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 and a first set of values 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, establishing a second set of values. Several fringe timing points are sampled. A drift amount is compared with a drift correction threshold value and the first optimal sampling point is shifted in time by the drift amount to revise the first optimal sampling point.
1. A data interface circuit wherein calibration adjustments for data bit capture are made without disturbing normal system operation, the circuit comprising;
a plurality of delay line (DLL) capture and delay circuits for sampling a trained optimal sampling point as well as leading and trailing sampling points;
wherein a first stream of data bits is input to the data interface circuit;
wherein using a first calibration method, a first optimal sampling point for sampling the data bits input to the data interface circuit is initially established;
wherein a second stream of data bits is input to the data interface circuit during normal system operation; and
wherein from time to time during normal system operation, and without disturbing normal system operation, the data interface circuit performs a second calibration method wherein the second calibration method is different from the first, the second calibration method being performed whereby:
the data interface circuit establishes at least one reference data path for sampling transition edges of the second stream of data bits input to the data interface during normal system operation;
using the at least one reference data path, the data interface circuit samples a plurality of fringe timing points, whereby several of the plurality of fringe timing points are associated with each of the transition edges of the second stream of data bits input to the data interface circuit;
wherein the sampling the fringe timing points associated with the transition edge of a particular data bit comprises sampling:
a) a plurality of interfringe timing points; and
b) an intrafringe timing point;
wherein the data interface circuit compares 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;
wherein the data interface circuit compares the drift amount with a drift correction threshold value; and
if the drift amount is greater than the drift correction threshold value, the data interface circuit shifts the first optimal sampling point in time by the drift amount to revise the first optimal sampling point.
2. The circuit 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 random data bit pattern.
3. The circuit of claim 1 wherein for the first calibration method a known and predictable data pattern is input to the data interface circuit; and
wherein for the second calibration method an unknown and unpredictable data bit pattern is input to the data interface circuit.
4. The circuit of claim 1 wherein multiple daisy-chained delay lines are used in construction of the data interface circuit, and wherein each of the multiple 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 said signal when it exits the delay line.
5. A data interface circuit wherein calibration adjustments are frequently made during normal system operation and without disturbing normal system operation, the circuit comprising;
a plurality of DLL circuits for establishing a trained optimal sampling point as well as dynamically establishing leading and trailing sampling points during normal system operation;
wherein an optimal sampling point for sampling data bits received by an input of the data interface circuit is initially established using a first calibration method; and
wherein from time to time during normal system operation, and without disturbing normal system operation, the data interface circuit performs a second calibration method is that is different from the first, the second calibration method performed whereby:
the data interface circuit samples transition edges of data bits received by the input, wherein values of the received data bits represent a random pattern from a perspective of the data interface circuit;
wherein for the second calibration method, sampling the fringe timing points associated with the transition edge of a data bit comprises the data interface circuit sampling:
a) a plurality of interfringe timing points; and
b) an intrafringe timing point;
wherein the data interface circuit determines from time to time that the transition edges have drifted relative to the optimal sampling point by a drift delay amount, the drift having occurred since a previous creation or adjustment of the optimal sampling point;
wherein the data interface circuit adjusts the optimal sampling point by subtracting the drift delay amount from, or adding the drift delay amount to, the optimal sampling point to create a revised optimal sampling point; and
wherein the first calibration method requires a specific data pattern to be provided to the input of the data interface circuit, and the second calibration method operates successfully on any random pattern of data bit values provided to the input of the data interface circuit.
6. The circuit 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 random data bit pattern.
7. The circuit of claim 5 wherein for the first calibration method a known and predictable data pattern is input to the data interface circuit; and
wherein for the second calibration method an unknown and unpredictable data bit pattern is input to the data interface circuit.
8. The circuit of claim 5 wherein multiple daisy-chained delay lines are used in construction of the data interface circuit, and where each of the multiple 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 said signal when it exits the delay line.
9. A data interface circuit wherein calibration adjustments for data bit capture are made without disturbing normal system operation, the circuit comprising;
a plurality of DLL circuits wherein said DLL circuits establish a trained optimal sampling point as well as dynamically establishing leading and trailing sampling points during normal system operation; and
a control circuit for controlling the DLL circuits and monitoring the sampling points, and for determining when and how much to adjust the optimal sampling point during normal system operation; wherein when operating a first calibration method, a data bit pattern received by the data interface circuit is known and predictable, and the optimal sampling point for sampling data bits received by the data interface circuit is initially established as the initial optimal timing point;
wherein during normal system operation and without disturbing normal system operation, the data interface circuit performs a second calibration method where the data bit pattern received by the data interface circuit is unknown and unpredictable, and wherein the data interface circuit determines an amount of timing drift for received data bit edge transitions and adjusts the initial optimal timing point determined by the first calibration method to create a revised optimal timing point;
wherein from time to time during system operation, and without disturbing normal system operation, the data interface circuit performs a second calibration method where the data bit pattern received by the data interface circuit is unknown and unpredictable, and wherein the second calibration method determines an amount of timing drift for received data bit edge transitions and adjusts the revised optimal timing point to create a new revised optimal timing point; wherein for the second calibration method sampling the fringe timing points associated with the transition edge of a data bit comprises sampling: a) a plurality of interfringe timing points; and b) an intrafringe timing point.
10. The circuit 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 random data bit pattern.
11. The circuit of claim 9 wherein multiple daisy-chained delay lines are used in construction of the data interface circuit, and where each of the multiple 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 said signal when it exits the delay line.