[SOLVED] Need recommendation for Bessel anti-aliasing filters around 100kHz

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eigenroot

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For this anti-aliasing filter, I need Bessel type. The closest one I find by now is LT1164-5 8th order Bessel filter, with maximum cut-off frequency of 20kHz. But I wish I could push it up to at least 100kHz since my ADC can run much faster than 20kHz. Does anyone have any recommendation?
 

Design an analogue filter instead of looking for a switched capacitor one. At 100kHz a passive LC one may be practical instead of an opamp based one.

Keith
 

The anti-alias filter frequency is determined by the highest signal frequency you want to convert, not the highest sample frequency. What is your highest signal frequency?
 

I guess two other questions are why Bessel and why 8th order?

Keith
 

crutschow said:
The anti-alias filter frequency is determined by the highest signal frequency you want to convert, not the highest sample frequency. What is your highest signal frequency?
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It is around 100kHz (maybe a little less), but is larger than 20kHz

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keith1200rs said:
I guess two other questions are why Bessel and why 8th order?

Keith
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I wanted Bessel filter to preserve the signal shape in time domain. The order of filter is not that important (>=2 is probably fine). 8-th order was just the order of LT1164-5 I referenced above.
 

If all you need is second order then a simple opamp based filter would do the job. I have used LC anti-alias filters around a few hundred kHz up to 5th order.

Keith
 

Eigenroot, in your first post you have asked for a recommendation.
For my opinion, an active filter seems to be appropriate.
However, because of the required bandwidth (around 100 kHz) you need an opamp with a unity-gain bandwidth (transit frequency) of at least (20...50) MHz.
Such amplifiers are available - perhaps are current feedback amplifiers (CFA) a good choice, in particular because of the excellent slew rate.
Perhaps you know that many different topologies are possible. My recommendation: Use low gain applications, for example Sallen-Key structures (4th order as a cascade of two 2nd order sections).
 
You might try the free download active filter design program FilterPro from Texas Instrument. It makes it easy to design many types and orders of active filter. It also tells you the gain-bandwidth required for the op amps.
 
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