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AD8307 - Detection of short burst with preceding filter delay

Question asked by groger on Mar 12, 2015
Latest reply on Apr 29, 2015 by groger

Hi,

 

Please see attached filter output display using LTspice, with AD8616 opamps. The filter is a pair of cascaded 8th order butterworth bessel bandpass filters, total 30dB gain. (Need very strong rejection out of band)  Unfortunately, even with minimal delay filters, delay *is* happening with a 16th order filter.

 

So...the question is this: With this filter/gain stage ahead of a AD8307 (yes, gain has been accounted for in output) what will the impact be when detecting a very short signal burst of, let's say duration 60ms? 100ms?

By T = 200ms, the filter has reached almost full magnitude. Does this mean that for any signals bursts under approximately 125ms, will not be seen at all by the AD8307 ? Or are they just delayed and will not reach the output (and be of significant amplitude) for a time period > approximately 125ms?

 

Thanks for your help !!

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