Ring oscillator in SKY130A

ring_osc.spice

* Ring Oscillator

.param TEMP=27

* Include SkyWater SKY130A device models.
.include "path/to/sky130_fd_pr/models/corners/tt.spice"

* Include SkyWater inv_1 standard cell model.
.include "path/to/skywater-pdk/libraries/sky130_fd_sc_hd/latest/cells/inv/sky130_fd_sc_hd__inv_1.spice"

vddi vdd gnd DC 1.8V

Xinv1 A1 gnd gnd vdd vdd A2 sky130_fd_sc_hd__inv_1
Xinv2 A2 gnd gnd vdd vdd A3 sky130_fd_sc_hd__inv_1
Xinv3 A3 gnd gnd vdd vdd A1 sky130_fd_sc_hd__inv_1

* Run the simulation for 10ns. Enough time for things to settle.
.tran 1ps 10ns

* Plot the voltages between the inverters and a fourier transform of one of them.
.control
run
plot A1 A2 A3
fft A1
plot mag(A1)
.endc

.end