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ahdlLib opamp model vref pin

olalivier
Hi there, I try to use the opamp model from ahdlLib but there's a few point about the model I don't understand... 1. what are ibias and iin_max parameters ? 2. Is vsoft used for output clipping ? Concerning the pins, I really don't understand the point of vref...? I can't find a decent doc about the model and the code does not provide explanations... Can you please help me on this one and if needed tell me which other opamp with a slew rate limited output i can use. Thnak you very much. Olivier
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  • The models are pretty old and from the early days of the SpectreHDL and then VerilogA standard. Some quick answers:

    1. ibias appears to be effectively a current drawn from the input pins to the reference node vref (which sets the common-mode reference for the output signal, mainly). iin_max is the maximum current the output stage can deliver (I think, from a quick glance) which is part of the slew limiting.
    2. vsoft is the voltage difference from the supplies that the output is soft-clipped to (actually it's fairly obvious from looking at the code).

    You might also want to try running the "modelwriter" tool (from the command line; although this is obsoleted too) which allows you to build an opamp model (with lots of comments) with whatever features you want. There are some other opamp models in bmslib (shipped in the same location as ahdlLib).

    Regards,

    Andrew.

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  • The models are pretty old and from the early days of the SpectreHDL and then VerilogA standard. Some quick answers:

    1. ibias appears to be effectively a current drawn from the input pins to the reference node vref (which sets the common-mode reference for the output signal, mainly). iin_max is the maximum current the output stage can deliver (I think, from a quick glance) which is part of the slew limiting.
    2. vsoft is the voltage difference from the supplies that the output is soft-clipped to (actually it's fairly obvious from looking at the code).

    You might also want to try running the "modelwriter" tool (from the command line; although this is obsoleted too) which allows you to build an opamp model (with lots of comments) with whatever features you want. There are some other opamp models in bmslib (shipped in the same location as ahdlLib).

    Regards,

    Andrew.

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