Information handling system half unit interval equalization
An information handling system communicates information across a physical link with high and low signal values sent at a unit interval. Feed forward equalization improves signal transfer with pre-emphasis of low-to-high signals and de-emphasis of high-to-low signals lasting for a fraction of the unit interval, such as one-half or one-quarter of the unit interval. Fractional unit interval pre-emphasis and de-emphasis reduce inter symbol interference to improve frequency domain eye structure at the physical link receiver.
1. An information handling system comprising:
a processor operable to execute instructions;
a memory operable to store the instructions and information processed by the instructions;
a communication link interfaced with the processor and memory, the communication link having a transmitter that transmits the information across a physical medium to a receiver;
a clock interfaced with the communication link and referenced by the transmitter to define a unit interval, the information sent as high and low bits held for the unit interval; and
a feed forward equalization module interfaced with the communication link, the feed forward equalization module applying pre-emphasis at a low-bit-to-high-bit transition, the pre-emphasis applied for a fractional portion of the unit interval;
wherein:
the feed forward equalization module further applies de-emphasis at a high-to-low-bit transition, the de-emphasis applied for the fractional portion of the unit interval; and
the fractional portion comprises one-half unit interval.
2. An information handling system comprising:
a processor operable to execute instructions;
a memory operable to store the instructions and information processed by the instructions;
a communication link interfaced with the processor and memory, the communication link having a transmitter that transmits the information across a physical medium to a receiver;
a clock interfaced with the communication link and referenced by the transmitter to define a unit interval, the information sent as high and low bits held for the unit interval; and
a feed forward equalization module interfaced with the communication link, the feed forward equalization module applying pre-emphasis at a low-bit-to-high-bit transition, the pre-emphasis applied for a fractional portion of the unit interval;
wherein:
the feed forward equalization module further applies de-emphasis at a high-to-low-bit transition, the de-emphasis applied for the fractional portion of the unit interval; and
the fractional portion comprises one-quarter unit interval.
3. An information handling system comprising:
a processor operable to execute instructions;
a memory operable to store the instructions and information processed by the instructions;
a communication link interfaced with the processor and memory, the communication link having a transmitter that transmits the information across a physical medium to a receiver;
a clock interfaced with the communication link and referenced by the transmitter to define a unit interval, the information sent as high and low bits held for the unit interval; and
a feed forward equalization module interfaced with the communication link, the feed forward equalization module applying pre-emphasis at a low-bit-to-high-bit transition, the pre-emphasis applied for a fractional portion of the unit interval; and
an eye utility interfaced with the communication link and operable to evaluate an eye opening at the communication link, the transmitter adjusting the fractional portion of the unit interval to increase the eye opening.
4. An information handling system comprising:
a processor operable to execute instructions;
a memory operable to store the instructions and information processed by the instructions;
a communication link interfaced with the processor and memory, the communication link having a transmitter that transmits the information across a physical medium to a receiver;
a clock interfaced with the communication link and referenced by the transmitter to define a unit interval, the information sent as high and low bits held for the unit interval; and
a feed forward equalization module interfaced with the communication link, the feed forward equalization module applying pre-emphasis at a low-bit-to-high-bit transition, the pre-emphasis applied for a fractional portion of the unit interval;
wherein the feed forward equalization module further adjusts the fractional portion of the unit interval to reduce bit error associated with information sent across the communication link.
5. A method for communicating information across a physical link, the method comprising:
sending the information from a transmitter as bits across the physical link, each bit having a high or low value held for a unit interval;
receiving the bits at a receiver interfaced with the physical link, the receiver determining the information from the high and low bit values; and
pre-emphasizing at least some of the bits associated with a transition from the low to the high value, the pre-emphasizing applied for a fraction of the unit interval not greater than one-half the unit interval.
6. The method of claim 5 further comprising:
de-emphasizing at least some of the bits associated with a transition from the high to the low value, the de-emphasizing applied for a fraction of the unit interval not greater than one-half the unit interval.
7. The method of claim 6 further comprising:
applying the pre-emphasizing and the de-emphasizing for the same fraction of the unit interval.
8. The method of claim 6 further comprising:
applying the pre-emphasizing and de-emphasizing for different fractions of the unit interval.
9. The method of claim 5 wherein the fraction of the unit interval is one-half the unit interval.
10. The method of claim 5 wherein the fraction of the unit interval is one-quarter the unit interval.
11. The method of claim 5 wherein the physical link comprises a PCIe communication link.
12. The method of claim 5 further comprising:
monitoring an eye opening associated with a signal communicated across the physical link; and
adjusting the fraction of the unit interval to increase the eye opening height provided through the monitoring.
13. A system for communicating information across a physical link, the system comprising:
a transmitter operable to communicate information as high or low values across a physical link, each bit of information held as a high or low signal for a unit interval; and
a feed forward equalization module interfaced with the transmitter and operable to apply pre-emphasis to at least some bits of information at a transition from the low to high signal, the pre-emphasis applied for one-half of a unit interval.
14. The system of claim 13 wherein the pre-emphasis is substantially twenty percent of the high value.
15. The system of claim 13 wherein the signal ramps downward in a graduated manner from the pre-emphasis value to the high value at the one-half unit interval through the unit interval.
16. The system of claim 15 wherein the feed forward equalization module is further operable to apply a de-emphasis to at least some bits of information at a transition from the high to the low signal, the de-emphasis applied for one-half of a unit interval.