I am interesting about high speed multiplexers. Now I have a question about Rds_on.
When turn on the FET, there are Rds_on and parasitic capacitance on the signal trace. It will be a RC delay circuit.
There are a description from E2E --> We use a rough formula “Bandwidth = (3/2)xDataRate” which will provide sufficient margin. Does it have a limitation about PCB trace?
I have another question. There are three different Ron characteristics – Ron, Ron(p), ∆Ron. How this three characteristics affect our design?
In reply to Fan.Wang:
In reply to Ben Kuo:
How do you choose device base on the on state resistance spec in real case performance, I can’t prevent this issue even when I know how this trace long I have.
The only thing I can make sure is “longer trace you need lower on resistor”. Because it have to consider about capability of receiver.
Do we have a roughly equation can figure out what value of on resistance performance I need in my switch? What is the worst case Ron of a switch I can have in my system.
In reply to Adam Torma:
Hi Adam, The data rate that a channel can carry is not only determined by Ron but also determined by the communication protocal. To be more specific, the data rate can be determined by the waveform, signal bandwidth, data pattern and the channel quality. Ron is just one factor of channel quality. For example, ethernet CAT-5 cable can carry 10Mbps, 100Mpbs and up to 1Gbps. The physcial Ron, in this case, does not change, but the data rate increases 100 times from 10Mpbs to 1Gbps. If you can share an example with me, we can discuss how to choose the Ron which best fits to your design.
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