DP83867E: How to measure the rise time(tr) and fall time(tf)

Sammi Shang

Part Number: DP83867E

Dear all,

From the datasheet the maximum value of tr and tf is 0.75ns, but when measured through GTX_CLK, the time is near 1.78ns. Is this the right pin to measure tr and tf? Could you tell me how to measure tr and tf? Thanks.

Best regards,

Sammi

over 8 years ago

0 Rob Rodrigues over 8 years ago

TI__Mastermind 19780 points

Hi Sammi,

The rise/fall of GTX_CLK should be measured from 20%*VDDIO to 80%*VDDIO. Also, by the RGMII standard, the loading on GTX_CLK should be 5pF.

Best Regards,

0 Sammi Shang over 8 years ago in reply to Rob Rodrigues

TI__Expert 4450 points

Hi Rob,

Thanks for your response. I have not found this 5pF in datasheet, so it was added as Cin?

Best regards,
Sammi

0 Ross Pimentel over 8 years ago in reply to Sammi Shang

TI__Mastermind 23675 points

Hi Sammi,

The 5pF referred to above by Rob is in regards to the actual RGMII specification.
RGMII specified a loading condition of 5pF for the 750ps rise/fall time. If you have higher capacitance, this value will increase.

Kind regards,
Ross

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DP83867E: How to measure the rise time(tr) and fall time(tf)