BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The present invention relates to an electronic timepiece, or watch. More particularly, the present invention relates to an electronic timepiece, or watch, which updates displayed time information based on received satellite signals for providing an accurate display of local time as the timepiece moves from time zone to time zone.

DESCRIPTION OF THE RELATED ART

Previously, when a user of a timepiece moved into a new time zone and wanted to know the new local time accurately, the user was forced to either manually update the time displayed by the timepiece by resetting the timepiece, or by mentally compensating the time displayed by the timepiece for the local time of the new time zone.

One solution to this problem, disclosed in U.S. Patent No. 4,316,272 to Naito, provides an electronic timepiece with a global time zone display. With the

Naito timepiece, a user can select a local time mode in which the time display is representative of a single selected time zone. By operating a select button, the local time mode can be changed to a world time mode. In the world time mode, time information is displayed

by manually indexing to any one of the global time zones, or by automatically indexing to a predetermined time zone. When a user enters a different time zone with this timepiece, the world time mode may be selected and the timepiece manually indexed to display the local time in the new time zone, or the local time of the timepiece can be reset to the time of the new time zone.

Another solution to this problem, disclosed in U.S. Patent No. 4,347,594 to Tschanz, is a watch which allows a user to manually rotate the body of the watch to display local time of a new time zone. The Tschanz watch includes a single watch hand attached to the body of the watch in a normal rotary manner for indicating hours. To display time in a new or in a different time zone, the body of the watch is manually rotated an amount corresponding to the new or different time zone. After the body of the watch has been rotated, the time displayed is determined by the position of the watch hand which has been rotated accordingly to correspond to the new time zone when the body was rotated.

Both of these approaches are inconvenient because a user must manually reset or adjust the display of a timepiece or watch for accurately displaying local time when a new time zone is entered. Frequently, a user forgets to do this or incorrectly resets the time.

Thus, there is a need to provide a convenient way for accurately and automatically resetting a timepiece

or watch not requiring user intervention for displaying local time whenever a new time zone is entered.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a timepiece that conveniently and automatically provides an accurate display of local time as it moves from time zone to time zone throughout the world so that a user is not required to manually reset the displayed time to the current local time or mentally compensate a displayed time for a local time when traveling.

These and other objects and advantages of the present invention are achieved by a timepiece which includes a receiver for receiving a radio signal having time and position data, a memory for storing time zone data corresponding to a plurality of world time zones, a processor which is coupled to the receiver and the memory for generating a local time based on the received time and position data and the time zone data stored in the memory, and a display which is coupled to the processor for displaying the local time generated by the processor. Preferably the radio signal is transmitted by a constellation of satellites providing global positioning information. The memory of the present invention preferably includes time zone data for all world time zones which

has been partitioned in an arrangement based on boun¬ daries of countries and on latitudinal and longitudinal data corresponding to the world time zones. Cyclical and seasonal time zone data, such as that corresponding to Daylight Savings Time, may also be included in the time zone data base.

The timepiece according to the present invention further includes an internal crystal-based source which is coupled to the processor so that the present invention can automatically provide a crystal-based time to the processor for generating the local time when the received time and position data is determined to be invalid by the processor. The present invention automatically returns to displaying local time based on the received time and position data when the time and position data is determined to again be valid. Preferably, the display provides an indication when the received time and position data is valid.

Another feature of the present invention is that the processor generates position information based on the received time and position data and the position information is displayed by the timepiece display.

According to a further aspect of the invention, the inventive timepiece includes a battery for supplying electrical energy, a solar panel for convert¬ ing solar energy to electrical energy, and a power supply logic circuit for selecting between the battery and the solar panel as a source of electrical energy

and for determining whether available power exceeds a minimum threshold necessary for activating satellite signal reception and processing functions. Insufficient electrical power for activating satellite signal reception will cause the timepiece to display crystal-based time. Desirably, an indication is provided on the display for visually indicating that the solar panel is selected as the source of electrical energy. The present invention also provides a method for generating local time of a timepiece comprising the steps of receiving a radio signal including time and position information, generating a local position of the timepiece from the received time and position information, comparing the local position to time zone data stored in a memory of the time piece, generating a local time of the timepiece based on the local position of the time piece and the time zone data stored in the memory, and displaying the local time of the timepiece. Preferably, the time zone data stored in the memory includes time zone data for all world time zones.

BRIEF DESCRIPTION OF THE DRAWINGS

The various objects of the present invention, together with other advantages and benefits which may be attained by its use, will become more apparent in view of the following detailed description of the invention taken in conjunction with the drawings. In

the drawings, wherein like reference numerals identify corresponding portions of the various embodiments of the timepiece of the present invention:

Figure 1 is a diagram which shows the principle of operation of the present invention which employs a constellation of global positioning system satellites; Figure 2 is a top view of a timepiece/watch face according to one embodiment of the present invention; Figure 3 shows a block circuit diagram of an embodiment of the electronics of a timepiece according to the invention;

Figure 4 is a table which shows a portion of an exemplary time zone data base partitioned by latitude and longitude for determining time zones and for generating accurate local time according to the present invention;

Figures 5a and 5b show a flow diagram for automatically changing between a primary and a backup mode of operation for generating accurate local time according to the invention;

Figure 6 shows a flow diagram for manually setting the initial parameters of time, time zone, date and for enabling/ disabling the primary mode of operation according to the present invention; and Figure 7 is a top view of a timepiece/watch face showing displayed position data according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is directed to an electronic timepiece or watch having a time display which is based upon time and position information transmitted as a radio signal by a satellite global positioning system. As the timepiece according to the present invention physically moves from time zone to time zone, the displayed time is automatically and accurately updated to the local time of a new time zone without a user intervening to manually reset the time.

In a preferred embodiment, the present invention receives time and position information transmitted by the Navigation Satellite Time and Ranging Global Positioning System (NAVSTAR GPS) . Thus, the present invention provides an accurate time display anywhere in the world based on the time and position information received from the GPS satellites, and which is traceable to the National Bureau of Standards. Other global positioning systems which transmit time and position information as a radio signal may also be used to provide an accurate local time display according to the present invention.

Figure 1 shows the principle of operation of the present invention employing GPS satellites. GPS space vehicles (SVs) 21 arranged in a constellation provide continuous earth coverage and transmit ranging codes and system data as radio signals needed for accomplishing a GPS navigational function. The

timepiece 10 according to the present invention uses time, latitudinal, and longitudinal information received from the GPS satellites for providing a time display. The default time display of the present invention includes the current time, day, month and year for Greenwich Mean Time (GMT) , also referred to sometimes as Universal Coordinated Time (UTC) . However, the present invention converts the received (default) time to local time for the convenience of a user. This is accomplished by using the latitude and longitude of the timepiece as determined from time and position data received from the GPS satellites and comparing this position with a time zone data base contained within the timepiece to provide a time zone number used for generating local time. The time zone number is an offset in one-half hour increments which is added (subtracted) to (from) the default UTC time for generating a local time. According to the invention, the time zone number can also account for cyclical or seasonal time zone adjustments, such as Daylight Savings Time.

Figure 2 shows the face of a timepiece/watch which may be used to display time generated according to the present invention. Timepiece 10 includes a body 11 having a display 12, a mode switch 13, a set switch 14, and a watchband 15. Display 12, preferably an electro- optical liquid crystal display (LCD) type display, includes a time display portion 16, a date display

portion 17, and a valid data display portion 18. A solar power display portion 19 is included in display 12 when timepiece 10 is equipped with a solar panel 20. Although Figure 2 shows that solar panel 20 is separate from display 12, panel 20 can be incorporated into the face of display 12 thus permitting a smaller timepiece body. While the timepiece of the present invention is shown configured as a watch in Figure 2, the invention may be configured by other types of timepieces such as a pocket watch or a travel alarm clock, or other devices having timekeeping features such as a calculator or an electronic calendar/notepad.

Figure 3 shows a block circuit diagram of the electronics of a timepiece according to the invention. An operator in line-of-sight with the GPS satellites receives an RF signal from two or more satellites via a ceramic patch aperture antenna 100. Antenna 100 is miniaturized to conform to the shape of watchband 15 or to body 11 (Figure 2) and can be any of a number of different well-known types of antennas suitable for receiving GPS signals. Antenna 100 feeds data signals received from the satellites to a GPS receiver 101 of known design which is miniaturized by techniques known by those skilled in the art of semiconductor electronics for decoding the data signals. Examples of commercially available devices which can be used for GPS receiver 101 are the Canadian-Marconi "microGPS", devices from the GEC-Plessey "GP 1010/1020" family, the

Motorola "VP Oncore", the Rockwell International "Norcard" and "MicroTracker", or equivalent.

GPS receiver 101 outputs a data stream in a standard format, such as a GPS Gold format which is detailed in ARINC Research Corporation Document ICD- DPS-200, "Navstar GPS Space Segment/Navigation User Interfaces" and incorporated by reference herein. GPS receiver 101 can be a commercially available integrated circuit for receiving and decoding GPS data or, an application specific integrated circuit (ASIC) performing the same functions.

Processor 102, in a known manner, extracts information from the data stream for determining UTC time, the latitude and longitude of the timepiece, and whether the data is valid. The extracted data is used for determining the current time zone in which the timepiece is located by comparison of the current latitude and longitude of the timepiece with a time zone data base contained in memory 103. An offset is added to the received UTC time based on the position of the timepiece and the time zone data base in memory 103 for generating a display of local time on display 12. Processor 102 can be embodied by a readily available microprocessor, an ASIC, or by dedicated logic configured to provide the functions of the present invention as long as the selected device has sufficient processing power and speed for the various functions. Memory 103 can be either a dedicated memory, such as a

read only memory (ROM) , or part of processor 102. Additionally, the functions of the GPS receiver 101, processor 102, memory 103, crystal 104 and clock chip 105 can be provided on a single ASIC or module. When the received satellite data is determined to be invalid, such as when the timepiece is not within line-of-sight of the satellite constellation and not receiving the transmitted data or when the GPS receiver outputs an indication in the data stream that the received data is invalid, the timepiece automatically changes from a primary mode of operation to a backup mode of operation, in which time is updated and displayed based on an internal crystal-based source. In Figure 3, the internal crystal-based source is formed by a crystal 104 and clock chip 105 which are embodied by a readily available crystal and clock chip integrated circuit which provides sufficient time keeping accuracy. Once the received satellite data is determined to again be valid, the timepiece automatically changes back to the primary mode of operation and time is updated and displayed based on the more accurate satellite-based time.

A data base contained in memory 103 contains a parameterization of the various time zones of the world as time zone offset counts from Greenwich Mean Time.

While the data base according to the invention includes data for all 24 world time zones, the concept is illustrated for a portion of an exemplary time zone

data base showing the time zones of only the United States in the Figure 4. Cyclical and seasonal time zone data can be included in the time zone data base as well. Generally speaking, the time zones of the world correspond to longitude lines with longitude (Ion) 0° passing through Greenwich, England. The first time zone, having a time zone offset count of zero, extends from 7.5 degrees east and west of Ion 0°. Every 15° longitude from the termination of time zone zero (±7.5° longitude) generally demarks the edge of another time zone. Due to the direction of the rotation of the earth, one hour is decremented for each time zone to the west of Ion 0", while one hour is added per time zone to the east of Ion 0° to generally give local time.

The time zone data base in memory 103 forms an exception table because each country can set its own time standard. For instance, Newfoundland is 3.5 hours behind Greenwich, whereas India is 5.5 hours ahead of GMT, while Saudi Arabia does not conform to the time zone system. Another requirement of the time zone data base is to compensate for the fact that borders of countries do not fall exactly along longitude/standard time zone lines. For example, the entire country of mainland China is eight hours ahead of GMT, even though it covers approximately 45° of longitude, or three time zones. Thus, reliance solely upon the 15° longitudinal

time zone lines would not necessarily generate local time correctly. Consequently, the time zone data base according to the present invention is partitioned in an arrangement of data based on boundaries of countries and on the latitudinal and longitudinal data of world time zones to provide an accurate display of local time. Cyclical and seasonal time zone data can also be incorporated in the arrangement of time zone data.

In Figure 4, the United States has been tabularly partitioned according to latitude and longitude of the respective time zones. If the timepiece is located to the east of Ion 85°, then the timepiece is in the Eastern Time Zone and an offset of -5 hours from GMT is required to derive local time. The time zone offset count is -10 because the timepiece resolves time zones by the half-hour. If the timepiece is located north of 36.18° latitude, and east of 88° longitude, an offset of -5 hours is required to give a correct local time in the Eastern Time Zone. Thus, different segments of different continents are partitioned by latitude and longitude corresponding to particular time zones for all of the remaining time zones of the world (which are not shown) in the time zone data base to provide global coverage. Errors introduced in the deduction of local time for each region can be minimized by the degree and accuracy of partitioning provided in the time zone data base. Of course, a time zone data base can be arranged

in any manner for producing local time in accordance with the present invention.

Desirably, the timepiece according to the present invention also includes a solar panel 20 for converting solar energy to electrical energy, a battery 107 and a power supply logic circuit 106. Power supply logic circuit 106 selects the source of power for the timepiece depending whether there is sufficient solar energy received by solar panel 20 for powering the timepiece over power buses 108 and 110. When insufficient energy is received via panel 20, battery 107 is selected to supply the timepiece. If power supply logic circuit 106 detects that available energy (solar and battery) is below a particular threshold, then satellite reception functions will not be energized and the timepiece will display crystal-based time. When solar panel 20 is selected, logic circuit 106 provides an indication over line 109 to processor 102 so that the solar power display portion 19 of display 12 is activated.

As mentioned, the present invention includes two operating modes for converting GMT to the correct local time. In the primary mode of operation, local time is automatically displayed based on the latitudinal and longitudinal position of the present invention, as determined from time and position data received from the constellation of GPS satellites. As the present invention enters a new time zone, that is, as the

present invention changes global position, time is automatically updated to reflect local time. When operating in the primary mode, the present invention provides a visual indication that valid data is currently being received from the GPS system.

In the back-up mode of operation, which occurs automatically when the present invention is not within line-of-sight with the GPS satellite constellation, displayed local time is based on the internal crystal- based source. The backup mode typically occurs when the present invention is in a building, an aircraft or the like, or when insufficient available electrical power precludes primary mode operation. When operating in the back-up mode, the displayed time can be manually updated by a user to reflect local time. However, this approach is not necessary because the present invention merely needs to be placed within line-of-sight with the GPS satellite constellation for automatically updating the local time using the features of the primary mode of operation. Time calibration errors which occur when operating in the back-up mode, caused by temperature instability or frequency drift of the internal crystal- based time source, are eliminated upon re-acquisition of the time and position data signals from the GPS satellite constellation as described below.

Figures 5a and 5b show a flow diagram according to the invention for automatically changing between the primary and backup modes of operation. At step 120,

processor 102 reads the satellite data output from GPS receiver 101. At step 121, processor 102 extracts satellite data valid, UTC, latitude, and longitude data from the data stream. If the satellite data is valid at step 122, then the Quartz Time flag is cleared at step 123. If the Quartz Time flag had been previously set, the backup mode of operation is automatically changed to the primary mode of operation when the time display is updated at step 141. The received UTC data is stored at step 124, and compared with the most recently stored UTC time at step 125. If the UTC time has not changed at step 125 (that is, incremented) , then flow returns to step 120 so that the next packet of time and position data can be read. If the UTC has changed at step 125, then processor 102 tests whether the Manual Time Zone Override condition is enabled at step 126. If Manual Time Zone Override condition is disabled, the latitude and longitude data extracted from the data stream is used to derive a Time Zone Offset Count at step 127. The Time Zone Offset Count is then added in one-half hour increments to the received UTC to create a local time- of-day at step 128. If the Manual Time Zone Override condition is enabled at step 126, a manually supplied Time Zone Offset Count is added in one-half hour increments to the UTC to create a local time-of-day at step 128. The half-hour increments of the Time Zone Offset Count allows the present invention to operate

correctly for geographical areas which do not have local time which is at a multiple hour unit from GMT, such as Newfoundland in which local time is -3.5 hours from GMT. If the satellite data is invalid at step 122, then the Quartz Time flag is tested to determined whether it is enabled at step 129. If the Quartz Time flag is not enabled, then the last received UTC is stored and becomes the Current UTC Base at step 130. The most recent Time Zone Offset Count is stored at step 131 and becomes the current Time Zone Offset Count. The Quartz Time flag is then enabled at step 0132 so that the backup mode is automatically entered after the display is updated at step 141. Afterward, the Time Zone Offset Count is added to the received UTC to create a local time-of-day at step 128.

If the Quartz Time flag is enabled at step 129, flow moves to step 133. After one second has expired at step 133, the UTC register is incremented at step 134 and the Time Zone Offset Count is added to the UTC to create a local time-of-day at step 128. If one second has not expired at step 133, the next packet of time and position data is read at step 120.

From step 128, it is determined whether the International Date Line has been crossed at step 135. If the previous longitude of the timepiece has changed from west to east at step 136, then the date line has been crossed from east to west and 1 day is added to

the date at step 137. Similarly, if the previous longitude of the timepiece has changed from east to west at step 136, then 1 day is subtracted from the current date at step 138. Afterwards at step 139, the local time is tested for the occurrence of midnight. If midnight local time has occurred, the date is incremented at step 140; if it has not, the date is not changed.

Finally, the local time displayed by the timepiece is updated at step 141. Accordingly, processing returns to step 120.

On power up, or after loss of RF signal, a user must wait briefly (typically less than 30 seconds) for the satellite acquisition time for accurately setting the time of the timepiece. If, at power up, the present invention is not within line-of-sight with the satellite constellation, the user can optionally set the current time manually. Time is then displayed based upon the internal crystal-based time source until the time and position information from the satellite constellation is acquired.

Figure 6 shows a flow diagram for manually setting various parameters of the timepiece according to the present invention, such as time, time zone, date and enabling/disabling the primary mode of operation. When the timepiece is in the normal TIME mode at step 180, the timepiece generates a time display in accordance with the primary and backup modes of operation.

Depressing set button 14 causes the display of the timepiece to toggle between local time and GMT. Upon depressing mode button 13 in the normal TIME mode, the timepiece enters the MANUAL TIME SET mode at step 181, causing the set hours function to become active. Set button 14 increments the currently active digits of display 12 for manually setting the hours. Depressing mode button 13 a second time causes the minutes digits to become active with set button 14 incrementing the active digits. Depressing mode button 13 yet again causes the MANUAL TIME ZONE OFFSET COUNT to become active at step 182. Pressing set button 14 increments the time zone counter.

The SET DATE mode is entered at step 183 by depressing mode button 13 causing the MONTH digits to become active. Set button 14 increments the active MONTH digits. Depressing mode button 13 again causes the DAY digits to become active. Depressing set button 14 manually increments the currently active DAY digits. Pressing mode button 13 enters the SAT EN mode at step 184. If the satellite data is manually disabled at step 184, the manually entered data is invoked. Otherwise, reacquisition of satellites causes the manual data to be overwritten when the manual set mode is exited. Depressing mode button 13 enables positional information of the timepiece to be displayed at step 185 (Figure 7) .

The foregoing is a complete description of the present invention. The scope of the invention should only be limited by the following claims.