* Self-biased current source testbench

* Include SkyWater sky130 device models
.lib "/usr/share/pdk/sky130A/libs.tech/ngspice/sky130.lib.spice" tt
.param mc_mm_switch=0

.subckt pch D G S B xm=10 xl=4.0 xwp=3.0
X0 D G S B sky130_fd_pr__pfet_g5v0d10v5 ad=4e+11p pd=2.8e+06u as=4e+11p ps=2.8e+06u w={xwp} l={xl} m={xm}
.ends

.subckt nch D G S B xm=10 xl=4.0 xwn=1.0
X0 D G S B sky130_fd_pr__nfet_g5v0d10v5 ad=4e+11p pd=2.8e+06u as=4e+11p ps=2.8e+06u w={xwn} l={xl} m={xm}
.ends

* circuit netlist

.subckt iref0 io vdd vss xm=1 xk=4 xr=1meg xl=4.0 xwp=3.0 xwn=1.0

cs  s vdd 1p
x0a gp  s   gn  vss nch xm={xm}    xl={xl} xwn={xwn}
x0b s   gn  vss vss nch xm={xm}    xl={xl} xwn={xwn}

x1a gp  gp  vdd vdd pch xm={xm}    xl={xl} xwp={xwp}
x1b gp  gn  a   vss nch xm={xk*xm} xl={xl} xwn={xwn}
ra  a   vss {xr/xm}

x2a gn  gp  vdd vdd pch xm={xm}    xl={xl} xwp={xwp}
x2b gn  gn  vss vss nch xm={xm}    xl={xl} xwn={xwn}

x3a io  gp  vdd vdd pch xm={xm}    xl={xl} xwp={xwp}

.ends

* circuit testbench

.param pVDD = 5.0

VDD  vdd 0 dc {pVDD}
VSS  vss 0 0

xdut io vdd vss iref0 xm=1 xk=4 xr=100k xl=4.0 xwp=3.0 xwn=1.0
vo io vss 0

.param k = 1000
.dc VDD {pVDD/k} {pVDD} {pVDD/k}
.option gmin=1e-15
.control
	run
	let io = i(vo)
		
	let psr = db(abs(deriv(io)/io))

	plot io
	plot psr

.endc

.end