Sampler offset calibration during operation

An apparatus comprising:

• a data sampler operating in a data signal processing path having a decision threshold associated with a decision feedback equalization (DFE) correction factor, the data sampler configured to sample a data signal;
• a spare sampler operating outside of the data signal processing path configured to measure an eye opening of the data signal by adjusting a decision threshold of to determine a center-of-eye value for the decision threshold of the spare sampler;
• a DFE-tap generator configured to provide the DFE correction factor to the eye-scope sampler to initialize the decision threshold of the spare sampler;
• the data sampler and spare sampler configured to generate respective sets of phase-error signals responsive to a detection of a predetermined data pattern;
• and
• an accumulator configured to update the decision threshold of the data sampler based on an accumulation of differences in phase-error signals of the respective sets of phase-error signals.