Rate-adaptive equalizer that automatically initializes itself based on detected channel conditions, and a method
A rate-adaptive equalizer automatically initializes its tap coefficients to values. During an initialization process, a linear search algorithm is performed that sweeps the tap coefficients through different combinations of tap coefficients while assessing information about an eye associated with an input signal received over a communications channel. When the eye information indicates that the eye is open, the current tap coefficients are selected as the initial tap coefficients to be used at the beginning of the main adaptation algorithm.
1. A rate-adaptive equalizer comprising:
equalizer circuitry having a plurality of clocked delay elements, the clocked delay elements having tap coefficients that can be varied to vary a delay provided by the clocked delay elements, the tap coefficients being applied to taps of the clocked delay elements, the equalizer circuitry receiving an input signal and outputting at least a first equalizer output signal;
clock-and-data recovery (CDR) circuitry, the CDR circuitry electrically coupled to the equalizer circuitry, the CDR circuitry receiving the equalizer output signal and recovering a clock signal from the received equalizer output signal, the CDR circuitry outputting the clock signal and a frequency lock signal, F_LOCK, the clock signal being delivered to the clocked delay elements; and
adaptive control logic configured to provide at least one control signal to the equalizer circuitry to select values of the tap coefficients being applied to the taps of the equalizer circuitry, wherein the adaptive control logic is configured to perform an initialization algorithm that generates different combinations of tap coefficients and causes the combinations of tap coefficients to be applied to the clocked delay elements while evaluating information relating to an eye associated with the input signal to determine which combination of tap coefficients results in a highest quality eye, and wherein the adaptive control logic designates the combination of tap coefficients resulting in the highest quality eye as initial coefficients to be applied to the taps of the equalizer circuitry.
2. The rate-adaptive equalizer of claim 1 , wherein the information that is evaluated relating to the eye includes the F_LOCK signal output by the CDR circuitry.
3. The rate-adaptive equalizer of claim 1 , further comprising:
mean squared error (MSE) circuitry electrically coupled to the equalizer circuitry and to the adaptive control logic, the MSE circuitry processing at least a second equalizer output signal outputted from the equalizer circuitry and generating an MSE output signal that represents an estimate of the mean squared error of the second equalizer output signal, a digitized version of the MSE output signal being received in the adaptive control logic, and wherein the information that is evaluated by the adaptive control logic relating to the eye includes the estimate of the mean squared error represented by the MSE output signal.
4. The rate-adaptive equalizer of claim 3 , wherein the information that is evaluated by the adaptive control logic relating to the eye includes the estimate of the mean squared error represented by the MSE output signal and the F_LOCK signal output by the CDR circuitry.
5. The rate-adaptive equalizer of claim 1 , further comprising:
eye monitor circuitry electrically coupled to the equalizer circuitry and to the adaptive control logic, the eye monitor circuitry processing said at least a first equalizer output signal and generating one or more eye monitor output signals representing one or more eye characteristics, and wherein the information that is evaluated by the adaptive control logic relating to the eye includes said one or more eye characteristics represented by said one or more eye monitor output signals.
6. The rate-adaptive equalizer of claim 5 , wherein the information that is evaluated by the adaptive control logic relating to the eye includes said one or more eye characteristics represented by said one or more eye monitor output signals and the F_LOCK signal output by the CDR circuitry.
7. The rate-adaptive equalizer of claim 1 , wherein the initialization algorithm includes a linear search algorithm that periodically varies the tap coefficients by a particular step amount to generate the different combinations of tap coefficients such that all possible combinations of tap coefficients are applied to the clocked delay elements while evaluating information relating to an eye associated with the input signal to determine which combination of tap coefficients results in a highest quality eye.
8. The rate-adaptive equalizer of claim 7 , wherein the step amount is at least 1.
9. The rate-adaptive equalizer of claim 8 , wherein the step amount is at least 2.
10. The rate-adaptive equalizer of claim 9 , wherein the step amount is at least 4.
11. The rate-adaptive equalizer of claim 7 , wherein the step amount is selected by choosing a number of least significant bits of the tap coefficients being applied to each tap that are not to be used in generating the different combinations of tap coefficients.
12. The rate-adaptive equalizer of claim 1 , further comprising:
mean squared error (MSE) circuitry electrically coupled to the equalizer circuitry and to the adaptive control logic, the MSE circuitry processing at least a second equalizer output signal outputted from the equalizer circuitry and generating an MSE output signal that represents an estimate of the mean squared error of the second equalizer output signal, a digitized version of the MSE output signal being received in the adaptive control logic; and
eye monitor circuitry electrically coupled to the equalizer circuitry and to the adaptive control logic, the eye monitor circuitry processing said at least a first equalizer output signal and generating one or more eye monitor output signals representing one or more eye characteristics, and wherein the information that is evaluated by the adaptive control logic relating to the eye includes said one or more eye characteristics represented by said one or more eye monitor output signals and the estimate of the mean squared error represented by the MSE output signal.
13. The rate-adaptive equalizer of claim 12 , wherein the information that is evaluated by the adaptive control logic relating to the eye further includes the F_LOCK signal output by the CDR circuitry.
14. A rate-adaptive equalizer comprising:
equalizer circuitry having a plurality of clocked delay elements, the clocked delay elements having tap coefficients that can be varied to vary a delay provided by the clocked delay elements, the tap coefficients being applied to taps of the clocked delay elements, the equalizer circuitry receiving an input signal and outputting at least a first equalizer output signal;
clock-and-data recovery (CDR) circuitry, the CDR circuitry electrically coupled to the equalizer circuitry, the CDR circuitry receiving the equalizer output signal and recovering a clock signal from the received equalizer output signal, the CDR circuitry outputting the clock signal and a frequency lock signal, F_LOCK, the clock signal being delivered to the clocked delay elements;
mean squared error (MSE) circuitry electrically coupled to the equalizer circuitry and to the adaptive control logic, the MSE circuitry processing at least a second equalizer output signal outputted from the equalizer circuitry and generating an MSE output signal that represents an estimate of the mean squared error of the second equalizer output signal, a digitized version of the MSE output signal being received in the adaptive control logic;
eye monitor circuitry electrically coupled to the equalizer circuitry and to the adaptive control logic, the eye monitor circuitry processing said at least a first equalizer output signal and generating one or more eye monitor output signals representing one or more eye characteristics; and
adaptive control logic configured to provide at least one control signal to the equalizer circuitry to select values of the tap coefficients being applied to the taps, wherein the adaptive control logic is configured to perform an initialization algorithm that generates different combinations of tap coefficients and causes the combinations of tap coefficients to be applied to the clocked delay elements while evaluating information relating to an eye associated with the input signal to determine which combination of tap coefficients results in a highest quality eye, and wherein the adaptive control logic designates the combination of tap coefficients resulting in the highest quality eye as initial coefficients to be applied to the taps, and wherein the information relating to the eye is based on at least one of the F_LOCK signal, said one or more eye monitor output signals, and the estimate of the mean squared error represented by the MSE output signal.
15. A method for performing tap coefficient initialization in a rate-adaptive equalizer, the method comprising:
in clock-and-data recovery (CDR) circuitry of the equalizer, receiving an equalizer output signal and recovering a clock signal from the received equalizer output signal;
outputting the clock signal and a frequency lock signal, F_LOCK, from the CDR circuitry;
in equalizer circuitry of the equalizer, receiving an input signal to be equalized and the clock signal output from the CDR circuitry;
passing the received input signal through a plurality of delay elements of the equalizer circuitry that are clocked by the received clock signal, the clocked delay elements having tap coefficients that can be varied to vary a delay provided by the clocked delay elements, wherein the tap coefficients are applied to taps of the clocked delay elements;
outputting at least a first equalizer output signal from the equalizer circuitry, said at least a first equalizer output signal being received by the CDR circuitry;
in adaptive control logic of the equalizer, providing at least one control signal to the equalizer circuitry to select values of the tap coefficients being applied to the taps of the equalizer circuitry;
in the adaptive control logic, performing an initialization algorithm that generates different combinations of tap coefficients and causes the combinations of tap coefficients to be applied to the clocked delay elements while evaluating information relating to an eye associated with the input signal to determine which combination of tap coefficients results in a highest quality eye; and
in the adaptive control logic, designating the combination of tap coefficients resulting in the highest quality eye as initial coefficients to be applied to the taps of the equalizer circuitry.
16. The method of claim 15 , wherein the information that is evaluated relating to the eye includes the F_LOCK signal output by the CDR circuitry.
17. The method of claim 15 , further comprising:
in mean squared error (MSE) circuitry of the equalizer, processing at least a second equalizer output signal outputted from the equalizer circuitry and generating an MSE output signal that represents an estimate of the mean squared error of the second equalizer output signal; and
providing a digitized version of the MSE output signal to the adaptive control logic, and wherein the information that is evaluated by the adaptive control logic relating to the eye includes the estimate of the mean squared error represented by the MSE output signal.
18. The method of claim 17 , wherein the information that is evaluated by the adaptive control logic relating to the eye includes the estimate of the mean squared error represented by the MSE output signal and the F_LOCK signal output by the CDR circuitry.
19. The method of claim 15 , further comprising:
in eye monitor circuitry of the equalizer, processing said at least a first equalizer output signal and generating one or more eye monitor output signals representing one or more eye characteristics, and wherein the information that is evaluated by the adaptive control logic relating to the eye includes said one or more eye characteristics represented by said one or more eye monitor output signals.
20. The method of claim 19 , wherein the information that is evaluated by the adaptive control logic relating to the eye includes said one or more eye characteristics represented by said one or more eye monitor output signals and the F_LOCK signal output by the CDR circuitry.
21. The method of claim 15 , wherein the initialization algorithm includes a linear search algorithm that periodically varies the tap coefficients by a particular step amount to generate the different combinations of tap coefficients such that all possible combinations of tap coefficients are applied to the clocked delay elements while evaluating information relating to an eye associated with the input signal to determine which combination of tap coefficients results in a highest quality eye.
22. The method of claim 21 , wherein the step amount is at least 1.
23. The method of claim 22 , wherein the step amount is at least 2.
24. The method of claim 21 , wherein the step amount is selected by choosing a number of least significant bits of the tap coefficients being applied to each tap that are not to be used in generating the different combinations of tap coefficients.
25. The method of claim 15 , further comprising:
in mean squared error (MSE) circuitry electrically coupled to the equalizer circuitry and to the adaptive control logic, processing at least a second equalizer output signal outputted from the equalizer circuitry and generating an MSE output signal that represents an estimate of the mean squared error of the second equalizer output signal;
providing a digitized version of the MSE output signal to the adaptive control logic; and
in eye monitor circuitry electrically coupled to the equalizer circuitry and to the adaptive control logic, processing said at least a first equalizer output signal and generating one or more eye monitor output signals representing one or more eye characteristics, and wherein the information that is evaluated by the adaptive control logic relating to the eye includes said one or more eye characteristics represented by said one or more eye monitor output signals and the estimate of the mean squared error represented by the MSE output signal.
26. The method of claim 25 , wherein the information that is evaluated by the adaptive control logic relating to the eye further includes the F_LOCK signal output by the CDR circuitry.