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  • TI Thinks Resolved

OPA4872: OPA4872: OPA4872 50R termination causes distorted input

Prodigy 160 points

Replies: 3

Views: 102

Part Number: OPA4872

Dear Sir/Madam,

I built the following circuit. There are three OPA4872 in the first stage, one OPA4872 in the second stage and OPA695 in the last stage to form a 10:1 multiplexer.
I have a total of eight, 10:1 multiplexers. Supplies are +/-4V5.

I find that the input at R4 (the input to U1) is distorted or possibly unstable for square wave. 

The square wave below is 400KHz for 50R input termination (R4).

I have removed the cable and the signal looks normal. I have changed 50R to 1K and the signal looks better but is still distorted or possibly unstable.

The square wave below is 400KHz for 1K input termination (R4).

Any ideas?

Regards Joe

  • Hello Joe,

     That is certainly strange, maybe the oscillation is a cause of the probe capacitance you are using to measure? Can you measure at the output of the amplifier?

    Best,

    Hasan Babiker

  • In reply to Hasan Babiker31:

    Hi Hasan,

    The output of the amplifier is also the same. This is why I worked my way back to the input and found the same thing.

    The circuit consists of 8 identical 10:1 multiplexers comprised of first stage 3x OPA4872, second stage 1x OAP4872 and third stage OPA695. In total there are 32x OPA4872 and 8x OPA695.

    What I also find strange is that the static power consumption I way higher than I expect. The circuit is drawing 0A45 at 12V approx. 5W4.  

    Regards Joe

  • In reply to Joe Miller:

    Hello Joe,

    I am closing this thread since it seems the issue was taken offline.

    Best,

    Hasan Babiker

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