[SI-LIST] Questions concerning DC-block Caps and coaxial optical packages ( ROSA/TOSA)

  • From: Bernard Harris <bharris@xxxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Wed, 18 Jan 2006 10:59:10 +0200

Hi All,
 
I would appreciate recommendations on layout for series DC block capacitors,
so as to minimize the impedance mismatch. The signal is 2.5Gb/s, 100 ohms
differential, with nominal 80ps rise and fall times and is fairly short -
only a few centimetres.  I would prefer to use 0402 size caps.  Do the caps
have to be special RF type or can standard X7R or NPO caps be used?
 
In addition, I would like to use the point where the series caps are
connected for a dual layout option - top layer to one device and bottom
layer to an alternative device. Is this a risky choice ? I've seen it on an
eval board from our device vendor, but I'd like some insight from the
experts.
 
Also does anyone have some guidance on interfacing to coaxial optical
packages, such as ROSA/TOSA/TO45 CAN. Our application requires mounting
parallel to the board, but the packages are through hole, vertical mount. I
suspect that the interfacing to the leads is not straightforward to get a
decent impedance match. I thought that it may be possible to mount on the
edge of the board, with leads soldered above and below. 
 
Thanks,
Bernard Harris 
Lynx Photonic Networks       
                      




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