[SI-LIST] Re: [SI-LIST Microstrip Loss Correlation: Need to look at TDR
- From: <hbarnes_2298@xxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Mon, 24 Oct 2005 05:30:48 -0600
Hello Chris,
Work done at Agilent technologies has shown that it is critical to look at the
Time domain discontinuities to determine how to tune a transition for better
performance and lower loss. The edge launch SMA's by design are 50ohms, the
transition to the PCB can be hugely inductive or capacitive depending on what
the layout designer does. The attached pdf file shows how one can use
simulations to dial in the transition to the PCB by using time domain to see
where the discontinuities are and whether signal to ground distances need to be
reduced to eliminate an inductive discontinuity or the other way around.
Typically the Johnson SMA edgelaunch connectors have the best performance when
one clips the signal pin short going onto the PCB and then one can get
reasonable 15dB type return loss up to maybe 8GHz with a good transition on the
PCB.
Best Regards,
Heidi Barnes
High Speed DUT Board Consultant
Application Development Center
Semiconductor Test Solutions
1400 Fountaingrove Pkwy
Bldg 3LS-W
Santa Rosa, CA 95403
707-577-2298
hbarnes_2298@xxxxxxxxxxx
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of bratfest
Sent: Friday, October 21, 2005 3:19 PM
To: tom@xxxxxxxxxxxxx; Christopher.Crowley@xxxxxxxxxxxxxxxxx; 'Mark Burford'
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Microstrip Loss Correlation
Might be a good idea to take a look using a TDR to check actual
impedances and locations of any discontinuities.
This will give you an idea of where to look for errors.
BR
Gus
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Tom Dagostino
Sent: Friday, October 21, 2005 2:23 PM
To: Christopher.Crowley@xxxxxxxxxxxxxxxxx; Mark Burford
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Microstrip Loss Correlation
You should be able to do much better bandwidth on FR4 than you are
seeing here for that length trace.
Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
tom@xxxxxxxxxxxxx
www.teraspeed.com
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of
Christopher.Crowley@xxxxxxxxxxxxxxxxx
Sent: Friday, October 21, 2005 11:16 AM
To: Mark Burford
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Microstrip Loss Correlation
Content-Type: text/plain; charset="us-ascii"
Hello Mark,
I have attached a copy of the insertion loss plot, but basically you can
see that there is a small rise, than a cliff after the 2.4Ghz. The gnd
plane under the trace is a full plane. The board is shaped like a stop
sign that is nearly 3"X3", so there is plenty of gnd under the trace.
The area where the gnd is cut away is only just under the top layer pad
for the signal conductor of the sma. The pad itself is 40 mils wide,
but the GND underneath is 50 mils wide. I have attached a .bmp for
reference.
Thanks,
Chris
"Mark Burford" <Mark_Burford@xxxxxxxxxxx>
10/21/2005 12:31 PM
To: Christopher Crowley/Corporate/FSC@Fairchild,
<si-list@xxxxxxxxxxxxx>
cc:
Subject: RE: [SI-LIST] Microstrip Loss Correlation
Is this loss a continuing attenuation i.e. does loss increase past
2.4GHz or are you experiencing a 'notch' type attenuation at the
frequency you stated where past 2.4GHz less loss is seen? You are right
in saying that the superior quality material should give less
attenuation at this frequency but then it all depends on rise time of
you signal, trace width (a wider trace will increase dielectric loss per
length), around this frequency dielectric losses should be dominating
skin depth (conductor) losses so perhaps reducing the line width if poss
may reduce your attenuation. Obvioulsy reducing trace length would help
too.
How wide is the ground plane under the trace? Is it at least 2.5 - 3
times the trace width where you have cut it away (not sure exactly what
you have done so couldn;t comment further) because this would affect the
return current if the return plane was not continuous at about 3 times
the trace width. Also this would cause reflections and affect your
measurement.
I hope these simple questions and reminders are of use to you.
Regards
Mark
--
Mark R Burford M.Eng M.I.E.E.
EngD Research Engineer
School of Electronics and Computer Science
University of Southampton
________________________________
From: si-list-bounce@xxxxxxxxxxxxx on behalf of
Christopher.Crowley@xxxxxxxxxxxxxxxxx
Sent: Fri 21.10.2005 16:53
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Microstrip Loss Correlation
Hello All,
I am working on measuring the bandwidth of a couple fixtures and am
surprised by the results. I am hoping that someone may be able to help
shed some light on the subject. I have two fixtures that are identical
other than the materials. One board is made of Isola's FR406 and the
other is Arlon 25N. The only minor difference is that the stackup may
have been changed slightly to accommodate for 50 ohm's on 12 mil trace
widths. Four layer board, 2.8" total length traces, routed only on the
top layer microstrip.
I have used edge launch sma's to interconnect to the network analyzer.
Johnson Components 142-0701-801 PN. The issue is that when making an
S21 measurement across the 2.8" trace I see both boards have a 3db loss
at approximately 2.4GHz. Since I would obviously expect the Arlon 25N
board to perform much further out in frequency one thing I am suspect of
is the sma interconnect. I know that the sma footprint should be
optimized and we have tried to do that by cutting away some GND under
the signal conductor of the sma. It seems like it is still causing an
issue though. Does anyone have any footprint or other recommendations?
Thank you,
Chris
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