From: Sreejith Varma (firstname.lastname@example.org)
Date: Tue Apr 17 2001 - 11:07:50 PDT
i am doing a differentail pair simulation using Cadence allegro
tool. as it is diff. pair i am doing the post route sim on the
it is a 2.5ghz signal (a clock). it is a CML interface. when i do
the simulation, i see the differential signals, both input and output
DC shifted, quite apart.
the topology is something like this
tx +/- ---> ac_coupling capacitor (10 nF) ---> trans. line ---> rx +/-
the cml inputs are internally biased and terminated. when i run the
rise time sim. the tool reports that the receiver doesnt meet the
thresholds(2.2 v of vih and 1.76v of vil). what i see is a waveform
of 500 mv peak to peak biased around 3 v (+ sig) and 2 v (- sig).
another observation is that the rising waveform as per the IBIS model
is not observed at the output pin, this also dc shifted and quite different
in rise time than in IBIS model..
any body have any idea what could be going wrong? or i am doing something
grossly wrong !!!!!
thanks in advance..
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