Hie,
Please check my replies to your questions above:
- To be able to observe PAM4 signals you will need to use a Real Time Scope (RTS) or Sampling Oscilloscope that support PAM4. The Rx architecture is different between NRZ and PAM4, hence you should be using a DCA that supports PAM4. As for whether external clock is required; RTS don't require external clock but some sampling scopes require it. However, the newer sampling scopes has a build in clock recovery module that don't require external clock trigger (typically sourced from the reference clock to Tx PLL or recovered clock from CDR). Please refer to your scope's applications notes on measuring PAM4 signals to understand if external clock source is needed. Also, due to non-linearity of the PAM4 eye's, you will need some level of soft equalization or FEC (typically soft feature in the scope) to be enabled to observe a clean eye. Please check this in the scope application notes on what to enable to observe the eye.
Regards,
Nathan
Occasional Contributor
