Hi Every One !
I would need some help regarding noise generated for the Delta sigma in single end configuration.
As you can see in the schematic as result of array scanning I am geting pulses which votage depend of the pressure applied to every cell in the array. My Vdda is 3.3 v . The issue is that with no pulse, ( checked with osciloscope) there is noise that you can watch in the graphic display picture.
The only way to avoid that is using a PGA before the Delta sigma..
I cannot undestan that. !!!!
And even using a PGA, I need to filter trough code , like high pass filter values above 0x80, wich represent almost a half of the ADC range.
I woul appreciate very much any help.
It would be helpful if you posted your project. Note you mentioned something
attached but there is nothing present in your post.
At high resolution layout, bypassing critical to getting noise floor capability
as shown in datasheet. These may help -
http://www.cypress.com/?rID=39677 AN57821 - PSoC® 3, PSoC 4, and PSoC 5LP Mixed Signal Circuit Board Layout Considerations
http://www.cypress.com/?rID=40247 AN58827 - PSoC® 3 and PSoC 5LP Internal Analog Routing Considerations
http://www.cypress.com/?rID=39974 AN58304 - PSoC® 3 and PSoC 5LP – Pin Selection for Analog Designs
http://www.cypress.com/?rID=43337 AN61290 - PSoC® 3 and PSoC 5LP Hardware Design Considerations
Consider the following when at hi res -
1) Shut off all digital I/O on pins adjacent to A/D inputs, also consider
stoping UDB resources to minimize internal ground bounce and coupling
2) Set Vref to external bypass, use a polymer tant to bypass it.
3) Simple averaging helps noise reduction
4) Using specturam analyzer determine noise source by its signature
Consider posting your project, makes life easier to troubleshoot.
“Create Workspace Bundle”
Route your Amux output to a pin, do you see 7 Mhz clock transients
on it ? I would posit the reason a PGA suppresses transients is because
of its slew rate limiting effect, eg. it acts as a LPF to edge transients like
clock feedthru in a CMOS switch.
Thank you Dana !!!
May be I cannot understand you complletelly.
I undestand that you said a bout PGA acting like a filter .
But , what do you mean saying tp pass the Amux output trough a pin ?
On the other hand, If I put ociloscope's test point at resistance of 2.2 k which is hooked up to pin 3 and there is no array cell touched, there are information going to the dipaly like random noise even when you cannot see any signal on the osciloscope.
Tnak you very much Danna
You accomplished what I stated by connecting your scope to the
2K R at the output of the Amux. The idea was to observe the noise
at the A/D input from the Amux output at a pin.
Do you still get a lot of noise when you short the 2K R to ground, therefore
making A/D input also ground ?
Best would be to post a project archive as I discussed earlier.