ring oscillator design problem

[ppat2006]

I am trying to build 5 stage single ended ring oscillator in simulink(matlab). How to set propagation delay of each stage inverter to get the desired frequency? also what parameters to set for pmos and nmos L,W, Kp,Kn,Vt etc.

I have taken some values from research paper like (W/L)p =5/2, (W/L)n=3/2,
vtn=0.6 V and vtp=0.53 V, tox=25 nm , Ld=0.1um. I have set solver in simulink as ode15s and output capacitance = 1pf.

I am not getting good square wave. it appears like sinusoidal . so is it correct or wrong . also is it necessary to give exciting pulse to the loop.

plz if anybody has knowledge in matlab / simulink, reply.

 

[vaibhavar]

Hi..

The values seem to be correct. I think you need to increase the number of stages, so that sine wave is properly shaped in to square wave. Right now, what frequency are you getting?


Best Regards
Vaibhav

 

[ppat2006]

approx. 200 Mhz

---------- Post added at 08:56 ---------- Previous post was at 08:55 ----------

and how to chk delay of each stage in simulink/matlab??

---------- Post added at 09:00 ---------- Previous post was at 08:56 ----------

also if u can give be some more design of 5 stage ring oscillator with all values and similarly for cmos differential ring oscillator

 

[Milad-D]

For sure you will not get square wave. You need also to model the nonlinearity of the loop.

 

[ppat2006]

how to model nonlinearity of the loop. plz give complete solution

 

[Milad-D]

For each stage do an sweep and find the dc characteristic of each inverter and then add this characteristic to each stage. In simulink, there is a soft limiter block, you can use that for this purpose.

 

[leo_o2]

For accurate simulation, pls use transistor-level simulation tools (like spice or spectre).

 

[ppat2006]

hello,
there is no soft limter block in matlab-simulink. also you told to add the characteristic to each stage . i didn,t get?

can you give a readymade prepared simulink file of 5 stage ring osc and cmos differential ring osc??it is urgent.

 

[Milad-D]

View attachment SIMPLE.txt

Here i attached a simple 5 stage ring resonator simulink file. Each stage consists of Laplace transform ( which you can the pole of each stage) and the DC characteristic of Inverter ( Using Look-up Table. Just add you data) and then a hard limiter. Also i have added a stimulation for the start-up of the oscillator.

P.S: to use the file, change the extension of the file from .txt to .mdl.

 

[ppat2006]

thank u so much for ur help. but it didnt simulate bcoz it took too much time for simulation. so i changed sim time = 1e-3 instead of 1e-1. but it didnt give square wave or oscillation??.

i have attached my model file build with simelectronics. can u suggest some changes in tht to get proper square wave.

does ur model gives proper output

also if possible give me cmos differential ring oscillator design build in simelectronics..

 

[Milad-D]

View attachment SIM2.txt

Here is the correct one. Please go to Simulation Menu, Configuration Parameters, change relative tolerance=1e-6 and and max. step size to 1e-8.

 

[ppat2006]

thanks a lot for ur help & cooperation.
can i add one simout(To workspace) block to transfer amplitude value to script file bcoz i have to further program for phase noise using tht amplitude value.

also how u have calculated the transfer function for one inverter 1/1e-6s +1??
and u have placed saturation block for only one stage is tht the reason to get proper square wave??

also please give me the design for cmos diifferential ring oscillator.

sorry for bothering u with too many questions