[sdiy] In praise of the ATM STM32F303

[Neil Johnson]

Checking the errata sheet for the F446 part I see that it also has ADC
noise issues  (section 2.1.6).

Neil
On 14 Feb 2016 11:17, "Simon Brouwer" <simon.o at brousant.nl> wrote:

> Hi Eric,
>
> If it is this errata sheet:
>
> http://www.st.com/web/en/resource/technical/document/errata_sheet/DM00037591.pdf
>
> It applies to specific revisions of the F40x and F41x families.
>
> So it is possible that in newer revisions and other parts such as the F446
> they
> fixed it.
>
> Anyway, thanks for the heads up, it is good to know that this problem may
> exist
> and may need a workaround.
>
> Best regards
> Simon
>
> > Op 13 februari 2016 om 16:17 schreef Eric Brombaugh <ebrombaugh1 at cox.net
> >:
> >
> >
> > I'm fairly certain that it's mostly down to the crosstalk from digital
> > circuits on the same die. The F4 parts errata sheets specifically
> > mention that the flash cache system interferes with the ADC and they
> > have a number of workarounds listed which unfortunately don't really
> > seem to help much. The best approach with the F4 ADCs is to do a lot of
> > filtering and hysteresis / guard-banding of the digitized values. This
> > is fine for slowly varying CVs and pots, but does tend to limit their
> > application for audio-rate modulation.
> >
> > While the F3 CPU which runs slower requires a less aggressive cache
> > system and hence has less on-chip interference, there may be other
> > circuit-level differences in the analog section - on the F303 there is a
> > high-speed SAR ADC which performs pretty well and as Olivier mentioned,
> > the F373 SD ADCs exhibit very good ENOB. I've got an F373 prototype
> > running that does stereo audio input/output without an external codec
> > and sounds quite good.
> >
> > Note that I've done some research on the F302 parts and the ADC in that
> > family seems to have issues that I've not seen on other F3xx parts. I
> > suspect that there may be some compromises on those lower-cost members
> > of the F3 series.
> >
> > Eric
> >
> > On 02/13/2016 04:05 AM, Simon Brouwer wrote:
> > > Hi Eric,
> > >
> > > Any idea whether that noise is due to worse (differential) linearity
> or to
> > > worse
> > > crosstalk from digital circuits?
> > >
> > > I am starting out with the STM32F446 for a one-off semimodular
> monophonic
> > > synth,
> > > and was thinking of using one of its built-in DACs for VCO control
> voltage.
> > > My
> > > plan is to deal with its nonlinearities by calibrating its output
> voltage at
> > > each semitone, then using a lookup table with correction values.
> > > But if the DAC output voltage contains LSB's of uncorrelated noise, I
> may be
> > > better off using an external SPI DAC.
> > >
> > > Best regards
> > > Simon
> > >
> > >> Op 13 februari 2016 om 4:37 schreef Eric Brombaugh <
> ebrombaugh1 at cox.net>:
> > >>
> > >>
> > >> A couple guesses why:
> > >>
> > >> 1) for high-volume production such as Waldorf usually does, every cent
> > >> makes a
> > >> difference. In large quantity F3 parts like the 303 are a few bucks
> cheaper
> > >> than F4 parts, so that adds up.
> > >>
> > >> 2) I've used both F3 and F4 parts in products so I've got some
> experience
> > >> with
> > >> them. The F3 parts analog sections are considerably higher quality
> than the
> > >> F4. Noise on F3 ADCs and DACs are a few lsbs lower amplitude than F4
> parts.
> > >>
> > >> Eric
> >
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