CMOS inverter using the skywater sky130 process (design with xschem and simulation with ngsice)
Design the inverter's circuit using xschem
1. start xschem
2. xschem's sky130 library provides a parameterizable inverter schematic (not.sch) and its symbol (not.sch)
3. create a new schematic (inv_sky130_a.sch)
instantiate and place the symbol not.sym (Tools > Insert symbol | Shift-I)
the symbol and its schematic are available both in the library Lib406 and in the library ~/share/pdk/sky130/libs.tech/xschem/sky130_tests
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customize the transistors’ dimensions (select the symbol, right click on it and edit its properties)
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instantiate and place an input pin (ipin.sym) and an output pin (opin.sym)
the symbols are available both in the library Lib406 and in the library ~/opt/xschem/share/xschem/xschem_library/deviceslabel the name of the input and output pins (select the pin, right click on it and edit its properties)
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wire the pins to the ports of the not.sym instance (Tools > Insert wire | W)
save the schematic (File > Save as | Ctrl+Shift+S)
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make a symbol inv_sky130_a.sym for the schematic (Symbol > Make symbol from schematic | Ctrl+L)
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Simulate the inverter
1. use xschem to create a simulation testbench (tb_inv_sky130_a.sch) for the inverter
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The spice directives TT_MODELS and control are code.sym instances with the following attributes:
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2. create netlist (netlist button)
**.subckt tb_inv_sky130_a Vin in GND DC 0 PULSE(0 1.8 0 1ns 1ns 4ns 10ns) VP VCC GND 1.8 VN VSS GND 0 x2 out in inv_sky130_a **** begin user architecture code .lib /home/utalarico/share/pdk/sky130A/libs.tech/ngspice/sky130.lib.spice tt .param mc_mm_switch=0 .param mc_pr_switch=1 .control * VTC analysis DC Vin 0 1.8 1m save all let VP = 1.8 let vo_mid = VP/2 let dvout = deriv(v(out)) meas DC VSW find v(in) when v(out)=vo_mid meas DC VIL find v(in) WHEN dvout=-1 CROSS=1 meas DC VIH find v(in) WHEN dvout=-1 CROSS=2 meas DC VOL find v(out) WHEN dvout=-1 CROSS=2 meas DC VOH find v(out) WHEN dvout=-1 CROSS=1 echo VTC measurements print VSW print VIL print VIH print VOH print VOL echo set filetype=binary write ./spiceout/tb_inv_sky130_a_vtc.raw v(out) v(in) dvout VSW VIL VIH VOL VOH * Transient analysis TRAN 0.01n 20n save all let VP=1.8 let per10 = Vp*0.1 let per50 = Vp*0.5 let per90 = Vp*0.9 meas TRAN t_rise TRIG v(out) VAL=per10 rise=2 TARG v(out) VAL=per90 rise=2 meas TRAN t_fall TRIG v(out) VAL=per90 fall=2 TARG v(out) VAL=per10 fall=2 meas TRAN t_delay TRIG v(in) VAL=per50 rise=1 TARG v(out) VAL=per50 fall=1 echo TRAN measurements print t_delay print t_rise print t_fall echo set filetype=binary write ./spiceout/tb_inv_sky130_a_tran.raw .endc **** end user architecture code **.ends * expanding symbol: inv_sky130_a.sym # of pins=2 * sym_path: /home/utalarico/ihome/ngs406/xSchems/inv_sky130_a.sym * sch_path: /home/utalarico/ihome/ngs406/xSchems/inv_sky130_a.sch .subckt inv_sky130_a out in *.ipin in *.opin out x1 out in VCC VSS not W_N=1 L_N=0.15 W_P=2 L_P=0.15 m=1 .ends * expanding symbol: not.sym # of pins=2 * sym_path: /home/utalarico/ihome/Lib406/not.sym * sch_path: /home/utalarico/ihome/Lib406/not.sch .subckt not y a VCCPIN VSSPIN W_N=1 L_N=0.15 W_P=2 L_P=0.15 *.opin y *.ipin a XM1 y a VSSPIN VSSPIN sky130_fd_pr__nfet_01v8 L=L_N W=W_N nf=1 ad='int((nf+1)/2) * W/nf * 0.29' as='int((nf+2)/2) * W/nf * 0.29' + pd='2*int((nf+1)/2) * (W/nf + 0.29)' ps='2*int((nf+2)/2) * (W/nf + 0.29)' nrd='0.29 / W' nrs='0.29 / W' + sa=0 sb=0 sd=0 mult=1 m=1 XM2 y a VCCPIN VCCPIN sky130_fd_pr__pfet_01v8 L=L_P W=W_P nf=1 ad='int((nf+1)/2) * W/nf * 0.29' as='int((nf+2)/2) * W/nf * 0.29' + pd='2*int((nf+1)/2) * (W/nf + 0.29)' ps='2*int((nf+2)/2) * (W/nf + 0.29)' nrd='0.29 / W' nrs='0.29 / W' + sa=0 sb=0 sd=0 mult=1 m=1 .ends .GLOBAL GND .GLOBAL VCC .GLOBAL VSS .end
3. run simulation (simulation button)
4. view results (waves button)
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