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I am studying the diode models from Sky130, and I ...
# analog-design
e
I am studying the diode models from Sky130, and I saw in the file models_diode.spice a parameter sw_func_psd_nw_cj that is not linked with another one. Can anyone explain its meaning?
t
Without looking it up, "Cj" should mean a junction capacitance, so I assume this parameter represents the junction capacitance of the reverse-biased P-N junction between p-diffusion (psd) and n-well (nw).
e
Hello Tim, thank you for your attention. This parameter is used in the model to define the junction capacitance. The line in the model is "cj = {7.8544e-005*1e-12*sw_func_psd_nw_cj}". So, in fact, CJ is dependent on this parameter, although I could not find in another place.
.subckt sky130_fd_pr__photodiode a c mult=1 + area=1 perim=1 Dsky130_fd_pr__photodiode a c diodeint area = {area} pj = {perim} .model diodeint d + level = 3 * *PARAMETERS TO MAKE MODEL INTO CADFLOW * + tlevc = 1 + area = 1e12 * *JUNCTION CAPACITANCE PARAMETERS * + cj = {7.8544e-005*1e-12*sw_func_psd_nw_cj} + mj = 0.49 + pb = 0.5348 + cjsw = {8.1664e-010*1e-6*sw_func_psd_nw_cj} + mjsw = 0.20024 + php = 0.5348 + cta = 0.0016157 + ctp = 0.0008 + tpb = 0.0025003 + tphp = 0.001675 * *DIODE IV PARAMETERS * + js = 6.1049e-017 + jsw = 8.1115e-016 + n = 1.0791 + rs = {900*1e-12} + ik = {2.08e-009/1e-12} + ikr = {0/1e-12} + bv = {16.95/sw_func_psd_nw_cj} + ibv = 0.00106 + trs = 0 + eg = 1.17 + xti = 1.0 + tref = 30 * *DEFAULT PARAMETERS * + tcv = 0 + gap1 = 0.000473 + gap2 = 1110 + ttt1 = 0 + ttt2 = 0 + tm1 = 0 + tm2 = 0 + lm = 0 + lp = 0 + wm = 0 + wp = 0 + xm = 0 + xoi = 10000 + xom = 10000 + xp = 0 + xw = 0 .ends sky130_fd_pr__photodiode
t
Depends on whether you're using the so-called "combined" models or the discrete-binned models; in the "combined" models, the parameter is defined in 
$PDK_ROOT/sky130A/libs.tech/combined/continuous/models_global.spice
:
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.param
...
+ sw_func_psd_nw_cj = {sw_psd_nw_cj/7.3802e-4}
In turn, 
sw_psd_nw_cj
is defined in specific corner parameter files; e.g., `$PDK_ROOT/sky130A/libs.tech/combined/continuous/parameters_fet_tt.spice`:
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.param sw_psd_nw_cj = {0.0007408+corner_factor*0.0} + process_mc_factor*MC_PR_SWITCH*GAUSS(0,0.025,1)
Is that the information you're looking for?
In the original "discrete-binned" models, this parameter does not exist as far as I can find.
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