THS4509: How to design the relative circuit as an 100OHM input-impedance ADC driver

Hello Nan,

If possible, could you share the part number or relevant specifications for the ADC you are considering?  The ADS52J90 is a rather complex ADC and it's EVM documentation takes a while to read through.  I found that within the THS4509 datasheet another ADC is referenced, Section 9.2.1.2.4.  This ADC, the ADS5500, has a bit easier datasheet and parameters to investigate for your comparison.  

I will investigate calculating a proper output impedance network for the THS4509 for a presumed 100 Ohm source impedance ADC, but I look forward to getting more details (and the name) of the ADC so I can observe the full specifications.

Best,

Alec

Hi Alec,

Thanks for your reply. I don't show the ADC part because it's "AD9083" which is designed by ADI.

You can find the ADC details from: AD9083 (Rev. 0) (analog.com)

Alec Saebeler said:

Section 9.2.1.2.4.  This ADC, the ADS5500,

For "ADS550", the input impedance is about 6.6 OHM. It doesn't suit me

Alec Saebeler said:

I will investigate calculating a proper output impedance network for the THS4509 for a presumed 100 Ohm source impedance ADC

I am waiting your result, thank you very much!

Best Regards,

Nan

Hi Alec,

Any results for the 100 OHM impedance?

Alec Saebeler said:

I will investigate calculating a proper output impedance network for the THS4509 for a presumed 100 Ohm source impedance ADC,

Best Regards,

Nan

Hi Alec,

May you answer my question?

I really want to solve this matter now.

Best Regards,

Nan

Hi Kal,

Yes you are right, but it's not my expected answer.

I need 100 OHM impedance match circuit because the analog input channels are not only bypass THS4509 but also transformers like"Test board of ADS52J90".

Thanks for your reply.

Best Regards,

Nan

Hi Kal,

kai klaas69 said:

So why not leaving it open?

Another question, if leave it open, the impedance match problem is solved? Why?

Best Regards,

Nan

Hi Nan,

because the non-ideal output impedance of THS4509 is no longer forming a frequency dependant voltage divider in combination with the input resistance of ADC.

Kai

Hi Kai,

I don't understand this point, may you give me one more detailed explanation?

Thanks for your reply!

Best Regards,

Nan