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This term is mentioned in the Micron Application Note: Hardware Tips for Point-to-Point System Design on page 10 (...For signals with lead-in termination...), however I've been struggling to find out exactly what lead-in termination means.

It's quite a difficult google search term: I finally found a reference to "Lead-in vs loaded routing" in this, one of the last pages.

Searching for "Lead in vs loaded routing" gives 3 results, one of which is the above, the other two are not particularly helpful.

Can anyone explain what lead-in termination is, or point to me to a book, or a synonym that's more widely used?

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    \$\begingroup\$ It now gives four results. It now includes this post! \$\endgroup\$
    – Connor Wolf
    Commented Feb 9, 2013 at 6:51
  • \$\begingroup\$ I'd guess from the mentor paper in the above search DDR memory so easy, a caveman could do - RTP Designers Council that is involved varying your trace impedance based on whether you're routing a DMM module or the backplane: The slide mentioning lead-in says: Neck down traces on DIMM modules to compensate for capacitive loads — Increases impedance on traces — 55 ohms on PCB and 60 ohms on module \$\endgroup\$
    – Connor Wolf
    Commented Feb 9, 2013 at 6:56

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For Un-buffered DIMMs (UDIMM) the CLK, CTRL and ADD/CMD topologies are divided into two segments The segments between the connector and the first DRAM are termed as the lead-in section while the segments between the first DRAM and the last DRAM to the termination are termed as the loaded section. In order to reduce the impedance mismatch seen at the first DRAM, the lead-in section is a lower impedance trace (typically 40 ohms) while the loaded section is 60 ohms. For Registered DIMMs (RDIMM) the post register nets are typically routed with same trace impedance.

From Micron material

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