On 10/29/2014 6:53 AM, Lostgallifreyan wrote:
rickman wrote in :

MSF time signals? Just a thought... If you're interfacing an analog
signal to digital, one trick I used (for audio but it ought to help
here too) is a CA3140 with a bit of positive feedback through a few
Mohms for hysteresis to clean the signal a bit. The resulting Schmitt
trigger, powered by about 5 or 6V, could be sensitive to take a lot of
strain off your antenna. Whether this alone gives you enough gain I
don't know, but it is cheap to try.

Thanks for the suggestion. I'm not sure this would be any better than
feeding it directly into my digital input. That is a differential input
and I expect to use feedback to overcome the residual input offset. So
the input will be pretty sensitive

Well, try it.

Yes, easier said than done. The receiver isn't built yet, I am
currently looking at the antenna design again and wish to improve my
simulation by adding the radiation resistance. If the antenna will only
put out microvolts even after tuning I will need to figure out how to
add the amp without having to double or quadruple the power budget.


If it works then inputs are better these days. Or at least,
more sensitive to small changes. As far as I know, digital inputs are usually
specified with a wide dead band for levels, amounting to HUGE hysteresis and
a need for a lot of gain first sp you already ned an op-amp stage no matter
what unless your digital inputs have hair triggers at exactly the threshold
you wanr.

This is a differential input which is not far from an analog input.
Actually even single ended digital inputs don't have much hysteresis
unless they are designed for that. But there is always some because of
the parasitic capacitance between the input and output of the buffer.


The thing about the CA3140 is that with just three passive parts: M-ohmage of
positive feedback, input series capacitance, and input ground resistor after
the cap, you can empirically set some very nice signal preconditioning as
well as raw gain, all on a very convenient single rail supply at 5V.

This design won't have a 5 volt rail. Most of the design will run on
1.2~1.8 volts with some I/O at 3.3 volts to drive an LCD. It's very low
power, remember?

--

Rick