Apptech wrote:
> Note that the circuit that Joe showed is not unconditionally unstable
> - it has a stable-off mode where if it doesn't start it won't run.
> This seldom happens in practice, but if you really really care there
> is a well known 3 gate version that always starts.

Oops, I just realized I said something wrong in the previous message.  I
meant to put the high value resistor accross the second inverter, not the
cap.  That is to guarantee it will wake up in "linear" mode as a inverting
amplifier.  However, that also means it needs to be AC coupled from the
previous stage.  You'd need to add a cap in there, making sure the time
constant is significantly longer than the cap and 33Kohm resistor currently
used to set the frequency.  That way the time constant doesn't get in the
way once normal oscillation starts.

This is all just to create a system that is just at the tipping point when
not running, so that any little noise becomes amplified and eventually
drives second inverter to full rail to rail output.  Once that happens, the
existing cap and 33Kohm resistor control the frequency.

I don't think a third gate is required to ensure there is no long term
stable state.


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