Something like this:
It really needs that nonzero prop delay param. LT Spice was apparently not intended to be a digital simulator!
I haven't had much luck with PLLs in LT Spice either. We usually write our own code for them. I've got one now that I want to simulate, but I'd need better than double floats to do the math. PowerBasic supports the 80 bit format, which just might do.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
As long as you are not too fussy, Helmut's 74hc.lib includes that automatically. Then you can use the whole range of 74HC devices without worrying about gate parameters. This is very useful for a quick check on a logic circuit.
Another alternaative if you just need a 74HC14 is Helmut's B-Source shown in items 8 and 9 in my oscillator page at
I have come across simulations using Laplace Transforms. They are really, really fast. However I never use them as I wrote my own software that gives the values for the loop components.
I want to resolve time-domain jitter to picoseconds, which gets numerically ugly fast. We might just do some proto boards and skip simulation.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Famous last words! The problem of metastability in flipflops, and of starting conditions in hysteretic chips, is that there's an insoluble bit of math in the center. There's TWO solutions at power-on, output HIGH and LOW initial states are both allowed, unless you break the symmetry somehow.
Temperature, roundoff error, or a fudge constant in a model, will break that symmetry, but those are all going to break it differently: the theory just doesn't have the randomness of thermal fluctuations and thus diverges from reality. The symptom, is that a SPICE model may always start in some phase after power-on, but the chip might not. Absolute phase usually doesn't matter (because we've learned not to depend on it), but that isn't the same as being able to predict it.
A power-on sequence usually geta a few dozen clock cycles completed THEN resets everything and starts the process. There's other good reasons for that, but oscillator startup predictability plays a part.
That does you no good. The output had to settle in one state or the other. It cannot remain suspended between the two.
In the event that both states exist, feedback will quickly resolve the issue and the circuit will settle to one state or the other.
Wordy nonsense. Metastability is resolved very fast. Many modern ic's in the EcliPse class sho no measurable metastability at all.
The hysteresis is not a flip-flop circuit. There is no metastability in a HC14. Once you hit on hysteresis voltage threshold, the output will switch to the opposite side. There is no way to avoid it.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.