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Ring oscillator in HSPICE

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Hi

I want to simulate a VCO using CMOS, and I'm trying to simulate a 5 stage ring oscillator in HSPICE first.
I'm not getting any oscillations even though I've specified an initial condition, and the output voltage appears to settle somewhere between VDD and 0 after some initial spikes.
This is the netlist:

Code: 
.MODEL n1 NMOS LEVEL=3 
.MODEL p1 PMOS LEVEL=3
.GLOBAL VDD GND

Vsupply VDD 0 3.3
Vground GND 0 0

.subckt inverter in out
M1 out in GND GND n1 L=120n W=280n
M2 out in VDD VDD p1 L=120n W=980n
.ends

X1 a5 a1 inverter
X2 a1 a2 inverter
X3 a2 a3 inverter
X4 a3 a4 inverter
X5 a4 a5 inverter

.IC v(a1)=3.3

.TRAN 1n 50n

.OPTION POST PROBE
.PROBE V(a1) V(a2) V(a3) V(a4) V(a5)
.END

Is there something I'm missing here? I'm fairly new to HSPICE.

Any help would be much appreciated.
 
Last edited by a moderator:

Still no luck.

Attaching a screenshot of my plots



The plots are for each of the five inverter stages.
 

Did you already try different .IC values, e.g. .IC v(a1)=1 ?

Or reduce the default ABSTOL value:
Code: 
.OPTION ABSTOL=1e-12
 

Tried that. Still doesn't work.
 

Ancient LEVEL=3 MOS models are not suited for 120nm channel length. Use LEVEL=54 (BSIM4) instead.
 
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