hi all

Please help me in verifying the schematic .The reference is AD9912 evaluation board schematic.The DAC reconstruction filter is modified 100MHz.

with regards

Durgarani B

hi all

Please help me in verifying the schematic .The reference is AD9912 evaluation board schematic.The DAC reconstruction filter is modified 100MHz.

with regards

Durgarani B

Thanks for the reply DSB

Answer to the queries you have asked

1)the filter topology used is elliptical ,the response of the filter is attached here.

4)the filter designed for source and load 50 ohms impedance.I refered to the evaluation board schematic and selected the resistor value.Will it cause any perforance degradation at DAC output.

- 1 person found this helpful
I typically use a stop band attentuation factor of -60dBc as my design target. Also, I like to use 0.1db for the passband ripple. That's the only two parameters I would suggest considering. I'm not sure about your end application but here's a coupIe application notes about filtering and clock generation.

I don't have enough information to comment. Filter component values can change drastically with filter parameter requirements. If you can tell me the following I can better comment.

1) This filter topology can be used for an elliptical or Chebyshev type 11 design. Which one do you desire?

2) Desired pass band ripple (dB)?

3) Desired stop band attenuation (dB)?

4) Desired source resistance? Note, looking back into the DDS (filter's source) the external resistors set the source impedance.

If you want 50 ohms for the filter's source impedance make the two resistors 50 ohms each instead.However, in this case, the DAC has an internal differential impedance of 100 ohms. So, 200 ohms externally in parallel with 100 ohms internally is 66.67 ohms for the equivalent source impedance..5) Desired filter load impedance?

If you want the source impedance at ?? ohms and 50 ohms for the load impedance that's OK. I just need to know. With 100 ohms source impedance you'll actually deliver more power to the load because the DDS is a current source.