What is an acceptable amount of jitter when using an external oscillator for the ADV7180?
I am looking at using an oscillator with 40 to 200 ps of peak to peak jitter.
What oscillator are you using that has 200 ps jitter. A quick look at 28.63636MHz oscillators show they are less then 10ps jitter to begin with.
It is a crystal oscillator with PLL that can be programmed to any frequency.
There are no 28.6363 MHZ fixed frequency oscillators in stock and they have a long lead time.
I would not use a programmable oscillator for video just because of the jitter problems. Programmable oscillators are good to run CPUs but not as a video clock references.
If for initial testing only get one of the factory programmable ones but design for a real non-PLL oscillator or design using a normal crystal circuit. Crystals are readily available.
I wanted to use an oscillator for several reasons:
Sometimes crystal oscillator circuits have startup problems depending on characteristics such as ESR and drive level.
Usually these parameters are not specified by IC manufacturers.
Crystal oscillator circuits tend to have high impedance which can be adversly by environments which have moisture or condensation.
We may conformal coat the board which would mitigate this.
I could use the following part which is in stock:
Let me know if you think it would work.
I fully understand you're wanting to use an oscillator due to conformal coating and such and I fully agree.
The link on your post is a crystal not an oscillator.
Another possible solution that I've done in the past is to get a 3.3V oscillator, available on digikey
and a 74lcv1g04, (search digikey or mouser, any will do)
Power the oscillator from 3.3V
Power the inverter from 1.8V
Connect oscillator output to the inverter input, and invert output to the XTAL input.
i.e. use the inverter as a level translator, the inverter input is 5V tolerant.
I've done this exact thing on an old design and it worked just fine.
I sent the link for the crystal because I would consider using it.
Do you think it will work, or is it higher risk than an oscillator?
We don't have time to debug a crystal oscillator circuit.
We could use the 3.3V oscillator as you suggested but it is in a larger package and togther with the logic gate will take more space.
That crystal isn't a prefect match but you can recalculate the load capacitors. The ESR seems a bit high. Attached is a recommended crystal we use for our testing on the ADV7181.
Also if this is going to work over extended temperature ranges I'd use C0G/NPO material for the PLL filter capacitors. X7R types have worse tempco's and could effect the PLL at the temperature corners.
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