Offset and decision feedback equalization calibration
AssigneeRambus Inc.
InventorsKambiz Kaviani, Amir Amirkhany, Jason Chia-Jen Wei, Aliazam Abbasfar
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Abstract
A decision feedback equalizer is calibrated to compensate for estimated inter-symbol interference in a received signal and offsets of sampling devices. The decision feedback equalizer is configured so that an output signal of a sampling circuit represents a comparison between an input signal and a reference of the sampling circuit under calibration. An input signal is received over a communication channel that includes a predetermined pattern. The predetermined pattern is compared to the output signal to determine an adjusted reference for configuring the sampling circuit that accounts for both offset and inter-symbol interference effects.
Claims20
A method for calibrating a decision feedback equalizer, the decision feedback equalizer having a first sampling circuit configured to produce a first output signal representing samples at a first set of sample instants corresponding to a first phase of an input signal, and a second sampling circuit configured to produce a second output signal representing samples at a second set of sample instants corresponding to a second phase of the input signal, the method comprising:
- causing the first output signal to represent a comparison between the input signal and a first reference of the first sampling circuit;
- receiving the input signal during a first calibration period, the input signal having first input symbols corresponding to the first phase of the input signal and second input symbols corresponding to the second phase of the input signal, the first input symbols including a first pattern and the second input symbols having a first level during the first calibration period;
- obtaining the first output signal sampled from the first pattern using the first reference of the first sampling circuit;
- and
- comparing the first pattern and the first output signal to determine a first adjusted reference of the first sampling circuit.
An equalizer apparatus comprising:
- an error comparator;
- a first sampling circuit configured to sample an input signal at a first set of sampling instants corresponding to a first phase of the input signal and generate a first output signal, the input signal comprising first input symbols corresponding to the first phase and second input symbols corresponding to a second phase, wherein during a first calibration period, the first input symbols include a first pattern and the second input symbols have a first level;
- and
- a second sampling circuit configured to sample the input signal at a second set of sampling instants corresponding to the second phase of the input signal and generate a second output signal,
- wherein the second output signal controls the first sampling circuit to select a first reference so that the first output signal represents a comparison between the input signal and the first reference, and wherein the error comparator compares the first pattern and the first output signal to determine a first adjusted reference of the first sampling circuit.
A method for calibrating a first sampling circuit in a multi-data rate decision feedback equalizer equalizing an input signal having multiple phases with respective sample instants, the decision feedback equalizer having at least two sampling circuits including the first sampling circuit sampling at first sample instants and a second sampling circuit sampling at second sample instants, the method comprising:
- causing the decision feedback equalizer to select a threshold of the first sampling circuit from a plurality of thresholds for the first sampling circuit;
- receiving an input signal from a transmitter that repeatedly drives the input signal to a level representing a first one of two specific symbol values for the second sample instants and that drives the input signal to levels representing respective symbols in a predetermined sequence of symbols for the first sample instants, wherein each of the predetermined sequence of symbols is intermediate to the two specific symbol values in the input signal;
- using the first sampling circuit to sample the input signal at the first sample instants while varying the threshold used by the first sampling circuit;
- and
- updating the threshold in dependence on at least one output symbol of the first sampling circuit outputted while varying the threshold.
Dependencies are inferred from the claim text.