I put a female bnc connector on the 74AC714 input and changed the input cable from the FG (10Mhz @ 3vpp, sine) to be a bnc to bnc jumper cable, so without the clipleads etc.
Do you have the calculation of FG's output amplitude set for a 50Ω load ? [ Utility->Ch1Set->Imped->Load (50Ω) ] 74AC14 supply voltage lowered to 3V.
So, now the 74AC14 needs 2V P-P input waveform centered at ½V CC to switch reliably. But you have only 1.6V P-P at the input pin of the 74AC14 chip ! So the chip is switching with lower input amplitude than specified. This could lead to instability later - especially if temperature changes... Using the RF probe tips on the probes i measured the input signal (yellow) and output (across a 1K resistor) signal (blue), see screenshots.
Looking much better compared to yesterday.
Yes, but you are on the edge. On the attached scopeshot, I have extended the rising edges of the blue squarewave with pink lines and I have drawn the lower red horizontal line through the points where these pink lines intersect the yellow sinewave. I have done a similar thing with the falling edges of the blue squarewave and drawn the upper red line. Note, that the lower red line is skirting the bottoms of the yellow sinewave*. That's how close you are to the switching threshold! So, consider lowering the supply voltage even further (you can go as low as 2V) or consider using the more sensitive chip, such as the 74AC04 or 74VHC04, which require only 1.2V P-P input, to switch reliably at 3V supply. * Note that the upper red line is NOT skirting the tops of the yellow sinewave, thus you do not have a problem there. This is because in the 74AC14 chip, the upper switching threshold is a little closer to ½VCC than the lower switching threshold.
« Last Edit: 2019-09-02, 09:55:13 by verpies »
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Topic: Itsu's workbench / placeholder. (Read 108324 times)
