Edge-based sampler offset correction
First Claim
1. A receive circuit, comprising:
- a receiver that samples a signal, the receiver comprising a first sampler that samples a voltage level associated with an expected edge of the signal and a second sampler that samples digital values represented by the signal, the samplers collectively generating a set of at least three samples associated with each one of plural edge crossings in the signal;
a phase alignment circuit that detects an edge of the signal; and
an offset-calibration circuit coupled to the phase alignment circuit to correct, responsive to correlation of specific signal patterns with edge timing represented by the signal, receiver voltage offset associated with sampling the signal in dependence upon detected correlation, wherein the offset-calibration circuit corrects the receiver voltage offset by varying the receiver voltage offset by a first polarity if a correlation is detected that indicates that an actual edge tends to be early with respect to an expected edge for a first signal transition and late with respect to an expected edge for a second signal transition, and by a second polarity if correlation is detected that indicates that the actual edge tends to be late with respect to the expected edge for the first signal transition and early with respect to the expected edge for the second signal transition.
2 Assignments
0 Petitions
Accused Products
Abstract
Embodiments of a circuit are described. This circuit includes a receiver circuit including a first sampler (312-1) and a second” sampler (312-2). A clock-data-recovery circuit (324) in the receiver circuit adjusts a sample time of the receiver circuit so that the sample time is proximate to a signal crossing point at an edge of an eye pattern associated with received signals. An offset-calibration circuit (326) in the receiver circuit determines and adjusts an offset voltage of a given sampler, which can be the first sampler or the second sampler. This offset-calibration circuit may determine a present offset voltage (412) of the given sampler in a timing region proximate to the signal crossing point (410-2) in which the clock-data-recovery circuit dithers about a present sample time based on the present offset voltage. Additionally, the clock-data-recovery circuit and the offset-calibration circuit may iteratively converge on the signal crossing point and a residual offset voltage of the given sampler.
19 Citations
24 Claims
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1. A receive circuit, comprising:
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a receiver that samples a signal, the receiver comprising a first sampler that samples a voltage level associated with an expected edge of the signal and a second sampler that samples digital values represented by the signal, the samplers collectively generating a set of at least three samples associated with each one of plural edge crossings in the signal; a phase alignment circuit that detects an edge of the signal; and an offset-calibration circuit coupled to the phase alignment circuit to correct, responsive to correlation of specific signal patterns with edge timing represented by the signal, receiver voltage offset associated with sampling the signal in dependence upon detected correlation, wherein the offset-calibration circuit corrects the receiver voltage offset by varying the receiver voltage offset by a first polarity if a correlation is detected that indicates that an actual edge tends to be early with respect to an expected edge for a first signal transition and late with respect to an expected edge for a second signal transition, and by a second polarity if correlation is detected that indicates that the actual edge tends to be late with respect to the expected edge for the first signal transition and early with respect to the expected edge for the second signal transition. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A receive circuit, comprising:
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a first sampler to sample edge crossings of a signal; a second sampler to sample data values of the signal; a phase adjustment circuit to generate an adjusted phase based upon sampled edge crossings and to provide the adjusted phase to the second sampler to time the sampling of the data values; and an offset-calibration circuit to provide a voltage offset correction to adjust the sampling of edge crossings by the second sampler; where the offset-calibration circuit is adapted to respond to correlation between specific data value transition patterns and timing of edge crossings by adjusting the voltage offset correction in an iterative manner to reduce detected correlation, where the offset-calibration circuit corrects the voltage offset by varying the voltage offset by a first polarity if a correlation is detected that indicates that an actual edge tends to be early with respect to an expected edge for a first signal transition and late with respect to an expected edge for a second signal transition, and by a second polarity if correlation is detected that indicates that the actual edge tends to be late with respect to the expected edge for the first signal transition and early with respect to the expected edge for the second signal transition; and where the phase adjustment circuit is adapted to converge on an edge crossing point of the signal based upon the voltage offset correction. - View Dependent Claims (12, 13)
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14. A receive circuit, comprising:
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a phase detector to adjust a clock phase dependent upon a signal edge crossing; an offset-calibration circuit to correct voltage offset to adjust voltage level of the edge crossing relative to the signal in response to correlation between (i) early/late tendencies of the signal with respect to the expected edge crossing, and (ii) at least one specific signal transition pattern, the offset-calibration circuit; a first sampler to sample the signal using the clock phase; a second sampler used to sample edge crossings, where the offset-calibration circuit is coupled to the second sampler to correct voltage offset in the second sampler; and circuitry for switching the role of each of the samplers, to alternatively correct voltage offset in each of the samplers. - View Dependent Claims (15, 16)
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17. A method of determining an voltage offset in a receiver circuit, comprising:
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detecting data level transitions in a digital signal; detecting data edges in the digital signal; detecting occurrence of at least one predetermined pattern based on the data level transitions; and monitoring correlation between an early/late tendency of the data edge and at least one predetermined signal pattern, and responsively adjusting voltage offset associated with detecting the data edges, wherein adjusting the voltage offset comprises varying the voltage offset by a first polarity if a correlation is detected that indicates that an actual edge tends to be early with respect to an expected edge for a first signal transition and late with respect to an expected edge for a second signal transition, and by a second polarity if correlation is detected that indicates that the actual edge tends to be late with respect to the expected edge for the first signal transition and early with respect to the expected edge for the second signal transition. - View Dependent Claims (18, 19)
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20. A method, comprising:
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sampling edge crossings of a signal; sampling data values of the signal; adjusting phase based upon sampled edge crossings and using the adjusted phase to time the sampling of the data values; and detecting correlation between specific data value transition patterns and timing of edge crossings; adjusting voltage offset associated with sampling of the edge crossings in an iterative manner to reduce detected correlation, wherein adjusting the voltage offset comprises varying the voltage offset by a first polarity if a correlation is detected that indicates that an actual edge tends to be early with respect to an expected edge for a first signal transition and late with respect to an expected edge for a second signal transition, and by a second polarity if correlation is detected that indicates that the actual edge tends to be late with respect to the expected edge for the first signal transition and early with respect to the expected edge for the second signal transition; and converging on an edge crossing point of the signal based upon the voltage offset correction.
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21. An apparatus comprising instructions stored on machine-readable media, the instructions, when executed, adapted to cause a machine to:
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detect data level transitions in a digital signal; detect data edges in the digital signal; detect occurrence of at least one predetermined pattern based on the data level transitions; monitor correlation between an early/late tendency of the data edge with at least one predetermined signal pattern; and responsive to correlation, adjust voltage offset associated with detecting the data edges, wherein adjusting the voltage offset comprises varying the voltage offset by a first polarity if a correlation is detected that indicates that an actual edge tends to be early with respect to an expected edge for a first signal transition and late with respect to an expected edge for a second signal transition, and by a second polarity if correlation is detected that indicates that the actual edge tends to be late with respect to the expected edge for the first signal transition and early with respect to the expected edge for the second signal transition.
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22. A computer-readable medium containing data representing a receive circuit, where the receive circuit includes:
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a phase detector to adjust a clock phase dependent upon a signal edge crossing; an offset-calibration circuit to correct voltage offset in response to correlation between (i) early/late tendencies of the signal with respect to the expected edge crossing, and (ii) at least one specific signal transition pattern, the offset-calibration circuit correcting voltage offset to adjust voltage level of the edge crossing relative to the signal; a first sampler to sample an input signal using the clock phase; a second sampler used to sample edge crossings, where the offset-calibration circuit is coupled to the second sampler to correct voltage offset in the second sampler; and circuitry for switching the role of each of the samplers, to alternatively correct voltage offset in each of the samplers. - View Dependent Claims (23, 24)
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Specification