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How to find correlation parameter between two layout devices?

jagadishdn

I have done schematic and layout of its design in layout XL. I use cadence 6.1.5 and UMC 90nm technology library. For a mismatch analysis I will be doing monte carlo simulation.

I have to understand that ADE XL asssumes the correlation coefficient cc = 0. But typically a statement is added to netlist file to indicate cc = 0.75. Matching could be improved by employing careful design techniques. Assuming that one follows such techniques, then the cc has be close to 1. My question here is, how do we know the cc between two transistors from the layout tool. Please suggest me how to find the cc.

Thanks

Jagadish

Parents

  • ADE XL doesn't assume anything - it's spectre that will assume the mismatch parameters on the devices are not correlated. Note that sometimes foundries produce mismatch models which give the remaining variation assuming good match - so you need to check how the foundry have produced the models.

    In ADE XL you can actually add a constraint to tell it the correlation coefficient for a particular mismatch parameter between two devices (using the constraint manager). Having done that, ADE XL will netlist (for spectre) the correlation coefficient for the simulator to use.

    However, the main challenge is identifying what that value should be. You can tell spectre which parameters are correlated for a pair of devices and what the correlation coefficient should be. The challenge is that you really need to know which of the parameters might be correlated and sometimes they don't have a direct physical meaning. 

    I think the only way of knowing this would be to have some guidance from the foundry on measurements they've made (or potentially measurements you've made on a test chip) - directly going from layout structures to correlation coefficients is pretty difficult for most people  As I said, you also need to know what assumptions (if any) the foundry has made when producing the monte carlo mismatch models.

    Regards,

    Andrew.

Reply

  • ADE XL doesn't assume anything - it's spectre that will assume the mismatch parameters on the devices are not correlated. Note that sometimes foundries produce mismatch models which give the remaining variation assuming good match - so you need to check how the foundry have produced the models.

    In ADE XL you can actually add a constraint to tell it the correlation coefficient for a particular mismatch parameter between two devices (using the constraint manager). Having done that, ADE XL will netlist (for spectre) the correlation coefficient for the simulator to use.

    However, the main challenge is identifying what that value should be. You can tell spectre which parameters are correlated for a pair of devices and what the correlation coefficient should be. The challenge is that you really need to know which of the parameters might be correlated and sometimes they don't have a direct physical meaning. 

    I think the only way of knowing this would be to have some guidance from the foundry on measurements they've made (or potentially measurements you've made on a test chip) - directly going from layout structures to correlation coefficients is pretty difficult for most people  As I said, you also need to know what assumptions (if any) the foundry has made when producing the monte carlo mismatch models.

    Regards,

    Andrew.

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