sensitivity in filters and number of bits of system

Status
Not open for further replies.
A

akbarza

Full Member level 2
Joined
Dec 18, 2013
Messages
131
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,296
Activity points
2,556
hi
i read a pdf file that i think belongs to book opamp for every one .
in chapter 16 of the book-filter design chapter-sensitivity is explained.
for a tolerance in a 8 order low pass butterworth filter, the difference between ideal response and real response is 0.35dB .
then in the book is written:
If this filter is intended for a data acquisition application, it could be used at best in a 4-bit
system. In comparison, if the maximum full-scale error of a 12-bit system is given with 1/2
LSB, then maximum pass-band deviation would be – 0.001 dB, or 0.012%
can you explain about these 4 bit and -0.001 dB?
how is reached to 4-bit from .35 db error?
thanks
 

Attachments

  • filterdesign.pdf
    292.8 KB · Views: 161

Sort by date Sort by votes
Above 16-51 pic discussed is 4.1% G error. 4 bits = 6.25% = 1 LSB error which is the closest bit

count to cover the 4.1% error.

12 bits to 1/2 LSB, then G = 1 + 1 / 2**13 = 1.000122 = .0122% G error = + .001 db error


Regards, Dana.
 
Last edited:
Upvote 0 Downvote
The calculation is simple, but as I think inappropriate for a typical data acquisition application. You'll expect full resolution at DC or low to mid frequency but not necessarily near the cut-off frequency.
 

Upvote 0 Downvote
I think of a true RMS meter, the high precision stuff HP/Agilent or Fluke
make. They would spec out to a BW, so to FVMs point that probably not the
actual 3 db BW but rather one that is << less to insure, in this case, no peaking
errors occur.

But these days high precision is done thru linearization and cal, a typical system
at manufacture looks like this process -




Regards, Dana.
 

Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…