×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

sigma delta oversampling rate.

sigma delta oversampling rate.

sigma delta oversampling rate.

(OP)
I have a couple of questions on sigma delta converters.  I hope someone can help.  

If I need 10 bits of resolution, what oversampling rate do I need?  I've seen in the literature that 64x should give 10 bits.  Does this mean a total of 640 bits from the analog portion of the converter?  I've seen it implied that 64 bits from the analog portion should give 10 bits.  This doesn't make any sense to me, as if I put in the voltage equivalent to a digital 1, it takes 512 samples for the integrator to even detect the signal.  
Any help or insight would be appreciated.

JJM2

RE: sigma delta oversampling rate.

Your question is a bit vague. Are you taking an 8 bit converter and oversampling to give higher resolution or are you just taking a "1-bit" converter and seeing what is possible?

RE: sigma delta oversampling rate.

(OP)
hi logbook,

I am trying to get 10 bits of accuracy from a single bit, 1st    
order sigma delta.  My real question relates as much to the digital portion as to the analog.

How many samples from the 1 bit converter are required to get  10 bits of resolution after filtering and decimation?

Some of the literature I have read implies that you can use 64 bits from the analog portion to get 10 bits of output resolution through the filtering/decimation process.  It appears to me that the minimum number of samples to get "10" bits of resolution is 513.  The very first sample, assuming the sigma delta is cleared every conversion point gives you the MSB.  You then need 512 more to get the value to the LSB.    This doesn't seem quite right either though, since you can just use an adder to calculate the output.  (essentially an LPF w/ 512 taps)

When I ran the AD simulator (linked above) It also took the 512 samples to measure a digital 0000000001 equivelent input.

Any thoughts or insight?

Thanks

RE: sigma delta oversampling rate.

What is the bandwidth of the signal that you want to read?  I have used a 20-bit sigma-delta converter quite a while ago (AD7710 maybe?) and sampling speed was a tradeoff between the bandwidth of the signal to be measured and the precision of the conversion.  The higher the bandwidth the lower effective bits, because of the higher samling rate incurred.

RE: sigma delta oversampling rate.

(OP)
The bandwidth I need is about 5kHz.  So I'd like to get 10 bits at 10kHz.

Thanks,
JJM

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources