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Si5351A frequency generator

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dr pepper

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Anyone played with this chip or module?
Looks like a nifty little dds chip with i2c control.
I'm thinking of getting one and adding it to one of my projects, only I'd need to operate it at a different clock frequency, I see the module has an xo block on board.
 

schmitt trigger

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You read my mind.
A couple of days ago I read about SiLabs in another forum.
I've a fairly decent 10 Mhz OCXO. For a long time I have wanted to build a dividing unit to obtain reference frequencies like 100Khz 1Khz or even 1 pps, which are straightforward to implement, even though it requires a lot of ICs.

But there are other frequencies, like 32.768Khz or 60 Hz, which require a variable divider modulus.

I know how to do those, and have successfully breadboarded them....but they require many more ICs. Thus, I've never built it. But SiLabs offers a multiple output, variable modulus divider IC, the 5350C.

So this device piqued my interest, went to the SiLabs website and downloaded their "clock builder"software. And have only started to play with it.

Of course, this is a different device from the one on your post, but this company appears to be making some very interesting, cutting edge devices.
 

dr pepper

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I wouldnt think theres much diference between the 1 and the 0 chips.
I'm doing a similar thing, my project is an off air standard at 10mc, the modules tend to use 20 to 30 Mc xtals, and produce around 10Kc to 200Mc, so with a clock of 10Mc's that ought to give 8Kc to 100Mc or so, that would be a nice little addition to a frequency standard.
Not sure how they work yet, in my system I also have 3Mc's available, so that might expand what I could do, and with a micro it would be seamless.

Done a little more research, seems the Si is a complex device, and its no easy to setup a particular o/p freq.
The clock i/p goes to 2 Pll's, either Pll can be used to clock any of the 3 o/p's on the Si, you can select a multiplication rate for each Pll, then there are 2 dividers for each of the 3 o/p's, so you multiply the clock by a factor, then divide by another and then divide by another.
Works well, but for an application like a function generator with continuously variable o/p frequency the algorithm is going to be tricky.
 
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schmitt trigger

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I don't think that these devices were really designed to be continuously variable...there are way too many registers which require updating.
 

dr pepper

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Maybe your right, but that doesnt mean to say we cant, the adafruit modules have 3 reverse sma's on the front so that kinda looks like they are meant for general purpose.

Github link to some demo code for this chip:
https://github.com/adafruit/Adafruit_Si5351_Library/blob/master/examples/si5351/si5351.ino

Edit: This is what I was looking for, a pice of code that accepts your xtal or clock frequency, and you just pass it the actual o/p frequency you want, the software crunches everything for you, its at the bottom of the page:
https://www.riyas.org/2016/11/a-simple-si5351-based-vfo-signal_5.html
 
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BobW

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SiLabs makes several very nice variable frequency generator chips. I hesitate to call them frequency synthesizers, because I'm not sure that they are traditional frequency synthesizer type circuits (not necessarily a bad thing). Several of the SiLabs chips have phase noise specs that are much better than typical frequency synthesizers. A couple of others are Si514, Si570/571. I think all of these are square wave output, not sine wave (unlike the Analog Devices AD9850/51).
 

dr pepper

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Some programs I've been looking at say phase noise isnt great with the '5351 when using non integer multipliers, thats an issue with a lot of these kind of chips though.
 
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