ArtyS7 microstrip impedance

[Jeonghyun]

Hello,

I am currently working on creating a PMOD to BNC board for an experiment, and it is crucial to ensure impedance matching.

According to the manual, there is a 200 Ohm resistor in the jc and jd PMOD connectors.

However, I am unsure whether this PMOD is connected to a 50 Ohm microstrip or a 200 Ohm microstrip line.

Can you specify characteristic impedacne of microtrip line?

Thank you for your assistance.

[zygot]

3 hours ago, Jeonghyun said:

it is crucial to ensure impedance matching

Impedance matching and PMOD are not compatible terms. Once you've gone through one right-angle 0.1" xn header and it male mate any impedance matching for the PCB traces between the driver and the receiver is pretty much destroyed. 

I've never seen any information from Digilent about their standard PMOD PCB trace characteristics. What they publish for the other PMOD headers without the series current limiting resistors varies but don't expect 50 ( I think that I've read 70-80 ohms one on of their board reference manuals, but I don't believe that this is consistent from product to product). They do provide trace lengths for FMC connector traces if requested. These are the only connectors requiring impedance matching that they use.

I do hope that someone from Digilent does provide the information that you are asking for though.

Edited June 20, 2023 by zygot

[asmi]

2 hours ago, zygot said:

These are the only connectors requiring impedance matching that they use.

They also provide length and matching info for SYZYGY connectors as required by the specification.

[zygot]

@asmi,

Yes, I just finished another post about SYZYGY and somehow managed to forget about the SYZYGY equipped carrier boards that Digilent sells; 1 A-100T, 1 Z7020 and two UltraScale+ ZYNQ boards. The eminently forgettable Eclypse-Z7 has 2 SYZYGY ports and a rather bizarre PMOD design, all of the others have only 1 ( but in at least 1 case an FMC connector ). Opal Kelly's tiny Z7012S based Brain-1 Crowd Supply board has 3 standard SYZYGY and 1 transceiver ports.

Opal Kelly supplies KiCAD footprints for a basic pod design, though it seems that every time KiCad releases an update all of the older component footprints become incompatible. Nevertheless, SYZYGY might be a reasonable option if you are going to design a custom board that you want to connect to an FPGA carrier board. I suggest looking at the boards that Opal Kelly has in stock at the moment ( though I don't know if that guarantees immediate shipment ).

The Mimas-A7 has a lot of well matched IO with an A7-75T FPGA. You can change one resistor to make them 1.8V or 2.5V logic compatible for true differential IO. Unfortunately Artix Series 7 devices have no HP IO banks and thus no internal differential termination, which is the ideal place to put them for receivers. You can view the Mimas IO length report without having to request it and before you decide on a purchase.

But thanks for the correction. 

Edited June 20, 2023 by zygot

[Jeonghyun]

Thx you for your answer!!

[JColvin]

Hi @Jeonghyun,

I reached out to our layout engineer and while I didn't get precise information that you and others would be hoping for, I did learn that the microstrips for the I/O lines on the Pmod JC and JD ports on the Arty S7 are 50 Ohms +- 10%.

Thanks,
JColvin