Continuous adaptive data capture optimization for interface circuits
A data interface circuit wherein calibration adjustments for data bit capture are made without disturbing normal system operation, is described. A plurality of DLL capture and delay circuits for sampling a trained optimal sampling point as well as leading and trailing sampling points are defined. A first stream of data bits is input to the data interface circuit and using a first calibration method, a first optimal sampling point for sampling the data bits input is established. A second stream of data bits is input to the data interface circuit during normal system operation. A second calibration method is performed that is different from the first, the second calibration method being performed whereby: at least one reference data path is established for sampling transition edges of the second stream of data bits input to the data interface during normal system operation.
1. A method for operating a data interface circuit whereby calibration adjustments for data bit capture are made without disturbing normal system operation, comprising;
receiving a first stream of data bits input to the data interface circuit, wherein a data bit pattern comprising the first stream is a predictable pattern;
establishing, using a first calibration method operating on the first stream of data bits and outside of normal system operation, an initial optimal sampling point for sampling the data bits input to the data interface circuit;
receiving a second stream of data bits input to the data interface circuit during normal system operation wherein a data bit pattern comprising the second stream is an unpredictable pattern;
from time to time during normal system operation and without disturbing normal system operation, performing a second calibration method different from the first, the second calibration method comprising:
establishing a plurality of reference data paths for performing fringe timing measurements on the second stream of data bits input to the data interface during normal system operation, the plurality of reference data paths including trailing fringe, leading fringe, and midpoint data paths;
comparing a first fringe timing measurement made during a first performance of the second calibration method, with a second fringe timing measurement made during a second performance of the second calibration method to determine a drift amount for transition edges of the second stream of data bits input to the data interface; and
based on the determined drift amount, adjusting the initial optimal sampling point.
2. The method of claim 1 wherein for the second calibration method the transition edges of the data bits may be rising edge transitions and/or falling edge transitions, and may be associated with any received data bit pattern.
3. The method of claim 1 wherein multiple daisy-chained delay lines are used in construction of the data interface circuit, and wherein each of the multiple daisy-chained delay lines is constructed such that a duty cycle of a signal entering the delay line is the same as the duty cycle of a delayed version of the same signal when it exits the delay line.
4. The method of claim 1 wherein the plurality of reference data paths comprises at least three delay lines for trailing fringe measurement, and at least three delay lines for leading fringe measurement.
5. A method for operating a data interface circuit whereby calibration adjustments for data bit capture are made without disturbing normal system operation, comprising;
receiving a first stream of data bits input to the data interface circuit;
initially establishing, using a first calibration method operating on the first stream of data bits and outside of normal system operation where a data bit pattern received by the data interface circuit is predictable, a trained midpoint comprising an initial optimal sampling point for sampling the data bits input to the data interface circuit;
receiving a second stream of data bits input to the data interface circuit during normal system operation, wherein a pattern of data bits in the second stream that are received during normal system operation is unpredictable;
from time to time during normal system operation and without disturbing normal system operation, performing a second calibration method different from the first, the second calibration method comprising:
establishing a plurality of reference data paths for performing fringe timing measurements on the second stream of data bits input to the data interface during normal system operation, the plurality of reference data paths including trailing fringe, leading fringe, and trained midpoint data paths;
determining a timing drift amount by recording variations in fringe timing measurements made over time during performance of the second calibration method; and
based on the determined timing drift amount, adjusting the initial optimal sampling point.
6. The method of claim 5 wherein for the second calibration method the transition edges of data bits may be rising edge transitions and/or falling edge transitions, and may be associated with any received data bit pattern.
7. The method of claim 5 wherein multiple daisy-chained delay lines are used in construction of the data interface circuit, and where each of the multiple daisy-chained delay lines is constructed such that a duty cycle of a signal entering the delay line is the same as the duty cycle of a delayed version of the same signal when it exits the delay line.
8. The method of claim 5 wherein the plurality of reference data paths comprises at least three delay lines for trailing fringe measurement, and at least three delay lines for leading fringe measurement.
9. A method for operating a data interface circuit whereby calibration adjustments for data bit capture are made without disturbing normal system operation, comprising;
initially establishing, using a first calibration method where a data bit pattern received by the data interface circuit is predictable, an initial optimal sampling point for sampling data bits received by the data interface circuit;
during normal system operation and without disturbing normal system operation, performing a second calibration method where the data bit pattern received by the data interface circuit is unpredictable, and wherein the second calibration method determines an amount of timing drift for received data bit edge transitions and adjusts the initial optimal sampling point determined by the first calibration method to create a revised optimal sampling point;
wherein the second calibration method samples fringe timing points associated with the transition edges of a data bit, and the sampling is performed using a plurality of reference data paths including trailing fringe, leading fringe, and midpoint data paths; and
wherein daisy-chained delay lines are used in construction of one or more of the plurality of reference data paths, where each daisy-chained delay line comprises multiple delay lines in a daisy-chain constructed such that a duty cycle of a signal entering the daisy-chained delay line is the same as the duty cycle of a delayed version of the same signal when it exits the daisy-chained delay line.
10. The method of claim 9 wherein for the second calibration method the data bit pattern transition edges may be rising edge transitions or falling edge transitions, and may be associated with any received data bit pattern.
11. The method of claim 9 wherein the plurality of reference data paths comprises at least three delay lines for trailing fringe measurement, and at least three delay lines for leading fringe measurement.