High speed signaling system with adaptive transmit pre-emphasis
A high-speed signaling system with adaptive transmit pre-emphasis. A transmit circuit has a plurality of output drivers to output a first signal onto a signal path. A receive circuit is coupled to receive the first signal via the signal path and configured to generate an indication of whether the first signal exceeds a threshold level. A first threshold control circuit is coupled to receive the indication from the receive circuit and configured to adjust the threshold level according to whether the first signal exceeds the threshold level. A drive strength control circuit is coupled to receive the indication from the receive circuit and configured to adjust a drive strength of at least one output driver of the plurality of output drivers according to whether the first signal exceeds the threshold level.
1. An apparatus, comprising:
a receiver to receive a digital sequence from a set of drivers over a serial link connecting the receiver to a transmitting device, the digital sequence equalized by a transmit equalizer in association with a plurality of taps; and
tap adjustment circuitry to generate feedback for updating a tap weight associated with at least one of the plurality of taps of the transmit equalizer, the feedback representing an adjustment for at least one of the plurality of taps for use in transmitting across the serial link connecting the receiver to the transmitting device, the feedback configured to ensure that the aggregate magnitudes of the tap weights associated with the plurality of taps of the transmit equalizer do not exceed a constraint; and
a transmitter to transmit the feedback to the set of drivers of the transmitting device.
2. The apparatus according to claim 1 , wherein:
the feedback generated by the tap adjustment circuitry represents an increment for at least one of the plurality of taps.
3. The apparatus according to claim 2 , wherein:
the feedback generated by the tap adjustment circuitry represents a positive increment up for at least one of the plurality of taps.
4. The apparatus according to claim 2 , wherein:
the feedback generated by the tap adjustment circuitry represents a negative increment up for at least one of the plurality of taps.
5. The apparatus according to claim 1 , wherein:
the feedback comprises an indicator of a predefined set of tap values.
6. The apparatus according to claim 5 , wherein:
the indicator comprises a channel response.
7. A method of operation within a signaling system, the method comprising:
receiving a digital sequence with a receiver over a serial link connecting the receiver to a transmit equalizer, the transmit equalizer having a plurality of taps;
transmitting, to the transmit equalizer, feedback representing an adjustment for at least one of the plurality of taps, the feedback configured to ensure that the aggregate magnitudes of the tap weights associated with the plurality of taps of the transmit equalizer do not exceed a constraint; and
wherein a tap weight associated with the at least one of the plurality of taps is updated responsive to the feedback.
8. The method according to claim 7 , wherein:
transmitting the feedback to the transmit equalizer comprises transmitting feedback representing an increment for at least one of the plurality of taps.
9. The method according to claim 8 , wherein:
transmitting the feedback to the transmit equalizer comprises transmitting feedback representing a positive increment up for at least one of the plurality of taps.
10. The method according to claim 8 , wherein:
transmitting the feedback to the transmit equalizer comprises transmitting feedback representing a negative increment up for at least one of the plurality of taps.
11. The method according to claim 7 , wherein:
the feedback comprises an indicator of a predefined set of tap values.
12. The method according to claim 11 , wherein:
the indicator comprises a channel response.
13. An integrated circuit (IC) chip, comprising:
a receiver to receive a digital sequence over a serial link connecting the receiver to a transmit equalizer, the transmit equalizer having at least one tap; and
tap adjustment circuitry to generate feedback, the feedback representing an adjustment for the at least one tap and configured to ensure that the aggregate magnitudes of the tap weights associated with the plurality of taps of the transmit equalizer do not exceed a constraint; and
a transmitter to transmit the feedback to the transmit equalizer.
14. The IC chip according to claim 13 , wherein:
the feedback generated by the tap adjustment circuitry represents an increment for at least one of the plurality of taps.
15. The apparatus according to claim 14 , wherein:
the feedback generated by the tap adjustment circuitry represents a positive increment up for at least one of the plurality of taps.
16. The apparatus according to claim 14 , wherein:
the feedback generated by the tap adjustment circuitry represents a negative increment up for at least one of the plurality of taps.
17. The apparatus according to claim 13 , wherein:
the feedback comprises an indicator of a predefined set of tap values.