Friday, April 1, 2016

Making Parametric RF layouts in Cadence (Pcell)

Once you are done deciding the inductor values for an RF design, you can directly generate a layout in Cadence. The library you use may generate either a rectangular or an octagonal inductor. The same can be calculated using any of the calculators available online.

Using the value you desire and the calculator that calculates inductance using the dimensions, you can enter the same in Cadence while selecting the instance as shown below.

Creating an instance by entering values

You will see a parametric cell block in the layout window for the same. To descend into how does your inductor unit cell look like, go to Window -> Hierarchy -> Descend Edit. To convert the block into layout, press Shift+f.

Menu to descend in to the hierarchy

Ignore all warnings and errors. You will see a layout as below. The blue layer is the inductor and the green crossed square is the metal in the other layer used to extract the terminal inside the loop. The same works for resistors, MIM capacitors and transistors.

The generated layout of the inductor

Sunday, March 6, 2016

LCalc - Inductor Calculator for RF Design

This tool is designed for planar inductor calculation and can be downloaded here. The calculations come from H M Greenhouse's paper "Design of Planar Rectangular Microelectronic Inductors". The paper can be downloaded from here.


Wednesday, November 25, 2015

Shortcuts to Using Cadence Virtuoso for Layout

These are a few keyboard shortcuts that you may find useful for easy layout practice in Cadence Virtuoso:

Chop = Shift + c
This function is used to delete an arbitrary region of a shape. for example, if you need to split a diffusion rectangle of 100u x 100u into two rectangle of 100u x 40u, or you want to trim a metal shape with respect to the edge of some other shape, you can use this command. For this, you need to select the shape to chop, press shift+c, draw a rectangle that will chop the shape. This will chop the intersecting areas of the selection and object rectangles.

Path = p
This function helps to draw metal or polysilicon areas without using broken rectangles. You will need to know the start of path, bends and end of path points for this. You will press p, then click on start of path, keep clicking at bends, and double click to end path.

One may note that by pressing F3, one can change the thickness of the path by changing the values in the dialog box that appears latter.

Copy in array = c -> F3
Copying in array is useful to draw multiple contacts. For this, you can select the shape to copy, press F3. A dialog box will appear which will show the number of rows and columns required. Also, the spacing in X and Y direction will be shown. Enter these and click in the drawing space. Move the selection first in X direction and click, then Y direction and click. Your array of contacts will be ready. This is useful when you are making a large number of contacts.

Merging abutments = Shift + m
We may draw a metal path from one point to other by aligning a series of rectangles, but this requires more memory when saving large files. Thus, one may merge paths such that abutments turn into a single shape. For this, select the rectangles to merge and press shift + m. This will merge the selected shapes if they exist in the same layer.

Merging can also be done after the whole layout it drawn, or a major part of it is drawn. In that, select all by pressing ctrl + a and then press shift + m.

Align ... to be continued

Group objects