Abstract:
Apparatuses, circuits, and methods for receiving at least one radio signal in a radio controlled timing apparatus using a single timing source. The present invention advantageously eliminates the need to provide an additional timing source to receive at least one radio signal, and therefore reduces the material cost and eliminates many engineering challenges.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to the field of radio controlled clocks. More specifically, embodiments of the present invention pertain to apparatuses, circuits, and methods for receiving at least one radio signal in a radio controlled clock using a single reference timing source. 
       DISCUSSION OF THE BACKGROUND 
       [0002]    A radio controlled clock is a timepiece capable of adjusting its time by receiving and decoding a special time code signal. The time code signal is encoded with the current time and date and may also contain a daylight savings time and/or leap year indicator. The time code signal may also contain parity bits for ensuring accurate reception. Typically, this time code signal modulates a low frequency carrier signal which is transmitted by a government-established radio station. Several governments throughout the world have established one or more radio stations to broadcast such time code signals, including: the United States&#39; WWVB broadcasting at 60 kHz; the United Kingdom&#39;s MSF broadcasting at 60 kHz; Germany&#39;s DCF77 broadcasting at 77.5 kHz; Japan&#39;s JJY broadcasting at both 40 kHz (transmitting in the Fukushima prefecture) and 60 kHz (transmitting on the border of the Saga prefecture and the Fukoka prefecture); China&#39;s BPC broadcasting at 68.5 kHz; Switzerland&#39;s HGB broadcasting at 75 kHz; and eastern Russia&#39;s RTZ broadcasting at 50 kHz. Additionally, some transmitters in the LORAN-C navigation system (which broadcast at 100 kHz) transmit time code signals which are synchronized to Coordinated Universal Time (UTC). Each of these radio stations modulates the carrier in substantially the same manner: reduced carrier pulse width modulation. However, since different radio stations generally broadcast time code signals on different frequencies, a radio controlled clock marketed for operation in more than one location and/or country needs to be designed to receive time code signals on multiple frequencies. 
         [0003]    Broadcast time code signals are generated by modulating a carrier signal with a time code signal. Generally, the modulation is accomplished by the following: a carrier signal is locked to a precise oscillator (such as a cesium oscillator); a 60-bit time code containing at least the current time and date is generated with reference to a national time source (such as UTC); and the carrier power is dropped and restored at pre-determined times, depending on the modulated value of a specific time code bit. 
         [0004]    Many radio controlled clocks contain one quartz crystal for time keeping purposes and at least one additional quartz crystal for demodulating the broadcast time code signal. The quartz crystal used for time keeping purposes is frequently divided to create a one pulse per second signal which drives a display mechanism. The frequency of the quartz crystal used for demodulating the broadcast time code signal correlates to the frequency of the particular radio station to be received. 
         [0005]      FIG. 1  shows an example of a conventional radio controlled clock marketed for operation in a single location and/or country. A first quartz crystal  11  is coupled with an oscillator circuit  12  to provide a reference timing signal  13 . Typically, this first quartz crystal  11  has a resonance frequency of 32768 Hz. The oscillator circuit  12  is further coupled to a frequency divider  20  which generates a real-time signal  21 . The real-time signal  21  is used to drive a timing mechanism  30 , and typically, has a frequency of one pulse per second. A low frequency broadcast time code signal  41  is received by an antenna  42  and amplified by an RF amplifier  43  to generate a modulated time code signal  44 . The RF amplifier  43  is coupled to a second quartz crystal  51  to produce a time code signal  55 . The resonance frequency of the second quartz crystal  51  is determined by the location and/or country in which the radio controlled clock is specified to operate. For example, a unit marketed for operation in the United States may have a second quartz crystal  51  with a resonance frequency of 60 kHz. The time code signal  55  is received by a radio receiver/time code decoder  60  which generates a time setting and/or correction signal  61 . The timing mechanism  30 , by receiving the time setting and/or correction signal  61 , may therefore be synchronized with the broadcast time code signal  41 . 
         [0006]    More recent radio controlled clocks are marketed for operation in multiple locations and/or countries and therefore are able to receive multiple broadcast time code signals on different frequencies.  FIG. 2  shows an example of how conventional multi-channel radio controlled clocks may differ from conventional single-channel radio controlled clocks. A low frequency broadcast time code signal  141  is received by an antenna  142  and amplified by an RF amplifier  143  which generates a modulated time code signal  144 . A quartz crystal matrix  150  receives the modulated time code signal  144 . The quartz crystal matrix may include quartz crystals  151 ,  152 ,  153  to convert the modulated time code signal  144  into the time code signal  155 . For example, a radio controlled clock marketed for operation in the United States, Japan, and Germany may have one each of quartz crystals with resonance frequencies of 60 kHz, 40 kHz, and 77.5 kHz. The switching matrix  154  determines which of the plurality of quartz crystals  151 ,  152 ,  153  are electrically connected and is configured by a selectable frequency control signal  170 . However, in some implementations, quartz crystals  151 ,  152 ,  153  are all electrically connected and thus the switching matrix  154  is not necessary. In such an implementation, the radio controlled clock will be used in locations where only one broadcast time code signal  141  is present, and thus, a valid time code signal  155  will be generated by only one of the quartz crystals  151 ,  152 ,  153 . Similar to the conventional single channel radio controlled clock, the time code signal  155  is received by a radio receiver/time code decoder  160  to produce a time setting and/or correction signal  161 . In addition to the multiple quartz crystals used in the quartz crystal matrix, the conventional multi-channel radio controlled clock might also have an additional quartz crystal to generate a real-time signal  21  as shown in  FIG. 1 . 
         [0007]    Quartz crystals are used in conventional radio time clocks because they have very high frequency stability. The use of quartz crystals to generate a real-time signal leads to timepieces which keep very accurate time. The inherent stability of quartz crystals also increases the likelihood of accurate demodulation of a broadcast time code signal, since, the carrier of the broadcast time code signal is locked to that of a very stable cesium oscillator. However, the inclusion of multiple quartz crystals significantly increases the cost and size of such radio controlled clocks. A conventional quartz crystal radio controlled clock may contain up to N+1 quartz crystals, where N is the number of radio frequencies that the quartz crystal radio controlled clock is configured to receive. For example, a radio controlled clock which is marketed for use in the United States, Japan, and Germany may contain up to four quartz crystals. In addition to the increased product cost, there are engineering and manufacturing difficulties as well: multiple quartz crystals need to fit within the device. Thus, using multiple quartz crystals in a radio controlled clock may be disadvantageous because of increased material costs and engineering challenges. 
         [0008]    Therefore, a need exists for a radio controlled clock that can receive radio signals at any of a plurality of frequencies but which enables the use of a single quartz crystal. 
       SUMMARY OF THE INVENTION 
       [0009]    Embodiments of the present invention relate to apparatuses, circuits, and methods for receiving at least one radio signal in a radio controlled clock using a single reference timing source. 
         [0010]    In one aspect, the invention concerns a radio controlled timing apparatus that can include: a radio receiver configured to (i) receive a local carrier signal derived from a reference timing signal and at least one modulated time code signal and (ii) generate a time code signal from the local carrier signal and at least one modulated time code signal; a decoder configured to (i) receive the time code signal and (ii) generate a time setting and/or correction signal therefrom; and a timing mechanism configured to receive (i) a real-time signal derived from the reference timing signal and (ii) the time setting and/or correction signal. 
         [0011]    In another aspect, the invention concerns a circuit for a radio controlled timing apparatus that can include: a reference timing signal source; a frequency synthesizer configured to (i) receive a reference timing signal and a selectable frequency control signal and (ii) generate a local carrier signal from the reference timing signal and the selectable frequency control signal; 
         [0012]    a radio receiver configured to (i) receive the local carrier signal and at least one modulated time code signal and (ii) generate a time code signal from the local carrier signal and at least one modulated time code signal; and a decoder configured to (i) receive the time code signal and (ii) generate a time setting and/or correction signal therefrom. 
         [0013]    In yet another aspect, the invention concerns a circuit for a radio controlled timing apparatus that can include: a frequency synthesizer configured to (i) receive a reference timing signal and a selectable frequency control signal and (ii) generate a local carrier signal from the reference timing signal and the selectable frequency control signal; and a radio receiver configured to (i) receive the local carrier signal and at least one modulated time code signal and (ii) generate a time code signal from the local carrier signal and at least one modulated time code signal. 
         [0014]    In a further aspect, the invention concerns a method of synchronizing a radio controlled timing apparatus that can include: multiplying and/or dividing a reference timing signal by a first ratio to generate a real-time signal; multiplying and/or dividing the reference timing signal by a second ratio to generate a local carrier signal; generating a time code signal from the local carrier signal and at least one modulated time code signal; and decoding the time code signal to generate a time setting and/or correction signal. 
         [0015]    The present invention advantageously provides an economical approach to receiving at least one radio signal in a radio controlled clock using a single reference timing source. Further, the present invention advantageously provides a novel implementation of a radio controlled clock which is capable of receiving time code signals broadcast on a plurality of frequencies. These and other advantages of the present invention will become readily apparent from the detailed description of preferred embodiments below. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a diagram showing a conventional single-channel radio controlled clock which uses one quartz crystal for demodulating a modulated time code signal. 
           [0017]      FIG. 2  is a diagram showing a portion of a conventional multiple-channel radio controlled clock wherein the single quartz crystal of  FIG. 1  has been replaced by multiple quartz crystals to demodulate a modulated time code signal. 
           [0018]      FIG. 3  is a diagram showing a multiple-channel radio controlled clock of the present invention. 
           [0019]      FIG. 4  is a diagram showing an implementation of a frequency synthesizer according to the present invention. 
           [0020]      FIG. 5  is a diagram showing an implementation of a radio receiver/time code decoder according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents that may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be readily apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present invention. 
         [0022]    For convenience and simplicity, the terms “data,” “signal,” and “signals” may be used interchangeably, as may the terms “connected to,” “coupled with,” “coupled to,” and “in communication with” (which terms also refer to direct and/or indirect relationships between the connected, coupled and/or communication elements unless the context of the term&#39;s use unambiguously indicates otherwise), but these terms are also generally given their art-recognized meanings. Also, for convenience and simplicity, the terms “computing,” “calculating,” “determining,” “processing,” “manipulating,” “transforming,” “operating,” “displaying,” and “setting” (or the like) may be used interchangeably, and generally refer to the action and processes of a computer, data processing system, logic circuit or similar processing device (e.g., an electrical, optical, or quantum computing or processing device), that manipulates and transforms data represented as physical (e.g., electronic) quantities. The terms refer to actions, operations and/or processes of the processing devices that manipulate or transform physical quantities within the component(s) of a system or architecture (e.g., registers, memories, other such information storage, transmission or display devices, etc.) into other data similarly represented as physical quantities within other components of the same or a different system or architecture. 
         [0023]    The present invention concerns apparatuses, circuits, and methods for receiving at least one radio signal in a radio controlled timing apparatus with a single clock source. In one aspect of the invention, the radio controlled timing apparatus can include: a radio receiver configured to (i) receive a local carrier signal derived from a reference timing signal and at least one modulated time code signal and (ii) generate a time code signal from the local carrier signal and at least one modulated time code signal; a decoder configured to (i) receive the time code signal and (ii) generate a time setting and/or correction signal therefrom; and a timing mechanism configured to receive (i) a real-time signal derived from the reference timing signal and (ii) the time setting and/or correction signal. 
         [0024]    A further aspect of the invention concerns a circuit for a radio controlled timing apparatus that can include: a reference timing signal source; a frequency synthesizer configured to (i) receive a reference timing signal and a selectable frequency control signal and (ii) generate a local carrier signal from the reference timing signal and the selectable frequency control signal; a radio receiver configured to (i) receive the local carrier signal and at least one modulated time code signal and (ii) generate a time code signal from the local carrier signal and at least one modulated time code signal; and a decoder configured to (i) receive the time code signal and (ii) generate a time setting and/or correction signal therefrom. 
         [0025]    A further aspect of the invention concerns a circuit for a radio controlled timing apparatus that can include: a frequency synthesizer configured to (i) receive a reference timing signal and a selectable frequency control signal and (ii) generate a local carrier signal from the reference timing signal and the selectable frequency control signal; and a radio receiver configured to (i) receive the local carrier signal and at least one modulated time code signal and (ii) generate a time code signal from the local carrier signal and at least one modulated time code signal. 
         [0026]    A further aspect of the present invention concerns a method of synchronizing a radio controlled timing apparatus that can include: multiplying and/or dividing a reference timing signal by a first ratio to generate a real-time signal; multiplying and/or dividing the reference timing signal by a second ratio to generate a local carrier signal; generating a time code signal from the local carrier signal and at least one modulated time code signal; and decoding the time code signal to generate a time setting and/or correction signal. 
         [0027]    The invention, in its various aspects, will be explained in greater detail below with regard to exemplary embodiments. 
         [0028]    An Exemplary Radio Controlled Timing Apparatus 
         [0029]    In one embodiment, an exemplary radio controlled timing apparatus includes: a radio receiver configured to (i) receive a local carrier signal derived from a reference timing signal and at least one modulated time code signal and (ii) generate a time code signal from the local carrier signal and at least one modulated time code signal; a decoder configured to (i) receive the time code signal and (ii) generate a time setting and/or correction signal therefrom; and a timing mechanism configured to receive (i) a real-time signal derived from the reference timing signal and (ii) the time setting and/or correction signal. 
         [0030]    Referring now to  FIG. 3 , a reference timing signal source  210  generates a reference timing signal  213 ,  214 . For the purposes of this discussion, reference timing signal  213  and reference timing signal  214  are typically the same signal. However, either or both of the reference timing signals may be adjusted, modified, or otherwise differently processed with respect to the other (e.g., delayed, inverted, divided, and/or multiplied). A real-time signal  221  is derived from the reference timing signal  213 . A local carrier signal  285  is derived from the reference timing signal  214 . A radio receiver/time code decoder  260  receives a modulated time code signal  244  and the local carrier signal  285 , and generates a time setting and/or correction signal  267  generally in response thereto. The time setting and/or correction signal  267  and the real-time signal  221  are received by the timing mechanism  230 . Generally, the real-time signal  221  and the time setting and/or correction signal  267  are synchronized by conventional logic within the timing mechanism  230 . However, such synchronization may occur outside of the timing mechanism  230  by using other conventional digital or analog methods that are well known to those skilled in the art. 
         [0031]    In one implementation, the radio controlled timing apparatus may include a real-time signal generator  220  which receives the reference timing signal  213  and generates the real-time signal  221 . The real-time signal generator  220  may include one or more multipliers and/or dividers, and the configuration of such real-time signal generators are well known to those skilled in the art. 
         [0032]    In a further implementation, the radio controlled timing apparatus may include a frequency synthesizer  280  configured to receive the reference timing signal  214  and generate a local carrier signal  285 . The frequency synthesizer  280  may include an integer or fractional-N (or “fractal-N”, as it is sometimes known) type phase locked loop and at least one divider. Frequency synthesizers comprising such a phase locked loop and a frequency divider are conventional, and their design, implementation, and operation are well known to those skilled in the art. An example of a frequency synthesizer comprising an integer type phase locked loop and a frequency divider is shown in  FIG. 4 . 
         [0033]    Referring to  FIG. 4 , a reference timing signal  314  is divided by a first frequency divider  381 . A phase and/or frequency detector  382  receives both the divided reference timing signal from a frequency divider  381  and a feedback signal  389 . The phase and/or frequency detector  382  is coupled to a loop filter  383  which is further coupled to a voltage controlled oscillator  384 . The phase and/or frequency detector  382 , loop filter  383 , and voltage controlled oscillator  384  are conventional, and their design, implementation, and operation are well known to those skilled in the art. For example, phase and/or frequency detector  382  may comprise a conventional Type I Phase Detector which responds to the phase difference between two input signals. In the simplest form, the Type I Phase Detector may function as a digital “exclusive-or” gate. Alternatively, the phase and/or frequency detector  382  may comprise a conventional Type II Phase-Frequency detector which responds to the timing difference between transition edges (i.e., rising edge or falling edge) of two input signals. The voltage controlled oscillator  384  is coupled to a frequency divider  387  to generate the local carrier signal  285 . Additionally, the voltage controlled oscillator  384  is coupled to a frequency divider  388  which generates a phase locked loop feedback signal  389 . The feedback signal  389  of the phase locked loop is received by the phase and/or frequency detector  382 . 
         [0034]    The divider ratios within the frequency dividers  381 ,  387 ,  388  are controlled by the status of a selectable frequency control signal  370 . The selectable frequency control signal  370  may be a digital multi-bit signal of n bits, where 2 n  is the number of configurable states of the frequency synthesizer (e.g., the number of possible local carrier frequencies to be produced). The number of configurable states of the frequency synthesizer may directly relate to the number of broadcast time code signal frequencies that the radio controlled timing apparatus is configured to receive. The selectable frequency control signal  370  is decoded by control signal logic  371  to produce control signals P  372 , Q  373 , and R  374  which determine the divider ratios of the respective frequency dividers  381 ,  387 ,  388 . Each control signal P, Q, or R may also be a digital multi-bit signal. For example, if the frequency divider  381  requires 8 configurable states, P may be a three-bit signal. The exemplary frequency synthesizer is thus programmable and can generate one or more local carrier signals with the same or different frequencies. Also, a single local carrier signal (e.g.,  285 ) can have one of a plurality of frequencies. 
         [0035]    In one implementation, and referring back to  FIG. 3 , each state of the selectable frequency control signal  270  may correlate to a particular broadcast radio time signal to be received [e.g., WWVB (broadcasting at 60 kHz) correlates to state one of the selectable frequency control signal, DCF77 (broadcasting at 77.5 kHz) correlates to state two of the selectable frequency control signal, JJY (broadcasting at 40 kHz) correlates to state three of the selectable frequency control signal, JJY (broadcasting at 60 kHz) correlates to state one or state four of the selectable frequency control signal, and MSF (broadcasting at 60 kHz) correlates to state one or five of the selectable frequency control signal.] In another implementation, each state of the selectable frequency control signal  270  may correlate to differential values for the purpose of frequency scanning (e.g., “up 17.5 kHz” correlates to state one of the selectable frequency control signal, “down 17.5 kHz” correlates to state two of the selectable frequency control signal; “down 20 kHz” correlates to state three of the selectable frequency control signal, and “up 20 kHz” correlates to state four of the selectable frequency control signal). The selectable frequency control signal  270  may be configured by a simple user interface device, such as an external switch or button. Alternatively, the selectable frequency control signal  270  may be configured within the radio controlled timing apparatus. In one implementation, the selectable frequency control signal  270  can be derived by the radio receiver/time code decoder  260 . For example, the radio receiver/time code decoder  260  may contain logic which determines the presence of a valid broadcast time code signal  241 . The radio receiver/time code decoder  260  may further contain logic which may be configured to sequentially select each state of the selectable frequency control signal  270  until a valid broadcast time code signal  241  is present. 
         [0036]    Furthermore, the implementation and configuration of frequency dividers  381 ,  387 ,  388  as shown in  FIG. 4  generally depends on the frequency of both the reference timing signal  314  and the local carrier signal  285  to be generated. For example, consider a radio controlled timing apparatus configured to receive a broadcast radio time signal on the United State&#39;s WWVB which broadcasts at 60 kHz. If the radio controlled timing apparatus has a direct conversion receiver, a local carrier signal  285  with a frequency of 60 kHz should be generated. Also, consider the same radio controlled timing apparatus where the reference timing signal  314  has a frequency of 32768 Hz. In one exemplary implementation, frequency divider  381  may be configured with a ratio of 1024, frequency divider  387  may be configured with a ratio of 3, and frequency divider  388  may be configured with a ratio of 5625. The phase and/or frequency detector  382  therefore will compare the reference timing signal  314  (frequency of 32768 Hz) divided by 1024 and the voltage controlled oscillator output signal  386  (frequency of 180 kHz) divided by 5625. As is shown, the phase and/or frequency detector  382  should be capable of operating at frequencies below 3 kHz (e.g., the comparison frequency is 32 Hz in the above example). However, where the frequency synthesizer comprises a fractional-N type phase locked loop, the comparison frequency could be equal to the frequency of the reference timing signal  314  (and thus, frequency divider  381  may be omitted). 
         [0037]    In yet another implementation, the radio controlled timing apparatus as shown in  FIG. 3  may include at least one antenna  242  and/or at least one RF amplifier  243  to receive and/or amplify at least one broadcast time code signal  241 . Although the broadcast time code signals are generally in the low frequency spectrum (between 30 kHz to 300 kHz), typically, broadcast time code signals have frequencies of: 40 kHz (for transmissions from Japan); 50 kHz (for transmissions in eastern Russia); 60 kHz (for transmissions from both the United States and Japan); 68.5 kHz (for transmissions from China); 75 kHz (for transmissions from Switzerland); and 77.5 kHz (for transmissions from Germany). In a typical implementation, the low frequency broadcast time code signal  241  is received by the antenna  242  and amplified by the RF amplifier  243 . The output of the RF amplifier  243  is a modulated time code signal  244 . 
         [0038]    The radio receiver/time code decoder  260  may consist of separate functional elements. As shown in  FIG. 5 , the local carrier signal  285  and the modulated time code signal  244  are inputs to the radio receiver  461 . The radio receiver  461  may consist of a mixer  463  and a signal conditioner  464 . The output of the radio receiver  461  is a time code signal  466  which is received by a time code decoder  462 . Typically, the time code signal  466  contains at least the current time, however the time code signal  466  may also contain: the date; daylight savings time and leap year indicators; parity information; and/or other information. In one implementation, the time code decoder  462  is contained within a microprocessor. In an alternative implementation, the time code decoder  462  is contained within a logic array element (such as a programmable logic device or field programmable gate array) or an application specific integrated circuit. The time code decoder  462  generates the time setting and/or correction signal  267 . As discussed above and as shown in  FIG. 3 , the time setting and/or correction signal  267  and the real-time signal  221  may be synchronized within the timing mechanism  230 . 
         [0039]    An Exemplary Circuit for a Radio Controlled Timing Apparatus 
         [0040]    In another embodiment, a circuit for a radio controlled timing apparatus can include: a reference timing signal source; a frequency synthesizer configured to (i) receive a reference timing signal and a selectable frequency control signal and (ii) generate a local carrier signal from the reference timing signal and the selectable frequency control signal; a radio receiver configured to (i) receive the local carrier signal and at least one modulated time code signal and (ii) generate a time code signal from the local carrier signal and at least one modulated time code signal; and a decoder configured to (i) receive the time code signal and (ii) generate a time setting and/or correction signal therefrom. 
         [0041]    Referring now to  FIG. 3 , a reference timing signal source  210  generates a reference timing signal  213 ,  214 . In one implementation, the reference timing signal source  210  may include a quartz crystal  211  and an oscillator circuit  212 . The quartz crystal  211  may further have a resonance frequency of about 2 X  Hz, where X may be an integer of from 10 to 20 (e.g., 14≦X≦18). In one implementation, the crystal has a frequency of about 32768 Hz (i.e., X equals 15). Reference timing signal  213  and reference timing signal  214  may be the same or different, as discussed above. A frequency synthesizer  280  receives the reference timing signal  214  and a selectable frequency control signal  270  and generates a local carrier signal  285 . A radio receiver/time code decoder  260  receives the local carrier signal  285  and a modulated time code signal  244  and generates a time setting and/or correction signal. The radio receiver/time code decoder  260  may include of separate elements as described above and shown in  FIG. 5 : a radio receiver  461  and a time code decoder  462 . 
         [0042]    In yet another implementation, and as shown in  FIG. 3 , the radio controlled timing apparatus may include at least one antenna  242  and/or at least one RF amplifier  243  to receive and/or amplify at least one broadcast time code signal  241 . Although the broadcast signals are generally in the low frequency spectrum (between 30 kHz to 300 kHz), typically, broadcast time code signals have frequencies of: 40 kHz (for transmissions from Japan); 50 kHz (for transmissions from eastern Russia); 60 kHz (for transmissions from both the United States and Japan); 68.5 kHz (for transmissions from China); 75 kHz (for transmissions from Switzerland); and 77.5 kHz (for transmissions from Germany). In a typical implementation, the low frequency broadcast time code signal  241  is received by the antenna  242  and amplified by the RF amplifier  243  as described above. 
         [0043]    In a further implementation, and referring back now to  FIG. 5 , the radio receiver  461  may be of the direct conversion type. When a broadcast carrier signal modulated with a baseband signal is mixed with a local carrier signal whose frequency is equal to the broadcast carrier signal, as in the case of direct conversion radio receivers, the signal that results is the modulating baseband signal. Thus, where the radio receiver  461  is of the direct conversion type, the local carrier signal  285  will have a frequency equal to that of the desired broadcast time code signal  241 . For example, a circuit for a radio controlled timing apparatus which contains a direct conversion radio receiver generates a local carrier frequency of 77.5 kHz to receive the German broadcast time code signal. In an alternative implementation, and for improved receiver selectivity, the radio receiver  461  may be of the super-heterodyne type. Super-heterodyne radio receivers combine a broadcast carrier signal modulated with a baseband signal and a local carrier signal whose frequency is equal to the broadcast carrier signal plus or minus a fixed offset (i.e. the intermediate frequency). Generally, the intermediate frequency is less than the local carrier frequency. The output of the mixer is then filtered to remove the undesired modulation products. The resulting signal is the modulating baseband signal. Thus, where the radio receiver  461  is of the super-heterodyne type, the local carrier signal  285  will have a frequency equal to that of the desired broadcast time code signal  241  plus the fixed intermediate frequency. For example, a circuit for a radio controlled timing apparatus which contains a super-heterodyne receiver with an intermediate frequency of 4.5 kHz generates a local carrier frequency of 82 kHz to receive the German broadcast time code signal (77.5 kHz plus 4.5 kHz). 
         [0044]    In another implementation, the radio controlled timing apparatus may include a real-time signal generator. Referring back to  FIG. 3 , the real-time signal generator  220  receives the reference timing signal  213  and generates the real-time signal  221 . The real-time signal generator  220  may include of one or more multipliers and/or dividers, and the configuration of such real-time signal generators are well known to those skilled in the art. Where the reference timing signal source  210  comprises or consists of a quartz crystal  211  with a resonance frequency of 32768 Hz, the real-time signal generator  220  may comprise or consist of a binary divider. Typically, the real-time signal  221  is used to drive the timing mechanism and has a frequency of one pulse per second. 
         [0045]    In a further implementation, the frequency synthesizer  280  may include an integer or fractional-N type phase locked loop and at least one divider. Frequency synthesizers comprising such a phase locked loop and frequency divider are conventional, and their design, implementation, and operation are well known to those skilled in the art. An example of a frequency synthesizer comprising an integer type phase locked loop and a frequency divider is shown in  FIG. 4  and is discussed above. 
         [0046]    Another Exemplary Circuit for a Radio Controlled Timing Apparatus 
         [0047]    In yet another embodiment, a circuit for a radio controlled timing apparatus that can include: a frequency synthesizer configured to (i) receive a reference timing signal and a selectable frequency control signal and (ii) generate a local carrier signal from the reference timing signal and the selectable frequency control signal; and a radio receiver configured to (i) receive the local carrier signal and at least one modulated time code signal and (ii) generate a time code signal from the local carrier signal and at least one modulated time code signal. 
         [0048]    Referring now to  FIG. 3 , a frequency synthesizer  280  receives a reference timing signal  214  and a selectable frequency control signal  270  and generates a local carrier signal  285 . The local carrier signal  285  and the modulated time code signal  244 , may be received by a radio receiver (such as receiver  461  as shown in  FIG. 5 ), which may include of a mixer  463  and a signal conditioner  464 , and which may generate the time code signal  466 . In one implementation, the circuit contains a time code decoder  462  which receives the time code signal and generates a time setting and/or correction signal  267 . 
         [0049]    In another implementation, the circuit may include at least one RF amplifier to amplify at least one broadcast time code signal. As discussed above and shown in  FIG. 5 , an RF amplifier  243  may be coupled to an antenna  241  and a radio receiver  461  for the purposes of amplifying a broadcast time code signal  241 . The RF amplifier  243  outputs a modulated time code signal  244 . 
         [0050]    In yet another implementation, the circuit may include a reference timing signal source. As shown in  FIG. 3 , the reference timing signal source  210  may be coupled both to the frequency synthesizer  280  and to the real-time signal generator  220 , and provide a reference timing signal  213 ,  214  thereto. In a further implementation, reference timing signal source  210  may be a crystal oscillator. 
         [0051]    An Exemplary Method of Synchronizing a Radio Controlled Timing Apparatus 
         [0052]    In a further embodiment, a method of synchronizing a radio controlled timing apparatus can include: multiplying and/or dividing a reference timing signal by a first ratio to generate a real-time signal; multiplying and/or dividing the reference timing signal by a second ratio to generate a local carrier signal; generating a time code signal from the local carrier signal and at least one modulated time code signal; and decoding the time code signal to generate a time setting and/or correction signal. Typically, the time code signal contains at least the current time, however the time code signal may also contain: the date; daylight savings time and leap year indicators; parity information; and/or other information. 
         [0053]    In one implementation, the method of generating a time code signal may include: receiving a modulated time code signal; and, demodulating the modulated time code signal with the local carrier. In another implementation, the method may also include adjusting the real-time signal in accordance with the time setting and/or correction signal so as to synchronize the radio controlled timing apparatus with a broadcast time code signal. 
         [0054]    In yet another implementation, the method may also include displaying a representation of the real-time signal. The representation may be displayed in a traditional analog form (movable time hands) or in a digital display element, such as a liquid crystal display (LCD). 
         [0055]    The frequency of the generated local carrier signal may correspond to the state of a selectable frequency control signal. The state of the selectable frequency control signal may be selected by a simple user interface, such as an external switch or button. Alternatively, the selectable frequency control signal may be configured within the radio controlled timing apparatus by a logic element. One method of configuring the selectable frequency control signal within the logic element may include the steps of: selecting a first state of the selectable frequency control signal corresponding to a first desired broadcast radio station; determining whether a valid time code signal was received; and if a valid time code signal was not received, selecting a second state of the selectable frequency control signal which corresponds to a second desired broadcast radio station and likewise determining whether a valid time code signal was received. The process may repeat, sequentially, selecting each state of the selectable frequency control signal corresponding to each broadcast radio station that to be received. 
       CONCLUSION/SUMMARY 
       [0056]    Thus, the present invention provides apparatuses, circuits, and methods which can enable a radio controlled clock to receive radio signals at any of a plurality of frequencies using a single quartz crystal. 
         [0057]    The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.