Oversampeling IC

General project help for Adafruit customers

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
geir102
 
Posts: 60
Joined: Sat Mar 29, 2008 3:01 pm

Oversampeling IC

Post by geir102 »

Hi

Is there an IC that lets you over sample. What I want to do is over sample a signal and then down sample befor it goes to the µC. I want to avoid aliasing of the noise, witch is what i think im seeing now.
People have reported that running a faster uC(oversample) solves the problem. I know i can do it using a FPGA but I want a simple soution.

User avatar
ImaginaryAxis
 
Posts: 267
Joined: Sat Nov 13, 2010 3:16 pm

Re: Oversampeling IC

Post by ImaginaryAxis »

You do not need to 'down sample' after you over sample a signal. One of the benefits of oversampling is to lessen the anti-aliasing filter requirements. Many A/D and D/A converters allow you to over sample - those included in uC should be no different. The oversampling rate required depends on the frequency and dynamic range requirements of your signal and the highest clock frequency supported by the A/D, D/A, uC, etc.

What is your input signal frequency you are trying to sample and avoid aliasing? What is the filter order you are currently using?

geir102
 
Posts: 60
Joined: Sat Mar 29, 2008 3:01 pm

Re: Oversampeling IC

Post by geir102 »

I'm trying to sample the output from a accelerometer (ADX330). I'm using a atmega328 running at 16mhz sampling the signal at 400hz. I've heard that sampling at 1khz solves the noise problem. I want zero mean noise but thats not what i getting now (aliasing i think).

User avatar
ImaginaryAxis
 
Posts: 267
Joined: Sat Nov 13, 2010 3:16 pm

Re: Oversampeling IC

Post by ImaginaryAxis »

Ok, but what is the lowest frequency of interest that you are trying to sample? Increasing the sampling rate will help as will a higher order filter. If you are sampling at 400 Hz then the signal you are trying to sample must be below 200 Hz. Do you know the desired dynamic range?

geir102
 
Posts: 60
Joined: Sat Mar 29, 2008 3:01 pm

Re: Oversampeling IC

Post by geir102 »

It's an accelerometer that I'm trying to use for INS. As I mentioned sampling at 1khz should be fine. but i cant get more then 400hz from the µC

User avatar
zener
 
Posts: 4567
Joined: Sat Feb 21, 2009 2:38 am

Re: Oversampeling IC

Post by zener »

What uC and what code? 400 Hz seems slow.

User avatar
ImaginaryAxis
 
Posts: 267
Joined: Sat Nov 13, 2010 3:16 pm

Re: Oversampeling IC

Post by ImaginaryAxis »

He said he is using the Atmega328. Checking the datasheet, it is capable of 79.5 kSPS for ~15kSPS at maximum resolution.

User avatar
zener
 
Posts: 4567
Joined: Sat Feb 21, 2009 2:38 am

Re: Oversampeling IC

Post by zener »

You need to figure out why you are sampling so slow. Your main loop must be going pretty slow.

Locked
Please be positive and constructive with your questions and comments.

Return to “General Project help”