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Entry  Sun Jul 24 20:36:03 2011, haixing, Summary, Electronics, AA filter tolerance analysis 6x
    Reply  Sun Jul 24 20:47:21 2011, rana, Summary, Electronics, AA filter tolerance analysis 
       Reply  Sun Jul 24 22:19:19 2011, haixing, Summary, Electronics, AA filter tolerance analysis low_pass_new.png
          Reply  Tue Jul 26 21:11:40 2011, haixing, Summary, Electronics, AA filter tolerance analysis 
Message ID: 5024     Entry time: Sun Jul 24 22:19:19 2011     In reply to: 5023     Reply to this: 5038
Author: haixing 
Type: Summary 
Category: Electronics 
Subject: AA filter tolerance analysis 

 

>> This sort of OK, except the capacitor connects across the (+) terminals of the two input opamps, and does not connect to ground:

low_pass_new.png

 

>> Also, we don't care about the CMRR at 64 kHz. We care about it at up to 10 kHz, but not above.

In this case, the conner frequency for the low-pass filter would be around 100kHz in order to satisfy the requirement.


>>And doesn't the value depend on the resistors?

Yes, it does. The error in the resistor (typically 0.1%)  is much smaller than that of the capacitor (10%). Since the resistor error propagates in the same as the capacitor,
we can ignore it.

Note that we only specify the conner frequency (=1/RC) instead of R and C specifically from the tolerance analysis, we still need to choose appropriate
values for R and C with the conner frequency fixed to be around 100kHz, for which we need to consider the output impedance of port 1 and port 2.

 

 

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