[SI-LIST] Re: [Fwd: coax to PCB transition - return loss]
- From: Perry Qu <perry.qu@xxxxxxxxxxx>
- To: jeff.loyer@xxxxxxxxx
- Date: Tue, 22 Apr 2003 12:46:53 -0400
Hi, Jeff:
Thanks for the info. This is pretty interesting stuff. I guess the void of
ground copper underneath the pin makes a big difference. Hopefully I got the
chance to test it out in a test PCB later. Do you have any S11 plots in
frequency domain ?
In our configuation, we used an "inverted" microstrip, i.e., ground copper
flood on the surface layer and microstrip trace on an inner layer.
Regards
Perry
"Loyer, Jeff" wrote:
> Ray Anderson put the information at:
> http://groups.yahoo.com/group/si-list/files/Technical%20Documents/
> under "SMA Launch Structure Info"
>
> I always went to microstrip. I would think your S11 resonance merely =
> indicates a noisy launch. I wouldn't be surprised to find that the =
> microstrip launch would be noisier than that for coplanar - the =
> transition (from SMA connector environment to PCB) is more complex and =
> easier to induce discontinuities.
>
> Jeff Loyer
>
> -----Original Message-----
> From: Perry Qu [mailto:perry.qu@xxxxxxxxxxx]
> Sent: Tuesday, April 22, 2003 7:29 AM
> To: scott@xxxxxxxxxxxxx; Loyer, Jeff
> Cc: si-list
> Subject: Re: [SI-LIST] Re: [Fwd: coax to PCB transition - return loss]
>
> Scott, Jeff:
>
> Thanks for your info. It's not clear to me what type of transmission =
> line you
> used on PCB, microstrip or coplannar waveguide ? Jeff, can you send me =
> the
> slides you are talking about ?
>
> I re-examined some of our measured data for various coax-to-PCB =
> interface and it
> appears that whenever microstrip is used, I see some resonance in S11 =
> frequency
> domain plot (10 - 240 MHz). This resonance basically screw up my return =
> loss out
> of -15 dB. However, for coplannar waveguide, it appears to be a =
> linearly-rising
> curve with no resonance and it meets -15dB faily well.
>
> BTW, I need to clarify a bit about the interface: The interface I'm =
> talking
> about here is the analogue link between SMZ connector and Tranceiver =
> analogue
> side. There are a bunch of passive elements in between (transformer, =
> protection
> diode, etc.). The "ground" in microstrip or coplannar waveguide is =
> completely
> isolated from PCB digital ground.
>
> Regards
>
> Perry
>
> Scott McMorrow wrote:
>
> > Bill,
> >
> > I'm not quite sure what you are asking. An SMA by nature is a
> > single-ended creature. Measurements were made single-ended with one
> > SMA, and differentially with two SMAs. But in both cases single-ended
> > cables and TDR heads were used. The TDR profiles matched simulation
> > with extremely good accuracy, including all high frequency resonances.
> >
> > In about a month we'll see how close the optimized SMA launch pattern
> > matches simulation. It will no doubt be better than our first try and
> > will allow us to further refine our modeling and simulation =
> techniques.
> >
> > scott
> >
> > bpanos wrote:
> >
> > >Scott-
> > >Were your measurements made with a single ended line or a =
> differential?
> > >
> > >-Bill
> > >
> > >
> > >
> > >Scott McMorrow wrote:
> > >
> > >
> > >
> > >> Ron,
> > >>
> > >>I have a vertical (top mount) SMA design that I've simulated and
> > >>measured with the following characteristics:
> > >>
> > >>Insertion loss -1 dB @ 16 GHz
> > >>Return loss -20 dB @ 12 GHz
> > >>
> > >>With this top mount sma we see a worst case TDR profile off a Tek
> > >>TDS8000 17 ps head of 49 to 54 ohms.
> > >>
> > >>This design has been correlated to 3D full-wave simulation by
> > >>measurement in both the time and frequency domain. As a result, I =
> have
> > >>redesigned the launch to have the following characteristics.
> > >>
> > >>Insertion loss -1 dB @ 27 GHz
> > >>Return loss -30 dB @ 12 GHz
> > >>-20 dB @ 22 GHz
> > >>
> > >>with a simulated TDR profile of 50 ohms +/- 1 ohm.
> > >>
> > >>Depending upon where the signal is that needs to be tested, the =
> launch
> > >>can either be done from top or the back side of the board, which =
> reduces
> > >>the via stub problem.
> > >>
> > >>regards,
> > >>
> > >>scott
> > >>
> > >>--
> > >>Scott McMorrow
> > >>Teraspeed Consulting Group LLC
> > >>2926 SE Yamhill St.
> > >>Portland, OR 97214
> > >>(503) 239-5536
> > >>http://www.teraspeed.com
> > >>
> > >>ron miller wrote:
> > >>
> > >>
> > >>
> > >>>Hi
> > >>>
> > >>>It looks like whether coplanar or coax the vertical mount is not to =
> be
> > >>>recommended.
> > >>>
> > >>>The big problem is the via,and the via capacitance, and the via =
> stub.
> > >>>This can go as low
> > >>>as 30 ohms. Your worst case stub is .093 mils or about 10 ps one =
> way or
> > >>>20 ps round trip and
> > >>>about two degrees 1/200 of error at 240 Mhz so it should probably =
> be ok
> > >>>unless you must have a very
> > >>>accurate timing edge in your signal.
> > >>>
> > >>>However, be sure to remove internal pads, and keep the spacing to =
> the
> > >>>antipads as large as possible.
> > >>>
> > >>>For test purposes it is better to connect a piece of semirigid .047 =
> or
> > >>>.093 OD with a female sma
> > >>>attached to two surface pads.
> > >>>
> > >>>Ron Miller
> > >>>
> > >>>dmitrik@xxxxxxxxxxx wrote:
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>>-------- Original Message --------
> > >>>>Subject: [SI-LIST] coax to PCB transition - return loss
> > >>>>Date: Wed, 16 Apr 2003 10:50:17 -0400
> > >>>>From: "Perry Qu" <perry.qu@xxxxxxxxxxx>
> > >>>>Reply-To: perry.qu@xxxxxxxxxxx
> > >>>>Organization: Alcatel Canada
> > >>>>To: si-list <si-list@xxxxxxxxxxxxx>
> > >>>>
> > >>>>
> > >>>>Hi,
> > >>>>
> > >>>>I have been having problems in designing STM1 electrical interface =
> to
> > >>>>pass return loss requirement (< -15 dB up to 240MHz). We don't =
> have a 3D
> > >>>>full wave tool in house so I can't really simulate the interface =
> and
> > >>>>provide proper design guidelines. My question, what will be the =
> best
> > >>>>coax to PCB transition (75 ohm vertically-mounted SMZ connector):
> > >>>>
> > >>>>1. a microstrip, where center conductor of SMZ is connected to
> > >>>>microstrip lines on PCB and the 4 ground pins are connected to the
> > >>>>reference copper on PCB;
> > >>>>
> > >>>>2. A coplannar waveguide structure, ground - signal -ground, where
> > >>>>signal is connected to center conductor and ground is connected to
> > >>>>ground pins on SMZ.
> > >>>>
> > >>>>As long as we maintain 75 impedance control, I don't see much =
> difference
> > >>>>in terms of return loss performance for the above two.
> > >>>>
> > >>>>Also, how significant will through hole via along the signal path =
> affect
> > >>>>return loss at 240 MHz (assume 0.093" thickness) ?
> > >>>>
> > >>>>Thanks for your input.
> > >>>>
> > >>>>Regards
> > >>>>
> > >>>>Perry
> > >>>>
> > >>>>--
> > >>>>Perry Qu
> > >>>>
> > >>>>SDN D & Q | 600 March Road
> > >>>>Alcatel Canada | Ottawa, ON K2K 2E6, Canada
> > >>>>
> > >>>>DID: (613) 7846720 | FAX: (613) 5993642
> > >>>>
> > >>>>
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> > >>>>
> > >>>>
> > >>>>
> > >>>>
> > >>>>
> > >>>>
> > >>>
> > >>>
> > >>>
> > >>--
> > >>Scott McMorrow
> > >>Teraspeed Consulting Group LLC
> > >>2926 SE Yamhill St.
> > >>Portland, OR 97214
> > >>(503) 239-5536
> > >>http://www.teraspeed.com
> > >>
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> > >>
> > >>
> > >>
> > >
> > >
> > >-- Binary/unsupported file stripped by Ecartis --
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> > >
> > >
> > >
> >
> > --
> > Scott McMorrow
> > Teraspeed Consulting Group LLC
> > 2926 SE Yamhill St.
> > Portland, OR 97214
> > (503) 239-5536
> > http://www.teraspeed.com
> >
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>
> --
> Perry Qu
>
> SDN D & Q | 600 March Road
> Alcatel Canada | Ottawa, ON K2K 2E6, Canada
>
> DID: (613) 7846720 | FAX: (613) 5993642
>
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--
Perry Qu
SDN D & Q | 600 March Road
Alcatel Canada | Ottawa, ON K2K 2E6, Canada
DID: (613) 7846720 | FAX: (613) 5993642
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