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Time Variable Resistor

Ahmed Taha

Hi,

I have RC network, and I am running transient simulation. I would like to have one of network's resistors value to change over time.

I have input signal array to the network (Volts vs. time) and a corresponding resistor array values over time (ohm vs. time)

Is it possible to create such resistor with its value defined by that array of data over time in Cadence, Spectre?

Thanks.

Parents
  • Andrew Beckett

    Hi Nicolas,

    Everything is correct here. It's because you have a linear sweep on the controlling voltage and hence a linear sweep of the resistance - and so if you're plotting the current, that will have a 1/x response on that linear sweep.

    I added save G0:oppoint to the netlist so I could plot the G0:lx0 parameter (and hence see the resistance changing). I then computed (in the calculator) both -3.3/v("net2" ?result "tran") and -3.3/getData("G0:lx0" ?result "tran") and plotted these. You can see that these two calculated currents overlay exactly with the current from the simulator. The top strip shows both the controlling voltage and the VCR value (the lx0) - again, they overlay exactly.

    Here's a zoomed in (in the y-direction) plot of the current - you can see it is gradually changing:

    This is not surprising - if you see the last red cross (at this zoom level) before the end of the ramp down, it's at about 0.5MV, which corresponds to 0.5MOhm in the VCR. Then the current will be 3.3/0.5M which is about 6uA. The scale of the current means  you hardly see this change. If you were to change the y-axis to a log scale for the current, this would be much more evident without the need to zoom in.

    So everything is working as it should - the results are correct.

    Regards,

    Andrew.

Reply
  • Andrew Beckett

    Hi Nicolas,

    Everything is correct here. It's because you have a linear sweep on the controlling voltage and hence a linear sweep of the resistance - and so if you're plotting the current, that will have a 1/x response on that linear sweep.

    I added save G0:oppoint to the netlist so I could plot the G0:lx0 parameter (and hence see the resistance changing). I then computed (in the calculator) both -3.3/v("net2" ?result "tran") and -3.3/getData("G0:lx0" ?result "tran") and plotted these. You can see that these two calculated currents overlay exactly with the current from the simulator. The top strip shows both the controlling voltage and the VCR value (the lx0) - again, they overlay exactly.

    Here's a zoomed in (in the y-direction) plot of the current - you can see it is gradually changing:

    This is not surprising - if you see the last red cross (at this zoom level) before the end of the ramp down, it's at about 0.5MV, which corresponds to 0.5MOhm in the VCR. Then the current will be 3.3/0.5M which is about 6uA. The scale of the current means  you hardly see this change. If you were to change the y-axis to a log scale for the current, this would be much more evident without the need to zoom in.

    So everything is working as it should - the results are correct.

    Regards,

    Andrew.

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