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. An integrated circuit, comprising:
an integrated circuit (IC) chip, the IC chip including
receiver circuitry to receive an electrical signal from over a serial link external to the integrated circuit, the receiver circuitry including
a continuous time linear equalizer (CTLE) to equalize the electrical signal and to generate a first equalized signal, the CTLE having at least one adjustable setting, the at least one adjustable setting providing at least one of adjustable gain and adjustable frequency response, and
a decision feedback equalizer (DFE) to receive the first equalized signal and equalize the first equalized signal to generate an output using at least one tap and a respective tap weight for each of the at least one tap; and
logic to automatically determine the at least one adjustable setting and each respective tap weight in dependence on at least one measured performance characteristic affecting transmission over the serial link.
2. The integrated circuit of claim 1 , wherein the logic is to repeatedly and automatically update the at least one adjustable setting and each respective tap weight during run-time of the integrated circuit.
3. The integrated circuit of claim 2 , wherein:
the at least one tap comprises at least five taps; and
the logic is to automatically determine the at least one adjustable setting and the respective tap weight for each tap of the at least five taps.
4. The integrated circuit of claim 1 , wherein:
in a high-performance mode, the logic is to adaptively determine the at least one setting adjustable setting and each respective tap weight; and
in a low-power mode, the logic is to adaptively determine each setting of the at least one adjustable setting, and application of the DFE is disabled.
5. The integrated circuit of claim 1 , wherein:
the electrical signal is a first electrical signal;
the integrated circuit further comprises transmitter circuitry to transmit a second electrical signal externally to the integrated circuit chip over the serial link.
6. The integrated circuit of claim 5 , wherein:
in a high-performance mode, the logic is to configure the transmitter circuitry to use a first transmit amplitude to transmit the second signal; and
in a low-power mode, the logic is to configure the transmitter circuitry to use a second transmit amplitude to transmit the second signal, the second transmit amplitude lower than the first transmit amplitude.
7. The integrated circuit of claim 5 , wherein the integrated circuit further comprises circuitry to deserialize symbols received as part of the first electrical signal and to serialize symbols to be transmitted by the transmitter circuitry as part of the second electrical signal.
8. The integrated circuit of claim 1 , wherein the at least one adjustable setting provides for adjustment of both gain and frequency response.
9. The integrated circuit of claim 1 , wherein:
the receiver circuitry comprises clock recovery circuitry to generate a recovered clock dependent on logic level transitions in the electrical signal;
the integrated circuit further comprises circuitry to generate an equalization clock dependent on the recovered clock, the equalization clock having an adjustable phase offset relative to the recovered clock; and
the output of the DFE is timed according to the equalization clock so as to align the output of the DFE with logic level transitions carried by the electrical signal.
10. The integrated circuit of claim 1 , wherein the logic is to perform a signal quality measurement and the measured performance characteristic is dependent on the signal quality measurement.
11. The integrated circuit of claim 10 , wherein the signal quality measurement is a function of bit error rate (BER), the logic is to repeatedly and automatically measure BER for alternative digital values of the at least one adjustable setting, and the logic is to configure the CTLE to use a particular digital value for each setting of the at least one adjustable setting in dependence on the BERs measured in association with the alternative digital values.
12. The integrated circuit of claim 10 , wherein the signal quality measurement is a function of bit error rate (BER), the logic is to repeatedly and automatically measure BER for alternative digital values of at least one tap weight, and the logic is to configure the DFE to use a particular digital value for the at least one tap weight in dependence on the BERs measured in association with the alternative digital values.
13. An integrated circuit, comprising:
an integrated circuit (IC) chip, the IC chip including
at least one transceiver to receive a first electrical signal from over a respective serial link external to the integrated circuit and to transmit a second electrical signal over the respective serial link external to the integrated circuit, each transceiver including
a continuous time linear equalizer (CTLE) to equalize the first electrical signal and to generate a first equalized signal, the CTLE having at least one adjustable setting, the at least one adjustable setting providing at least one of adjustable gain and adjustable frequency response,
circuitry to sample the first electrical signal to produce data samples;
a decision feedback equalizer (DFE) to receive the first equalized signal and to equalize the first equalized signal in dependence on previously-received data samples using at least five receive taps each representing a respective data sample latency and a respective tap weight for each receive tap, and
transmitter circuitry including at least three transmit taps to collectively drive each current symbol of the second electrical signal onto the serial link, the at least three transmit tap including a main tap and at least one precursor tap; and
logic to automatically determine the at least one adjustable setting and each respective tap weight for each of the at least five receive taps in dependence on at least one measured performance characteristic affecting transmission over the serial link.
14. The integrated circuit of claim 13 , wherein the logic is adapted to repeatedly and automatically update the at least one adjustable setting and the tap weight for each of the at least five receive taps during run-time of the integrated circuit.
15. The integrated circuit of claim 13 , wherein:
in a high-performance mode, the logic is to adaptively determine the at least one setting adjustable setting and the tap weight of each of the at least five receive taps; and
in a low-power mode, the logic is to adaptively determine each setting of the at least one adjustable setting, and application of the DFE is disabled.
16. The integrated circuit of claim 13 , wherein the transmitter circuitry comprises at least four taps including at least two precursor taps and at least one postcursor tap.
17. The integrated circuit of claim 13 , wherein:
in a high-performance mode, the logic is to configure the transmitter circuitry to use a first transmit amplitude to transmit the second electrical signal; and
in a low-power mode, the logic is to configure the transmitter circuitry to use a second transmit amplitude to transmit the second electrical signal, the second transmit amplitude lower than the first transmit amplitude.
18. The integrated circuit of claim 13 , wherein the integrated circuit further comprises circuitry to deserialize symbols received as part of the first electrical signal and to serialize symbols to be transmitted by the transmitter circuitry as part of the second electrical signal.
19. The integrated circuit of claim 13 , wherein:
the receiver circuitry comprises clock recovery circuitry to generate a recovered clock dependent on logic level transitions in the first electrical signal;
the integrated circuit further comprises circuitry to generate an equalization clock dependent on the recovered clock, the equalization clock having an adjustable phase offset relative to the recovered clock;
an equalization output of the DFE is timed according to the equalization clock so as to align an output of the DFE with logic level transitions carried by the first electrical signal.
20. The integrated circuit of claim 13 , wherein:
the logic is to perform a signal quality measurement and the measured performance characteristic is dependent on the signal quality measurement;
the signal quality measurement is a function of bit error rate (BER);
the logic is to repeatedly and automatically measure BER for alternative digital values of the at least one adjustable setting and for alternative digital values of the tap weights of the at least five receive taps, and the logic is to configure the CTLE to use a particular digital value for each setting of the at least one adjustable setting and for each tap weight of the at least five receive taps in dependence on the BERs measured in association with the alternative digital values.
21. A method of operating an integrated circuit chip, comprising:
receiving an electrical signal from over a serial link external to the integrated circuit chip;
equalizing the electrical signal using a continuous time linear equalizer (CTLE) having at least one adjustable setting to generate a first equalized signal, wherein the at least one adjustable setting providing at least one of adjustable gain and adjustable frequency response;
equalizing the first equalized signal using a decision feedback equalizer (DFE), the DFE having at least one tap and a respective tap weight for each tap, each tap of the at least one tap to apply equalization dependent on a previously-received digital value of respective latency relative to a current symbol; and
automatically determining in situ in a signaling system the at least one adjustable setting and each respective tap weight, using logic within the integrated circuit, in dependence on at least one measured performance characteristic affecting transmission over the serial link.
22. The method of claim 21 , wherein automatically determining includes configuring the logic to repeatedly and automatically update the at least one adjustable setting and each respective tap weight during run time of the integrated circuit chip.