Yes, I was planning to include bypasses, and I've been convinced to put
at least the 1.8V regulator on the board as well. And to think about
the interconnects.
Adding the crystal does make the layout more complex -- they put a
ground pour on its own layer underneath it, and I think (but am not
sure) that the connections complicate selecting an external oscillator.
I'll look into the pain tradeoff.
On 01/25/2018 04:08 PM, Robert LaJeunesse wrote:
John, I appreciate your minimalist goal, but I'll second Bill's section about including
the power supply voltage regulator and bypassing. Finding a good regulator with wideband
line regulation/rejection could prove a real search, and such a fast chip as the Si5340
will need excellent broadband supply bypassing. So keep these key components tight to the
chip, on the same PCB obviously. The need for a 4- to 6-layer board screams "keep
critical loops tight"! FYI a regulator (of needed RF performance) producing 3.3V for
VDDA will likely have an absolute max input voltage of 6V or so. Having a 5V supply
requirement will not be a serious limitation of the overall system design. I'm sure you
know the 1.8V supply regulators should not be fed from VDDA (3.3V), but I'll mention it
anyway.
With that much on the PCB adding a small crystal can't add significantly to the cost,
so why not? It allows R&D of the chip and outputs before having to hook up one's
10MHz reference. As such crystal quality / stability / etc. are of little concern -
just size & cost.
I also like the previous suggestion of castellated connections on the board edge -
easy to solder to a board and easy to solder wires to. If you make the castellations
on 0.1" (or 2mm) centers then it becomes possible to use common header pins as
well. Just keeping your options open there.
Bob L.
Sent: Thursday, January 25, 2018 at 3:23 PM
From: "John Ackermann N8UR" <j...@febo.com>
To: time-nuts@febo.com
Subject: Re: [time-nuts] Slightly OT: interest in a four-output, ultra-low
jitter, synthesizer block?
Hi Bill --
And that's exactly what I *don't* want to do. :-) The reason is that I
have several different projects in mind (and everyone else will have
their own requirements) and only want to deal with the difficult package
once.
The idea is to make a minimal carrier to deal with the tiny part and
six-layer board. Then all the ancillary stuff (including the MCU that's
needed to program the chip) goes onto the board designed for that
project. This isn't intended to be a finished product, just a building
block.
73,
John
----
On 01/25/2018 03:12 PM, wb6bnq wrote:
Hi John,
Thanks for the response. Here is my 2 cents:
Well, due to the level of difficulty in chip mounting, I would prefer to
see a complete project. I.E., power supply for a single input of 12
volts and regulators the necessary chip values, proper input protection
for the 10 MHz input level and single ended outputs of the appropriate
levels (I am assuming more than 3 volts) or an amplifier stage for
arriving at such. Equally have RF connectors (SMA would be good) on the
board perhaps.
Of course as cheap as possible, hi hi. A carrier board arrangement
would be useless to me. My application would be to provide signals for
things like my Quicksilver SDR receiver, among other uses.
If you are interested, I can show you a nice little ABS (I think) box
that has EMI built-in that I used for a project that should be more than
large enough for your needs.
Thanks for reading,
73....Bill....WB6BNQ
John Ackermann N8UR wrote:
Hi Bill --
I should have been more clear: this design will be for a simple case:
one reference clock input, four outputs. The chip can do all sorts of
fancy tricks, but I'm looking for a source of four low jitter outputs
derived from a 10 MHz external reference (not using crystal or
on-board oscillator). Many of the pins are unused in that configuration.
I'm not looking to make a universal carrier for the chip, but to meet
what I suspect is a common time-nut/ham radio desire for a clean
multi-channel synthesizer.
On 01/25/2018 02:02 PM, wb6bnq wrote:
Hi John,
After looking at the data sheet, it seems way more involved then just
making a carrier board for it. Besides the power supply
requirements, various design selections would dictate different
circuit layouts for different purposes. Even trying to do a general
purpose application would possibly require having several different
output configurations and possibly a couple of input configurations
as well. That would imply a rather detailed PCB and that chip
package style is a serious pain in the ass for [what amounts to]
hobbyists. So it would seem the logical course would be to do
serious design application and see if an in-house component mounting
job would be feasible.
I notice that the data sheet says the jitter specs are only best when
using The internal crystal oscillator frequency between 48 and 54
MHz. It was unclear to me that the same would apply to using the
non-crystal inputs.
Perhaps you could indicate what you are attempting to do with it and
how you are going to accomplish your goals ?
73....Bill....WB6BNQ
John Ackermann N8UR wrote:
After the recent discussion about Silicon Labs clock generators, I
looked at their Si5340A part and think it will be useful for a ham
radio project I'm working on. While it can do other things, for my
use it would use a 10 MHz input clock and generate 4 independent
outputs in the range of 100 kHz to 1028 MHz. Its jitter is <100fs,
which translates to "not bad" phase noise. Here's the data sheet if
you're interested:
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.
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.
If you'd be interested acquiring in one or more of these, please
drop me a line off-list (jra at febo dot com). I don't think this
will be a TAPR project, but if there's enough interest to build 25
of these carriers, I can probably make that happen. And remember --
this is just the chip; you'll need to provide the rest of the circuit.
John
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