Intermodulation Distortion with AD1938

Hello echoskope,

I will need some more specific information and then I will be glad to go into the lab to see if I can duplicate what you are seeing and then try to figure out a resolution.

So what IM test are you performing? Frequencies?, Levels?

What are the numbers you are seeing?

What are the requirements you need to meet?

I will also need the details of how you are driving the part. Sample rate? Clocking details?

There will probably be some more questions once we get further but let's start with these.

Thanks,

Dave

Well I did some more testing, and discovered it isn't the AD1938, but the op-amps that are used to condition the signal (AD8608). I traced the tone and every time I made a jump over an op-amp circuit I saw a drop in the IMD.

As far as I know, our test unit send out a 23-tone signal into our system, and on the receiving end it checks for the harmonics and, I believe, it returns to me the biggest difference in dB between the sent frequency and the picked up harmonic. Ideally a system would have greater than +60dB but right now we are seeing, after a full run through of the system, around +45 dB, and to pass VG8 requirements we need +48 dB or greater.

When I probe the signal from the beginning to the end, I didn't see any change in the IMD across the AD1938, eliminating it from the equation. I do see ~4 dB drop in our readings everytime I jump across an AD8608.

Hi echoskope,

Maybe somebody in the Operational Amplifiers community could help you!

This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

Thank you,
EZ Admin