Transitioning between signal constellations

A receiving method that comprises:

• negotiating a link speed having PAM4 signaling;
• performing adaption of at least one gain or filter coefficient during PAM2 signaling;
• switching to PAM4 detection before receiving PAM4 signaling, said switching to PAM4 detection including using adjusted PAM4 detection values that cause PAM2 symbols to be detected only as outer PAM4 symbols;
• disabling said adaptation before said switching to PAM4 detection;
• detecting PAM4 signaling using at least one statistic of detected PAM4 symbols;
• and
• enabling said adaptation after PAM4 signaling is detected.

A receiving method that comprises:

• negotiating a link speed having PAM4 signaling;
• performing adaption of at least one gain or filter coefficient during PAM2 signaling;
• switching to PAM4 detection before receiving PAM4 signaling;
• disabling said adaptation before said switching to PAM4 detection;
• detecting PAM4 signaling using at least one statistic of detected PAM4 symbols;
• enabling said adaptation after PAM4 signaling is detected;
• and
• reducing a bandwidth of a clock recovery loop before said switching to PAM4 detection.

A receiver that comprises:

• a controller that coordinates with a remote node to negotiate a link speed having PAM4 signaling;
• an equalizer with at least one filter coefficient, the controller performing adaptation of the at least one filter coefficient during PAM2 signaling;
• and
• a decision element that switches from PAM2 detection to PAM4 detection before receiving PAM4 signaling, the decision element initially using adjusted PAM4 detection values that cause PAM2 symbols to be detected only as outer PAM4 symbols,
• the controller monitoring at least one statistic of symbols detected by the decision element to detect when PAM4 signaling is received, and
• the controller disabling said adaptation before said switching to PAM4 detection, and enabling said adaptation after PAM4 signaling is detected.

A method of receiving a data stream, the method comprising:

• negotiating a link speed having PAM4 signaling;
• adapting at least one of gain and filter coefficients during PAM2 signaling;
• monitoring for a change in at least one signal characteristic while performing PAM2 detection, said change indicating reception of PAM4 signaling;
• and
• transitioning to PAM4 detection after detecting said change.

A receiver that comprises:

• a controller that coordinates with a remote node to negotiate a link speed having PAM4 signaling;
• an equalizer with at least one filter coefficient, the controller performing adaptation of the at least one filter coefficient during PAM2 signaling;
• and
• a decision element configured to switch from PAM2 detection to PAM4 detection,
• the controller monitoring for a change in at least one signal characteristic while the decision element is configured for PAM2 detection and configuring the decision element for PAM4 detection after detecting said change, said change indicating reception of PAM4 signaling.