Bert,
Hard to predict without looking at the details. The main battle for a
sine-to-square is to fight white and flicker phase noise as well as
additive repetitive signals such as 50 Hz power noise creeping into the
jitter. At the same time we try to get the conversion more long-term
stable, so that temperature and voltage changes has less impact on the
comparator point as it will convert voltage shifts into phase-shifts.
However, as any active device, it too will add noise and phase-shifts.
I think that this is a field where you need to experiment and learn, and
I try to show some alternative routes and some known traps which may
solve one problem but cause another.
So, properly built, they should contribute if this is where you are
having troubles, if it's not, they will add to long term ADEV for sure.
Cheers,
Magnus
On 07/10/2014 09:51 PM, [email protected] wrote:
Will the added stage negatively effect ADEV?
Bert
In a message dated 7/10/2014 3:48:44 P.M. Eastern Daylight Time,
[email protected] writes:
Bert,
OK, good that you are familiar with it, it was not obvious in that message.
If you consider it as the first stage, and that you then can put another
(faster) stage after it until you go for comparator. It's just the same
thing as the multistage for beat-note, but you run at a higher
frequency. That way you should increase your slew-rate step-wise.
Cheers,
Magnus
On 07/10/2014 09:37 PM, [email protected] wrote:
Magnus
Thank you for your recommendation I use Wenzel extensively as a matter of
fact I just completed in the last three days two boards that have Wenzel
on
it and in my projects I can count 14 boards. Rise and fall time is my
concern but I am open to suggestions that is why I turned to the list
looking
for the best.
Thanks again Bert Kehren
In a message dated 7/10/2014 3:09:52 P.M. Eastern Daylight Time,
[email protected] writes:
Bert,
On 07/10/2014 04:55 PM, [email protected] wrote:
As part of the FE 405 B project a separate output circuit is in the
works.
The universal controller and auxiliary board are the same as used in
the
FE5680A GPSDO but because of the very low ADEV a separate circuit
board
that
divides by three and has also two ground isolated transformer outputs
is in
the works.The question is what is the best sine to square wave
converter
with the lowest ADEV contribution. I am looking at Bruce's circuit
using the
ADCMP600. Any other ideas?
Do look at the Wenzel clockshaper [1], look at the TADD-2 [2] schematic.
It's a PNP long-tail pair. The strategy is to provide modest gain. A
known strategy to reduce 1/f noise and to some degree thermal
differences is naturally feedback, as you will find in the NIST papers.
Once you have the slew-rate up, going in for the kill with a straight
comparator should give you all the nice output slew-rate you can wish
for.
Thus, this is not all that different to the mixer-setup you have done.
I have modified my TADD-2 such that one of the output channels is fed
from the input circuit, and this provides me with a squared up version.
For a counter such as DTS-2070C, the difference is significant, which
helps to show the potential of this simple design.
I think the basic approach can be improved, and how far one has to go
depends on how "clean" source you have. You end up with interesting
measurement problems.
An indirect way to measure the goodness of a squarer is to insert some
known sine disturbance at say 30 or 40 dB below the signal. A straight
comparator won't work very well. Be careful with selectivity of LC, as
it is a nice way to become temperature dependent, so low-Q solutions is
needed.
Cheers,
Magnus
[1] http://www.wenzel.com/documents/waveform.html
[2] https://www.tapr.org/kits_tadd-2.html
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