Hello, I'm starting to use magic for layout and I was wondering it is better to instantiate each sky130 device separately or just import the devices straight from the spice netlist. I ask because when I import from the spice netlist, the devices are automatically generated with a guard ring, and I don't really know if the guard rings are needed all the time for all the devices. Thank you.

You can remove the guard ring by selecting the device and bringing up the parameterization window with

Ctrl-p

. Then unselect the guard ring options. The guard rings are there for better analog performance, but they are optional.

@Tim Edwards I am encountering a situation where I want to utilize a common centroid layout to match transistors in a differential pair, so in the schematic we increased the multiplier of these transistors in the hopes of being able to individually arrange each unit transistor. This means that we would not be able to use the guard ring, though. Would this be a problem? Also, I was having trouble opening the parameterization window using ctrl-p (I received this error: "magic::gencell {} ; raise .params: No gencell device is selected!"). Is there some other way to select a device other than clicking 's'? Thanks.

@Tim Edwards if the guard ring is removed from the transistor pictured in Emmi's photo, would it be possible then for her to move the individual transistors around? Or would both transistors still be locked to one another?

@Emmi Wyttenbach: You cannot raise the parameter window while editing the layout (because the mechanism will delete and regenerate the cell whenever a parameter changes). You need to have an empty/test layout, with the parameterized cell placed in it as an instance. Then select the instance, and type Ctrl-p. If you want to make very specific layouts for the common-centroid layout, you might want to avoid using the parameterized devices altogether, and just draw the transistor directly. Alternately, you can directly edit the parameterized cell (but don't use the parameter GUI window after you do, because as mentioned above, the cell will get deleted and regenerated, and any edits you make inside the cell will be lost). @Jon Ho: If using the parameterized device generator, then the individual transistors within a single parameterized device (using M or number of fingers) are locked. But you can also just remove the guard ring, instantiate (or array) the transistor multiple times and place them in whatever arrangement suits you.

Thanks @Tim Edwards