I have a question. I'm trying to simulate a ring oscillator with variation on Vth ,..., in hspice, but I get no convergence in dc sweep curves error. I tried some of solutions to convergence, but have not got any success, can you help me. The netlist & the errors are as followings:

V1 vdd 0 0.9V
V2 vss 0 0V

.PARAM bias=1m
 MN11 vss 15 11 vss N1 L=120n W=280n x=-7000u y=2000u
 MP11 vdd 15 11 vdd P1 L=120n W=980n x=-7000u y=6000u
 MN12 vss 11 12 vss N1 L=120n W=280n x=-5500u y=2000u
 MP12 vdd 11 12 vdd P1 L=120n W=980n x=-5500u y=6000u
 MN13 vss 12 13 vss N1 L=120n W=280n x=-4000u y=2000u
 MP13 vdd 12 13 vdd P1 L=120n W=980n x=-4000u y=6000u
 MN14 vss 13 14 vss N1 L=120n W=280n x=-2500u y=2000u
 MP14 vdd 13 14 vdd P1 L=120n W=980n x=-2500u y=6000u
 MN15 vss 14 15 vss N1 L=120n W=280n x=-1000u y=2000u
 MP15 vdd 14 15 vdd P1 L=120n W=980n x=-1000u y=6000u


  Parameter var=N() Y='180 + 8.02 * var' Z='17.5 + 0.37 * var'
  Nmos N1
 + VTH0=Perturb('Y')
  Pmos P1
 + VTH0=Perturb('Y')
  Parameter var=N() T='11.46 * var' U='0.54 * var'
  Nmos N1
 + VTH0=Perturb('T')
  Pmos P1
+ VTH0=Perturb('T')



.dc bias 1m 1m 1m monte=10
.print I(MN11) I(MN12)
.measure dc I11 find I(MN11) at=1m
.measure dc I12 find I(MN12) at=1m


dcop: begin pseudo transient
dcop: ...failed with iteration exhausted
dcop: end pseudo transient
dcop: gshunt =      0.1000000E-03
dcop: gshunt =      0.5050000E-03
dcop: gshunt =      0.7277500E-03
dcop: gshunt =      0.8502625E-03
dcop: gshunt =      0.9176444E-03
dcop: gshunt =      0.9547044E-03
dcop: gshunt =      0.9750874E-03
dcop: gshunt =      0.9862981E-03
dcop: gshunt =      0.9924639E-03
dcop: gshunt =      0.9958552E-03
dcop: gshunt =      0.9977203E-03
dcop: gshunt =      0.9987462E-03
dcop: gshunt =      0.9993104E-03
dcop: gshunt =      0.9996207E-03
dcop: gshunt =      0.9997914E-03
dcop: gshunt =      0.9998853E-03
dcop: gshunt =      0.9999369E-03
dcop: gshunt =      0.9999653E-03
dcop: gshunt =      0.9999809E-03
dcop: gshunt =      0.9999895E-03
dcop: gshunt =      0.9999942E-03
dcop: gshunt =      0.9999968E-03
dcop: gshunt =      0.9999983E-03
dcop: gshunt =      0.9999990E-03
dcop: gshunt =      0.9999995E-03
dcop: gshunt =      0.9999997E-03
dcop: gshunt =      0.9999998E-03
dcop: gshunt =      0.9999999E-03
**error** no convergence in dc sweep curves at  1.00000E-03

I ask you to help me.


closed as unclear what you're asking by Olin Lathrop, dim, Bence Kaulics, Autistic, Daniel Grillo Jul 8 '16 at 13:41

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  • \$\begingroup\$ Show a schematic so we don't have to decode you spice code. Not everyone has Hspice \$\endgroup\$ – Voltage Spike Feb 1 '16 at 21:13
  • 1
    \$\begingroup\$ A ring oscillator has no stable DC operating point. Perhaps @laptop2d's suggestions will allow you to move past that obstacle... \$\endgroup\$ – Brian Drummond Feb 1 '16 at 21:37
  • \$\begingroup\$ I want to measure leakage current of a ring oscillator with variation on Vth, in 45 nm node technology. variation is a gaussian distribution with a mean and sigma, ( T & Y in the code). I do a monte carlo simulation as is mentioned in the code. So the result must be a distribution of leakage currents. \$\endgroup\$ – lili94 Feb 2 '16 at 12:43

My best guess is the solver can't find the DC operating point. Here are the ways I've overcome this problem in other simulators.

  • Turn the DC operating point analysis off.
  • If you can set initial conditions for voltage on your nodes try that
  • It doesn't look like you have a definite DC path to a lot of your nodes, try adding some parasitic resistance (a resistor on the order of 10^9 or above on some of the nodes to ground (on a board you'll have the same parasitic resistance anyway). And see if it helps the solver converge.

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