datasheets.com EBN.com EDN.com EETimes.com Embedded.com PlanetAnalog.com TechOnline.com   UBM Tech
UBM Tech
Home    Bloggers    Blogs    Article Archives    Messages    About Us   
Tw  |  Fb  |  In  |  Rss
Jonathan Harris

ADC Noise: A Second Look, Part 1

Jonathan Harris
Victor Lorenzo
Victor Lorenzo
12/1/2013 2:42:18 PM
User Rank
Blogger
Re: Most important factor
"Another important point while bypassing is to place several capacitors in parallel instead of lumping it into a single capacitor".

We could add also that not only to place several capacitors in parallel, it should be taken into account the capacitor's behaviour at high frequencies when selecting the capacitors that will 'filter' the high frequency noises (usually ceramic, commonly 0.01uF-to-0.1uF).

50%
50%
amrutah
amrutah
12/1/2013 9:49:42 AM
User Rank
Master
Re: Most important factor
@Yalanand:  Another important point while bypassing is to place several capacitors in parallel instead of lumping it into a single capacitor.

50%
50%
amrutah
amrutah
12/1/2013 9:45:17 AM
User Rank
Master
Re: Most important factor
@Yalanand: There are many techniques to reduce the noise from power supplies and depends on the scope of application, few of them that I know

1> Reduce the effect of noise by using cascode devices, avoid any high switching digital and sensitive analog sharing the same supply (this can be done to some extent by proper laying out the powerlines)

2> bypassing the power supplies at the load so that the peak current (di/dt), which usually leads to noise, can be taken care to some extent

3> Low pass filters can be used to reduce the effect of noise at the load (but this may cause functional problems).

4> Snubber circuits to isolate the noisy elements.

   As far as ground is concerned, which is a reference node for the entire application, I think making it strong (wide routings) is the trick that suffices.

 

50%
50%
yalanand
yalanand
11/30/2013 9:15:45 AM
User Rank
Newbie
Re: Most important factor
The main culprits I consider are the noise from Supply and Ground.  

@amrutah, thanks for sharing your analysis. I am curious to know how can we reduce noise from ground and supply ? What techniques can be used to reduce noise from ground and supply.

50%
50%
amrutah
amrutah
11/15/2013 5:26:49 PM
User Rank
Master
Most important factor
@Jonathan:

  Thanks for the Blog and also updating th e sources of Noise.  I think the noise from reference or common mode is very less due the huge capacitors on that node.  The main culprits I consider are the noise from Supply and Ground.  We may have star connections to these nodes but they are still significant.  Also the inherent devices noise will add a lot to the output noise.  The network used for switching, sampling will introduce new set of noise.

50%
50%
More Blogs from Jonathan Harris
I thought it would be good to continue looking at the example I gave in my last blog where we looked using fewer LDOs and combining power supply rails on an ADC while maintaining isolation with ferrite beads.
There are some disadvantages when driving low input supply voltages, where multiple LDOs may be required.
Keeping the power supply inputs on separate domains can minimize crosstalk and make it much harder for noise to interfere with ADC performance.
As is typically the case, at least from my observance in the last four years, the second day of the show proved to be the busiest.
After a good first two days and very enjoyable evenings of the IMS show, it was time for the last day, when traffic is typically good in the morning but tapers off as the day moves toward lunch and beyond.
flash poll
educational resources
 
follow Planet Analog on Twitter
Planet Analog Twitter Feed
like us on facebook
our partners
Planet Analog
About Us     Contact Us     Help     Register     Twitter     Facebook     RSS