Help find appropriate board for LVDS application

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1

We are looking for a simple test board PCB that connects two SMA signal lines together via on-chip 100 ohm SMD resistor (which we call solder ourselves).

Ultimately, we will be driving LVDS signals via the two SMA inputs so with V+ and V- flipping at 250 MHz coming in at the two SMA inputs.

We then want to measure the differential voltage across the 100 ohm SMD resistor using a Keysight differential probe.

As such, the differential probe will be measuring the voltage at two points around the 100 ohm resistor (marked x in the diagram below).

V+ ----.. --→ |

          x

          100 Ohm SMD

          x

V- ----.. --← |

Therefore, the most important characteristics we are looking for are:

  • Two SMA inputs connected by a strip line with a gap for SMD components.
  • Bandwidth includes 250 - 500 MHz

The closest product I have found with this circuit is product number 1465-1560-ND. More specifically the top half of it where there are two capacitors, one of which could be replaced by a 100 ohm SMD and another which could be removed and shorted across. This seems like it would fulfill our needs. Could someone confirm and/or suggest any better suited products? As this definitely seems like overkill for our purposes.

Thank you

2

With something this simple it seems like you’d be wasting money on that evaluation board just for the trace and two of the connectors, to be frank. I didn’t have any luck finding a prototype or breakout board similar to what you’re describing here, but you might want to consider ordering a custom board using the PCB builder- https://www.digikey.com/en/pcb-builder/

Even if you aren’t familiar with the programs used for designing PCBs it seems worthwhile to invest a little bit of time in learning something like Eagle to get the basic design printed, then all you have to do is solder a pair of SMA connectors once it’s fabricated.

That’s what makes the most sense to me, maybe one of the engineers on here will have some additional insight.

3

Hello @gyan,

This sounds like a perfect application for a cast aluminum box such as this:

The box provides radio frequency shielding and a convenient place to physically mount the connectors.

In the past I’ve mounted RF connectors to the cover plate—it’s flat and easy to drill.

Let us know if you need assistance finding the SMA connectors or other supporting materials.

Sincerely,

Aaron

P.S. This assumes you can use through hole resistors as opposed to the SMD in your original post.

4

Hi Chris, thank you for your suggestion. We are avoiding custom PCBs as they’d probably take a while longer to receive.

5

Hi Aaron, thank you for the suggestion. We only plan on using SMD components, and so ideally we’re looking for a PCB that fits our need.

6

Understood @gyan,

Let me point you to:

  • @chris_groom suggestion of making your own PCB. If you are thinking multiple copies, this is the way to go as you have complete control over the product.

  • Consider the specialized RF solutions offered by companies such as thorlabs

  • Reconsider the cast aluminum box. With close spacing of the SMA connectors it would be very hard to tell the difference.

Sincerely,

Aaron

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