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Plotting gain versus output range

Nicolas Callens

Hi everyone,

I am currently designing an OTA, I have achieved my specs but I wanted to examine how the gain of the OTA depends on the output range. How can I plot gain versus output range?

Kind regards,

Nicolas

Parents
  • Andrew Beckett

    Hi Nicolas,

    It's a bit unclear what you are trying to do - but isn't this a matter of sweeping the output range and then plotting the gain? If the output range is the sweep variable, it will end up on the x-axis.

    Otherwise you'll have to give more detail on precisely what it is you are sweeping and what you're measuring.

    Regards,

    Andrew.

  • Nicolas Callens
    in reply to Andrew Beckett

    Hi Andrew,

    Well, the OTA is part of a switched-capacitor integrator. However, I want to see the effect of the output swings of the integrator on the gain of the OTA. Generally, the OTA DC gain should vary across the output range of the integrator. Therefore, I wanted to have a plot that tells me what the gain is at that specific output voltage. I hope this is clear?

    Kind regards,

    Nicolas

Reply
  • Nicolas Callens
    in reply to Andrew Beckett

    Hi Andrew,

    Well, the OTA is part of a switched-capacitor integrator. However, I want to see the effect of the output swings of the integrator on the gain of the OTA. Generally, the OTA DC gain should vary across the output range of the integrator. Therefore, I wanted to have a plot that tells me what the gain is at that specific output voltage. I hope this is clear?

    Kind regards,

    Nicolas

Children
  • Andrew Beckett
    in reply to Nicolas Callens

    Hi Nicolas,

    I still don't really know what you want or how the circuit is configured. Maybe you could set up an ac analysis and then use the actimes/acnames options on the transient option form to specify some times to run the ac analysis during the transition of the output - so you can see the transfer function at various output voltage levels. But this is just a guess without more insight into what you're doing.

    A few pictures might help you to clarify your requirement?

    Regards,

    Andrew.

  • Nicolas Callens
    in reply to Andrew Beckett

    Hi Andrew, 

    I wil try to explain it with some additional figures. 

    The discrete integrator is part of a delta-sigma, but I am currently simulating the integrator separately. However, due to the fact that the internal nodes (e.g. output of integrators) can have different output voltages from one cycle to another, the open-loop gain of the OTA can vary. What I really want to plot, is shown in the attachment. I also want to address that the plot is from "Understanding delta-sigma data converters" of Shanthi Pavan. 

    Thanks!

    Kind regards, 

    Nicolas

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