AD9444: Exceeding the trace length

Document created by analog-archivist Employee on Feb 23, 2016
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On the date sheet designers are encouraged to use of modality LVDS. But it is
recommended to keep the trace length less than 1 inch to 2 inches.
I would have to use trace length of approximately 5 inches. E' possible to
arrive to this distance?
Which problems we can have?

 

The following extract from our Converter Seminar notes explains the reason for
keeping the trace length to less than 2 inches:

LVDS outputs for high-performance ADCs should be treated differently than
standard LVDS outputs used in digital logic. While standard LVDS can drive 1 to
10 meters in high-speed digital applications (dependent on data rate), it is
not recommended to let a high-performance ADC drive that distance. It is
recommended to keep the output trace lengths short (< 2 in.), minimizing the
opportunity for any noise coupling onto the outputs from the adjacent
circuitry, which may get back to the analog inputs. The differential output
traces should be routed close together, maximizing common-mode rejection, with
the 100 Ω termination resistor close to the receiver. Users should pay
attention to PCB trace lengths to minimize any delay skew.

The full text of this section is available in chapter 9 and can be downloaded
from the following webpage:
http://www.analog.com/library/analogDialogue/archives/39-06/data_conversion_hand
book.html

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