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AFE58JD28: requirement of the fully differential amplifier connected after I-Q on CW mode

Part Number: AFE58JD28
Other Parts Discussed in Thread: ADS8881, THS4130

Dear team,

I am using the AFE58JD28 with the THS4130 driving ADS8881 for the CW mode.

1. However, except for the noise requirement, I don't know how to evaluate the GBW requirement of the FDA connecting after the I-Q. I use THS4130 because there are a lots of people using the THS4130 for the ultrasound application.In my opinion , the GBW requirement shouldn't be as higher as 215MHz because the signal of I,Q is about 20Hz to 20KHz and the minimum bandwidth needed to drive ADS8881 is just about 42MHz. Could you please give some rough caculation about how to get the GBW requirement of the FDA? why 215MHz is needed here.

2. what about the other requirement of the FDA in the CW mode, such as (offset, THD,offset drift )? It would be nice if you can also give some rough calculation about these spec based on my application. many things!

Best Regards 

Zhihong Huang

  • Hi Zhihong,

    Thanks for reaching out to us.

    Due to a lot of queries coming in, please allow me some time to get back to you.

    You should hear from me by tomorrow.

    Thanks & regards,

    Abhishek 

  • Hi Zhihong, 

    My apologies for not getting back on this E2E. 

    Somehow this thread was missed and I am really sorry for missing your reply.

    So, about the bandwidth requirements on the external amplifier, there is no compulsion to use such high bandwidth amplifier after the internal summing amplifier. 

    The main concern for this amplifier is the input referred noise, which should be low. Other than that, there is nothing specific restriction on any other parameter. 

    Many people use THS4130 due to its noise performance only. If you are able to find a low noise amplifier with similar noise performance. You can use the same.

    Btw, for your information, we do have a reference design for this CW path. which you might be interested in. Please do have a look at the technical details shared in the design guide.

    https://www.ti.com/tool/TIDA-01351

    Thanks & regards,

    Abhishek