On Sun, Apr 13, 2025 at 05:54 PM, Tony Scaminaci wrote:
have either of you looked at the output waveforms of the 74ACT08 at 6m?
I just happened to have an open QMX+ and an oscilloscope in front of me when I read this, so I did some quick measurements.
The oscilloscope is inexpensive (FNIRSI DPOX180H), so keep that in mind - but it should be reasonably good at 50MHz.
Using a 10x probe, I see the following at the driver (IC503) outputs.
Measurements are at 3MHz, 14MHz, and 50MHz for comparison.
Then there is a measurement of the 3.3V IC502 output (XOR gate pre-driver) at 50MHz, so you can see what the scope does at that frequency on a signal with (presumably) less loading.
?
So yes, according to these measurements, at 50MHz the driver does give a full-rail 5V signal to the BS170s, but it is no longer a clean square wave, starting to look more sinusoidal on the bottom half, due to the undershoot rebound time.?? I'm not sure how the BS170s will internally see the low-going gate signal when it is below ground potential - maybe it is still treated as 0V, cleaning up the square wave.? And these measurements should be repeated on a higher-quality scope for verification that this isn't just scope/probe measurement degradation.
