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AD8021 and DAC AD9102 noise and limitation

Category: Hardware
Product Number: AD8021 and AD9102


I use the DAC 9102 and I need to be able to generate an output in -10/+10v or -5/+5v on frequencies of a few hertz up to several tens of MHz ideally. For this I added the AD8021 because it is one of the only ones to my knowledge that allows a -10/+10v output on high frequencies (the hundred MHz at -3dB). Below is my schematics based on evalboard AD9102-ARDZ-EBZ_Schematic.pdf:

The ADG1401 is there to control the switch to go from an amplification of 5 to 10.

Are there anything that shocks you about this schematics?

I have several "problems" with this setup, I have an SMB output and when I connect a cable I reinject noise on my board which alters my output signal because I interfere with my output signal from the DAC. 

I added a capa of 0.5pF on the feedback resistor R220 and a series resistance of 49.9 and a capa of 1uF just before the SMB connector, and I increased my resistance value for generating the gain (initially R186 and R219 was from 499 and pass to 4k99 and R220/R198/R126/R187 was from 4k99 and pass to 49k9),  
this improves the situation a little but it does not seem sufficient to me.
I also have to redo the general routing of the function but first I would like to be sure that I have not missed something...
Currently I also have a problem because I should have an amplification of 10 compared to my signal in DAC output and I have rather an x6 I don't understand why, I have to change the AD8021 to check that I haven't damaged it...
Thank you in advance for your response.

Best Regards.

Thread Notes

Top Replies

    •  Analog Employees 
    in reply to ZoltanDTI +1 verified


    As what Zoltan said,  you can refer to the recommended component values on the datasheet. [See table 6]

    Can you try to adjust resistor values, remove the switch and observe the results?