It is known that the use of an auto-adjusting oscillator is to synchronize an internal clock to the data rate of an USB interface for ensuring data to be transmitted accurately and stably. Conventional approaches for matching an internal clock to an incoming data stream, such as Phase Lock Loops (PLL) and/Delay Lock Loops (DLL), are not appropriate to be used for locking a data stream inputted from an USB interface by the following reasons:                (1) Such conventional approaches, e.g. PLL and DLL, typically require a continuous stream of input reference clocks to match the data rate of incoming data, however, such continuous stream is not available in data communication systems using USB interface.        (2) Such conventional approaches, e.g. PLL and DLL, typically require a very long data training sequence, however, such a long data training sequence will require a long locking time that is not suitable for USB.        (3) Such conventional approaches, e.g. PLL and DLL, typically require a precision timing component for preventing timing error, however, such precision timing component is usually not available in USB applications.        
From the above description, it is clear that those conventional approaches, such as PLL and DLL, are not suitable to be applied in USB applications.
USPTO Backgrounds
USPTO Backgrounds