Paragon-neo: Why are only certain PAM4 transceivers qualified for use in the instrument?

To guarantee integrity of timing measurements, the characteristics of the PAM4 transceivers inserted into the Paragon-neo must be known, of acceptable performance, and correctly configured with their delays compensated for by Paragon-neo.

A transceiver that links up and passes data reliably is acceptable for data transfer but may not have good enough performance characteristics for use in making accurate timing measurements.

A transceiver that links up, has good enough performance characteristics for making use in timing measurements but is not qualified by Calnex will not be recognised by Paragon-neo and therefore may have incorrect timing compensations applied to it.

Using non-Calnex qualified transceivers means that timing test results may be incorrect

Generated and/or measured values could be wrong with no indication that this is the case. Do not rely on timing test results when using non-Calnex qualified PAM4 transceivers in the instrument.

Not all PAM4 transceivers have the required performance characteristics to be used in Paragon-neo to perform within-specification timing tests

Some transceivers have excessive timing variance (see below). This makes them unsuitable for generating and measuring accurate timing signals and checking conformance to standards. Transceivers qualified by Calnex are guaranteed to meet the required performance characteristics.

A link-up using an unqualified transceiver does not mean that the timing tests performed using them are correct

As well as the configuration parameters that result in a link-up, Paragon-neo also applies latency compensation to allow generation and measurement of timing signals to be within the specified accuracy. Latency compensation values are only known for transceivers that have been qualified by Calnex.

Non-Calnex approved transceivers can be used at the users own risk

Calnex allow customers to use non-Calnex-qualified transceivers using the Transceiver Configuration and Signal Conditioning functions of Paragon-neo. The on-instrument documentation in the Help screen provides comprehensive guidance regarding this.

What characteristics are evaluated to qualify PAM4 transceivers?

Timing Performance

The timing performance characteristics that Calnex test and compensate for are:

• Absolute Rx/Tx latency through the module: These delays will appear in test results if not compensated for. Paragon-Neo applies the correct compensation for detected qualified transceivers.

• Transceiver absolute Rx/Tx asymmetry. This asymmetry will appear in test results if not compensated for. Paragon-Neo applies the correct compensation for detected qualified transceivers.

• Run-to-run latency variation and changes in Rx/Tx asymmetry through the module, a very low variation between runs is required as any variation adds error to the measurement. Calnex characterises and qualifies modules based on this factor.

Signal Conditioning

Empirical testing is performed at Calnex and the settings are tuned to values that give a reliable link, Paragon-neo applies the optimal settings for qualified transceivers meaning the link should always be reliable. With other optics there could be link stability and integrity issues.