Hi,
Im designing 4 stage ring oscillator. Each delay cell consists of 2 cross-coupled inverters.
It can oscillate in any corners but the time to start oscillation is uncertain. I believe this has annoyed not only me, so can you suggest me to get this oscillate properly on start-up?

Assumption; current starved type ring oscillator, enable signal is on much earlier than current is actually supplied.

Hi,

I understand your point. But nonetheless, it does not assure it oscillates right after specific time point, does it? If it becomes like inp=inn=op=on=..., which is so rare but possible, it might to take uncertain time to oscillate.

Hi,

In simulation, yes, I can observe oscillation no mater what. As you pointed out, some fluctuation was amplified.
However, what I think problematic is it depends on something unpredictable, somethign uncertain.  For example, ss process at -40, gain becomes small enough probably.

Therefore, I think its better to have sort of start up to provide the seed of oscillation to ensure it oscillates in certain time.

Thanks,

Quote:

In some chips at 40nm & below, silicon results showed that oscillation on internal oscillator nodes die down too slowly sometimes.
Hence, I generally do that in all oscillators, but i power down all nodes to GND.
That works too, because cross-coupled inverters force opposite movements on psuedo-differential nodes at power-up.

--
Mayank.