Statistically-adapted receiver and transmitter equalization
In described embodiments, adaptive equalization of a signal in, for example, Serializer/De-serializer transceivers by a) monitoring a data eye in a data path with an eye detector for signal amplitude and/or transition; b) setting the equalizer response of at least one equalizer in the signal path while the signal is present for statistical calibration of the data eye; c) monitoring the data eye and setting the equalizer during periods in which received data is allowed to contain errors (such as link initiation and training periods) and periods in which receive data integrity is to be maintained (such as normal data communication).
1. Apparatus for adaptive equalization of a signal representing serial data, the apparatus comprising:
a real-time eye monitor configured to monitor data eye characteristics in a data path circuit for a change in equalization parameters to generate eye statistics;
at least one equalizer in a signal path circuit, each equalizer having a corresponding response;
an adaptive controller configured to set, based on the eye statistics, the response of the at least one equalizer in the signal path circuit when the signal is present for statistical calibration of the data eye;
wherein the eye monitor monitors the data eye and the adaptive controller re-sets each equalizer based on the eye statistics in a first manner when received data has a first allowed error rate; and
wherein the eye monitor monitors the data eye and the adaptive controller re-sets each equalizer based on the eye statistics in a second manner when received data has a second allowed error rate that is lower than the first allowed error rate.
2. The invention of claim 1 , wherein the monitored change in the eye characteristics is a change in at least one of an eye amplitude, an eye width, and a data transition.
3. The invention of claim 2 , wherein the adaptive controller is configured to:
i) initializing one or more equalization parameters of the equalizer to a corresponding initial value;
ii) receive at least one of an eye height and an eye width of the data eye from the eye-monitor;
iii) update the one or more equalization parameters to a next available value based on at least one of the received eye height and the received eye width of the data eye to scan a range of the one or more equalizer parameters; and
iv) select the values of the one or more equalization parameters of the range for the equalizer with a relative optimum eye height and an eye width of the data eye.
4. The invention of claim 1 , wherein, for the setting and re-setting by the adaptive controller:
the adaptive controller comprises at least one of an analog adaptive controller and a DFE adaptive controller; and
the at least one equalizer of a receiver comprises at least one of an analog equalizer and a decision feedback equalizer (DFE), the analog equalizer having poles and zeros of an analog filter response set and re-set by the analog adaptive controller and the DFE having one or more taps of a DFE filter response set and re-set by the DFE adaptive controller.
5. The invention of claim 1 , wherein, for the setting and re-setting by the adaptive controller:
the adaptive controller comprises a transmit adaptive controller; and
the at least one equalizer of a transmitter comprises at least one of an analog equalizer and a finite impulse response (FIR) filter, the analog equalizer having poles and zeroes of an analog filter response set and re-set by the transmit adaptive controller and the FIR filter having one or more taps of a FIR filter response set and re-set by the transmit adaptive controller.
6. The invention of claim 1 , wherein the at least one equalizer of a transmitter comprises at least one of an analog equalizer and a finite impulse response (FIR) filter, the analog equalizer having an analog filter response set and re-set by the adaptive controller and the FIR filter having one or more taps of a FIR filter response set and re-set by the adaptive controller.
7. The invention of claim 1 , wherein the first allowed error rate is when a training sequence is present in the received data, and the second allowed error rate is when user data is present in the received data.
8. The invention of claim 1 , wherein the apparatus is embodied in an integrated circuit.
9. A method of adaptive equalization of a signal representing serial data, the method comprising the steps of:
a) monitoring, by a real-time eye monitor, a data eye in a data path circuit for a change in eye characteristics;
b) generating a set of eye statistics based on the monitored change in the data eye;
c) setting, based on the eye statistics, an equalizer response of at least one equalizer in a signal path circuit when the signal is present for statistical calibration of the data eye;
d) monitoring the data eye and re-setting each equalizer based on the eye statistics in a first manner when received data has a first allowed error rate; and
e) monitoring the data eye and re-setting each equalizer based on the eye statistics in a second manner when received data has a second allowed error rate that is lower than the first allowed error or rate.
10. The invention of claim 9 , wherein, for step a), the monitored change in the eye characteristics is a change in at least one of an eye amplitude, an eye width, and a data transition.
11. The invention of claim 10 , wherein, for step b), the generated set of eye statistics for measuring eye width might include a set of mismatch count values for at least one the eye amplitude, the eye width, and the data transition.
12. The invention of claim 10 , wherein step c) comprises the steps of:
c1) initializing one or more equalization parameters to a corresponding initial value;
c2) monitoring at least one of an eye height and an eye width of the data eye;
c3) updating the one or more equalization parameters to a next available value based on step c2);
c4) scanning a range of the one or more equalizer parameters by repeating steps c2) and c3) over the range; and
c5) selecting the values of the one or more equalization parameters of the range for the equalizer with a relative optimum eye height and an eye width of the data eye.
13. The invention of claim 9 , wherein, for the setting and re-setting steps, the at least one equalizer of a receiver comprises at least one of an analog equalizer and a decision feedback equalizer (DFE), the analog equalizer having an analog filter response set and re-set by an analog adaptive controller and the DFE having one or more taps of a DFE filter response set and re-set by a DFE adaptive controller.
14. The invention of claim 9 , wherein, for the setting and re-setting steps, the at least one equalizer comprises a transmit equalizer of a transmitter, the transmit equalizer having a response set by a transmit adaptive controller, and the method further comprises the step of communicating parameters of the transmit equalizer response from a receiver to the transmitter through a back channel control link.
15. The invention of claim 9 , wherein, for step a), the eye monitor monitors the data with a sampler array, and step a) comprises the steps of sampling, with a top error sampler of the array, a top edge of the data eye, sampling, with a data sampler of the array, a data value at the relative center of the data eye, and sampling, with a bottom error sampler of the array, a bottom edge of the data eye.
16. The invention of claim 15 , wherein step a) generates as one of the eye characteristics, an error in vertical height of the data eye based on the sampled top edge, the sampled bottom edge, and the sampled data value at the relative center of the data eye.
17. The invention of claim 15 , wherein, for step a), the data sampler comprises a first data error sampler and a second data error sampler measuring a relative error in width of the data eye as one of the eye characteristics, and the method further comprises the step of adjusting a clock phase of each sampler based on the relative error in width of the data eye.
18. The invention of claim 9 , wherein, for the setting and re-setting steps, the at least one equalizer of a transmitter comprises at least one of an analog equalizer and a finite impulse response (FIR) filter, the analog equalizer having an analog filter response set and re-set by a transmit adaptive controller and the FIR filter having one or more taps of a FIR filter response set and re-set by the transmit adaptive controller.
19. The invention of claim 9 , wherein the method is implemented as steps in a serializer/deserializer (SERDES) device.
20. A machine-readable medium, having encoded thereon program code, wherein, when the program code is executed by a machine, the machine implements a method for adaptive equalization of a signal representing serial data, comprising the steps of:
a) monitoring, by a real-time eye monitor, a data eye in a data path circuit for a change in eye characteristics
b) generating a set of eye statistics based on the monitored change in the data eye;
c) setting, based on the eye statistics, an equalizer response of at least one equalizer in a signal path circuit when the signal is present for statistical calibration of the data eye;
d) monitoring the data eye and re-setting each equalizer based on the eye statistics in a first manner when received data has a first allowed error rate; and
e) monitoring the data eye and re-setting each equalizer based on the eye statistics in a second manner when received data has a second allowed error rate that is lower than the first allowed error rate.