Hello magic, I have to make the layout of the VCO in the picture below. It is a hierarchical design. Can any one guide how to move forward? When I import the spice file in magic, all the blocks are being imported but the hierarchical block is not editable for making connections. Also can anyone let me know the purpose of the guard ring in an imported nfet/pfet. I have seen in videos that it is used to connect vdd and gnd. but why?

Each MOSFET transistor has 4 terminals. One of those connections is the substrate. That guard ring is the connection to the substrate. You don't need a full guard ring for each transistor, as most NMOS and PMOS, if not all, are connected to the same substrate.

@Himanshu Singh: The "Import SPICE" function knows nothing about the design, so it applies default options to every device it creates. The default options include the guard ring. Layouts where every device is in a guard ring will be large but you will not need to worry about any latch-up issues. The guard rings are generally intended for large device arrays. If you do not want the guard ring or want to make any changes to the parameterized device, select the device with the "i" ("instance") key, then type "Ctrl-p" to bring up the window with parameter options for the device. If you want to edit down in the hierarchy, select the subcell you want to edit with the "i" key, then either use "e" to edit it in place, or ">" to descend into the subcell to edit ("<" to return to the previous layout).

Thanks @Luis Henrique Rodovalho, thanks @Tim Edwardsyou're contributions will be worthwhile to the opensource community

Use m1 metal layer to make a metal resistor. You must insert it in your schematic later, I think

i didnt get you. m1 has a resistance itself. thats one fact. but is there any element of resistor in sky130? or i would have to add it in my layout spice file?

A metal resistor splits the nodes without you needing to extract the netlist from layout with resistances. This means you can locate the actual resistor and its nodes. But if you really want a resistor, there are high resistance polysilicon resistors. Is it what you want? What are you trying to do with this circuit?

@Luis Henrique Rodovalho this resistor is a part of the voltage controlled oscillator ckt. I have made the vco layout, only adding a 1ohm resistor between vctrl pin and input if nmos gate is needed

As far as I see, this resistor has no function at all. You could replace it with a metal resistor with arbitrary low value, or remove from you design all together. Later, try to tighten you layout cells. You're wasting too much area, which means more routing, which will decrease your oscillator maximum frequency. It also will decrease matching. Also, you don't need to make the layout exactly as the schematic. You can bend it,so the last inverter is close to the first one. So make two rows of inverters.

You may have to type

run

at the ngspice prompt to get ngspice to run the transient analysis if you use

.tran

instead of a control block.

thanks tim