[time-nuts] Slightly OT: interest in a four-output, ultra-low jitter, synthesizer block?

Attila Kinali attila at kinali.ch
Thu Jan 25 12:42:53 EST 2018

On Thu, 25 Jan 2018 09:32:56 -0500
John Ackermann N8UR <jra at febo.com> wrote:

> http://www.silabs.com/documents/public/data-sheets/Si5341-40-D-DataSheet.pdf
> The challenge is that the chip is a 7x7 mm 44-QFN package and really 
> wants to be put on a six-layer circuit board.  That's doable, but 
> challenging, for home assembly.

Solderpaste stencil and a temp controlled frying pan helps :)
> Rather than designing the chip into a larger circuit board, I'm thinking 
> of doing a small "carrier" board that would include just the chip and 
> critical bypass caps and have headers to plug into the main board. 
> Then, you could just drop the carrier into a project-specific board and 
> not have to worry about the complex layout and mounting.  I have a 
> contract manufacturer who can build these up, if there's enough quantity 
> to justify the setup cost.

I'd be carefull with header pins at these frequencies. The slew-rate
of the chip is high enough that you get frequency components well into
the 10GHz range. I think a better idea would be just have castellation
at the PCB edge, with the right distances to meet impedance requriements,
and solder the PCB directly onto the main PCB without any connector inbetween. 

Also be aware that these kind of chips are quite peculiar about
the quality of their power supply. You need to design it for the
internal VCO, such that it has good regulation well into the MHz range
and high quality blocking capacitors rated for GHz use. Using 3-terminal
pass through capacitors like the Murata EMIFIL[1] goes a long way
for these kind of applications (at only a slightly higher price than
normal capacitors).

			Attila Kinali

[1] https://www.murata.com/en-global/products/emc/emifil/chip

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