Isometric wiring for DS100MB203

Hi Y.I.,

I am not sure what you mean by "isometric wiring."

Are you asking about routing recommendations or a general block diagram of how the DS100MB203 is used in a system application? Is there something specific you are looking for that is not in the application information section of the datasheet?

Thanks,

Michael

Hi y.i.,

There are some guidelines for routing high-speed WQFN packages in the Layout Guidelines section of the DS100MB203 datasheet. In general, when routing traces to and from the device, the most critical factor is maintaining the 100-ohm differential impedance required to match impedance and avoid reflections. The differential impedance is affected by trace width, trace thickness, intra-pair separation distance, and height of dielectric in between the trace and the nearest reference plane. 

I have a feeling you are asking about tolerances for the routing length. Regarding the routing length, you do not need to match the positive and negative polarity routing lengths exactly, as this would make the layout design nearly impossible. Typically the tolerance is determined by the operating data rate and the corresponding edge rate. for the DS100MB203 operating at 10 Gbps, the edge rate is around 40 ps. In order to assure that intra-pair skew does not introduce significant common mode noise, a rule of thumb you can apply is to ensure that the routing length tolerance maintains that the intra-pair skew is no more than 10% of the edge rate.

In a simple calculation, let's assume propagation delay for microstrip is 150 ps/in (This is also 150 ps per 1000 mils). To assure that we maintain at most 40 x 0.1 = 4 ps of intra-pair skew, we determine that the tolerance in routing length to be (4 x 1000) / 150 = 26.7 mils. Considering a plus-minus tolerance, you can have an acceptable intra-pair routing tolerance of +/-10 mils.

For more routing resource, please also take a look at the Design and Layout Guidelines section of the LVDS Owner's Manual.

Thanks,

Michael