DS100MB203 / about ac coupling capacitor and setting for GbE

Hi Kato-san,

Please see answers to questions below:

Q1: DC Coupling is not advised, since the DS100MB203 inputs/outputs are designed for CML signaling topology. CML signals require AC coupling.

Q2: The DS100MB203 can support 1.25 Gbps in limiting mode. The configuration you have described are correct to enable that setting in either Pin Mode or SMBus Slave Mode. Make sure to change the mode register bit for all relevant channels in use.

Thanks,

Michael

Michael - san,

Thank you for the reply. I have one more question.

>The DS100MB203 can support 1.25 Gbps in limiting mode.

What does "in limiting mode" mean ? The data sheet doesn't have a description of limiting mode.

Best Regards,

Kato

Hi Kato-san,

Limiting mode means that the signal runs through a buffer that will act to improve the edge rate between input signal transitions in order to distinguish a digital 1 and 0 more clearly. Non-Limiting (or Linear) mode uses a linear buffer to track the input signal more linearly in order to provide a heightened level of transparency. Please see the simplified sketch below as an example to illustrate the difference between the two modes.

The use of non-limiting mode is necessary for protocols that specifically call for link training. In limiting mode, the repeater typically eliminates precursor/postcursor characteristics of the input signal when driving out the newly conditioned signal from the repeater TX (Note: I did not illustrate this in the graphic above). If the repeater operates in limiting mode, it is difficult for the endpoint RX to distinguish between different link training coefficients.

Thanks,

Michael

Hi Michael-san,

Thank you for the detailed explanation.I understood non-limiting and limiting mode. How should we configure limiting mode ?

Best Regards,

kato