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No Layout Exists for Resistor Cadence Virtuoso

sirtaza

Hello everyone. I am using Virtuoso XL Schematic for designing a current source. In my design i need to use the resistor of 18k ohms. Right now i am using cadence gpdk045 for the transistors and analoglib for the resistor. I was able to run the simulations on ADE XL. When i open the layout XL, i can see all the instances from my schematic. The only problem i am facing is that when i try to generate the layout of resistor by right clicking on the resistor instance and selecting generate selected from the source, it gives me error "No layout exists". What could be the problem. Thankyou.

  • That's hardly surprising, since analogLib is a library of simulation-only components with no layout representation (as it's a technology independent library).

    Why not use one of the resistors from gpdk045? Enable categories in the library browser and you'll see the available resistors. The documentation for the PDK will also give you some details of the makeup of each type of resistor.

    Regards,

    Andrew.

  • Thank you for your quick reply. Since i am just the beginner of cadence and exploring different options. I don't know which resistor to use for my schematic. There are many options available like, resnsndiff, resnsndiff_2, resnsnpolly, resnsnpolly_2 and many more. I don't know which one to use. i just need a normal resistor with a value of 18k ohms. Also can i perform the simulation on ADE XL using the resistors from gpdk045? Thanks.

  • As the documentation for the PDK points out, there are three types of resistors: diffused, isolated and metal. The metal resistors are always 2 terminal, whereas the other resistors have a bulk node. The _2 versions have 2 terminals on the symbol, with the bulk node specified by an inherited connection - but it's still a 3 terminal device. The resistors vary in their linearity and sheet resistance - so for example, the metal resistors have very low sheet resistance, and so would require a very large number of squares to make an 18k resistor - even with 100 series segments of a 60nm width, 100um long resistor, you'd only get 12.2kohms when using resm1. The diffusion resistors will be higher sheet resistance, but more non-linear. Some of the poly resistors are more linear and some have reasonable sheet resistance.

    The sheet resistance shows up as a property on the edit properties form - so you can see the sheet resistance. They also allow you to enter the resistance and have it calculate the corresponding length. Anyway, you can experiment and see how they behave in your circuit.

    All the gpdk045 resistors will work OK in ADE XL.

    Regards,

    Andrew

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