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Show us your square wave
Dave_g8:
Hi Bill,
As previously mentioned, I suspect the noise may be from other elements switching in the 74AC14 chip.
U1 Pin 2 and U1 Pin 12 will be changing just before the final output.
I am not sure if you are using a Schmitt type device, if not, the slow edge on U1 Pin 1 may also lead to high frequency oscillations as the signal passes through the threshold voltage.
Regards, Dave
BillyO:
Here is sequence through the circuit. Probes used are Tektronix P6205s through an 1103 power supply. Yellow trace is directly connected via an adapter to the output of the pulser.
The blue trace is used to probe various points using a spring ground.
The first screen shot is at pin 2. The output of the oscillator.
The second is at the output of the buffer (pin 12)
The 3rd is at the output of one of the drive inverters before the series resistor (pin 6)
You can see how the anomaly builds as the signal goes through the system.
BillyO:
--- Quote from: Dave_g8 on June 09, 2024, 03:08:24 pm ---Hi Bill,
As previously mentioned, I suspect the noise may be from other elements switching in the 74AC14 chip.
U1 Pin 2 and U1 Pin 12 will be changing just before the final output.
I am not sure if you are using a Schmitt type device, if not, the slow edge on U1 Pin 1 may also lead to high frequency oscillations as the signal passes through the threshold voltage.
Regards, Dave
--- End quote ---
Yes, the 74AC14 is a Schmitt hex inverter. And I agree. It's not a problem with the scope, or phase noise, group delay, sinc interpolation or Gibbs artifiacts.
It's simply switching noise created in the chip itself.
T3sl4co1l:
Just to cross and dot eyes and tees -- these probes are skew matched, right?
Seems plausible it's propagation delay (74AC is a buffered family, and schmitt on top of that), supply (and ground) bounce, and the DIP isn't helping things at all.
Always kind of perplexed that they made 74LVC in DIP, let alone bus drivers and such... but I guess it works well enough on the whole, for logic purposes. Makes a bit of a mess this way though.
Tim
BillyO:
--- Quote from: T3sl4co1l on June 09, 2024, 03:19:33 pm ---Just to cross and dot eyes and tees -- these probes are skew matched, right?
--- End quote ---
Yes. The propagation delay displayed is within specification of the chip.
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