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We are currently intending to purchase a TDR device (or maybe 2) to measure the impedances of various traces on PCBs but we are just at the beginning. Can you recommend some good devices or devices which are commonly used in the industry at the moment? What are the parameters I have to look at (I know that the rise time is the most critical one; but what else characterizes such a system)?

I know that shopping questions for parts are forbidden here but I hope that the some does not apply for gear as well. At least it doesn't for soldering irons from what I've seen in the past.

Tom L.
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2 Answers2

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Are you just making pcbs and want to measure the impedance at 1Mhz? If so I think there are some cheaper boxes that will work but I've never used them.

If you're doing high speed engineering work the sparq is awesome. It's a TDR and a s-param extractor, like a network analyzer but easier to use and built for pcb guys.

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I've also used the tek sampling scope with TDR option.

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The main thing I'd look for would be edge speed of the test signal, the faster it is the more detail you're going to see. After that software and what it can extract for you. Oh and probing both these tools are SMA input and output which means your test card should have SMA connectors on it.

If it doesn't take a look at gigaprobes extremely highspeed probes for use with the above kind of TDRs (or scopes). I've used them to get s-param and impedance measurements for motherboards from the intel processor connector down the pci-e pins.

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I found the Lecroy and giga guys very knowledgable and willing to help, but none of the above is cheap!

Some Hardware Guy
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  • Thanks for your info. We (in fact) are "PCB guys" but we intend to transition to high speed designs (Gbps range) and since I hate relying on the fab guys telling me what they measured, I would like to perform these measurements by myself (just to be sure the design is in fact correct). As always: measuring is better than just guessing. – Tom L. May 18 '15 at 12:44
  • Well then the above may be overkill. Do you require the fab to send you the test coupons and reports with every build? That at least tells then you may be checking them. – Some Hardware Guy May 18 '15 at 13:18
  • Btw polar instruments is the company I was trying to think of before that a lot of fab houses use for this http://www.polarinstruments.com. If you just want to double check you could probably pay a second fab house to re test the coupons :) – Some Hardware Guy May 18 '15 at 13:20
  • We also do have quite a lot of customer PCBs going in (we're an assembly company as well) so we would like to do this testing also in the process of receiving goods (whenever possible) - therefore the cost is not the only issue, but also usability and flexibility. Therefore I was interested in the options available to get the big picture. Thanks :) – Tom L. May 18 '15 at 13:25
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Consider a Vector Network Analyser with the time domain option.

Frequency domain is the new Time Domain, at least according to Agilent / Keysight. It plots eye diagrams, measures length, impedance, mismatch...

But seriously, for measuring trace impedance, a network analyser is a good choice of instrument.

tomnexus
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