[SI-LIST] testing LVPECL signal with 50ohm system
- From: "Dan.Zhu" <dan.zhu@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 2 Sep 2003 17:25:56 -0400 (EDT)
Hi,
I have a question on how to test LVPECL signal with 50ohm system like digital
oscilloscope or Spectrum Analyzer (not
probeing, just SMA connector on board ->cable-> scope).
Background -
For the LVPECL(VCC=3.3v & VEE=0v) output, normally a 50ohm termination resistor
is used between LVPECL output pin and
a voltage source of Vtt(=VCC-2v) to get a common-mode PECL output level of
VCC-1.3v. When testing a standalone PECL
device, people can lower the supply/gnd of pecl device by -2v so VCC'=1.3v,
VEE'=-2v -> Vtt'=0v, then a digital
oscilloscope with 50ohm input resistor(to GND) can be used to replace the 50ohm
termination resistor and test the
signal directly.
Question -
My question is that if due to some reason, the supply of PECL device can't be
changed(for example, the pecl device is
integrated on a mixed-signal IC and change of supply of PECL device is not
allowed), there is any other way we can
still test the PECL output signal directly(not probeing, just SMA connector on
board ->cable-> scope)?
Thanks for your suggestion
Best Regards,
Dan Zhu
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