[SI-LIST] Attaching coax cable to board
- From: "mittalr@xxxxxxxxxx" <mittalr@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 23 May 2002 17:31:32 -0400 (EDT)
Suppose you attach 50ohm cables from a synthesiser to you board through SMA .
Its 10G differential setup. The board contains a microstrip/coplanar waveguide
connecting the SMA to your IC which has 50ohm termination connected to Vcc
It seems to me you have field lines in the coax between the center conductor
and the sheathing. This then somehow has to transfer to fields between the
differential microstrip/coplanar wg on your board. The field lines between the
surface line and the ground provides the common mode impedence whereas the
field lines between the conductors provides the differential mode Z.
Now my question is: should you connect your SMA ground to the IC ground or
should you keep it isolated. If you keep it isolated, should you connect
decoupling caps between your IC ground (ie the board ground) and the SMA ground.
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