SynthModules

Any ADC is going to dither at a bit boundary because of noise.

The normal solution is to put in a rolling average filter where you 
store successive readings in a buffer and average the number of 
samples in the buffer. Then kick the oldest reading out, add a 
new reading and average again for each new output. This forms 
a digital low pass filter to filter out the LSB dither.

--- In SynthModules@yahoogroups.com, "djbrow54" 
<davebr@e...> wrote:
> I'm using the standard MOTM power supply, a linear PowerOne
> HAA15-0.8-A with no other modules connected except the 
PSIM.  I can
> measure very little noise on it.
> 
> When using the Quantizer software, I can vary the control 
voltage
> very slightly and get it in a mode where the quantizing will
> alternate between current value or one step higher.  I'm 
assuming
> this is the ADC repeatability coupled with the noise on the input
> voltage.  I've cleaned up the input voltage and it's much better 
but
> I can still find a couple of spots where it will vary between two
> values.
> 
> I wrote some code to add input hysteresis and the variation
> completely goes away if I require the input to change at least 
two
> bit positions.
> 
> I have no reason to believe the PSIM is defective.  I think I'm 
just
> up against the limits of the power supply and input CV noise.
> 
> Dave 
> 
> 
> -- In SynthModules@yahoogroups.com, "Brice D. Hornback"
> <synthmodules@s...> wrote:
> > I don't see any jitter.  Remember, your signal to noise ratio is
> only as
> > good as your power supply.  What kind of power supply are 
you
> using?  What
> > other modules are connected to it?  What software are you 
running
> for this
> > test?
> > 
> > If you believe you have a problem, send your PSIM-1 back to 
me and
> I'll test
> > it.
> > 
> > Thanks,
> > Brice
> > http://www.SynthModules.com
> > 
> > ----- Original Message ----- 
> > From: "djbrow54" <davebr@e...>
> > To: <SynthModules@yahoogroups.com>
> > Sent: Sunday, May 02, 2004 7:44 PM
> > Subject: [SynthModules] ADC input jitter
> > 
> > 
> > > How much jitter are you folks experiencing on IN-1 to IN-4?  
If
> you
> > > put a constant voltage source into the input and then 
sample the
> > > input, how much variation are you seeing in the 10 bit 
result?
> > >
> > > I'm seeing a fair amount and I don't know if it's noise in my
> system
> > > or there is that much jitter in the ADCs.  Anyone 
implemented
> > > hysteresis code for the inputs?
> > >
> > > Thanks - Dave
> > >