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No oscillations in ring oscilator in Hspice

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sridhara

sridhara

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hspice + construct a ring oscillator

I designed a 5 stage ring oscillator using inverters....and i simulated in hspice
i found the output to be a dc voltage of 2.5V for a supply of 0-5V....
what could be the possible problem ......
 

ring oscillator spice

I think u must check bankhaursen condition for oscillation i.e. Loop gain = 1

Try to increase transconductance gain gm of each inverter .
 

ring oscilator with inverter in hspice

maybe the gain of inverter is not enough
 

zero-time oscillation in node ring oscillator

try more stages like 13 15 stages... then perhaps use a nand or nor gate to start/stop the oscillation :)

and use bigger W and L... 2um/1um, 3um/1um

i am not really good at how to count loop gain stuff...
 

trapezoidal integration oscillations

you need to give an initial condition to start the oscillator, is it a 5 stage ring inverter based oscillator or 5 stage differential ring oscillator.For the former you need to just connect the inverters back to back, for the latter you need to set the gain of the differential pairs such that barkhausen criterion is satisfied.



amarnath
 

spice ring oscilator

if you are simulated using transient, try to decrease the step time....sometimes it is because of the accuracy of the spice....
 

ring oscillator in hspice

amarnath said:
you need to give an initial condition to start the oscillator, is it a 5 stage ring inverter based oscillator or 5 stage differential ring oscillator.For the former you need to just connect the inverters back to back, for the latter you need to set the gain of the differential pairs such that barkhausen criterion is satisfied.



amarnath
Click to expand...

it is a 5 stage inverter based oscillator
 

ring oscillator, hspice

then u have not given an intial condition, use the .ic statement to give an intial condition on the output node.


amarnath
 

how to trigger ring oscillater in hspice

The initial condition is important.
In the real circuit, the noise can let the ring to oscillate. but in spice, there are no noise, so we shoud add a initial condition at one node of the ring oscillator, as a noise. and that will trigger the ring to oscillate.

Ryan
 

how to trigger ring oscillater in spice

set initial condition in one node to .ic Vnode1=5 and in the previous node set .ic Vnode0 = 0, then run the transient simulation with .tran tincr tstop UIC so that
the initial conditions are taken into account.
make sure that the trapezoidal integration method is being used, BE or GEAR make it harder for oscillators to start-up.
 

hspice ring oscillator initial condition

when i give a pulse input it is working fine.....but i have one more doubt.....
before the pulse was given.....
how come 2.5 V(for a Vdd=5V) is coming as output ...(ie) inverter acts as a voltage divider.......????
i get the same value (Vdd/2)for different values of W and L in both pmos and nmos.....
 

hspice ring osc

Usually, you can add a enable/disable by insert a NAND gate into the inverter chain. And use a disable->enable squence and your oscillator wil function
 

yeah ,u need to add inital condition

khouly
 

spice add gmin in parallel/DC for convergence DC solve. Equal gmin all nodes make perfect divider. replace one inverter with nand, all ring need enable/disable nand.
 

Try to set initial condition to kick it.
 

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