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Tunable filter for AD9958

Hi all,

Just wondering whether anyone here can help me in my amateur journey into DDS circuit design?

I've finally settled on the AD9958 as my DDS and have made some headway in using a PIC to program it, but I've begin to wonder about reconstruction filters on the output side of the AD9958.

I've looked over the LTC6603 from Linear, which looks like a good tunable 9th-order filter with dual inputs (for the dual outputs of the AD9958).

So my question is this -

Would I have to go: DDS Output -> 1:1 Matching Transformer -> LTC6603 Input -> Filtered Output

Or is there a circuit design that could go straight from DDS Output to LTC6603 input without a matching transformer. In other words, do I need a matching transformer between the output of the AD9958 and the differential input of the LTC6603?

Many thanks in advance,

-Rob.

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  • Thanks for your reply Georgy,

    I can't quite figure out how to shift the inputs by 1.8V.

    Would a simple high-pass filter arrangement between the AD9958 and the LTC6603 work, with a capacitor in between the AD9958 output and LTC6033 input, and then a resistor off to ground (or maybe 1.8V?) which matches the input impedance of the LTC6033's pin?

    Yours,

    -Rob.

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  • Thanks for your reply Georgy,

    I can't quite figure out how to shift the inputs by 1.8V.

    Would a simple high-pass filter arrangement between the AD9958 and the LTC6603 work, with a capacitor in between the AD9958 output and LTC6033 input, and then a resistor off to ground (or maybe 1.8V?) which matches the input impedance of the LTC6033's pin?

    Yours,

    -Rob.

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