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Basic inverter problem

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Deepon

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This is a simple problem that has been haunting me from a very very long time.
I am explaining it with a simple example of an inverter. Lets see the outputof this simple Spice command:

* Waveform probing commands
.probe
.options probefilename="sedit.dat"
+ probesdbfile="Inverter2.sdb"
+ probetopmodule="inv"

* Main circuit: inv
M1 Out In Gnd Gnd NH L=2u W=.45u AD=66p PD=24u AS=66p PS=24u
M2 Out In Vdd Vdd PH L=.15u W=.9u AD=66p PD=24u AS=66p PS=24u
v3 In Gnd bit({0100101111} pw=100n on=5.0 off=0.0 rt=.01n ft=.01n delay=0 lt=10n ht=10n)
v4 Vdd Gnd 5.0
.tran 1n 400n
.print In Out
.include "dual.md"
* End of main circuit: inv

OUTPUT:
inverter.JPG

Now, notice the transitions Now,the Supply Vdd is fixed at 5v. Then how come during the transition it goes to 6v???
Moreover during low-high transition, it also goes as low as -1v. But how exactly can it happen?

Then I modified the width-length according to the dual.md model file and 2:1 ratio of PMOS:NMOS width,now the SPICE code is:

* Waveform probing commands
.probe
.options probefilename="sedit.dat"
+ probesdbfile="Inverter2.sdb"
+ probetopmodule="inv"

* Main circuit: inv
M1 Out In Gnd Gnd NH L=.15u W=.9u AD=66p PD=24u AS=66p PS=24u
M2 Out In Vdd Vdd PH L=.15u W=.45u AD=66p PD=24u AS=66p PS=24u
v3 In Gnd bit({0100101111} pw=100n on=5.0 off=0.0 rt=.01n ft=.01n delay=0 lt=10n ht=10n)
v4 Vdd Gnd 5.0
.tran 1n 400n
.print In Out
.include "dual.md"
* End of main circuit: inv

OUTPUT:
inverter.JPG


Now the output is fine. What I couldn't understand is that by modifying width/length, I simply varied the resistances and the o/p showed fine.

THEN WHAT IS THE SOURCE OF THAT EXTRA 1v (6v-5v) IN THE EARLIER OUTPUT???:!::!::sad:
 

FvM

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The spike is simply caused by Cgd crosstalk. You don't show the transistor model, but apparently it involves capacitances. In a real device, you won't see the effect, because series resistance most likely cancels it. Also applying reasonable rise/falltimes for the input waveform would reduce the effect.
 
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    Deepon

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Deepon

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The spike is simply caused by Cgd crosstalk. You don't show the transistor model, but apparently it involves capacitances. In a real device, you won't see the effect, because series resistance most likely cancels it. Also applying reasonable rise/falltimes for the input waveform would reduce the effect.
Can you please explain me more about that 'Cgd crosstalk'... I know the transistors consists of several junction capacitances, but I didn't understand that voltage shift.. please explain it a little more..:(
The transistor model 'dual.md':


**************************************************************************


.MODEL NH NMOS
+ LEVEL=49
+ TOX = 2.5482e-09
+ XJ = 1e-07
+ NCH = 5.3000e+17
+ VTH0 = 2.3792e-01
+ K1 = 4.1727e-01
+ K2 = -6.9563e-02
+ K3 = -2.39062
+ K3B = 0.774099
+ W0 = 1e-10
+ NLX = 9.7000e-08
+ DVT0 = 1.80969
+ DVT1 = 0.980574
+ DVT2 = 0.231
+ DVT0W = 0
+ DVT1W = 0
+ DVT2W = -1
+ VBM = -5
+ U0 = 1.1356e-01
+ UA = 5.22604e-09
+ UB = 4.14244e-21
+ UC = -0.000185245
+ VSAT = 1.02e5
+ A0 = 1.73172
+ AGS = 0.250746
+ B0 = 0
+ B1 = 0
+ KETA = 0.00150815
+ A1 = 0
+ A2 = 1
+ RDSW = 169
+ PRWG = -0.001
+ PRWB = 0
+ WR = 1
+ WINT = 8.3800e-10
+ LINT = 5.6290e-08
+ DLC = 4.8290e-08
+ DWG = 0
+ DWB = 0
+ VOFF = -0.147191
+ NFACTOR = 0.877606
+ ETA0 = 0.0375228
+ ETAB = -0.0165048
+ DSUB = 0.852986
+ CIT = 0
+ CDSC = 1.17e-9
+ CDSCD = 0.0
+ CDSCB = -0.00157407
+ PCLM = 0.766957
+ PDIBLC1 = 0.0000e+00
+ PDIBLC2 = 2.1263e-02
+ PDIBLCB = 0.1042
+ DROUT = 1
+ PSCBE1 = 1e+23
+ PSCBE2 = 1e-09
+ PVAG = 1.19623e-05
+ DELTA = 0.0243272
+ ALPHA0 = 0
+ BETA0 = 30
+ NGATE = 1e+23
+ RSH = 0
+ JS = 9.893e-08
+ MOBMOD = 3
+ CAPMOD = 2
+ XPART = 1
+ CGSO = 2.7500e-10
+ CGDO = 2.7500e-10
+ CGBO = 0
+ CJ = 0.001
+ CJSW = 7e-11
+ CJSWG = 2.9e-10
+ MJ = 0.478174
+ MJSW = 0.15
+ MJSWG = 0.5
+ PB = 0.897187
+ PBSW = 0.933043
+ PBSWG = 0.933043
+ CGSL = 0
+ CGDL = 0
+ CKAPPA = 0.6
+ CF = 8.2816e-11
+ CLC = 0
+ CLE = 1
+ TNOM = 27
+ PRT = 0
+ UTE = -1.76714
+ KT1 = -0.202113
+ KT1L = 8.56695e-10
+ KT2 = -0.0118898
+ UA1 = 6.44988e-09
+ UB1 = -1.21308e-17
+ UC1 = -0.118859
+ AT = 65206
+ WL = 0
+ WLN = 1
+ WW = 0
+ WWN = 1
+ WWL = 0
+ LL = 0
+ LLN = 1
+ LW = 0
+ LWN = 1
+ LWL = 0
+ BINUNIT = 1
+ LMIN = 0.15u
+ WMIN = 0.15u
+ AF = 1
+ EF = 1
+ KF = 1.6288e-27
+ NOIMOD = 4
***+ TEMPMIN = -55
***+ TEMPMAX = 150
***+ VDSMAX = 1.88
***+ VGSMAX = 1.88
***+ VBSMAX = -1.88
***+ VBDMAX = -1.88
***+ VGBMAX = 1.88
**************************************************************************

**************************************************************************
.MODEL PH PMOS
+ LEVEL = 49
+ TOX = 2.6029e-09
+ XJ = 1e-07
+ NCH = 6.1000e+17
+ VTH0 = -3.2009e-01
+ K1 = 2.9414e-01
+ K2 = -1E-9
+ K3 = -3.57199
+ K3B = 0.789162
+ W0 = 1e-10
+ NLX = 9.3760e-08
+ DVT0 = 1.67173
+ DVT1 = 1.118
+ DVT2 = 0.2463
+ DVT0W = 0
+ DVT1W = 0
+ DVT2W = -1
+ VBM = -5
+ U0 = 1.2576e-02
+ UA = 8.61555e-10
+ UB = 1e-24
+ UC = -0.5394
+ VSAT = 57536.3
+ A0 = 1.75955
+ AGS = 0.00829154
+ B0 = 0
+ B1 = 0
+ KETA = -0.1
+ A1 = 0
+ A2 = 1
+ RDSW = 1000
+ PRWG = -0.001
+ PRWB = 0
+ WR = 1
+ WINT = 2.5800e-10
+ LINT = 5.8989e-08
+ DLC = 5.2489e-08
+ DWG = 0
+ DWB = 0
+ VOFF = -0.137805
+ NFACTOR = 0.693798
+ ETA0 = 0.0327046
+ ETAB = -0.0198843
+ DSUB = 1.2427
+ CIT = 0
+ CDSC = .003
+ CDSCD = 0.000802743
+ CDSCB = -0.000986389
+ PCLM = 1.48716
+ PDIBLC1 = 4.0774e-02
+ PDIBLC2 = 1.5018e-02
+ PDIBLCB = 0.311678
+ DROUT = 0.826292
+ PSCBE1 = 1e+23
+ PSCBE2 = 1e-09
+ PVAG = 0
+ DELTA = 0.0193385
+ ALPHA0 = 0
+ BETA0 = 30
+ NGATE = 1e+23
+ RSH = 0
+ JS = 2.00192e-07
+ MOBMOD = 3
+ CAPMOD = 2
+ XPART = 1
+ CGSO = 2.9800e-10
+ CGDO = 2.9800e-10
+ CGBO = 0
+ CJ = 0.001
+ CJSW = 7e-11
+ CJSWG = 3.4e-10
+ MJ = 0.502569
+ MJSW = 0.15
+ MJSWG = 0.5
+ PB = 0.897187
+ PBSW = 0.933043
+ PBSWG = 0.933043
+ CGSL = 0
+ CGDL = 0
+ CKAPPA = 0.6
+ CF = 8.2379e-11
+ CLC = 0
+ CLE = 1
+ TNOM = 27
+ PRT = 0
+ UTE = -1.8
+ KT1 = -0.188147
+ KT1L = -1.24202e-09
+ KT2 = -0.0225334
+ UA1 = -1.10987e-09
+ UB1 = 0
+ UC1 = 0.0880042
+ AT = 34989
+ WL = 0
+ WLN = 1
+ WW = 0
+ WWN = 1
+ WWL = 0
+ LL = 0
+ LLN = 1
+ LW = 0
+ LWN = 1
+ LWL = 0
+ BINUNIT = 1
+ LMIN = 0.15u
+ WMIN = 0.15u
+ AF = 1
+ EF = 1
+ KF = 2.30686e-27
+ NOIMOD = 4
***+ TEMPMIN = -55
***+ TEMPMAX = 150
***+ VDSMAX = -1.88
***+ VGSMAX = -1.88
***+ VBSMAX = 1.88
***+ VBDMAX = 1.88
***+ VGBMAX = -1.88
**************************************************************************

**************************************************************************
* Low Vt Models
**************************************************************************
.MODEL NL NMOS
+ LEVEL = 49
+ TOX = 2.5124e-09
+ XJ = 1e-07
+ NCH = 5.5000e+17
+ VTH0 = 2.3596e-01
+ K1 = 3.5244e-01
+ K2 = -3.7699e-02
+ K3 = -3.56454
+ K3B = 1.51752
+ W0 = 1.98335e-08
+ NLX = 5.4480e-08
+ DVT0 = 0.897394
+ DVT1 = 0.793056
+ DVT2 = 0.10944
+ DVT0W = 0
+ DVT1W = 0
+ DVT2W = -1
+ VBM = -5
+ U0 = 4.34676e-02
+ UA = 1.29546e-09
+ UB = 1e-24
+ UC = 0
+ VSAT = 99239.6
+ A0 = 1.51931
+ AGS = 0.303174
+ B0 = 9.80759e-09
+ B1 = 1e-08
+ KETA = 0.00147672
+ A1 = 0
+ A2 = 1
+ RDSW = 205
+ PRWG = -0.001
+ PRWB = 0
+ WR = 1
+ WINT = 1.5000e-09
+ LINT = 5.7966e-08
+ DLC = 4.8690e-08
+ DWG = 0
+ DWB = 0
+ VOFF = -0.13137
+ NFACTOR = 0.1
+ ETA0 = 0.057855
+ ETAB = -0.0234008
+ DSUB = 1.19336
+ CIT = 0
+ CDSC = 1.621e-9
+ CDSCD = 0.000464641
+ CDSCB = -0.00112816
+ PCLM = 0.868404
+ PDIBLC1 = 8.95590e-03
+ PDIBLC2 = 6.69668e-03
+ PDIBLCB = 0.185351
+ DROUT = 0.364935
+ PSCBE1 = 1e+23
+ PSCBE2 = 1e-09
+ PVAG = 0
+ DELTA = 0.0128447
+ ALPHA0 = 0
+ BETA0 = 30
+ NGATE = 1e+23
+ RSH = 0
+ JS = 9.173e-08
+ MOBMOD = 3
+ CAPMOD = 2
+ XPART = 1
+ CGSO = 2.75e-10
+ CGDO = 2.75e-10
+ CGBO = 0
+ CJ = 0.001
+ CJSW = 7e-11
+ CJSWG = 2.9e-10
+ MJ = 0.444585
+ MJSW = 0.15
+ MJSWG = 0.5
+ PB = 0.897187
+ PBSW = 0.933043
+ PBSWG = 0.933043
+ CGSL = 0
+ CGDL = 0
+ CKAPPA = 0.6
+ CF = 8.3126e-11
+ CLC = 0
+ CLE = 1
+ TNOM = 27
+ PRT = 17.3064
+ UTE = -1.8
+ KT1 = -0.191438
+ KT1L = 6.80559e-10
+ KT2 = -0.0125778
+ UA1 = 3.40124e-10
+ UB1 = 0
+ UC1 = -0.0722735
+ AT = 60507.8
+ WL = 0
+ WLN = 1
+ WW = 0
+ WWN = 1
+ WWL = 0
+ LL = 0
+ LLN = 1
+ LW = 0
+ LWN = 1
+ LWL = 0
+ BINUNIT = 1
+ LMIN = 0.15u
+ WMIN = 0.15u
+ AF = 1
+ EF = 1
+ KF = 1.65575e-27
+ NOIMOD = 4
***+ TEMPMIN = -55
***+ TEMPMAX = 150
***+ VDSMAX = 1.88
***+ VGSMAX = 1.88
***+ VBSMAX = -1.88
***+ VBDMAX = -1.88
***+ VGBMAX = 1.88
**************************************************************************

.MODEL PL PMOS
+ LEVEL = 49
+ TOX = 2.5875e-09
+ XJ = 1e-07
+ NCH = 5.7000e+17
+ VTH0 = -2.3793e-01
+ K1 = 2.6591e-01
+ K2 = -1E-9
+ K3 = -1
+ K3B = 2.88652
+ W0 = 1.71968e-08
+ NLX = 6.2290e-08
+ DVT0 = 1.9266
+ DVT1 = 1.32039
+ DVT2 = 0.2
+ DVT0W = 0
+ DVT1W = 0
+ DVT2W = -1
+ VBM = -5
+ U0 = 9.2870e-03
+ UA = 1e-18
+ UB = 3.09522e-19
+ UC = -1
+ VSAT = 64709.9
+ A0 = 2
+ AGS = 0.107324
+ B0 = 0
+ B1 = 0
+ KETA = -0.0201928
+ A1 = 0.1
+ A2 = 0.9
+ RDSW = 830
+ PRWG = -0.001
+ PRWB = 0
+ WR = 1
+ WINT = -5.0150e-09
+ LINT = 5.8559e-08
+ DLC = 5.2559e-08
+ DWG = 0
+ DWB = 0
+ VOFF = -0.113472
+ NFACTOR = 0.5
+ ETA0 = 0.03518
+ ETAB = -0.0198843
+ DSUB = 0.645407
+ CIT = 0
+ CDSC = 0.01212
+ CDSCD = 0.00242378
+ CDSCB = -0.00468842
+ PCLM = 0.664906
+ PDIBLC1 = 3.5290e-02
+ PDIBLC2 = 4.1027e-02
+ PDIBLCB = 0.3
+ DROUT = 1
+ PSCBE1 = 1e+23
+ PSCBE2 = 1e-09
+ PVAG = 0
+ DELTA = 0.010203
+ ALPHA0 = 0
+ BETA0 = 30
+ NGATE = 1e+23
+ RSH = 0
+ JS = 1.93219e-07
+ MOBMOD = 3
+ CAPMOD = 2
+ XPART = 1
+ CGSO = 2.98e-10
+ CGDO = 2.98e-10
+ CGBO = 0
+ CJ = 0.001
+ CJSW = 7e-11
+ CJSWG = 3.4e-10
+ MJ = 0.500667
+ MJSW = 0.15
+ MJSWG = 0.5
+ PB = 0.897187
+ PBSW = 0.933043
+ PBSWG = 0.933043
+ CGSL = 0
+ CGDL = 0
+ CKAPPA = 0.6
+ CF = 8.2508e-11
+ CLC = 0
+ CLE = 1
+ TNOM = 27
+ PRT = 100
+ UTE = -1.19632
+ KT1 = -0.22238
+ KT1L = -1.0044e-09
+ KT2 = -0.0226282
+ UA1 = -1.89458e-10
+ UB1 = 0
+ UC1 = 0.45635
+ AT = 25292.7
+ WL = 0
+ WLN = 1
+ WW = 0
+ WWN = 1
+ WWL = 0
+ LL = 0
+ LLN = 1
+ LW = 0
+ LWN = 1
+ LWL = 0
+ BINUNIT = 1
+ LMIN = 0.15u
+ WMIN = 0.15u
+ AF = 1
+ EF = 1
+ KF = 2.39236e-27
+ NOIMOD = 4
***+ TEMPMIN = -55
***+ TEMPMAX = 150
***+ VDSMAX = -1.88
***+ VGSMAX = -1.88
***+ VBSMAX = 1.88
***+ VBDMAX = 1.88
***+ VGBMAX = -1.88
**************************************************************************

**************************************************************************
 

FvM

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You can simply imagine a capacitance between inverter in- and output.
 

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