how to use 6 bit ADC/DAC to gain 8 bit ADC/DAC performance?

no, by oversampling

balchand wrote:
> no, by oversampling

Actually (as the smilie implied), my reply was a humourous response to
the fact that you (presumably accidentally -- Google Groups in
particular is notorious for that) posted *your* first reply twice in
quick succession. :-)

kiki wrote:
> Hi all,
>
> Can anybody suggest some methods of gaining 8-bit ADC/DAC performance
with 6
> bit only ADC/DAC?
>
> Any thoughts? Thanks a lot!

Depends how good your 6 bit a/d is, integral nonlinearity is the spec
you need to look at, if its only good to 6 bits, then the answer is you
can't do it by oversampling. In this case you can still achieve your
goal by using multiple 6 bit a/ds for each signal (basically break the
analog signal into 6bit dynamic range chunks and feed it to a 6 bit a/d
and digitally combined them)

bungalow_steve@yahoo.com wrote:
> 
> kiki wrote:
> > Hi all,
> >
> > Can anybody suggest some methods of gaining 8-bit ADC/DAC performance
> with 6
> > bit only ADC/DAC?
> >
> > Any thoughts? Thanks a lot!
> 
> Depends how good your 6 bit a/d is, integral nonlinearity is the spec
> you need to look at, if its only good to 6 bits, then the answer is you
> can't do it by oversampling. In this case you can still achieve your
> goal by using multiple 6 bit a/ds for each signal (basically break the
> analog signal into 6bit dynamic range chunks and feed it to a 6 bit a/d
> and digitally combined them)

I think it depends on what you want to achieve. By oversampling, you can certainly improve the SNR
(in all cases!). However, integral nonlinearity will limit the linear behaviour of the device
(generation of harmonics of the input signal), oversampling or not. I did not do any calculations on
this, but is it possible that the harmonic spurious in the signals's spectrum due to integral
nonlinearity are smaller than the inband quantization noise?

   Jeroen

Jeroen Boschma wrote:
> bungalow_steve@yahoo.com wrote:
> >
> > kiki wrote:
> > > Hi all,
> > >
> > > Can anybody suggest some methods of gaining 8-bit ADC/DAC
performance
> > with 6
> > > bit only ADC/DAC?
> > >
> > > Any thoughts? Thanks a lot!
> >
> > Depends how good your 6 bit a/d is, integral nonlinearity is the
spec
> > you need to look at, if its only good to 6 bits, then the answer is
you
> > can't do it by oversampling. In this case you can still achieve
your
> > goal by using multiple 6 bit a/ds for each signal (basically break
the
> > analog signal into 6bit dynamic range chunks and feed it to a 6 bit
a/d
> > and digitally combined them)
>
> I think it depends on what you want to achieve. By oversampling, you
can certainly improve the SNR
> (in all cases!). However, integral nonlinearity will limit the linear
behaviour of the device
> (generation of harmonics of the input signal), oversampling or not. I
did not do any calculations on
> this, but is it possible that the harmonic spurious in the signals's
spectrum due to integral
> nonlinearity are smaller than the inband quantization noise?
>
>    Jeroen

I believe oversampling only improves SNR when the noise is evenly
distributed, a rogue clock signal near the a/d, for instance, would
induce noise that could not be removed by oversampling. Integral
nonlinearity can be improved by characterizing the a/d, so I guess that
with oversampling could work (although I think hysteresis could bite
you in the foot)