Exploring FPGA Pin Performance with Digilent's New High-Bandwidth Oscilloscopes

RE: Exploring FPGA Pin Performance with Digilent's New High-Bandwidth Oscilloscopes

jc2048 — Wed, 16 Apr 2025 12:38:30 GMT

Thanks for the blog.

This is a 72MHz LVCMOS output from the PMOD connector on an iCEstick, as viewed on an old Tek 2000 series 200MHz scope using a passive x10 probe and probing as well as I can directly on the connector with a springy-clip ground (I've done what you did, and generated a clock with the PLL and pushed it out of an IO pin).

Although the very fast edges without termination make for a somewhat messy waveform, even with just the short length of track to the connector, I don't think you'd complain that the chip was tardy in leaping between the rails. The risetime that you see (~2ns) is that listed for the scope, not the FPGA pin driver.

You've got a faster FPGA and a faster scope, so why are you seeing such a slewrate limitation on all your waveforms?

You've probably considered these, but worth asking. Are you using the probes x1 (lower bandwidth than x10)? Do you have a bandwidth filter enabled on the scope? Have you set the FPGA pin slewrate to slow (that might be the default in the design software)? Are you using the lowest drive current on the pin?

RE: Exploring FPGA Pin Performance with Digilent's New High-Bandwidth Oscilloscopes

michaelkellett — Mon, 14 Apr 2025 17:01:01 GMT

Looking at your test rig I think you are measuring the frequency response of the inductive loop formed by your ground leads and the capacitance of the probe, suitably modified by any imperfections in the probe and its cable.

What probes were you using ?

Most probes come with little spring clips to attach to BNC sockets and the like - you will be impressed by how much the waveforms change when you use them !

(The are not the ideal solution for the ARTY board but much better than the long earth leads.)

RE: Exploring FPGA Pin Performance with Digilent's New High-Bandwidth Oscilloscopes

dougw — Mon, 14 Apr 2025 16:12:41 GMT

1.5 GS/s & 2 GS/s .... pretty useful