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AD9834 filter

Question asked by sitti on Oct 9, 2012
Latest reply on Oct 9, 2012 by sitti

Hi,

 

I am currently using AD9834 making use of its capability to have sine, triangle and square wave outputs.

My application needs a 10MHz cut-off frequency. When I tried to populate an RC filter (with Fc = 10.61MHz) in the AD9834 eval board, the sine wave output is not that good thus I decided to choose other type of filter.

I was able to see this thread http://ez.analog.com/thread/7281?start=0&tstart=0 and downloaded the attachment of LiamR in which a 1st order and 3rd order schematic with corner frequency of 3.3MHz is provided. I tried to simulate it using the Nuhertz Filter Solutions trial version in which I came up with the same, and I was also able to simulate for 5th order. Attached is my filter solutions screenshots.

I am working at this first before going to 10MHz cut-off frequency.

However, when I tried to simulate the generated schematic in MultiSim, the response seems to be different.

 

multisim_1st order.png

This is the Multisim simulation for the 1st order.

multisim_3rd order.png

In this 3rd order simulation, instead of having a corner frequency of 3.3MHz, the -3dB frequency is just around 475kHz.

 

When I proceeded to 10MHz, still the same.

multisim_5th order_10MHz.png

Instead of a 10MHz at -3dB bandwidth, it's just around 2MHz. Can someone advise on this?

 

Thank you very much.

Sittie

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