Data-valid window tracking for high speed interface

1 . An apparatus, comprising:

one or more control circuit configured to connect to a data bus, the one or more control circuit configured to:

compare a first bit sampled on a first side of a Data Voltage Window (DVW) of a data signal with a middle bit from the middle of the DVW to detect first misalignment of sampling with the DVW, compare a second bit sampled on a second side of the DVW with the middle bit to detect second misalignment of sampling with the DVW and adjust sampling times for the data signal according to detection of the first or second misalignment wherein for sampling that is aligned with DVWs, either the first and second bits are both sampled outside the DVW such that detecting the first misalignment of sampling with the DVW includes detecting equality of the first bit and the middle bit and detecting the second misalignment of sampling with the DVW includes detecting equality of the second bit and the middle bit or both the first and second bits are sampled inside the DVW such that detecting the first misalignment of sampling with the DVW includes detecting inequality of the first bit and the middle bit and detecting the second misalignment of sampling with the DVW includes detecting inequality of the second bit and the middle bit.

2 . The apparatus of claim 1 , wherein the one or more control circuit includes:

a first comparator to compare the first bit and the middle bit;

a first counter to count first misalignments;

a second comparator to compare the second bit and the middle bit; and

a second counter to count second misalignments.

3 . The apparatus of claim 2 , wherein the one or more control circuit is further configured to adjust sampling time in a first sense according to a first number in the first counter and adjust sampling time in a second sense that is opposite to the first sense according to a second number in the second counter.

4 . The apparatus of claim 3 , wherein the one or more control circuit is further configured to adjust sampling time in the first sense by adding an offset time for sampling of subsequent DVWs and to adjust sampling in the second sense by subtracting the offset time for sampling of subsequent DVWs.

5 . The apparatus of claim 2 , wherein the one or more control circuit is further configured to compare a first number in the first counter with a threshold number, compare a second number in the second counter with the threshold number and to generate an error signal if the first and second numbers exceed a threshold.

6 . The apparatus of claim 1 , wherein the one or more control circuit is further configured to sample the data signal at a plurality of times over a period that is longer than the DVW to identify the first time and the second time from transitions at either side of the DVW.

7 . The apparatus of claim 1 , wherein the one or more control circuit is further configured to detect logic transitions between DVWs and to selectively apply the detection of first and second misalignment of sampling with the DVW to first and second sides of DVWs at which logic transitions are detected.

8 . The apparatus of claim 1 , wherein the data bus extends between a memory controller die and one or more nonvolatile memory die and the data signal is a data input from the memory controller die to the one or more nonvolatile memory die or a data output from the one or more nonvolatile memory die to the memory controller die.

9 . The apparatus of claim 8 , wherein the one or more control circuit is located on the memory controller die, the data signal is an output from the one or more nonvolatile memory die to the memory controller die and the one or more nonvolatile memory die includes one or more additional control circuit configured to connect to the data bus, the additional control circuit configured to receive an input data signal from the memory controller die, compare a third bit sampled on a first side of an input DVW of the input data signal with a center bit from the center of the input DVW to detect first misalignment of sampling with the input DVW, compare a fourth bit sampled on a second side of the input DVW with the center bit to detect second misalignment of sampling with the input DVW and adjust sampling times for the input data signal according to detection of the first or second misalignment.

10 . A method of Data Valid Window (DVW) tracking, the method comprising:

in a training period, sampling a training data signal at a plurality of times over a period that is longer than a DVW to identify a first time and a second time for sampling the data signal from transitions at either side of the DVW;

subsequently, receiving a data signal;

sampling the data signal at a first time on a first side of a DVW to obtain a first bit;

sampling the data signal at a second time on a second side of the DVW to obtain a second bit;

sampling the data signal at a third time between the first time and the second time to obtain a middle bit;

comparing the first bit and the middle bit to detect first misalignment of sampling with the DVW;

comparing the second bit and the middle bit to detect second misalignment of sampling with the DVW; and

in response to detecting first DVW misalignment or second DVW misalignment, adjusting timing of sampling the data signal.

11 . The method of claim 10 , further comprising:

comparing the middle bit with middle bits from neighboring DVWs to determine that a first logic transition occurs at the first side of the DVW and a second logic transition occurs at the second side of the DVW.

12 . The method of claim 10 , wherein the first time and the second time are sampling times immediately outside the DVW such that when sampling is aligned with DVWs the first and second bits are different to the middle bit, comparing the first bit and the middle bit to detect first misalignment of sampling with the DVW includes detecting equality of the first bit and the middle bit and comparing the second bit and the middle bit to detect second misalignment of sampling with the DVW includes detecting equality of the second bit and the middle bit.

13 . The method of claim 10 , wherein the first time and the second time are sampling times immediately inside the DVW such that when sampling is aligned with DVWs the first and second bits are identical to the middle bit, comparing the first bit and the middle bit to detect first misalignment of sampling with the DVW includes detecting inequality of the first bit and the middle bit and comparing the second bit and the middle bit to detect second misalignment of sampling with the DVW includes detecting inequality of the second bit and the middle bit.

14 . The method of claim 10 , further comprising:

counting a first number of occurrences of the first misalignment;

counting a second number of occurrences of the second misalignment;

in response to the first number exceeding a threshold number, adjusting timing of sampling by a first time offset; and

in response to the second number exceeding the threshold number, adjusting timing of sampling the data signal by a second time offset.

15 . The method of claim 10 , further comprising:

counting a first number of occurrences of the first misalignment;

counting a second number of occurrences of the second misalignment; and

in response to the first number exceeding a threshold number and the second number exceeding the threshold number, generating an error signal.

16 . A system comprising:

a memory controller die;

one or more nonvolatile memory dies;

a data bus connecting the memory controller die to the one or more nonvolatile memory dies, the data bus configured to convey data signals between the memory controller die and the one or more nonvolatile memory dies;

means for comparing a first bit sampled on a first side of a DVW of a data signal of the data bus with a middle bit from the middle of the DVW to detect first misalignment of sampling with the DVW, comparing a second bit sampled on a second side of the DVW with the middle bit to detect second misalignment of sampling with the DVW and adjusting sampling times for the data signal according to detection of the first or second misalignment, the means for comparing located on the memory controller die to perform DVW tracking for data signals output from the one or more nonvolatile memory dies to the memory controller die; and

additional means for comparing located on the one or more nonvolatile memory dies to perform DVW tracking for data signals input to the one or more nonvolatile memory dies from the memory controller die, the additional means for comparing a third bit sampled on a first side of an input DVW of an input signal with a middle bit from the middle of the input DVW to detect first misalignment of sampling with the input DVW, comparing a fourth bit sampled on a second side of the input DVW with the middle bit to detect second misalignment of sampling with the input DVW and adjusting sampling times for the input data signal according to detection of the first or second misalignment in the input data signal.

17 . The system of claim 16 , wherein the one or more nonvolatile memory dies is bonded to a control die to form an integrated memory assembly and the means for comparing is located in the control die.

18 . The system of claim 16 , wherein the one or more nonvolatile memory dies include NAND flash memory cells.