[time-nuts] Frequency divider design critique request

WB6BNQ wb6bnq at cox.net
Thu Jul 10 16:58:16 EDT 2008

In my best "HAL 9000" voice;

Hi Dave.  Dave, what are you doing ?  Dave we need BNC connectors.  Those SMB's
are hard to work with.  Dave, are you intending to have those SMB's stick out
through a panel ?  Dave ?  Dave, let me suggest that you layout the connector
pattern so either one can be used and stick out a panel.

Dave ?  Dave ?  Why are you unplugging my internet feeeeeee--------


"David C. Partridge" wrote:

> As I've mentioned before, I've been working on the design of a frequency
> divider to go with my TB.
> The idea is 10MHz sine in from TB, output 2.5Vp-p 50% duty cycle square wave
> into 50R (5V into 1M), at 10Mhz, 5MHz, 1MHz and decade selectable 100kHz
> down to 1Hz.  All rising edges synchronised to the 10MHz clock rising edge
> (or as near as I can get with 74AC logic).   With a considerable amount of
> constructive criticism from Bruce Griffiths (thank you again Bruce) I
> believe the design now to be complete.
> The aim is to have as low a level of nasties as possible (i.e. fit for
> time-nuts).
> All faults are my own - no blame attaches to Bruce!
> I've not yet subjected this design to the ultimate simulation tool (PCB,
> parts and solder) yet, and I have no means to test it for levels of jitter
> (phase noise) or similar nasties.
> I think that it's now the right time to open the design up for critique from
> a wider audience before I commit it to copper.
> I'm therefore attaching the design as a PDF file for your comments.
> A few comments are in order:
> 1) The 5Mhz and 1MHz outputs are re-clocked TWICE deliberately to delay them
> by one clock cycle so they line up with the 1MHz and lower outputs.
> 2) The selected output (at the '4051 mux) from the ripple counter chain is
> re-clocked to 1MHz before re-clocking to 10MHz as the worst-case delay in
> the chain of '4017s is large enough that the lower frquencies wouldn't
> reliably re-clock directly to 10MHz.
> I have also done a PCB layout (4-layer) and I'm happy to send a print of the
> top/bottom layers to anyone who feels that they want to comment on that
> (inner layers are ground and power).
> Let the brick-bats be thrown!
> Cheers
> Dave
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>   ------------------------------------------------------------------------
>                               Name: Frequency Divider 2.pdf
>    Frequency Divider 2.pdf    Type: Portable Document Format (application/pdf)
>                           Encoding: base64
>   ------------------------------------------------------------------------
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