Strange warning in 'pnoise' simulations with IC613(ADE-XL) andMMSIM70

Hello All,

I am trying to analyze phase noise for a design involving cross-
coupled LC oscillator. I am able to get the PSS working, however, the
pnoise analysis throws up a strange warning. I have attached the
simulator log file below.

I tried implementing the suggestion posted at

http://www.cadence.com/Community/bl...ors-phase-noise-simulations.aspx?postID=10863

but it didnt seem to make any difference in the results.

Has anyone faced this kind of issue while simulating their oscillator
design? Any inputs is highly appreciated.

Regards,
VP

_____________________________________________________________________________________________

SIMULATOR log file :

**************************************************************
Periodic Steady-State Analysis `pss': guessed fund = 106.2 GHz
**************************************************************

Warning from spectre during IC analysis, during periodic steady state
analysis `pss'.
WARNING (SPECTRE-16255): Initial condition of 0 V between nodes
OUTp and 0 converted into initial guess (nodeset) because there is no
capacitive path to ground.


=================================
`pss': time = (0 s -> 2.04708 ns)
=================================
Important parameter values in tstab integration:
start = 0 s
outputstart = 0 s
stop = 2.04708 ns
period = 9.4162 ps
step = 2.00942 ps
maxstep = 376.648 fs
ic = all
skipdc = no
reltol = 1e-06
abstol(I) = 1 pA
abstol(V) = 1 uV
temp = 27 C
tnom = 27 C
tempeffects = all
method = gear2only
lteratio = 3.5
relref = sigglobal
cmin = 0 F
gmin = 1 pS

pss: time = 51.22 ps (2.5 %), step = 376.6 fs (18.4 m%)
pss: time = 153.7 ps (7.51 %), step = 376.6 fs (18.4 m%)
pss: time = 256.1 ps (12.5 %), step = 376.6 fs (18.4 m%)
pss: time = 358.6 ps (17.5 %), step = 376.6 fs (18.4 m%)
pss: time = 460.6 ps (22.5 %), step = 376.6 fs (18.4 m%)
pss: time = 563.1 ps (27.5 %), step = 376.6 fs (18.4 m%)
pss: time = 665.5 ps (32.5 %), step = 376.6 fs (18.4 m%)
pss: time = 767.7 ps (37.5 %), step = 9.276 fs (453 u%)
pss: time = 870 ps (42.5 %), step = 29.51 fs (1.44 m%)
pss: time = 972.4 ps (47.5 %), step = 46.02 fs (2.25 m%)
pss: time = 1.075 ns (52.5 %), step = 36.8 fs (1.8 m%)
pss: time = 1.177 ns (57.5 %), step = 29.57 fs (1.44 m%)
pss: time = 1.279 ns (62.5 %), step = 30.46 fs (1.49 m%)
pss: time = 1.382 ns (67.5 %), step = 24.38 fs (1.19 m%)
pss: time = 1.484 ns (72.5 %), step = 34.03 fs (1.66 m%)
pss: time = 1.586 ns (77.5 %), step = 29.02 fs (1.42 m%)
pss: time = 1.689 ns (82.5 %), step = 32.04 fs (1.57 m%)
pss: time = 1.791 ns (87.5 %), step = 21.18 fs (1.03 m%)
pss: time = 1.894 ns (92.5 %), step = 31.87 fs (1.56 m%)
pss: time = 1.996 ns (97.5 %), step = 28.98 fs (1.42 m%)
The Estimated oscillating frequency from Tstab Tran is = 106.176 GHz
(Hz).

=======================================
`pss': time = (2.04708 ns -> 2.0565 ns)
=======================================
Important parameter values in pss iteration:
start = 2.04708 ns
outputstart = 0 s
stop = 2.0565 ns
period = 9.41835 ps
steadyratio = 10e-03
step = 2.00942 ps
maxstep = 94.1835 fs
ic = all
skipdc = no
reltol = 1e-06
abstol(I) = 1 pA
abstol(V) = 1 uV
temp = 27 C
tnom = 27 C
tempeffects = all
errpreset = liberal
method = gear2only
lteratio = 3.5
relref = sigglobal
cmin = 0 F
gmin = 1 pS

pss: time = 2.047 ns (2.63 %), step = 27.66 fs (294 m%)
pss: time = 2.048 ns (7.55 %), step = 27.02 fs (287 m%)
pss: time = 2.048 ns (12.7 %), step = 27.51 fs (292 m%)
pss: time = 2.049 ns (17.6 %), step = 29.57 fs (314 m%)
pss: time = 2.049 ns (22.7 %), step = 31.31 fs (332 m%)
pss: time = 2.05 ns (27.7 %), step = 35.86 fs (381 m%)
pss: time = 2.05 ns (32.5 %), step = 18.33 fs (195 m%)
pss: time = 2.051 ns (37.5 %), step = 10.9 fs (116 m%)
pss: time = 2.051 ns (42.5 %), step = 9.163 fs (97.3 m%)
pss: time = 2.052 ns (47.8 %), step = 31.33 fs (333 m%)
pss: time = 2.052 ns (52.6 %), step = 29.66 fs (315 m%)
pss: time = 2.053 ns (57.6 %), step = 28.94 fs (307 m%)
pss: time = 2.053 ns (62.5 %), step = 29.41 fs (312 m%)
pss: time = 2.053 ns (67.8 %), step = 31.73 fs (337 m%)
pss: time = 2.054 ns (72.5 %), step = 33.36 fs (354 m%)
pss: time = 2.054 ns (77.9 %), step = 38.53 fs (409 m%)
pss: time = 2.055 ns (82.6 %), step = 17.55 fs (186 m%)
pss: time = 2.055 ns (87.5 %), step = 9.45 fs (100 m%)
pss: time = 2.056 ns (92.6 %), step = 9.585 fs (102 m%)
pss: time = 2.056 ns (97.5 %), step = 31.47 fs (334 m%)
Pinning node: 46, harm: 1, name: U1.M3.Mpx:int_b, value: (0.242847,
0.343320)

==============================
Harmonic balance
==============================
Important harmonic balance parameters:
RelTol=1.00e-06
abstol(I)=1.00e-12 A
abstol(V)=1.00e-06 V
ResidualTol=1.00e+00
LTE_Ratio=3.50e+00
Steady_Ratio=1.00e+00
MaxNewtonIter=50
********** initial residual **********
Resd Norm=2.18e+05 at node U1.M4.Mpx:int_b harm=(10)

********** iter = 1 **********
Frequency= 1.0792e+11 Hz, delta f= 1.75e+09
Damping Factor is 0.1
Delta Norm=1.56e+03 at node L1.L1:1 harm=(1)
Resd Norm=1.73e+05 at node U1.M4.Mpx:int_b harm=(10)

********** iter = 2 **********
Frequency= 1.0241e+11 Hz, delta f= -3.94e+09
Damping Factor is 0.1
Delta Norm=2.94e+03 at node U1.M1.Mnx:int_b harm=(0)
Resd Norm=2.13e+05 at node U1.M3.Mpx:int_b harm=(1)

********** iter = 3 **********
Frequency= 1.0012e+11 Hz, delta f= -5.84e+09
Damping Factor is 0.1
Delta Norm=2.65e+03 at node U1.M1.Mnx:int_b harm=(0)
Resd Norm=2.86e+05 at node U1.M3.Mpx:int_b harm=(1)

********** iter = 4 **********
Frequency= 9.9741e+10 Hz, delta f= -5.64e+09
Damping Factor is 0.1
Delta Norm=2.51e+03 at node U1.M1.Mnx:int_b harm=(0)
Resd Norm=3.26e+05 at node U1.M3.Mpx:int_b harm=(1)

********** iter = 5 **********
Frequency= 9.5476e+10 Hz, delta f= -9.35e+09
Damping Factor is 0.1
Delta Norm=3.65e+03 at node Vcntrl harm=(2)
Resd Norm=2.98e+05 at node U1.M3.Mpx:int_b harm=(1)

********** iter = 6 **********
Frequency= 9.6159e+10 Hz, delta f= -7.73e+09
Damping Factor is 0.1
Delta Norm=3.60e+03 at node Vcntrl harm=(2)
Resd Norm=2.69e+05 at node U1.M3.Mpx:int_b harm=(1)

********** iter = 7 **********
Frequency= 9.7305e+10 Hz, delta f= -5.81e+09
Damping Factor is 0.1
Delta Norm=5.02e+03 at node Vcntrl harm=(2)
Resd Norm=2.51e+05 at node U1.M3.Mpx:int_b harm=(1)

********** iter = 8 **********
Frequency= 9.9880e+10 Hz, delta f= -2.65e+09
Damping Factor is 0.1
Delta Norm=3.75e+03 at node Vcntrl harm=(2)
Resd Norm=2.35e+05 at node U1.M3.Mpx:int_b harm=(1)

********** iter = 9 **********
Frequency= 9.6903e+10 Hz, delta f= -5.36e+09
Damping Factor is 0.1
Delta Norm=4.90e+03 at node Vcntrl harm=(2)
Resd Norm=2.20e+05 at node U1.M4.Mpx:int_b harm=(1)

********** iter = 10 **********
Frequency= 9.9599e+10 Hz, delta f= -2.13e+09
Damping Factor is 0.1
Delta Norm=3.40e+03 at node Vcntrl harm=(2)
Resd Norm=2.05e+05 at node U1.M4.Mpx:int_b harm=(3)

********** iter = 11 **********
Frequency= 9.6472e+10 Hz, delta f= -5.04e+09
Damping Factor is 0.1
Delta Norm=4.71e+03 at node Vcntrl harm=(2)
Resd Norm=1.95e+05 at node U1.M4.Mpx:int_b harm=(3)

********** iter = 12 **********
Frequency= 9.9387e+10 Hz, delta f= -1.62e+09
Damping Factor is 0.1
Delta Norm=3.00e+03 at node Vcntrl harm=(2)
Resd Norm=1.91e+05 at node U1.M3.Mpx:int_b harm=(3)

********** iter = 13 **********
Frequency= 9.6238e+10 Hz, delta f= -4.61e+09
Damping Factor is 0.1
Delta Norm=4.29e+03 at node Vcntrl harm=(2)
Resd Norm=1.80e+05 at node U1.M3.Mpx:int_b harm=(3)

********** iter = 14 **********
Frequency= 9.9296e+10 Hz, delta f= -1.09e+09
Delta Norm=2.45e+04 at node Vcntrl harm=(2)
Resd Norm=1.08e+05 at node U1.M3.Mpx:int_b harm=(5)

********** iter = 15 **********
Frequency= 9.4567e+10 Hz, delta f= -4.73e+09
Damping Factor is 0.1
Delta Norm=3.68e+03 at node Vbias1 harm=(2)
Resd Norm=1.01e+05 at node U1.M3.Mpx:int_b harm=(5)

********** iter = 16 **********
Frequency= 9.4380e+10 Hz, delta f= -4.44e+09
Damping Factor is 0.1
Delta Norm=3.78e+03 at node Vbias1 harm=(2)
Resd Norm=9.30e+04 at node U1.M3.Mpx:int_b harm=(5)

********** iter = 17 **********
Frequency= 9.4267e+10 Hz, delta f= -4.11e+09
Damping Factor is 0.1
Delta Norm=3.67e+03 at node Vbias1 harm=(2)
Resd Norm=8.57e+04 at node U1.M3.Mpx:int_b harm=(5)

********** iter = 18 **********
Frequency= 9.7314e+10 Hz, delta f= -6.55e+08
Delta Norm=3.28e+04 at node Vbias1 harm=(2)
Resd Norm=1.70e+05 at node U1.M4.Mpx:int_b harm=(3)

********** iter = 19 **********
Frequency= 1.0286e+11 Hz, delta f= 5.55e+09
Damping Factor is 0.1
Delta Norm=4.20e+03 at node Vbias1 harm=(3)
Resd Norm=1.60e+05 at node U1.M4.Mpx:int_b harm=(3)

********** iter = 20 **********
Frequency= 1.0071e+11 Hz, delta f= 2.83e+09
Damping Factor is 0.3
Delta Norm=5.87e+03 at node Vbias1 harm=(2)
Resd Norm=1.28e+05 at node U1.M4.Mpx:int_b harm=(3)

********** iter = 21 **********
Frequency= 1.0057e+11 Hz, delta f= 1.85e+09
Delta Norm=1.15e+04 at node Vbias1 harm=(6)
Resd Norm=4.19e+04 at node U1.M2.n3 harm=(9)

********** iter = 22 **********
Frequency= 9.8922e+10 Hz, delta f= -1.65e+09
Damping Factor is 0.4
Delta Norm=9.67e+03 at node Vbias1 harm=(2)
Resd Norm=1.55e+04 at node U1.M2.n3 harm=(0)

********** iter = 23 **********
Frequency= 1.0054e+11 Hz, delta f= 6.23e+08
Delta Norm=9.56e+03 at node Vbias1 harm=(2)
Resd Norm=4.19e+04 at node U1.M2.n3 harm=(3)

********** iter = 24 **********
Frequency= 9.8916e+10 Hz, delta f= -1.62e+09
Damping Factor is 0.2
Delta Norm=4.84e+03 at node Vbias1 harm=(2)
Resd Norm=7.59e+03 at node U1.M2.n3 harm=(0)

********** iter = 25 **********
Frequency= 1.0053e+11 Hz, delta f= 3.15e+08
Damping Factor is 0.4
Delta Norm=2.18e+03 at node Vbias1 harm=(2)
Resd Norm=4.50e+03 at node U1.M2.n3 harm=(0)

********** iter = 26 **********
Frequency= 1.0052e+11 Hz, delta f= 1.76e+08
Damping Factor is 0.1
Delta Norm=3.05e+02 at node Vbias1 harm=(2)
Resd Norm=3.78e+04 at node U1.M2.n3 harm=(3)

********** iter = 27 **********
Frequency= 9.8904e+10 Hz, delta f= -1.45e+09
Damping Factor is 0.1
Delta Norm=2.42e+03 at node Vbias1 harm=(2)
Resd Norm=7.50e+03 at node U1.M2.n3 harm=(0)

********** iter = 28 **********
Frequency= 1.0053e+11 Hz, delta f= 3.16e+08
Damping Factor is 0.4
Delta Norm=2.16e+03 at node Vbias1 harm=(2)
Resd Norm=4.45e+03 at node U1.M2.n3 harm=(0)

********** iter = 29 **********
Frequency= 1.0052e+11 Hz, delta f= 1.78e+08
Damping Factor is 0.1
Delta Norm=3.04e+02 at node Vbias1 harm=(2)
Resd Norm=1.54e+03 at node U1.M4.Mpx:int_b harm=(3)

********** iter = 30 **********
Frequency= 1.0036e+11 Hz, delta f= -2.51e+05
Delta Norm=7.06e+01 at node Vcntrl harm=(9)
Resd Norm=5.39e+01 at node U1.M3.Mpx:int_b harm=(9)

********** iter = 31 **********
Frequency= 1.0036e+11 Hz, delta f= -7.17e+03
Delta Norm=2.26e-01 at node Vcntrl harm=(8)
Resd Norm=5.35e-01 at node U1.M3.Mpx:int_b harm=(7)


*************************************************
Fundamental frequency is 100.357 GHz.
*************************************************

CPU time=0 s

Total time required for pss analysis `pss' was 33.66 s.


Augmented Jacobian mode is on
Compute Floquet Modes for autonomous circuits ... ...
.... ... ... ... ... ... ... ... ... ... ... ... Done!

************************************************************************
Periodic Noise Analysis `pnoise': freq = 100.357 GHz + (1 kHz -> 10
MHz)
************************************************************************
The corner frequency of the oscillator is 5.46788e-05
pnoise: freq = 1.318 kHz (3 %), step = 116 Hz (1 %)
pnoise: freq = 2.089 kHz (8 %), step = 183.8 Hz (1 %)
pnoise: freq = 3.311 kHz (13 %), step = 291.4 Hz (1 %)
pnoise: freq = 5.248 kHz (18 %), step = 461.8 Hz (1 %)
pnoise: freq = 8.318 kHz (23 %), step = 731.9 Hz (1 %)
pnoise: freq = 13.18 kHz (28 %), step = 1.16 kHz (1 %)
pnoise: freq = 20.89 kHz (33 %), step = 1.838 kHz (1 %)
pnoise: freq = 33.11 kHz (38 %), step = 2.914 kHz (1 %)
pnoise: freq = 52.48 kHz (43 %), step = 4.618 kHz (1 %)
pnoise: freq = 83.18 kHz (48 %), step = 7.319 kHz (1 %)
pnoise: freq = 131.8 kHz (53 %), step = 11.6 kHz (1 %)
pnoise: freq = 208.9 kHz (58 %), step = 18.38 kHz (1 %)
pnoise: freq = 331.1 kHz (63 %), step = 29.14 kHz (1 %)
pnoise: freq = 524.8 kHz (68 %), step = 46.18 kHz (1 %)
pnoise: freq = 831.8 kHz (73 %), step = 73.19 kHz (1 %)
pnoise: freq = 1.318 MHz (78 %), step = 116 kHz (1 %)
pnoise: freq = 2.089 MHz (83 %), step = 183.8 kHz (1 %)
pnoise: freq = 3.311 MHz (88 %), step = 291.4 kHz (1 %)
pnoise: freq = 5.248 MHz (93 %), step = 461.8 kHz (1 %)
pnoise: freq = 8.318 MHz (98 %), step = 731.9 kHz (1 %)

Warning from spectre at freq = 10 MHz during PNoise analysis `pnoise'.
WARNING (SPECTRE-16518): Arithmetic exception in analysis
`pnoise' .

Total time required for pnoise analysis `pnoise' was 17.19 s.

modelParameter: writing model parameter values to rawfile.
element: writing instance parameter values to rawfile.
outputParameter: writing output parameter values to rawfile.
designParamVals: writing netlist parameters to rawfile.
primitives: writing primitives to rawfile.
subckts: writing subcircuits to rawfile.