PMODs on PYNQ ZU

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Hi there,

I’ve recently been experimenting with the PYNQ ZU and had some questions regarding the PMOD.
The schematics mention that it’s got a capacity to transmit upto 20MHz I believe and the bank it’s connected to (66) are only supplied with 1.8V supply.

The main reason I bring this up is that I’ve ben trying to send out pulses ranging from 10kHz to 2 MHz via the PMOD as an outlet and the pulses I’ve been acquiring are not coherent. I can attach photos if necessary. I initially specified LVCMOS18 then even tried LVDS but I just wanted an idea on whether what I’m trying to do is possible or if I should add a DAC or something. At frequencies below say 25kHz, the pulses look pretty good but from 50kHz to 1MHz the pulses are not good enough to work with.

I’ve read up all the digilent pmod articles and even general pmod articles and I understand that the pmod ports are in a high density high performance bank. (high performance in that they can exceed 10MHz). I’m just looking for insights as to what’s missing as I feel like I’ve checked everything there is to check. Maybe a reference that goes into detail on the PMODs used on the ZU could help.

Below is a 1.25MHz pulse signal on LVDS setting from the PMOD.

plot
plot1600×1023 247 KB

2

So, the idea I went for while working on this was to use the Digitally Controlled Impedance from ug 571 and the respective IOSTANDARD that went with it. I switched from LVDS to LVDCI or HSLVDCI. The guide is fairly explanatory so I’ll leave it at that to keep this brief. Significant improvement noted especially in signal stability. Still overshoot with oscillations for an output impedance of 48 but that’s probably because it’s not properly matched to the scope.

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