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Bidirectional pin in wreal domain for AMS simulations

MonsieurCascode

Hi Cadence forum,

I am currently modelling a piece of circuitry with a wreal model, that is intended to drive an internal connection, that can be overwritten externally.

The basic idea that as long as the external pin is left floating, the block itself sets the value of the external pin and the internal signal (this is done through a pull-up resistor in the analog model).

However, if the external pin is set either high or low, the internal signal should follow that, and disregard the block's desire to control it. This is to ensure, the analog block can be bypassed.

I have tried triggering with "`wrealZState" of the external pin, but it seems like when left floating in Virtuoso, AMS/spectre automatically ties it to GND. This in turn means my wreal model always sees the external signal being pulled to GND.

Have any of you dealt with this issue and solved it, or do you have any suggestions as to a better approach?

  • This doesn't make sense. AMS does not pull floating wreal outputs to ground. If it had been a floating electrical output then there's a possibility of a gmin conductance (1e-12 siemens or 1e12 ohms) being added to ground, but that wouldn't happen with a wreal output.

    I suggest you contact customer support so that you can share your models (if you're not able to share them here) and ideally an example that shows the problem you're facing.

    Thanks,

    Andrew.

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