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calculator expression to compare wreal value with voltage value

Monica123

Hello

I am working on testbench to compare wreal models with schematic output, to verify behavior of wreal models with schematic.

using following calculator expression in Virtuoso to subtract schematic output from wreal output, getting output which does not look right when compare with waveform.

clip((VT("/Ildo_bmod/vref_adck_out_ana") - VT("/Ildo/vref_adck_out_ana")) start_enable_adck end_enable_adck)

VT("/Ildo_bmod/vref_adck_out_ana") wreal value is constant over period of time 614m

VT("/Ildo/vref_adck_out_ana") schematic output is also constant to 616 mv during same period time

subtraction of above signals during same period of time gives ramp output, following are the waveform

I am not sure what exactly I am doing wrong, is there different function, which should be used to compare wreal with voltage

Thanks

  • Andrew Beckett

    The issue is that ViVA automatically plots wreal signals as type Sample Hold and the points are relatively sparse on the waveform. What will be happening is that between the actual events on the wreal signal, the subtraction will interpolate the values between those events - in other words the waveform itself is not treated as Sample Hold during numeric operations.

    I have a calculator function in this article How to hold the value of each point of a waveform so that the dft function does not interpolate between points abHoldPoints which could (I think) solve this - it certainly did in an experiment I just tried. You'd do: 

    clip((abHoldPoints(VT("/Ildo_bmod/vref_adck_out_ana")) - VT("/Ildo/vref_adck_out_ana")) start_enable_adck end_enable_adck)

    The code in the article can be added to the calculator and expression builder using the "fx" button in the function panel in the calculator, or the + button in the expression builder.

    I should update the article to cover this additional usage of the function (or write a new article which refers to it).

    Andrew

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