AD8137: Terminate differential lines

Document created by analog-archivist Employee on Feb 23, 2016
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I am developing measuring system. I have to lead signal for quite long distance
(400 mm) from OPAMs to AD. So I have decided to use differential lines. Lines
are driven by AD8137 and conversion is done by ADuC7027.  How to correctly
terminate differential lines? - How to route PCB in best way? Distance of lines
(same or opposite layers) and shielding.

 

The AD8137 had a BW of <60 MHz.
The wavelength of a 60 MHz signal in the microstrip line formed by a PC track
over ground plane is a little less than 4000 mm. 400 mm is therefore a little
more than 10% of a wavelength.

Your signal bandwidth will be much less than this since the Nyquist limit for
an ADuC7027 is <500 kHz.

I think it is very unlikely that you will need to terminate your lines.

You may, however, need to put a small resistor in each output to minimise
ringing due to the line capacitance and the ADuC7027 input capacitance.

I would suggest that your lines are parallel and on the same side of the board
- and run over unbroken ground (or power) plane.

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