FPGA Central

Hi ,
*
I'm making Characteristic Impedance measurements using TDR , of a connector soldered to a test fixture. I'm using a Single ended probe . I find that at the point of contact of probe on the pad, there is a inductive impedance approx. 78-82 ohms , Intially I thought I was measuring the impedance of the connector, and then realised I was wrong.
I then tried to solder a co-ax cable to the pad . It is still shows a high inductive impedance depending on the amount of solder at the joint.
*
Has anyone come across this? *Do I need to look into the details of the probe rating , bandwidth?
*
Thanks
*
Padma


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Padma

You may want to consider adding a test connector to your design and put it right onto the circuit board. Lets find a connector that works with your probe and simply add it. It makes for ease of testing in the future.

Richard Jungert

> Date: Sun, 12 Jul 2009 21:52:44 -0700
> From: pgundala2001 (AT) yahoo (DOT) com
> Subject: [SI-LIST] Impact of Probe -TDR Measurement
> To: si-list (AT) freelists (DOT) org
>
> Hi ,
>
> I'm making Characteristic Impedance measurements using TDR , of a connector soldered to a test fixture. I'm using a Single ended probe . I find that at the point of contact of probe on the pad, there is a inductive impedance approx. 78-82 ohms , Intially I thought I was measuring the impedance of the connector, and then realised I was wrong.
> I then tried to solder a co-ax cable to the pad . It is still shows a high inductive impedance depending on the amount of solder at the joint.
>
> Has anyone come across this? Do I need to look into the details of the probe rating , bandwidth?
>
> Thanks
>
> Padma
>
>
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Padma,
You may be able to reduce this "parasitic" loop inductance with some modifications and physical compensation added to the contact structure of your connector on your existing board. A set of drawings or detailed pictures of your current structure would help getting specific advice on what can be done. If you consider fixing/compensating your current fixture to reduce this parasitic inductance and you need some help send me drawings/pictures and TDR waveforms and we can take it from there.

Cosmin Iorga, Ph.D.
NoiseCoupling.com
http://www.noisecoupling.com



________________________________
From: padma gundala <pgundala2001 (AT) yahoo (DOT) com>
To: si-list (AT) freelists (DOT) org
Sent: Sunday, July 12, 2009 9:52:44 PM
Subject: [SI-LIST] Impact of Probe -TDR Measurement

Hi ,

I'm making Characteristic Impedance measurements using TDR , of a connector soldered to a test fixture. I'm using a Single ended probe . I find that at the point of contact of probe on the pad, there is a inductive impedance approx. 78-82 ohms , Intially I thought I was measuring the impedance of the connector, and then realised I was wrong.
I then tried to solder a co-ax cable to the pad . It is still shows a high inductive impedance depending on the amount of solder at the joint.

Has anyone come across this? Do I need to look into the details of the probe rating , bandwidth?

Thanks

Padma


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