tuning range of vco in cosmos scope

[Fractional-N]

look @ this pic

how can I display the tuning range of a ring vco in Cosmos Scope, like this
is there a special command (in hspice or hspicerf) to calculate the frequency
or
is there a special tool in Cosmos Scope to measure the freq of a waveform?
thnx!

 

[Hughes]

You can use hspice ".meas" command to calculate the frequency:

vtune ... ... ...
.option post autostop
.tran 0.01n 100u sweep vtune 0.3 0.8 0.05
.meas tran posc trig v(vco_out) val = 1.25 rise=2
+ targ V(vco_out) val = 1.25 rise=3
.meas tran fosc param='1/posc'

Then plot the file with extension ".mt0", set the x-axis to vtune.

Cosmos scope can also measure the frequency of a wave by measurement tool. You can access this tool by a button at the bottom of the window. Use hspice ".meas" command is better in this case.

 

[AdvaRes]

Hi all,

I'm doing manually that task using an Excell Spreadsheet. I plotted manually the curve an I found a curve like this. I didn't saw something like that before. Is that kind of curves familiar in VCO ? I need your commments.

 

[Fractional-N]

thnx Hughes you help a lot!

Hi all,

I'm doing manually that task using an Excell Spreadsheet. I plotted manually the curve an I found a curve like this. I didn't saw something like that before. Is that kind of curves familiar in VCO ? I need your commments.

Generally speaking, No, it is not a familiar curve for a VCO, also it is not impossible for a VCO to have a curve like that. let us see your circuit