency band R 1  in both the upper side and the lower side can be equal to each other, whereby an influence of the electromagnetic noises can be suppressed most effectively. 
     Moreover, an interval between the occurrence frequencies of the electromagnetic noises is widened as the frame frequencies become larger. Hence, the frame frequencies are raised, whereby the occurrence frequencies of the electromagnetic noises can be spaced more apart from the pass frequency band R 1 . Meanwhile, as the frame frequencies are rising, power consumption is increased. In consideration of these advantages and disadvantages, a rise range of the frame frequencies at the time of receiving the standard wave is set as appropriate. According to the instruction from the CPU  42 , the setting of the frequency division ratio in the frequency divider circuit  48  is changed, and frame frequency signals thus changed are outputted, and are inputted to the display driver  46 . 
     Moreover, the following configuration may also be adopted. To the display driver  46 , high frequency signals are inputted from the frequency divider circuit  48 , and the display driver  46  counts the high frequency signals, thereby counts desired frame period lengths, and controls the output of the SEG voltage signal waveform. Furthermore, the following configuration may also be adopted. The CPU  42  counts the high frequency signals outputted from the frequency divider circuit  48 , and sends period signals to the display driver  46  for each of the desired frame period lengths. 
     Note that, desirably, the frame frequencies at the time of receiving the standard wave are set so that harmonic frequencies thereof can have values different not only from that of the pass frequency band R 1  of the BPF  414  but also from those of an image frequency and a spurious frequency of the local oscillator. 
     Next, a description is made of an operation procedure when the standard wave is received in the radio wave timepiece  1  of this embodiment. 
       FIG. 6  is a flowchart showing a procedure of control operations which the CPU  42  executes in the event of performing standard wave receiving processing. 
     In the case where the current time counted by the time counter circuit  49  reaches a preset time, or in the case where an execution command of the standard wave receiving processing is inputted by operation input to the operation unit  51  by the user, this standard wave receiving processing is executed after the program  44   a  is read out from the ROM  44  and is expanded in the RAM  43 . 
     When the standard wave receiving processing is started, the CPU  42  first switches on the radio wave receiver unit  41  (Step S 11 ). Subsequently, the CPU  42  changes the setting of the tuned circuit according to needs and sets the receiving frequency of the standard wave based on setting information stored in the RAM  43  (Step S 12 ). For example, this setting information is city information inputted by the user operation, and information of the standard wave transmitting station, which is received in the event of the previous standard wave receiving processing. 
     Next, the CPU  42  reads the standard wave reception setting table  44   b  stored in the ROM  44  in association with the set receiving frequencies, and changes the frame frequencies related to the output signals of the display driver  46  that drives the display unit  45  (Step S 13 ). With regard to the frame frequencies thus already changed, any of harmonic frequencies as halves thereof does not have a value included in the pass frequency band R 1  of the BPF  414  in the radio wave receiver unit  41 . The CPU  42  executes decryption processing for the time data by using the TCO inputted from the radio wave receiver unit  41  (Step S 14 ). Specifically, the CPU  42  decodes the time code to obtain values of the date and hour/minute/second, and in addition, determines a second synchronization point that indicates timing of the head of every second. 
     Then, the CPU  42  determines whether or not to succeed in obtaining the time data (Step S 15 ). In the case where the CPU  42  determines to fail to obtain the time data (Step S 15 ; NO), the processing of the CPU  42  returns to Step S 12 , and the CPU  42  changes the receiving frequency to another a frequency of another standard wave, and repeats the respective pieces of processing for obtaining the time (Steps S 12  to S 15 ). 
     In the determination processing of Step S 15 , in the case where the CPU  42  determines to succeed in obtaining the time data (Step S 15 ; YES), the CPU  42  returns the frame frequencies of the drive signals for the display unit  45 , which are outputted from the display driver  46 , to the original values (Step S 16 ). Moreover, the CPU  42  corrects the time data of the time counter circuit  49  based on the obtained time data (Step S 17 ), and turns off the radio wave receiver unit  41  (Step S 18 ). Then, the CPU  42  ends the standard wave receiving processing. 
     Note that, in the above-described standard wave receiving processing, the processing is repeated while changing the receiving frequency until the obtainment of the time is succeeded; however, in the case where the obtainment of the time is not succeeded at the point of time when all of the standard waves of the receiving frequencies set and registered in the ROM  44  are received, then the correction of the time is not performed, and the standard wave receiving processing is ended at that point of time. 
       FIGS. 7A and 7B  show display examples to the display unit during the standard wave receiving processing. 
     In the radio wave timepiece  1  of this embodiment, it is possible to allow the display unit  45  to perform the continuous display even during the standard wave receiving processing. For example, as shown in  FIG. 7A , during the standard wave receiving processing, the display unit  45  may be allowed to display “RC” (radio control) indicating that the standard wave receiving processing concerned is under execution, and in addition, to display the standard wave transmitting station from which the standard wave is being received, and the receiving frequency (for example, the station JJY, 40 kHz). Alternatively, as shown in  FIG. 7B , the display unit  45  may be allowed to display the usual display of the date and time continuously, and to display a mark  451  “RC” indicating that the standard wave is under receiving processing. 
     As described above, the radio wave timepiece  1  of this embodiment includes: the display unit  45  capable of digital-displaying the current time by the LCD and the like; the display driver  46  that drives this display unit  45  by the drive signal of the drive waveform frequency, which is based on the frame frequency set based on the control command from the CPU  42 ; and the antenna ANT and the radio wave receiver unit  41 , which receive the standard wave in tune with the receiving frequency of the standard wave. Then, in the event where the radio wave receiver unit  41  is tuned with the receiving frequency of the standard wave in order to receive the standard wave, the drive waveform frequency is set so that such a tuned frequency of this radio wave receiver unit  41  and the harmonic frequency of the drive waveform frequency of the display unit  45  by the display driver  46  can have values different from each other. In such a way, there can be reduced an adverse effect to the receiver sensitivity of the standard wave, which is caused by the matter that the electromagnetic noise caused by driving the display unit  45  is received by the radio wave receiver unit  41 . 
     Moreover, in this radio wave timepiece  1 , during the reception of the standard wave by the radio wave receiver unit  41 , the receiving frequency of the standard wave as a reception subject is set so as to be equal to an intermediate value between two frequencies adjacent to or side by side with each other among the harmonic frequencies with respect to the drive waveform frequency of the display unit  45  by the display driver  46 . Hence, the frequencies of the electromagnetic noises are spaced farthest from the standard wave as the reception subject, whereby the effect of the electromagnetic noises received by the radio wave receiver unit  41  can be reduced. 
     Moreover, in the radio wave receiver unit  41 , the BPF  414  is provided, which allows the signal to selectively pass therethrough, the signal being within the frequency range narrower than the frequency interval in the harmonics of the drive waveform frequency. At the time when the standard wave is received by the radio wave receiver unit  41 , the frame frequency, that is, the drive waveform frequency is set so that the harmonic frequencies of the drive waveform frequency of the display unit  45  by the display driver  46  cannot enter the pass frequency band R 1  of the BPF  414 . Hence, the electromagnetic noises caused by the drive signal in the event where the display unit  45  is driven are cut by the BPF  414 , and the receiving sensitivity in the event of decoding the time code from the standard wave can be maintained. 
     Moreover, in this radio wave timepiece  1 , during the reception of the standard wave by the radio wave receiver unit  41 , the center value of the pass frequency band of the BPF  414  and the intermediate value between the two frequencies adjacent vertically to each other among the harmonic frequencies with respect to the drive waveform frequency of the display unit  45  by the display driver  46  are set so as to be equal to each other. Hence, the frequencies of the electromagnetic noises are spaced farthest from the pass frequency band R 1  of the BPF  414 , whereby the effect that the electromagnetic noises are mixed into the radio wave received by the radio wave receiver unit  41  can be suppressed to the minimum. 
     Moreover, in this radio wave timepiece  1 , at the time when the standard wave is received by the radio wave receiver unit  41 , the frame frequency of the display unit  45 , that is, the drive waveform frequency is changed from the frequency of the usual time, whereby the display unit  45  is enabled to perform the display. Accordingly, the drive waveform frequencies suitable to the respective cases where the standard wave is received and otherwise can be set. 
     In particular, in this radio wave timepiece  1 , at the time when the standard wave is received by the radio wave receiver unit  41 , the drive waveform frequency of the display unit  45  is set so as to be higher than at the usual time, and otherwise, the power consumption is suppressed without raising the drive waveform frequency more than necessary. Meanwhile, at the time when the standard wave is received, the frequency interval among the harmonics is widened by the drive waveform frequency that is a little higher than usual, whereby the harmonic frequencies can be made to go out of the pass frequency band R 1  of the BPF  414  more surely. 
     Moreover, in this radio wave timepiece  1 , the frame frequency to be changed at the time of receiving the standard wave, that is, the drive waveform frequency is prestored in the standard wave reception setting table  44   b  of the ROM  44  in association with the receiving frequency of the standard wave. In such a way, even in the case where the reception is performed while switching the receiving frequencies of the plurality of standard waves, the drive waveform frequency by the display driver  46  can be changed to an appropriate value easily. 
     Moreover, this radio wave timepiece  1  sets the drive waveform frequency at the time of receiving the standard wave so that the harmonic frequencies of the drive waveform frequency cannot only be included in the pass frequency band R 1  of the BPF  414  but also not be superimposed on such a frequency that can lower the sensitivity of the radio wave reception, such as the image frequency and the spurious frequency of the local oscillator  412 , whereby the receiving sensitivity to the standard wave can be maintained more stably. 
     Moreover, at the time of receiving the standard wave, this radio wave timepiece  1  can enable the display, which informs that the standard wave is being received, simultaneously while displaying the time information. Accordingly, this radio wave timepiece  1  does not inhibit the user from obtaining the time information, and can inform the user so as not to move to a position where a state of the radio wave is bad. 
     Note that the present invention is not limited to the above-described embodiment, and is modifiable in various ways. 
     For example, in the above-described embodiment, at the time when the standard wave is received, the frame frequency is changed from the usual value, whereby the mixing of the electromagnetic noises is prevented; however, from the first time, the display unit  45  may always be driven by such a frame frequency at which the electromagnetic noises are not mixed into the time code signal. 
     Moreover, in the above-described embodiment, the frame frequencies are individually set for each of the receiving frequencies of the standard wave by using the standard wave reception table  44   b ; however, one frame frequency may be set, in which the harmonic frequencies are not included in the pass frequency band R 1  of the BPF  414  with respect to receiving frequencies of all of such receivable standard waves. By setting the frequency as described above, the display can be continuously performed while simplifying the configuration of the display unit  45 . 
     Moreover, in the above-described embodiment, the processing is performed, which is for allowing the display unit  45  to perform the display to the effect that the standard wave is being received at the time when the standard wave is received; however, the display unit  45  may be allowed to perform the time display as usual without performing any processing as described above. 
     Moreover, in the above-described embodiment, the description has been made of the digital radio wave timepiece including only the display unit  45 , which performs the digital display, as the display unit; however, the present invention is also applicable in a similar way to a radio wave timepiece including both of the digital display unit and an analog display unit by indicator needles. 
     Besides the above, the specific structure, the arrangement, the control order and the like, which are described in the above-described embodiment, are modifiable as appropriate within the scope without departing from the spirit of the present invention. 
     The entire disclosure of Japanese Patent Application No. 2011-111017 filed on May 18, 2011 including description, claims, drawings, and abstract are incorporated herein by reference in its entirety. 
     Although various exemplary embodiments have been shown and described, the invention is not limited to the embodiments shown. Therefore, the scope of the invention is intended to be limited solely by the scope of the claims that follow.