CONTINUOUS ADAPTIVE DATA CAPTURE OPTIMIZATION FOR INTERFACE CIRCUITS
A method for operating a data interface circuit whereby calibration adjustments for data bit capture are made without disturbing normal system operation includes initially establishing, using a first calibration method where a data bit pattern received by the data interface circuit is predictable, an optimal sampling point for sampling data bits received by the data interface circuit, and during a normal system operation and without disturbing the normal system operation, performing a second calibration method where the data bit pattern received by the data interface circuit is unpredictable. The second calibration method determines an amount of a timing drift for received data bit edge transitions and adjusts the optimal timing point determined by the first calibration method to create a revised optimal timing point. The second calibration method samples fringe timing points associated with the transition edges of a data bit.
1 . A timing calibration method for aligning digital data bit and data strobe signals, the method comprising:
in a first calibration phase, determining, among a set of sampling points, a first sampling point associated with a transition edge of a data bit to obtain a known sampling point; and
in a second calibration phase, performing steps comprising:
sampling a set of interfringe timing points and an intrafringe timing point;
at the set of intrafringe timing points, examining data bit edge transitions to detect a timing drift association with data bits; and
using the timing drift to adjust the known sampling point.
2 . The method according to claim 1 , wherein the set of sampling points is received by the data interface circuit.
3 . The method according to claim 2 , wherein the data interface circuit is configured to couple to an interfringe delay line and an intrafringe delay line.
4 . The method according to claim 3 , wherein the interfringe delay line and the intrafringe delay line have the same length.
5 . The method according to claim 3 , wherein the interfringe delay line is a full-length delay line that is shorter than a standard delay line.
6 . The method according to claim 3 , wherein the interfringe delay line provides a delay that is greater than one quarter clock period.
7 . The method according to claim 3 , wherein the interfringe delay line provides an interfringe delay that is approximately one half clock period to enable an appropriate delay between tap points, and the intrafringe delay line provides an intrafringe delay that facilitates a setup and hold gap for a set of capture flops.
8 . The method according to claim 7 , wherein the delay further facilitates a margin for expected transition times of incoming signals.
9 . The method according to claim 7 , further comprising, automatically setting a value for the interfringe delay based on a number of delay elements needed for a full clock cycle and the intrafringe delay.
10 . The method according to claim 3 , wherein the data interface circuit is configured to a daisy chain structure having a characteristic of a single delay line.
11 . The method of claim 10 , wherein a delay line in the daisy chain structure is constructed such that a duty cycle of a signal entering the delay line is the same as a duty cycle of a delayed version of the same signal when it exits the delay line.
12 . The method of claim 10 , wherein, the data interface circuit comprises at least three delay lines for trailing fringe measurement, and at least three delay lines for leading fringe measurement.
13 . The method according to claim 3 , wherein values for at least one of the interfringe delay line or the intrafringe delay line are programmable.
14 . The method according to claim 1 , wherein adjusting the timing drift comprises shifting the known sampling point in time relative to the transition edge.
15 . The method according to claim 1 , wherein the first calibration phase is performed within a time period in which a PHY does not actively read data from memory.
16 . The method according to claim 1 , wherein the second calibration phase is performed during a circuit operation phase.
17 . The method according to claim 1 , wherein the set of interfringe timing points and the intrafringe timing point are sampled in response to receiving an unknown data bit pattern.
18 . The method of claim 1 , wherein the timing drift is caused by an environmental variable.
19 . The method of claim 18 , wherein the timing drift is iteratively determined.
20 . The method of claim 1 , wherein the known sampling point is a trained midpoint.