On Sat, 7 Apr 2018 22:54:42 -0300
Daniel Mendes <dmend...@gmail.com> wrote:

> I´m a long time time-nuts lurker (I posted here just a dozen times). I make
> a few impedance measurement systems for material analysis (i´m a single man
> shop doing custom hardware for clients). Usually they´re based around a
> STM32F4 / F7 microprocessor: DAC generates sine signal (1-400KHz), ADCs
> measure them back, a few calculations later we have modulus / phase. I
> always used internal ADCs and DACs (12 bits each).

The STM32's are known for their poorly performing ADCs and DACs,
even using an external one with the same bit width will increase
your performance. That said, what is your actual sample rate?
I would guess, if you use the timer unit to generate the pulses,
your jitter would be less than 10ps rms, probably even less than 1ps rms.
10ps rms limits your resolution to something like 14-15bit @500kHz,
1ps rms should be around 18bits, if I'm not mistaken. 

To measure the performance, I would just build the device and feed it
with an appropriate sine wave. Then analyze the SNR and spurs of the
sampled signal.

                        Attila Kinali

It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson
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