Hi All. I am just looking into the resistor options in SKY130 - the P+ and P- Poly precision resistors. 1.) Both have a 'b' connection to connect the nwell below the resistor (which shields it from substrate noise). Naturally one would connect this to vdd but given that the substrate is vss, it should also be possible to connect this nwell bulk to vss also. I've done this before in a process which allowed it but just want to confirm it is indeed allowed in this process. Can anyone confirm it is? Context of the question is supply rejection as placing the resistor on a vss referred net would favor connecting the bulk to vss also. 2.) Rs of the P+ resistor is 300ohms/sq while that for the P- resistor is 2kohms/sq. This would make the P- resistor more favorable to low power applications w.r.t area. However, Im a little spooked by the below line in the P- resistor documentation: "Electrical and e-test specs are still TBD, once sufficient silicon has been evaluated." Is the P- resistor mature enough to be used or is it still under development? Thanks,

I don't know the answer, but I'm also considering using the P- resistor. Unfortunately, you've made me have some doubts about its real potential. Can someone clarify?

@Diarmuid Collins the poly resistor bulk connection can be nwell, isolated pwell, or psubstrate. It should not straddle nwell.

Thanks @Mitch Bailey. So how exactly do specify the well below the resistor? In schematic I just have the option to connect the bulk but don't have an option to select the bulk type.

Schematic does not care about bulk type - only the bulk voltage.

Thanks @Mitch Bailey. So in Magic (which I have not started using yet) I can draw a poly resistor above nwell, isolated pwell, or psubstrate, tieing off the schematic bulk accordingly. That's quite flexible as I'm used to being restricted to poly resistor over nwell only.