An RF short is need at the launch end as well.
On 11/01/2016 04:05 PM, Orin Laney wrote:
Both planes cooperate to define the transmission line impedance, even if one
of them is not connected to anything at all. Mere proximity is enough.
However, when the signal reaches the far end, unless the planes are shorted
together RF-wise (using adequate capacitor coupling) so that HF current can
return through both, you create mode conversion and cause ringing. The DC
case remains unchanged. Bottom line: best practice ties the planes together
with caps if there is a DC potential difference, or uses shorting vias if
there is not.
Orin
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Paul Huang
Sent: Tuesday, November 01, 2016 3:05 PM
To: patolfo@xxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Transmission line terminated to Vdd only
Thank you Patolfo and Orin,
If I don't have a capacitor between Vdd and ground at the termination
resistor does it mean that my trace referenced to ground operates in
unterminated mode and the same trace referenced to vdd plane operates in
matched impedance terminated mode?
Then if I add a capacitor does it mean that I create an AC termination for
trace referenced to ground too? Does this mean that I lower the overall
termination and I may have reflections?
Thanks,
Paul
Sent: Tuesday, November 01, 2016 at 2:22 AM------------------------------------------------------------------
From: "Patolfo Nery Velya" <patolfo@xxxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Transmission line terminated to Vdd only
The current will flow through the parasitics too, so ac will be couple
partly to ground plane, al cabo de la vida quisiera descansar en un
bosque de paz y sin preguntas y desde la espesura escuchar en sosiego
el preludio de un réquiem privadÃÂsimo Benedetti **Cansancio
On Mon, Oct 31, 2016 at 6:26 PM, Paul Huang <paul.huang7531@xxxxxxxx> wrote:
Hello Si-list,------------------------------------------------------------------
I have a question: I have a CMOS driver that drives a strip-line
trace referenced at top to Vdd supply power plane and at bottom to
vss ground plane. The trace is terminated to vdd only. Since there
is no termination to ground, will it be any return current flowing
through the ground plane or only through the Vdd power plane?
Thanks,
Paul
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