From 68fd8b8fa1dfc3a2d87ff58d1dba550c51b157dd Mon Sep 17 00:00:00 2001
From: Holger Vogt <holger.vogt@uni-due.de>
Date: Wed, 18 Feb 2026 14:54:26 +0100
Subject: [PATCH] PMOS and ring oscillator degradation examples

---
 examples/degradation/PMOS_degmon_new.cir   | 38 +++++++++
 examples/degradation/psp_ihp_ro_deg_new.sp | 92 ++++++++++++++++++++++
 src/frontend/com_fft.c                     |  3 +
 3 files changed, 133 insertions(+)
 create mode 100644 examples/degradation/PMOS_degmon_new.cir
 create mode 100644 examples/degradation/psp_ihp_ro_deg_new.sp

diff --git a/examples/degradation/PMOS_degmon_new.cir b/examples/degradation/PMOS_degmon_new.cir
new file mode 100644
index 000000000..61e39e32b
--- /dev/null
+++ b/examples/degradation/PMOS_degmon_new.cir
@@ -0,0 +1,38 @@
+test of integrated degradation monitor
+
+* NMOS transistor with const drain voltage
+
+.lib "$PDK_ROOT/$PDK/libs.tech/ngspice/models/cornerMOSlv.lib" mos_tt
+
+.include "aging_par_ng.scs"
+
+* the voltage sources: 
+Vdd vdd gnd DC -1.8
+Vss vss 0 0
+V1 in gnd dc 0 pulse(0 -1.8 0p 100p 100p 0.5n 2n)
+
+xm02 vdd in vss vss sg13_lv_pmos  l=0.15u  w=0.99u as=0.131175p ad=0.131175p ps=1.52u   pd=1.52u
+*adegmon1 %v([z a vss vss]) mon degmon1
+*.model degmon1 degmon (tfuture=315336e4 l=0.15e-6 devmod="sg13_lv_nmos")
+
+* simulation command: 
+.tran 1ps 20ns 0 10p
+
+.options method=gear
+
+.control
+pre_osdi ../lib/ngspice/psp103_nqs.osdi
+pre_osdi ../lib/ngspice/psp103.osdi
+run
+rusage
+plainsim
+run
+degsim
+run
+*set nolegend
+set xbrushwidth=2
+* plainsim, degsim
+plot tran2.Vss#branch Vss#branch
+.endc
+
+.end
\ No newline at end of file
diff --git a/examples/degradation/psp_ihp_ro_deg_new.sp b/examples/degradation/psp_ihp_ro_deg_new.sp
new file mode 100644
index 000000000..f5df1963b
--- /dev/null
+++ b/examples/degradation/psp_ihp_ro_deg_new.sp
@@ -0,0 +1,92 @@
+psp103 CMOS NAND gate ring oscillator after HCI stress
+
+* In .spiceinit: set ngbehavior=hsdea; de denotes: we want degradation simulation
+
+* Upon loading the netlist: load the .agemodel data, add
+* the degradation monitors, store the netlist internally
+
+* First tran run: measure the degradation, store deg data for each instance.
+* The degradation may be enhanced by raising the supply voltage.
+
+* Second tran run, initiated by command 'plainsim': reload netlist from internal
+* storage, remove degradation monitors, quasi a standard run without degradation
+
+* Third tran run, initiated by command 'degsim': reload netlist from internal,
+* storage, remove degradation monitors, add degradation data to device instances,
+* simulate degraded circuit.
+
+
+* stress temperature
+.param CurTemp=21
+
+* some intermediate parameters
+.temp 'CurTemp'
+
+* IHP Open Source PDK
+.lib "$PDK_ROOT/$PDK/libs.tech/ngspice/models/cornerMOSlv.lib" mos_tt
+
+.include "aging_par_ng.scs"
+
+* Library name: sg13g2_stdcell
+* Cell name: sg13g2_nand2_1
+* View name: schematic
+* Inherited view list: spectre cmos_sch cmos.sch schematic veriloga ahdl
+* pspice dspf
+.subckt sg13g2_nand2_1 A B VDD VSS Y
+XP1 Y B VDD VDD sg13_lv_pmos w=1.12e-06 l=130.00n ng=1 ad=1p as=1p pd=1u ps=1u m=1
+XP0 Y A VDD VDD sg13_lv_pmos w=1.12e-06 l=130.00n ng=1 ad=1p as=1p pd=1u ps=1u m=1
+XN1 net1 B VSS VSS sg13_lv_nmos w=740.00n l=130.00n ng=1 ad=1p as=1p pd=1u ps=1u m=1
+XN0 Y A net1 VSS sg13_lv_nmos w=740.00n l=130.00n ng=1 ad=1p as=1p pd=1u ps=1u m=1
+.ends
+* End of subcircuit definition.
+
+* sg13g2_nand2_1 A B VDD VSS Y
+Xu1 out5u out5u VDD VSSu out1u sg13g2_nand2_1
+Xu2 out1u out1u VDD VSSu out2u sg13g2_nand2_1
+Xu3 out2u out2u VDD VSSu out3u sg13g2_nand2_1
+Xu4 out3u out3u VDD VSSu out4u sg13g2_nand2_1
+Xu5 out4u out4u VDD VSSu out5u sg13g2_nand2_1
+
+Vmeas2 VSSu 0 0
+
+Vsupp VDD 0 1.2
+
+.control
+pre_osdi ../lib/ngspice/psp103_nqs.osdi
+pre_osdi ../lib/ngspice/psp103.osdi
+
+save out5u i(vmeas) i(vmeas2)
+
+* create and measure degradation
+* use higher stress voltage, 1.2V results in negligible degradation.
+alter Vsupp = 1.8
+tran 10p 200n
+rusage
+
+* simulate without degradation
+plainsim
+alter Vsupp = 1.2
+tran 10p 200n
+rusage
+
+simulate with degradation
+degsim
+alter Vsupp = 1.2
+tran 10p 200n
+rusage
+
+
+* output characteristics
+*set color0=white
+set xbrushwidth=2
+let out5u_prev =  tran2.out5u
+let out5u_prev_prev =  tran1.out5u
+plot out5u_prev_prev out5u_prev out5u xlimit 86n 90n
+
+linearize out5u_prev_prev out5u_prev out5u
+fft out5u_prev_prev out5u_prev out5u
+plot mag(out5u_prev_prev) mag(out5u_prev) mag(out5u) xlimit 1.5G 3.5G
+plot mag(out5u_prev_prev) mag(out5u_prev) mag(out5u) xlimit 1.5G 2G ylimit 0 500m
+
+.endc
+.end
diff --git a/src/frontend/com_fft.c b/src/frontend/com_fft.c
index 2d592525b..d6405e1fa 100644
--- a/src/frontend/com_fft.c
+++ b/src/frontend/com_fft.c
@@ -60,6 +60,9 @@ com_fft(wordlist *wl)
     length = (plot_cur->pl_scale)->v_length;
     time = (plot_cur->pl_scale)->v_realdata;
     span = time[length-1] - time[0];
+    if (length > 1) {
+        span += time[1] - time[0];
+    }
 
 #ifdef HAVE_LIBFFTW3
     fpts = length/2 + 1;