| Products > Test Equipment |
| Cheap Fast Rise Time Oscillator |
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| tggzzz:
--- Quote from: BillyO on February 03, 2023, 04:50:27 pm --- --- Quote from: tggzzz on February 03, 2023, 04:26:59 pm ---When measuring risetimes, it is also good to avoid overshoot in the signal. Sometimes the scope setup procedures require/allow a little overshoot in order to get the best useful risetime. Having ringing in the signal will affect those setup procedures, of course :) --- End quote --- Absolutely. I take the internal risetime measurement with a grain of salt when looking at less than ideal waveforms (which is most of the time). When I want to be accurate I use cursors. --- End quote --- How you measure the displayed waveform doesn't matter. What matters is what causes the displayed waveform to be the way it is. To make the point with a ludicrous example... If you look at the waveforms I added to my earlier post, and use the unterminated waveform with overshoot to twiddle your scope's risetime so that it is nice and sharp+flat, then when you observe a decent edge it would be rather distorted and slower than expected. |
| tggzzz:
--- Quote from: magic on February 03, 2023, 05:12:36 pm ---The right resistor value is 180~190Ω, depending on RDS(on) of the chip's internal FETs. --- End quote --- 7ohms was about right for a 74LVC1G output. Hence I used a 143ohms resistor to make it up to 150ohms. |
| BillyO:
Well, being an impatient man, I went ahead and built one up anyway using the 220R resistors I have. Yeah, the logo on the 74AC14 looks a little sloppy. I bought a large batch of IC's from Digi Key back in 2010. These, I think, were part of the batch. I don't recall getting any others, but then 13 years is a long time. Look at the last picture though. It shows the logos on the ICs on the TDR version. The '14 and the '02 look like proper TI logos. The 555 did come from China. It's only a 555 though, so meh. However, on my scope with a measured risetime of 660 ps, this version did 1.27 ns. Taking the scope RT in account that's a risetime of about 1.09ns! Not too bad. Yeah, but I'd not use a $5 oscillator to tweak my scope's front end. :-DD |
| tautech:
Good work Bill as you can't get much simpler than that ! :-+ :-+ :clap: Send me one to look at with this 2 GHz SDS6204A. ;) I had something very similar laid out in Altium and expected ~3ns RT but had a mission trying to do a toner transfer with a new printer (Yep, for some things I'm tight as !) so I gave up on it and ordered a Bodnar pulser that only took ~10 days to arrive in NZ from UK. |
| BillyO:
--- Quote from: tautech on February 03, 2023, 08:20:44 pm ---Good work Bill as you can't get much simpler than that ! :-+ :-+ :clap: Send me one to look at with this 2 GHz SDS6204A. ;) --- End quote --- Thanks and sure. I'll send you a board from the final version. I have a couple of tweaks in mind. --- Quote from: tautech on February 03, 2023, 08:20:44 pm ---I had something very similar laid out in Altium and expected ~3ns RT but had a mission trying to do a toner transfer with a new printer (Yep, for some things I'm tight as !) so I gave up on it and ordered a Bodnar pulser that only took ~10 days to arrive in NZ from UK. --- End quote --- Mine took a month. :-// |
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