This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

OPA2891: Crosstalk, asymmetry between channels (datasheet figure 5-21)

Part Number: OPA2891
Other Parts Discussed in Thread: OPA891, OPA892

Tool/software:

I am considering using OPA2891 for a high-speed servo (dc to100 MHz, but with the OPAx891 being mostly responsible for the signal component at or above about ~10 MHz). And, this high-speed analogue domain being the one where I have most uncertainty of meeting the design requirements for my servo.

I am pondering between use of OPA2891 (to reduce both board size and cost) and OPA891 (to have simpler ability to fine-tune the dc offset build-up in my fast signal path before branching off to slower precision op amps for the content below 10 MHz and 1 MHz, respectively; and to not have to worry as much about any inside package cross-talk of signal from my separate rf input path to the low-noise signal pathway). 

The solution with only OPA2891 is very tempting, but the datasheet crosstalk figure for OPA2891 is only up to 10 MHz, and it further shows that "Ch-A to Ch-B" has much less crosstalk than vice versa from "Ch-B to Ch-A".

1. Is this massive difference real, or just an effect of a very small sample?

2. Which direction is this? Is Ch-A Ch-1, as in a large signal going through Ch-1 causes much less error signal in Ch-2 than a large signal in Ch-2 causes in Ch-1?

3. Do you have the data for the typical figure past 10 MHz?

Any reply, even to just one of the three questions would be greatly appreciated as it would simplify my constraints on which two signal parts can share a physical package, and would inform me if I should use Ch-1 or Ch-2 for the more critical signal side at each point in the circuit where cross-talk can be an issue.

  • Hi Lari,

    Let me look into this for you and ask our validation team. I will get back to you as soon as I have a response.

    Best Regards,

    Ignacio

  • Hi Lari,

    I was able to get some clarity on the questions you asked. For most of our AC validation we test a small sample of devices for our plots. For this crosstalk measurement specifically, this data was tested, and results were repeatable, so we believe this is real and can be expected from the device. For your second question, that is correct. Channel A to Channel B means a signal is presented to channel A and the output of channel B is measured. I can look for more data past 10MHz, but we can expect the crosstalk to follow the same general trend as frequency increases past 10MHz. Is there a specific frequency range you are looking for?

    Best Regards,

    Ignacio

  • Hi Ignacio,

    Thanks! Knowing that there is a real asymmetry at low frequencies that already solves most of my problems as the better direction of channel separation should be plenty for my needs below a few MHz (as it also gives a better understanding of the expected unit-to-unit variability of channel separation).

    Past 10 MHz, the expected channel separation at around ~30 MHz would be nice to know, especially as there is a very sharp uptick on the better-at-lower-frequency crosstalk direction. This is even more clear for the decompensated OPA892 which has sharp change of slope between 3 and 4 MHz for its Figure 5-20, and then already worse performance by 8 MHz.

    Kind regards,

    Lari

  • Hi Lari,

    I sent you a private message and can continue this offline if needed so I will go ahead and close this thread.

    Best Regards,

    Ignacio