Issues when use AD8001 as Adder

Hello Guys,

We are using AD8001 as Adder. We can use it in our previous product, now, we are using it in our new prototype and test board. We didn't change anything in the schematic, only replace and route a test board. As attached imag file shows, there are something like ripples coupling into the Adder's output. What happens on the AD8001?

We have isolated the next stage, and nothing change. The input signal is exponent from function generator, and across AD8264(VGA), then input to AD8001. We also input sine, square and sawtooth signals. It seems the low speed signal can get better result. The output imag as below(violet channel is VGA's output, and blue channel is AD8001's output):

Thanks in advance.

Jerry

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  • 0
    •  Analog Employees 
    on Jan 12, 2017 6:08 PM

    Hi Jerry,

    I don't normally support the AD8001 but I can make a suggestion that may help. What you're seeing is called 'ringing and occurs when an amplifier is operated beyond it's stable bandwidth limit. Ringing occurs during a transition, as you see here. You said you this issue showed up with a new test board with new routing. Both these factors could easily occur with a new board, different passives (especially capacitors), grounding, and rise/fall times of the applied signal. A combination of all these factors can conspire to create ringing where none has been observed before.

    As a first step, and if you have the hardware, look at the same waveform on an old board and new board using the same part and driving signal. If this isn't feasible, you can try adjusting the rise and fall times of the signal source. if you determine that the same part has ringing in the new board but not in the old, then you could examine the board and circuit more closely.

    I hope this helps.

    js

Reply
  • 0
    •  Analog Employees 
    on Jan 12, 2017 6:08 PM

    Hi Jerry,

    I don't normally support the AD8001 but I can make a suggestion that may help. What you're seeing is called 'ringing and occurs when an amplifier is operated beyond it's stable bandwidth limit. Ringing occurs during a transition, as you see here. You said you this issue showed up with a new test board with new routing. Both these factors could easily occur with a new board, different passives (especially capacitors), grounding, and rise/fall times of the applied signal. A combination of all these factors can conspire to create ringing where none has been observed before.

    As a first step, and if you have the hardware, look at the same waveform on an old board and new board using the same part and driving signal. If this isn't feasible, you can try adjusting the rise and fall times of the signal source. if you determine that the same part has ringing in the new board but not in the old, then you could examine the board and circuit more closely.

    I hope this helps.

    js

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