SynthModules

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

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
> >

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@earthlink.net>
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
>
>
>
>
>
> Be sure to check out the primary Web site at:
> http://www.SynthModules.com
>
> Yahoo! Groups Links
>
>
>
>
>

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
> > >