>  In a message dated 17/09/00 03:58:08 GMT Daylight Time, RADIOTEL@....... 
>  writes:  
>  > TO: ALL
>  >  MAXIM has a 5 pole Bessel analog filter (Part # 7409)  which is an 8 
pin   
>  >  dip package which operates with 5 volts.  Since they only require 
several 
>  >  additional components (resistor and two capacitors) to operate, they  
>  >  would appear to be useful for a seismograph.
>      
>      The temperature output offset drift Spec doesn't look very good at ~ 
+/-  
>  0.1 V over the ambient range and I'm not over enthusiastic about 5 mV 
clock 
>  feedthrough. 1 Hz is right on the bottom of it's range. Might be OK, but 
it 
>  needs to be checked out carefully.

    My apologies. I miss-read my screen. The temperature output offset drift 
should read  -0.1 mV to +0.2 mV over the ambient range, which is fine. The 5 
mV clock comment still applies, although at clock frequency = 100 x corner 
frequency this is easily reduced by more filtering, since the output needs to 
be buffered anyway. There doesn't seem to be any drift / error spec for the 
signal at 1 Hz and with a capacity of only 2.1 pF, this could be significant. 
Most of the graphs seem to be for 1 KHz. The MAX7409 uses a 5 V supply with 
the zero level of 2.5 V and the quoted range is 1 Hz to 15 KHz. The internal 
clock drift of 1% over 20 C Deg looks OK, but you will need to select the 
capacity to get the correct clock frequency - the centre frequency spec seems 
to be +27% to -30% .

    Chris Chapman
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