DIGITAL PLL

341

04:01:35

I thought about how a Digital PLL would look like for weeks when today i completed my mental map of it and made this.
Wait like 15 seconds to let it stabilize.
The two DACs are just for making a digital comparator because EC does not have one.
-niki

published 8 years ago

hurz

8 years ago

Can you give a little information for a better understanding what you try to do? Input, internal reference clock, output. Anything helpful for orientation.

nikisalli

8 years ago

The small bottom right square wave generator is the input. The green wire has the output of the PLL and the orange wave is the digitally filtered output of the phase comparator. The top left self clocking counter is the high frequency clock and the xor gate is the phase comparator

nikisalli

8 years ago

The only analog part are the DACs and the comparator but i had to use them to make a Digital compact binary number comparator.

hurz

8 years ago

Ok, one can see already while startup the loop filter voltage swings a lot even it finally finds the frequency and phase and lock to it (think about a LED and lock indicator as feature, there are some tricks to do so) but back to the filter, this overshoot swing means the loop gain is to high and will cause stability problems. E.g. how much gain does your digital VCO, [Hz/Volt] is one part of the loop you can lower.

nikisalli

8 years ago

Here i lowered the gain of the filter and you can see that After 2 rapid oscillations it goes slowly to its setpoint http://everycircuit.com/circuit/6614388848197632

hurz

8 years ago

Doesn't look stable. Still much to high loop gain.

nikisalli

8 years ago

Ok it needs some other work

hurz

8 years ago

We need more screws to tune 😁

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