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Altera_Forum's avatar
Altera_Forum
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11 years ago

Ring oscillator output always high

Hi Folks, I've built three simple ring oscillators (3, 7 and 15 NOT gates), they are connected to 3 standard I/O ports on my board (EP4CE6E22C8) but unfortunately their outputs are all high and...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
11 years ago

Ring oscillators are not easy in FPGAs. Unless you've specifically locked some of the logic Quartus is going to 'optimise' all but one inverter away. That's not going to leave much of your circuit. It's no wonder it's not oscillating...

Ring oscillators have been discussed on this forum before. It's worth having a good search. Look at the following post for starters:

[url]http://www.alteraforum.com/forum/showthread.php?t=48727 (http://www.alteraforum.com/forum/showthread.php?t=48727)[/URL]

It also refers to an Altera Wiki page (Altera Wiki seems to be down at present) which I've referred to before. Very useful.

Cheers,

Alex