[SI-LIST] Re: [Fwd: coax to PCB transition - return loss]
- From: "Scott McMorrow" <scott@xxxxxxxxxxxxx>
- Date: Fri, 18 Apr 2003 09:39:18 -0700
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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