[SI-LIST] Re: [Fwd: coax to PCB transition - return loss]
- From: bpanos <bill.panos@xxxxxxxxxxxxxxx>
- To: scott@xxxxxxxxxxxxx
- Date: Mon, 21 Apr 2003 08:01:54 -0700
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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