Methods and apparatus for tuning lookup table circuits in a transmitter of optical and electrical communication systems
Embodiments are disclosed for generating a lookup table value for calibrating a lookup table circuit in an optical transmitter. The example method includes generating a calibration signal. The calibration signal encodes a plurality of bits in a number of amplitude levels. The example method further includes transmitting the calibration signal to a module under calibration and transmitting a symbol sequence of defined length to a reference module. The reference module compares the symbol sequence with a distorted signal received from the module under calibration to generate a set of condition count statistics. The example method further includes receiving the set of condition count statistics from the receiver in the reference module and calculating a lookup table value based on the set of condition count statistics. The example method further includes transmitting the lookup table value to a transmitter associated with the module under calibration.
1. A method for generating a lookup table value for calibrating a lookup table circuit in an optical transmitter, comprising:
generating a calibration signal, wherein the calibration signal encodes a plurality of bits in a number of amplitude levels;
transmitting the calibration signal to a module under calibration;
transmitting a symbol sequence with a defined length to a reference module, wherein the reference module is configured to compare the symbol sequence with the defined length with a distorted signal received from the module under calibration to generate a set of condition count statistics;
receiving the set of condition count statistics from a receiver in the reference module;
calculating a lookup table value based on the set of condition count statistics; and
transmitting the lookup table value to a transmitter associated with the module under calibration.
2. The method of claim 1 , wherein the calibration signal is a pulse amplitude modulation signal encoding a plurality of symbols in four amplitude levels, and wherein the calibration signal is encoded in a plurality of triplets.
3. The method of claim 2 , wherein the distorted signal comprises three eyes, and wherein the reference module comprises:
a histogram slicer configured to slice the distorted signal;
three slicer modules configured to slice the distorted signal to generate three distorted symbol values;
a detection module comprising:
three symbol comparators configured to compare three transmitted symbol values from the symbol sequence with the three distorted symbol values; and
a first AND gate configured to receive three outputs from the three symbol comparators, wherein an output of the first AND gate is a condition flag;
a first counter configured to count the condition flag over a period of time to generate a set of condition counts;
a second AND gate configured to receive the condition flag and an output of the histogram slicer; and
a second counter configured to count an output of the second AND gate.
4. The method of claim 2 , wherein the distorted signal comprises three eyes, and wherein the reference module comprises:
a histogram slicer configured to slice the distorted signal;
three slicer modules configured to slice the distorted signal to generate three distorted symbol values;
one or more detection modules, wherein each detection module comprises:
three symbol comparators configured to compare three transmitted symbol values from the symbol sequence with the three distorted symbol values; and
a first AND gate configured to receive three outputs from the three symbol comparators;
an OR gate configured to receive an output of each of the first AND gates of the one or more detection modules, wherein an output of the OR gate is a condition flag;
a first counter configured to count the condition flag over a period of time to generate a set of condition counts;
a second AND gate configured to receive the condition flag and an output of the histogram slicer; and
a second counter configured to count an output of the second AND gate.
5. The method of claim 1 , wherein the distorted signal is generated by the module under calibration based on the calibration signal.
6. The method of claim 4 , wherein the period of time is one of: a predefined period of time or a period of time determined based on a pre-defined statistics condition for a set of condition flags.
7. The method of claim 1 , wherein the method comprises generating sixty four lookup table values.
8. An apparatus for generating a lookup table value for calibrating a lookup table circuit in an optical transmitter, wherein the apparatus is configured to:
generate a calibration signal, wherein the calibration signal encodes a plurality of bits in a number of amplitude levels;
transmit the calibration signal to a module under calibration;
transmit a symbol sequence with a defined length to a reference module, wherein the reference module is configured to compare the symbol sequence with the defined length with a distorted signal received from the module under calibration to generate a set of condition count statistics;
receive the set of condition count statistics from a receiver in the reference module;
calculate a lookup table value based on the set of condition count statistics; and
transmit the lookup table value to a transmitter associated with the module under calibration.
9. The apparatus of claim 8 , wherein the calibration signal is a pulse amplitude modulation signal encoding a plurality of symbols in four amplitude levels, and wherein the calibration signal is encoded in a plurality of triplets.
10. The apparatus of claim 9 , wherein the distorted signal comprises three eyes, and wherein the reference module comprises:
a detection module comprising:
a histogram slicer configured to slice the distorted signal;
three slicer modules configured to slice the distorted signal to generate three distorted symbol values;
three symbol comparators configured to compare three transmitted symbol values from the symbol sequence with the three distorted symbol values; and
a first AND gate configured to receive three outputs from the three symbol comparators, wherein an output of the first AND gate is a condition flag;
a first counter configured to count the condition flag over a period of time to generate a set of condition counts;
a second AND gate configured to receive the condition flag and an output of the histogram slicer; and
a second counter configured to count an output of the second AND gate.
11. The apparatus of claim 9 , wherein the distorted signal comprises three eyes, and wherein the reference module comprises:
a histogram slicer configured to slice the distorted signal;
three slicer modules configured to slice the distorted signal to generate three distorted symbol values;
one or more detection modules, wherein each detection module comprises:
three symbol comparators configured to compare three transmitted symbol values from the symbol sequence with the three distorted symbol values; and
a first AND gate configured to receive three outputs from the three symbol comparators;
an OR gate configured to receive an output of each of the first AND gates of the one or more detection modules, wherein an output of the OR gate is a condition flag;
a first counter configured to count the condition flag over a period of time to generate a set of condition counts;
a second AND gate configured to receive the condition flag and an output of the histogram slicer; and
a second counter configured to count an output of the second AND gate.
12. The apparatus of claim 8 , wherein the distorted signal is generated by the module under calibration based on the calibration signal.
13. The apparatus of claim 11 , wherein the period of time is one of: a predefined period of time or a period of time determined based on a pre-defined statistics condition for a set of condition flags.
14. The apparatus of claim 8 , wherein the apparatus is configured to generate sixty four lookup table values.
15. An apparatus for generating condition statistics used for generating a lookup table value for calibrating a lookup table circuit in an optical transmitter comprising:
a histogram slicer configured to slice a distorted signal;
three slicer modules configured to slice the distorted signal to generate three distorted symbol values;
a detection module comprising:
three symbol comparators configured to compare three transmitted symbol values from a symbol triplet with the three distorted symbol values; and
a first AND gate configured to receive three outputs from the three symbol comparators, wherein an output of the first AND gate is a condition flag;
a first counter configured to count the condition flag over a period of time to generate a set of condition counts;
a second AND gate configured to receive the condition flag and an output of the histogram slicer; and
a second counter configured to count an output of the second AND gate.
16. The apparatus of claim 15 , wherein a calibration signal associated with the detection module is a pulse amplitude modulation signal encoding a plurality of symbols in four amplitude levels, and wherein the calibration signal is encoded in a plurality of triplets.
17. The apparatus of claim 16 , wherein the distorted signal comprises three eyes.
18. The apparatus of claim 15 , wherein the period of time is one of: a predefined period of time or a period of time determined based on a pre-defined statistics condition for a set of condition flags.
19. The method of claim 1 , wherein the reference module is integrated with the module under calibration via an optical loop-back.
20. The apparatus of claim 8 , wherein the reference module is integrated with the module under calibration via an optical loop-back.