Creating a Parameterized Cell in Cadence

Creating a Custom Parameterized Cell in Cadence

Often during circuit design, it is necessary to have multiple instances of a single cell (e.g., an inverter) but each instance may have different parameters (e.g., different transistor sizes). For example, consider the case where a circuit has a chain of inverters where each inverter has been scaled for minimum delay. One way in which this can be realized is to simply instance multiple transistors each having their own size. This is fine if there is only one such chain. If, however, multiple such inverter chains exist in a circuit is can be cumbersome if it is necessary to change one stage in the chain. This is especially true if the circuit is more complex than a simple chain of inverters.

A better solution is to create a parameterized cell (p-cell). The p-cell can then be instanced and the parameters of interest individually set. Then if a circuit change within the p-cell is required, only one change must be made and it will automatically be reflected in all instances. This tutorial discusses how to create such a p-cell using a realistic inductor model as an example. The inductor model that we will be using is shown below:

where:

R_s = -0.0296*L^2 + 1.83*L + 2.288

C_sub = -0.0005*L^2 + 0.0312*L + 0.0543

R_sub = 0.0789*L + 31.707 + 3.4892/L

In the above equations, L is in nH, R_s and R_sub are in Ohms, and C_sub is in pF.