Parametric standard cell in Xschem

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Ming Sun / November 07, 2022

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Cell name: SIM_nand2
PDK: Skywater130
Schematic capture: Xschem
Simulator: Ngspice

Modify the nand2 schematic

  • Let us modify the nand2 schematic. Make the channel width, length and multiplier as generic parameters as shown in Fig. 1.
Set channel width, length and multiplier to be parameters
Fig. 1Set channel width, length and multiplier to be parameters
  • Do the same for NMOS Mn1 and Mn0. Set channnel width to be W_N, channel length to be L_N and multiplier to be m.

Modify symbol

  • Next, we need to modify the nand2 symbol as shown in Fig. 2.
Modified symbol for nand2
Fig. 2Modified symbol for nand2

For the symbol properties, please use the following contents:

format="@name @pinlist @symname m=@m L_P=@L_P L_N=@L_N"
template="name=x1 m=1 
+ W_N=1 L_N=0.15 W_P=2 L_P=0.15 "

New test bench

  • Create a new test bench as shown in Fig. 3. Let us use the nand2 gate to drive a 10pF cap. One nand2 gate has all the default dimensions, while another nand2 gate has multiplier m equal to 10.
SIM_nand2 test bench
Fig. 3SIM_nand2 test bench

From Fig. 3, we can clearly tell that the nand2 gate with m euqals to 1 has weaker driving capability compared with the one of m=10.

References and materials


[2] Xschem - 101

[3] SIM_nand2_parametric.sch - download

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