Data compensation/resynchronization circuit for phase lock loops

Abstract

A circuit that compensates for delays induced by clock generation logic and distributed clock drivers in phase lock loop applications is disclosed. The circuit is a phase lock loop (PLL) which contains a clock synchronization circuit that operates to synchronize a transition edge of a signal generated by a frequency divider against a distributed clock signal generated by a clock output driver of the circuit. The synchronization occurs unless the clock synchronization circuit is disabled.

What is claimed is:  
     
       1. A circuit that compensates for delays induced by clock generation logic and distributed clock drivers in phase lock loop applications, comprising: 
       a phase detector element which receives a reference clock signal as a first input signal and which generates a voltage signal representative of a phase difference between the reference clock signal and a second input signal to the phase detector element;  
       a filter element that has the voltage signal generated by the phase detector element as an input signal and that generates an output signal;  
       a voltage controlled oscillator element that has the output signal of the filter element as an input signal and that generates a frequency signal, wherein the frequency signal varies according to the input signal of the voltage controlled oscillator element;  
       a frequency divider element that receives the frequency signal generated by the voltage controlled oscillator element as a first input signal, a programming signal as a second input signal and that generates a frequency divider signal as an output signal;  
       a clock output driver element that receives the frequency signal generated by the voltage controlled oscillator element as an input signal and that generates a distributed clock signal; and  
       a clock synchronization element that receives the frequency divider signal generated by the frequency divider element as a first input signal, the distributed clock signal of the clock output driver element as a second input signal, a control signal as a third input signal, and that generates an output signal which is the second input signal to the phase detector element, wherein the clock synchronization element operates to synchronize a transition edge of the frequency divider signal generated by the frequency divider element using the distributed clock signal generated by the clock output driver element unless the clock synchronization element is disabled by the control signal.  
     
     
       2. The circuit of  claim 1 , wherein the clock synchronization element comprises: 
       a control element that receives the distributed clock signal as a first input signal and the control signal as a second input signal and that generates a control output signal; and  
       a logic element that receives the control output signal generated by the control element as a first input signal, the distributed clock signal as a second input signal, and the frequency divider signal generated by the frequency divider element as a third input signal and that generates the output signal of the clock synchronization element,  
       wherein the logic element samples the frequency divider signal on a transition edge of the distributed clock signal in order to synchronize the transition edge of the frequency divider signal unless the control output signal generated by the control element disables the logic element.  
     
     
       3. The circuit of  claim 2 , wherein when the control signal is asserted, the control output signal generated by the control element disables the logic element and when the control signal is not asserted, the control output signal generated by the control element does not disable the logic element. 
     
     
       4. The circuit of  claim 2 , wherein the logic element is a parallel D-type Flip-Flop. 
     
     
       5. The circuit of  claim 4 , wherein the when the control signal is not asserted, the control output signal generated by the control element enables a master portion and a slave portion of the parallel D-type Flip-Flop. 
     
     
       6. The circuit of  claim 2 , wherein the logic element samples the frequency divider signal on a first transition edge and a second transition edge of the distributed clock signal. 
     
     
       7. The circuit of  claim 6 , wherein the first transition edge is the rising edge of the distributed clock signal and the second transition edge is the falling edge of the distributed clock signal. 
     
     
       8. The circuit of  claim 1 , wherein the filter element is a low pass filter with gain. 
     
     
       9. The circuit of  claim 1 , wherein the clock output driver is one of a plurality of clock output drivers. 
     
     
       10. The circuit of  claim 1 , wherein the control signal of the clock synchronization element is a disable control signal. 
     
     
       11. A circuit that compensates for delays induced by clock generation logic and distributed clock drivers in phase lock loop applications, comprising: 
       a phase detector element which receives a reference clock signal as a first input signal and which generates a voltage signal representative of a phase difference between the reference clock signal and a second input signal to the phase detector element;  
       a filter element that has the voltage signal generated by the phase detector element as an input signal and that generates an output signal;  
       a voltage controlled oscillator element that has the output signal of the filter element as an input signal and that generates a first frequency signal, wherein the frequency signal varies according to the input signal of the voltage controlled oscillator element;  
       a first frequency divider element that receives the first frequency signal generated by the voltage controlled oscillator element as a first input signal, a programming signal as a second input signal, and that generates a first frequency divider signal as an output signal;  
       a second frequency divider element that receives the first frequency signal generated by the voltage controlled oscillator element and that generates a second frequency divider signal as an output signal;  
       a state machine element that receives the second frequency divider signal as a first input signal, the reference clock signal as a second input signal, and the programming signal as a third input signal and that generates a second frequency signal;  
       a clock output driver element that receives the second frequency signal generated by the state machine element as an input signal and that generates a distributed clock signal; and  
       a clock synchronization element that receives the first frequency divider signal generated by the first frequency divider element as a first input signal, the distributed clock signal of the clock output driver element as a second input signal, a control signal as a third input signal, and that generates an output signal which is the second input signal to the phase detector element, wherein the clock synchronization element operates to synchronize a transition edge of the first frequency divides signal generated by the first frequency divider element using the distributed clock signal generated by the clock output driver element unless the clock synchronization element is disabled by the control signal.  
     
     
       12. The circuit of  claim 11 , wherein the clock synchronization element comprises: 
       a control element that receives the distributed clock signal as a first input signal and the control signal as a second input signal and that generates a control output signal; and  
       a logic element that receives the control output signal generated by the control element as a first input signal, the distributed clock signal as a second input signal, and the first frequency divider signal generated by the first frequency divider element as a third input signal and that generates the output signal of the clock synchronization element,  
       wherein the logic element samples the first frequency divider signal on a transition edge of the distributed clock signal in order to synchronize the transition edge of the first frequency divider signal unless the control output signal generated by the control element disables the logic element.  
     
     
       13. The circuit of  claim 12 , wherein when the control signal is asserted, the control output signal generated by the control element disables the logic element and when the control signal is not asserted, the control output signal generated by the control element does not disable the logic element. 
     
     
       14. The circuit of  claim 12 , wherein the logic element is a parallel D-type Flip-Flop. 
     
     
       15. The circuit of  claim 14 , wherein the when the control signal is not asserted, the control output signal generated by the control element enables a master portion and a slave portion of the parallel D-type Flip-Flop. 
     
     
       16. The circuit of  claim 12 , wherein the logic element samples the first frequency divides signal on a first transition edge and a second transition edge of the distributed clock signal. 
     
     
       17. The circuit of  claim 16 , wherein the first transition edge is the rising edge of the distributed clock signal and the second transition edge is the falling edge of the distributed clock signal. 
     
     
       18. The circuit of  claim 11 , wherein the filter element is a low pass filter with gain. 
     
     
       19. The circuit of  claim 11 , wherein the clock output driver is one of a plurality of clock output drivers. 
     
     
       20. The circuit of  claim 11 , wherein the control signal of the clock synchronization element is a disable control signal. 
     
     
       21. The circuit of  claim 11 , wherein the state machine element additionally generates a third frequency signal. 
     
     
       22. A circuit, comprising: 
       
         a phase detector operable to receive a reference signal and a synchronized signal and to generate a difference signal having a value that is related to a phase difference between the reference and synchronized signals;  
       
         a signal - controlled oscillator coupled to the phase detector and operable to generate an oscillator signal having as frequency that is related to the value of the difference signal;    
       
         a driver coupled to the oscillator and operable to generate a buffered oscillator signal from the oscillator signal; and  
       
       
         a synchronizer coupled to the phase detector, the oscillator, and the driver, the synchronizer operable to synchronize the oscillator signal to the buffered oscillator signal and to generate the synchronized signal equal to the synchronized oscillator signal. 
       
     
     
       23. The circuit of  claim 22  wherein: 
       
         the phase detector is operable to generate the difference signal having a voltage that is related to the phase difference between the reference and synchronized signals;  
       
         the signal - controlled d oscillator is operable to generate the oscillator signal having a frequency that is related to the voltage of the difference signal.   
     
     
       24. The circuit of  claim 22  wherein the synchronizer is operable to generate the synchronized signal having a transition edge that is aligned with a transition edge of the buffered oscillator signal. 
     
     
       25. The circuit of  claim 22  wherein: 
       
         the synchronized signal and the buffered oscillator signal each have a respective transition edge; and  
       
       
         the synchronizer is operable to align the transition edge of the synchronized signal with the transition edge of the buffered oscillator signal. 
       
     
     
       26. The circuit of  claim 22  wherein: 
       
         the buffered oscillator signal has a transition edge; and  
       
       
         the synchronizer is operable to synchronize the oscillator signal to the buffered oscillator signal by sampling the oscillator signal on the transition edge of the buffered oscillator signal. 
       
     
     
       27. The circuit of  claim 22  wherein the synchronizer is operable to receive a disable signal and to generate the synchronized signal equal to the unsynchronized oscillator signal in response to the disable signal having a disable value. 
     
     
       28. A circuit, comprising: 
       
         a phase detector operable to receive a reference signal and a synchronized signal and to generate a difference signal having a value that is related to a phase difference between the reference and synchronized signals;  
       
       
         a filter coupled to the phase detector and operable to generate from the difference signal a filtered difference signal having a value;  
       
         a signal - controlled oscillator coupled to the filter and operable to generate an oscillator signal having a frequency that is related to the value of the filtered difference signal;    
       
         a driver coupled to the oscillator and operable to generate a buffered oscillator signal from the oscillator signal; and  
       
       
         a synchronizer coupled to the phase detector, the oscillator and the driver, the synchronizer operable to synchronize the oscillator signal to the buffered oscillator signal and to generate the synchronized signal equal to the synchronized oscillator signal. 
       
     
     
       29. The circuit of  claim 28  wherein the filter comprises a low- pass filter.   
     
     
       30. The circuit of  claim 28  wherein: 
       
         the phase detector is operable to generate the difference signal having a voltage that is related to the phase difference between the reference and synchronized signals;  
       
       
         the filter is operable to generate the filtered difference signal having a voltage; and  
       
         the signal - controlled oscillator is operable to generate the oscillator signal having a frequency that is related to the voltage of the filtered difference signal.   
     
     
       31. A circuit, comprising: 
       
         a phase detector operable to receive a reference signal and a synchronized signal and to generate a difference signal having a value that is related to a phase difference between the reference and synchronized signals;  
       
       
         a filter coupled to the phase detector and operable to generate from the difference signal a filtered difference signal having a value;  
       
         a signal - controlled oscillator coupled to the filter and operable to generate an oscillator signal having a first frequency that is related to the value of the filtered difference signal;    
       
         a driver coupled to the oscillator and operable to generate a buffered oscillator signal from the oscillator signal;  
       
         a frequency divider coupled to the oscillator and operable to generate from the oscillator signal a frequency - divided oscillator signal having a second frequency that is lower than the first frequency; and    
         a synchronizer coupled to the phase detector, the frequency divider, and the driver, the synchronizer operable to synchronize the frequency - divided oscillator signal to the buffered oscillator signal and to generate the synchronized signal equal to the synchronized frequency - divided oscillator signal.   
     
     
       32. The circuit of  claim 31  wherein: 
       
         the buffered oscillator signal has a transition edge; and  
       
         the synchronizer is operable to synchronize the frequency - divided oscillator signal to the buffered oscillator signal by sampling the frequency - divided oscillator signal on the transition edge of the buffered oscillator signal.   
     
     
       33. The circuit of  claim 31  wherein the synchronizer is operable to receive a disable signal and to generate the synchronized signal equal to the unsynchronized frequency- divided oscillator signal in response to the disable signal having a disable value.   
     
     
       34. A method, comprising: 
       
         generating an oscillator signal having as a frequency that is related to a phase difference between a reference signal and a synchronized signal;  
       
       
         distributing the oscillator signal; and  
       
       
         generating the synchronized signal by synchronizing the oscillator signal to the distributed oscillator signal. 
       
     
     
       35. The method of  claim 34  wherein generating the synchronized signal comprises aligning a transition edge of the synchronized signal with a transition edge of the distributed oscillator signal. 
     
     
       36. The method of  claim 34  wherein generating the synchronized signal comprises: 
       
         sampling the oscillator signal on transitions edge of the distributed oscillator signal; and  
       
       
         generating the synchronized signal equal to the samples of the oscillator signal. 
       
     
     
       37. The method of  claim 34  wherein generating the synchronized signal comprises setting the synchronized signal equal to the oscillator signal during a synchronization- disable mode.   
     
     
       38. A method, comprising: 
       
         generating an oscillator signal having a frequency that is related to a phase difference between a reference signal and a synchronized signal;  
       
       
         distributing the oscillator signal;  
       
       
         reducing the frequency of the oscillator signal; and  
       
         generating the synchronized signal by synchronizing the reduced - frequency oscillator signal to the distributed oscillator signal.   
     
     
       39. The method of  claim 38  wherein generating the synchronized signal comprises aligning a transition edge of the synchronized signal with a transition edge of the distributed oscillator signal. 
     
     
       40. The method of  claim 38  wherein generating the synchronized signal comprises: 
         sampling the reduced - frequency oscillator signal on transitions edge of the distributed oscillator signal; and    
         generating the synchronized signal equal to the samples of the reduced - frequency oscillator signal.   
     
     
       41. The method of  claim 38  wherein generating the synchronized signal comprises setting the synchronized signal equal to the reduced- frequency oscillator signal during a synchronization - disable mode.