High-speed signaling systems with adaptable pre-emphasis and equalization
A signaling system includes a pre-emphasizing transmitter and an equalizing receiver coupled to one another via a high-speed signal path. The receiver measures the quality of data conveyed from the transmitter. A controller uses this information and other information to adaptively establish appropriate transmit pre-emphasis and receive equalization settings, e.g. to select the lowest power setting for which the signaling system provides some minimum communication bandwidth without exceeding a desired bit-error rate.
1. A method of operation for a first integrated circuit (IC), comprising:
equalizing first data to be transmitted to a second integrated circuit, the equalizing first data carried out by a transmitter having a transmit equalizer; and
equalizing second data to be received from the second integrated circuit, the equalizing second data carried out by a receiver having a receive equalizer;
wherein for a first mode,
mitigating intersymbol interference (ISI) using the transmit equalizer and the receive equalizer, the ISI arising from respective, different symbol latencies relative to a main bit of the first data and a main bit of the second data, respectively, and
wherein for a second mode,
configuring the receive equalizer to not address a specific symbol latency relative to the main bit of the second data that is addressed by the receive equalizer in the first mode, and
configuring the transmit equalizer to address ISI arising from a symbol of latency relative to the main bit of the first data which matches the specific symbol latency.
2. The method of claim 1 , further comprising:
in the first mode, equalizing ISI corresponding to a precursor to the main bit of the first data with the transmit equalizer; and
in the second mode, not equalizing the ISI corresponding to the precursor to the main bit of the first data with the transmit equalizer.
3. The method of claim 2 , further comprising:
configuring a tap of the transmit equalizer to compensate for precursor interference in the first mode, and
configuring the tap of the transmit equalizer to compensate for the post-cursor interference in the second mode.
4. The method of claim 3 , wherein the receive equalizer includes a partial response decision feedback equalizer (PrDFE), and wherein the method further comprises:
configuring the PrDFE to compensate for first post-cursor ISI in the first mode;
wherein the PrDFE is not configured to compensate for first post-cursor ISI in the second mode; and
configuring the tap of the transmit equalizer to compensate for the first post-cursor ISI in the second mode.
5. The method of claim 1 , wherein the transmitter is operable to receive parallel data, and wherein the method further comprises:
converting the parallel data into a sequence of bits; and
consecutively transmitting the sequence of bits with the transmitter to the second integrated circuit as a serial, differential output signal.
6. The method of claim 1 , wherein the transmitter is operable to receive ten-bit parallel data, and wherein the method further comprises:
converting the ten-bit parallel data into a sequence of bits; and
consecutively transmitting the sequence of bits with the transmitter to the second integrated circuit as a serial, differential output signal.
7. The method of claim 1 , further comprising:
equalizing the second data with a linear equalizer to produce an output signal;
receiving the output signal with the receiver; and
equalizing the output signal with the receive equalizer.
8. A method of operation for a first integrated circuit (IC), comprising:
equalizing first data to be transmitted to a second integrated circuit with a transmitter having a transmit equalizer with at least one tap; and
equalizing second data to be received from the second integrated circuit with a receiver having a receive equalizer with at least one tap;
operating the first IC in at least two different equalization modes, wherein
for a first mode,
mitigating intersymbol interference (ISI) arising from respective, different symbol latencies relative to a main bit of the first data and a main bit of the second data, respectively, with at least one tap of the transmit equalizer and the at least one tap of the receive equalizer; and
for a second mode,
disabling a tap of the at least one tap of the receive equalizer such that it is not operable to mitigate ISI, and
mitigating ISI arising from a symbol latency mitigated by the receive equalizer in the first mode, with a tap of the transmit equalizer.
9. The method of claim 8 , wherein disabling the tap in the second mode includes disabling a partial-response tap.
10. The method of claim 8 , where the receive equalizer includes a partial response decision feedback equalizer having plural sample paths, and wherein the method further comprises:
disabling at least one of the plural sample paths in the second mode.
11. The method of claim 8 , wherein the receive equalizer includes a decision feedback equalizer and wherein the method further comprises:
disabling a tap of the decision feedback equalizer in the second mode.
12. The method of claim 11 , wherein disabling the tap in the second mode corresponds to disabling a tap associated with a first post cursor, the first post cursor representing a symbol received immediately prior to the main bit of the second data.
13. The method of claim 8 , further comprising:
equalizing the second data with a linear equalizer to produce an output signal, where the receive equalizer is operable to receive and equalize the output signal;
receiving the output signal with the receiver; and
equalizing the output signal with the receive equalizer.
14. The method of claim 13 , further comprising:
enabling the linear equalizer in the first mode; and
disabling the linear equalizer in one of the second mode or a third mode.
15. The first integrated circuit of claim 8 , further comprising:
receiving from the second integrated circuit a measure of signal quality; and
automatically setting the first or the second mode as a register setting in response to the measure of signal quality.
16. The method of claim 8 , further comprising:
configuring the at least one tap of the transmit equalizer in accordance with the first and second modes, in response to a register setting.
17. A method of operation for a first integrated circuit (IC), comprising:
equalizing first data to be transmitted by a transmitter to a second integrated circuit; and
equalizing second data to be received from the second integrated circuit by a receiver having a decision-feedback equalizer with at least one tap;
operating the first IC in at least two different equalization modes, wherein
for a first operational mode,
equalizing the second data with each tap of at least one tap of the decision-feedback equalizer, and
for a second operational mode,
disabling one tap of the at least one tap of the decision-feedback equalizer, such that irrespective of instantaneous channel characteristics, it is not operable to equalize the second data; and
configuring the circuitry in the transmitter to equalize the first data to mitigate interference corresponding in post-cursor latency to intersymbol interference mitigated by the one tap in the first mode.
18. The method of claim 17 , further comprising:
equalizing the second data with a linear equalizer to produce an output signal, where the decision-feedback equalizer is operable to receive and equalize the output signal;
receiving the output signal with the receiver; and
equalizing the output signal with the decision-feedback equalizer.
19. The method of claim 17 , further comprising:
enabling the linear equalizer in the first mode; and
disabling the linear equalizer in one of the second mode or a third mode.
20. The method of claim 17 , further comprising:
receiving from the second integrated circuit a measure of signal quality; and
automatically setting the first or the second mode as a register setting in response to the measure of signal quality.