Abstract:
A method and apparatus for suspending the operation of a rotating optical media player that uses simplified and efficient logic circuitry is described. When an operator initiates a pause operation, for example, by pressing a pause key, the current location of an optical pickup (e.g., a value of the current track ID) is stored. Then, a tracking servo loop is opened and a near zero offset is provided to the input of the tracking actuator. The condition of the optical disk system is then maintained in a “wait” state until the operator decides to end the pause process by selecting an alternate operation, such as “Play”, “Search”, or some other functions. When an alternate operation is received, the tracking servo loop is closed. The system then enters a search mode to reposition the optical head to the position indicated by the track ID, which was previously saved. Finally, the selected function command is activated. In an alternate embodiment, in the case where “Search” is selected during “Pause”, the stored location is ignored, the search instead being directed to the desired location associated with the search.

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates generally to rotating optical media players, and specifically, to a method and apparatus which simplifies the requirements for implementing a pause function on a rotating optical media player. 
   2. Background of the Invention 
   A pause function is typically initiated when a user presses a pause button on a media player. In response, the media player stops its current activity and waits until the pause function ends. When the pause function ends, the media player usually resumes its prior activity at the same place it was when the pause function was initiated. Current techniques for pausing a rotating optical media player are complicated and require precise and expensive circuitry to implement the pause functionality. The precision and expense of such circuitry make it disadvantageous to implement pause functionality using current techniques. Before further discussing this problem, and overview of rotating optical media players is provided. 
   Rotating Optical Media Players 
   A rotating optical media player can be either a device or system that is capable of retrieving information stored by an optical disc, or a device or system that is capable of both recording information to and retrieving information from an optical disc. Examples of devices that are capable of retrieving information from an optical disc include compact disc (CD) players, video laser disc (LD) players, digital video disc (DVD) players, and compact disc read-only-memory (CD-Rom) drives. Examples of devices that are capable of both recording information to an optical disc and retrieving information from an optical disc include recordable mini-disc (MD) players, magneto-optical (MO) disc drives and compact disc recordable (CD-R) drives. 
   Information is generally stored by an optical disc in the form of concentric or spiral tracks sometimes referred to as information tracks. In the case where information is already stored by an optical disc, the information tracks contain regions of optical contrast that represent the stored information. In the case of an unrecorded or blank optical disc containing preformatted tracks for recording information, a track that will become an information track may or may not have regions of optical contrast. The area located between two information tracks on an optical disc is sometimes referred to as a non-information track. 
   When an optical storage device is in its normal mode of operation, (i.e. retrieving information from or recording information to an optical disc), the storage device rotates the disc while using a light beam to retrieve information from or record information to the disc. As the optical disc rotates, the light beam radially traverses the disc. While the light beam traverses the optical disc, a tracking servo loop in the optical disc storage device keeps the beam of light centered on the information track, or the track that will become the information track in the case of recording information to a disc. 
   Tracking Servo 
   An optical disc tracking servo is a closed loop system that allows a light beam to remain centered on an optical disc information track during normal operation of an optical disc storage device. The tracking servo readjusts the radial position of the light beam by sensing when the light beam drifts off the center of the information track. The tracking servo senses when the light beam is not centered on an information track by measuring the intensity of light reflected by the surface of the optical disc. 
   Generally, the intensity of light reflected by the surface of an optical disc is the least when it is reflected by the center of an information track. Using this principle, a tracking servo generally senses the intensity of light reflected at one or both edges of an information track to detect when a light beam is drifting off center and to determine in which direction the light beam is drifting. Therefore, a tracking servo system that is in a closed loop mode of operation senses when the light beam floats off the center of the information track by detecting changes in the intensity of light reflected at one or both edges of an information track and moves the beam back into a position where the intensity of reflected light is optimal for center tracking. 
   In the case where a tracking servo measures the intensity of light reflected at both edges of an information track, the intensity of reflected light that is optimal for center tracking occurs when the intensity of light reflected at both edges of an information track is the same. The same principle holds true for both one and three beam optical disc storage devices. In the case where a tracking servo measures the intensity of light reflected at one edge of an information track, the intensity of reflected light that is optimal for center tracking is based on some calibrated value. The latter method is less favored due to difficulties associated with calibrating an appropriate centering value. 
   Special Operations 
   Rotating optical disc media players are generally capable of performing various special operations in response to user input. One such operation is a pause, or still mode operation. Using current techniques, a pause operation is implemented in a manner that is illustrated in  FIG. 1 . Spiral track  100  of rotating optical medium  101  has a current position  110 . The current position is where the laser was located on the spiral track  100  when the pause operation was initiated. The tracking servo remains closed after the pause operation is initiated by the user. Since the tracking servo loop remains closed at this point, the laser continues to spiral around the information track even after the pause operation starts. 
   When the loop reaches a second point  120 , a full track has been cycled through spiral track  100 . The second point  120  and the current position  110  are related by a radial line  121  drawn from the center of the medium  101  to its outside edge. Once the second point  120  is reached, the tracking servo loop is briefly opened and special circuitry causes the optical pickup controlling the laser to jump back to position  110 , at which time the tracking servo loop is again closed. At this point, the laser continues to spiral to point  120  again and jump back to point  110  until the pause operation terminates. 
   Causing the optical pickup to jump between points  120  and  110  requires a great deal of precision. Typically the distance between tracks is 2 micrometers, so the jump is across a very small distance. To jump such a small distance, special jump circuitry is needed. Furthermore, the spiral pattern on a rotating disc is not perfect, so even a perfect 2 micrometer jump might not bring the laser to the correct location. Typically with such a small jump, the optical pickup has a tendency to jump to far (i.e., across more than one track), so zero crossing circuitry and break circuitry must also be used in conjunction with the jump circuitry, to sense when the laser has jumped halfway between the two tracks and to keep the pickup from moving too far (i.e., centering it on the next track). As a whole, the pause operation performed in this manner is complex and requires very expensive and precise equipment. 
   The use of such expensive and precise equipment is disadvantageous. The disadvantage becomes even more problematic and wasteful in media player applications that do not require absolute precision. For instance, when a pause operation is implemented by a user of a CD player who is listening to a song, it might be tolerable to emerge from the pause state at a location on the track that is not precisely where the pause operation was started. Instead, a location that is reasonably close to where the pause operation was started is tolerable. The end result might be a very small gap in the song of one or two notes that would be unnoticeable to the listener. Implementing a pause operation with expensive and complex circuitry in this application is wasteful and unnecessary. 
   SUMMARY OF INVENTION 
   An object of the invention is to achieve a pause function in a simplified manner. According to the present invention, when an operator initiates a pause operation, for example, by pressing a pause button on a media player, the current location of an optical pickup is determined and saved. Then, a tracking servo loop is opened and a near zero offset is provided to the input of the tracking actuator. The condition of the optical disk system is then maintained in a wait state until the operator decides to end the pause process by selecting an alternate operation, such as play, search, record, or some other functions. When an alternate operation is received, the tracking servo loop is closed. The system then enters a search mode to reposition the optical head to the position indicated by the current location that was saved when the pause operation began. Finally, the selected function command is activated. 
   In one embodiment, a search command is selected while in the wait state. In this case, the current location need not be used since the operator desires to move to another location. In this scenario, the stored current location is ignored. Instead, the search is directed to the desired location associated with the search. In another embodiment, the tracking servo loop is opened and closed using a switch. In another embodiment, the current location is saved by reading a track ID located in a sub-code that exists as a property of the pattern imprinted on the spiral or concentric track of the rotating optical medium. In another embodiment, a frame ID is used for constant linear velocity (CLV) discs, such as CD, DVD, and MiniDisc, where a frame within a track is used to record a current location. The term track ID as used throughout this application refers to the use of both a track ID and a frame ID. 
   In one embodiment, an acceptable amount of error is allowed to be introduced. The introduction of the error further simplifies the process by removing the need to store the current location of the system when the wait state is initiated and to search for the current location when the wait state terminates. In another embodiment, an acceptable amount of error is allowed to be introduced into the system and a limited domain search algorithm is employed within the acceptable error range. 
   An advantage of the present invention is it simplifies the circuitry and logic needed to implement a pause function because the simplified pause only requires a switch to open the tracking servo loop. Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention will be more fully understood by reference to the following drawings, which are for illustrative purposes only: 
       FIG. 1  is a diagram that illustrates the operation of a prior art pause technique. 
       FIG. 2  is a block diagram of a player capable of implementing a simplified pause according to an embodiment of the present invention. 
       FIG. 3  is a flowchart showing the steps taken during a simplified pause according to an embodiment of the present invention. 
       FIG. 4  is a flowchart showing the steps taken during a simplified pause according to another embodiment of the present invention. 
       FIG. 5  is a block diagram of a player capable of implementing a simplified pause according to an embodiment of the present invention. 
       FIG. 6  is a flowchart showing the steps taken during a simplified pause according to yet another embodiment of the present invention. 
       FIG. 7  is a diagram showing the movement of two tracking beams between tracks. 
       FIG. 8  is a diagram of a waveform generated by the motion of the tracking beams of  FIG. 7 . 
       FIG. 9  is a waveform showing an error tracking signal as it focuses a beam on the track of a disk. 
       FIG. 10  is a flowchart showing the steps taken during a simplified pause that allows for an acceptable error according to an embodiment of the present invention. 
       FIG. 11  is a flowchart showing the steps taken during a simplified pause that allows for a limited domain search algorithm according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention relates to pause control for a player having a movable optical pickup. Referring more specifically to the drawings, for illustrative purposes the present invention is implemented in a system shown with respect to  FIG. 2 . Media player  200  includes at least a rotating optical medium, such as a disc  201 , that has a spiral track  210  located on a recording surface of the medium. Note that spiral track  210  is used for the purpose of example only. A concentric track having multiple substantially circular patterns may be used in the present invention as well. An optical pickup  220  is used to direct at least one beam  230  onto the track  210 . As the disc  201  spins, the pickup  220  is configured to cause the laser to follow the track  210  whereby data signals, error signals, and other information is detected by the pickup  220  when it senses the reflection of the beam  230  off the track  210 . 
   Various patterns  240  exist in the track  210 . This includes, for instance, a sub-code that contains a track ID that relates to the current location of the beam  230 , as well as data patterns and other appropriate information. Control systems  295  are also coupled to the media player  200 . The control systems  295  act, for instance, to guide the beam in the appropriate direction and to keep it centered on the spiral track  210 . It should be noted that the system above might contain other elements (not shown) that are well known to those skilled in the art. An input area  250  is coupled to the media player  200  wherein a user is able to provide input to the system to cause it to act in a suitable manner. For instance, input area  250  might include a pause key  260 , a search key  270 , a play key  280 , or other keys  290 . 
   If the media player  200  is currently playing a song and the user wishes to pause the song, for instance, the user would depress pause key  260 , which sends a signal to the system to initiate the actions needed to enter a pause state. Likewise, if the user wants to search somewhere else on the disc  201 , they would depress the search key  270 , and so on. 
   Pause Control 
   The manner in which one embodiment of the present invention simplifies the use of a pause technique is shown in  FIG. 3 . At block  300  a pause operation occurs. The pause operation is initiated, for instance, by depressing a pause key as illustrated in  FIG. 2 . At block  310 , the current location is determined and saved. At block  320 , the tracking servo loop is opened. The tracking servo loop is a component of the control system described in block  295  of  FIG. 2 . At block  330  a near zero offset is provided for the tracking actuator. The providing of a near zero offset to the tracking actuator is described in more detail below. It functions generally to provide the system with information about where to place the lens. Since the tracking servo was opened at step  320 , there is no tracking error signal to provide feedback telling the system where to place the lens. So, by providing a near zero offset the lens can remain as close as possible to the center of the track in the absence of a tracking error signal while the loop is open. 
   At block  340 , a wait state is entered. At block  350 , it is determined if the wait state should terminate. This may occur, for instance, if the user initiates a play, search, or some other function. If the wait state should not terminate, then block  350  repeats. Otherwise, at block  360  the tracking servo loop is closed. At block  370  the saved current location is searched for, and at block  380  the selected command is activated. 
     FIG. 4  shows another embodiment of the present invention and how it handles the initiation of a search operation when it is in a wait state. At block  400  a pause operation occurs. At block  410 , the current location is determined and saved. At block  420 , the tracking servo loop is opened. At block  430  a near zero offset is provided for the tracking actuator. At block  440 , a wait state is entered. 
   At block  450 , it is determined if the wait state should terminate. If the wait state should not terminate, then block  450  repeats. Otherwise, at block  460  it is determined if a search operation is terminating the wait state. If not, then at block  470  the tracking servo loop is closed. At block  480  the saved current location is searched for, and at block  490  the selected command is activated. Otherwise, at block  460  a search function is terminating the wait state, so at block  492  the location to search for is obtained. At block  494 , the tracking servo loop is closed and at block  496  the read beam is placed at the location to search for. 
     FIG. 5  is a block diagram of a media player that implements a simplified pause according to an embodiment of the present invention. Recording medium  500  is used by player  510  to play data embedded in a track  520  in the medium. It should be noted that medium  500 , by way of example, is a circular disc having a spiral track. The present invention, however, is not limited to such a medium. An optical pickup  530  is used to direct a laser  540  onto the surface of recording medium  500 . A tracking servo  525  is used to control and guide the laser along the track  520 . Laser  540  in optical pickup  530  is shown for the purpose of example only. The present invention may also implement electrical, radio, or other suitable signals from the pickup  530 . 
   Player  510  also includes a memory  545 . A device for input  560  is used wherein a user can implement a pause or other operation, for instance by depressing a button or using a remote control. In operation, once a pause operation is sensed at input device  560 , the sub-code  561  embedded in the track is examined. The sub-code reveals a track ID  565 , which is saved in memory  545 . A switch  570  in the tracking servo  525  is then opened. This causes the motion of the optical pickup  530  to stop. A tracking actuator  575  in the optical pickup  530  is given a near zero offset. The near zero offset is provided, for instance, by a connection to ground or an offset device in the tracking servo  525 . Once the offset is provided, the system waits for the wait state to terminate. When it does, switch  570  is closed and track ID  565  is obtained from memory  545 . The actuator  570  then moves the pickup  530  such that laser  540  is directed to the location of the track ID  565 , for instance using a search function  599 , and the selected command that terminated the wait state is activated. 
     FIG. 6  is a flowchart showing another embodiment of the present invention that is configured to operate on the system described in  FIG. 5 . At block  600  a pause operation occurs. At block  610 , the sub-code on the disc is obtained. At block  611 , current track ID is determined. This may occur, for instance by deciphering the sub-code on the disc. Typically the sub-code is scrambled in a manner wherein one sub-code is not contiguous but spread throughout a given area on the track in a known manner. Various methods for scrambling the sub-code are well known to those skilled in the art. 
   The sub-code is scrambled because discs and the like are subject to degradation on specific centralized locations. For example a scratch or defect in a small area might destroy data in that small area. By spreading the sub-code across a larger area and employing error detection mechanisms, the entire sub-code is not lost if a defect occurs in a small area. At block  615 , the track ID, which was obtained from the deciphered sub-code, is stored in a memory location of the player. At block  620 , a switch on the tracking servo loop is opened. At block  630  a near zero offset is provided for the tracking actuator. At block  640 , a wait state is entered. 
   At block  650 , it is determined if the wait state should terminate. This may occur, for instance, if the user initiates a play, search, or some other function. If the wait state should not terminate, then block  650  repeats. Otherwise, at block  660  the tracking servo loop is closed by closing the switch that was opened at block  620 . At block  670  the saved track ID is searched for in memory. At block  675 , the track ID is obtained from the memory. At block  676  the location for the track ID is searched for and found, and at block  680  the selected command is activated. 
   Near Zero Offset 
   Within the optical pickup of an optical media player there are one or more driver devices that control the position of the lens. The tracking servo keeps the lens centered on the information track by using a tracking error signal in a feedback loop. When the pause state is entered, the tracking servo loop is opened so the tracking error signal stops directing the position of the lens. In this state there is no incentive for the lens to be in any position because there is no signal to the lens. In one or more embodiments of the present invention, a near zero offset is provided to the tracking actuator when a pause operation is initiated and after the tracking servo loop is opened. In this manner, it is ensured that the lens is as near to the center of the information track as possible so that when the tracking servo loop is again closed, the lens needs to be moved the minimal distance. 
   It is possible to use the present invention by not providing any offset at all to the tracking actuator. In this case, when the tracking servo loop is again closed, there will be a large error signal. The tracking servo loop will eventually drive the lens position back to the center of the track, but it will take more time moving the carriage back to center. The near zero offset is implemented, for instance by adding a connection to ground to the tracking servo, or by adding an offset device in the tracking servo configured to provide a near zero offset tot he tracking actuator. Theoretically, a zero offset would be an ideal offset to provide to the tracking actuator, but in reality it is impossible to generate a signal having a voltage of exactly zero. 
   Acceptable Error 
   It should be noted that the simplified pause mechanisms of the embodiments of the present invention described with respect to  FIGS. 2 through 6  above are precise. This means that the exact location that the pickup was at when the pause operation started is the location that will be used when the pause operation terminates. In some applications, however, when exiting the wait state, it is acceptable to allow for a small amount of error. These applications include, for instance, the use of a CD player, where it is tolerable for the user to start a PAUSE at a first location and to finish the PAUSE at a second location, wherein the first and second locations are reasonably close together but not at the same location. 
   An acceptable amount of error may be introduced when the tracking servo loop is opened initially in response to the initiation of the wait state. For example, a system when stopped may be subject to eccentricity or imperfections in the manufacture of the disc that cause the pickup to move across tracks. Based on manufacturer″s standards, this movement should not exceed a pre-defined limit, fifty tracks for example. When the wait state terminates, the tracking servo loop is closed and a tracking error signal is provided to the tracking actuator, which focuses the laser beam back onto the track rather than searching of the track ID. The location where the beam focuses back onto the track will not exceed a pre-determined number of tracks away from the stored track ID and simplifies the process by removing the need to store the track ID and to search for it later. 
     FIG. 7  is a diagram showing a position of a beam as it moves between tracks and how the error signal is used to focus it on a given track. In the present example a two beam tracking system is used, although it should be noted that single or triple beam tracking systems can be used as well.  FIG. 7  includes three tracks, track  0 , track  1 , and track n. Beam  700  is in position  701  and beam  702  is in position  703  at time 1. Beam  700  is in position  705  and beam  702  is in position  707  at time 2. Beam  700  is in position  709  and beam  702  is in position  711  at time 3. Beam  700  is in position  713  and beam  702  is in position  715  at time 4. Beam  700  is in position  717  and beam  702  is in position  719  at time 5. Beam  700  is in position  721  and beam  702  is in position  723  at time 6. Beam  700  is in position  725  and beam  702  is in position  727  at time 7. Beam  700  is in position  729  and beam  702  is in position  731  at time 8. Beam  700  is in position  733  and beam  702  is in position  735  at time 9. 
   Thus, times 1 through 9 track the position of the beams as they move between tracks  1  and  2 . When the beam  700  is tracked through times 1 through 9, its voltage values are shown in Table 1: 
   
     
       
             
             
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
               1 
               2 
               3 
               4 
               5 
               6 
               7 
               8 
               9 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
               Beam 700 
                .5 v 
                .75 v 
               1 v 
                .75 v 
                .5 v 
                .25 v 
                0 v 
                .25 v 
                .5 v 
             
             
               Beam 702 
               −.5 v 
               −.25 v 
               0 v 
               −.25 v 
               −.5 v 
               −.75 v 
               −1 v 
               −.75 v 
               −.5 v 
             
             
                 
             
           
        
       
     
   
   By summing the voltage values of beams  100  and  102  through positions  1  through  9 , a sinusoidal curve is generated as shown in  FIG. 8 , where point  800  of curve  810  corresponds to the center of track  0  in  FIG. 7 . Correspondingly, point  820  the position directly between tracks  0  and  1  and point  830  is the position in the center of track  1 . 
   Thus, with respect to the radial position of the pickup, an error signal is generated as shown in  FIG. 9 . If the pause state is exited at point  900  of  FIG. 9 , then as the radial position moves to the right on the diagram, the amplitude of negative slope  910  decreases. The decrease in amplitude is used to drive the radial position in the direction of arrow  930  to counter the voltage, until the signal reaches point  940  wherein it is centered on the track. Likewise, if position  950  is the location where the pause state exits, then the signal is driven in the direction of arrow  960  toward point  940 . 
   When the tracking servo loop is closed in response to the termination of a wait state, the signal may be in a positive portion of its slope  970 . In this case, the tracking signal will guide the beam back to the track as indicated by arrow  980  until it eventually centers itself at point  990 . In either case, the signal will center itself on the track and the wait state will terminate. The location where the wait state terminates will be a pre-determined maximum distance from the location where the wait state was initiated. In many applications, this pre-determined distance is 50 tracks. 
   The steps taken by an embodiment of the present invention that allows for an acceptable error are shown in  FIG. 10 . At block  1000  a pause operation occurs. At block  1010 , the tracking servo loop is opened. At block  1020  a near zero offset is provided for the tracking actuator. At block  1030 , a wait state is entered. At block  1040 , it is determined if the wait state should terminate. If the wait state should not terminate, then block  1040  repeats. Otherwise, at block  1050  the tracking servo loop is closed and at block  1060  the selected command is activated. 
   Limited Domain Search 
   The present invention is configured to use any search algorithm known to those skilled in the art. In cases where acceptable error is not tolerable, it is desirable to perform a search function within the range of acceptable error. This is termed a limited domain search. Performing a limited domain search is beneficial because it reduces the domain for the search, thereby reducing the instructions that must be computed by the player in performing the search. 
   Scenarios where it is not tolerable to have error include, for instance, CD-R applications where data is being recorded onto the spiral track. In this case to not record data to fifty tracks or some other pre-determined amount might result in an inoperable disc. Similarly, a CD-ROM application might not tolerate any error because data is being read that is needed to operate an executing computer program. An error in this scenario might result in a crashed computer program. 
   In cases such as these, a search algorithm is employed once the wait state terminates. For example, it is known that implementing the steps of opening the servo loop in response to a wait state and closing it in response to its termination of the wait state results in a maximum error of a pre-defined amount (e.g., fifty tracks). A search algorithm used by the present invention may be limited to the domain of the pre-defined amount and thereby reduce the amount of tracks it searches over. 
   One example of a search algorithm is called a hunting method. In the limited domain of a fifty track maximum error, one example of how the algorithm could operate is as follows. The system would jump back 20 tracks, close the tracking servo loop, play the system briefly, and determine the present location compared to the saved track ID. If the present location was still too far ahead, it would jump back 20 tracks again and repeat. When the system jumped too far, it would jump forward again at a smaller interval, and the process repeats until the system jumps to a location just slightly proceeding the desired track. At that point the system is started and the sound or other data output is initiated when it reaches the track ID that was saved when the wait state began. 
     FIG. 11  is a flowchart showing the use of a search algorithm within an acceptable error range according to an embodiment of the present invention. At block  1100  a pause operation occurs. At block  1105  the current location is saved. At block  1110 , the tracking servo loop is opened. At block  1120  a near zero offset is provided for the tracking actuator. At block  1130 , a wait state is entered. At block  1140 , it is determined if the wait state should terminate. If the wait state should not terminate, then block  1140  repeats. Otherwise, at block  1150  the tracking servo loop is closed. At block  1160 , a search algorithm is employed within the range of acceptable error. At block  1170 , the current location saved in block  1105  is obtained using the restricted domain search algorithm, and at block  1180  the selected command is activated. 
   Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Thus the scope of this invention should be determined by the appended claims and their legal equivalents.