DS160PR410: PCIe Gen 1 to Gen 3 transition issue

In my case i have two boards as a device and host, device redriver  out connected to host redriver through 6 inch cable samtec cable,  will it causing issue? can i connect to redriver back to back to compensate  external channel lose?

also am terminating redriver out with 50R. there wont be any associated circuitry  while testing

Hi Abi,

This setup shouldn't cause an issue in the data of the waveforms shown on your scope. The data pattern sent would be based on the PCIe transmitter.

In regards to termination, as long as you are not terminating both the redriver and the scope with 50Ohms, there wouldn't be a problem there.

Best,

David

Hi David,

Redriver is used as Buffer by terminating RXDET pin with 59K in my application with Index 10. I am attaching input waveform to redriver and corresponding output waveform.  Output is terminated with  50R. Can you give insight to why undershoot and overshoot is dominated at output side. 

Hi Abi,

What EQ setting are you using on the redriver? Have you seen this problem with multiple redriver settings, or just this one in particular?

Best,

David

Hi David,

Equaliser settings are given  below:

Equalisation   index :11

DC gain :0dB

RX_det : Buffer mode

Tried with different index values and changed DC gain to 3.5dB,issue remains same. 

Observing  this behaviour on every boards we have. Find attached PPT where i summarise testing  report.

Bugatti_PCIe_Initial_Transition_Error_Ver_04.pptx

Hi Abi,

Thanks for sending your report over. Could you set your Root Complex to Gen3 compliance mode at Preset 4 and capture/send the screenshots at the same points as you had in the presentation?

Also, could you try reducing the EQ Index on the redriver?

Best,

David