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# how to plot the frequency v.s. differential bias curve

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#### jxzhang

##### Junior Member level 3
hello folks,

Anyone knows how to plot the frequency v.s. differential bias voltage curve of a VCO using spice script in HSPICE netlist?
differential voltage sweep from -0.4v ~ 0.4v

first run tran analysis and sweep the bias voltage
measure the delay of vco cell
then open .mt0 file with awaves
change x-axis to bias voltege and plot the measured delay
use f(x,y) function to plot frequency vs bias

I've measured the delay by trig and targ and inversed to derive Fvco
and sweep the difference voltage in .tran
but I cannot find the measure type in awave
how to write the netlist for the differential control voltage sweep in .tran?
........

.param vcm=0.9
Vctlp VCP 0 dc='vcm + 0.5*vdif'
Vctlm VCM 0 dc='vcm - 0.5*vdif'
.......
.tran 100ps 10us start=0us UIC
+ sweep vdif lin 9 -0.4 0.4

.meas tran tvco trig v(CKP) val='supply*0.8' td=0.1us rise=100
+ targ v(CKP) val='supply*0.8' td=0.1us rise=111
.meas tran fvco param=('10/tvco')

what's wrong ?

Thanks!

jxzhang said:
I've measured the delay by trig and targ and inversed to derive Fvco
and sweep the difference voltage in .tran
but I cannot find the measure type in awave
how to write the netlist for the differential control voltage sweep in .tran?
........

.param vcm=0.9
Vctlp VCP 0 dc='vcm + 0.5*vdif'
Vctlm VCM 0 dc='vcm - 0.5*vdif'
.......
.tran 100ps 10us start=0us UIC
+ sweep vdif lin 9 -0.4 0.4

.meas tran tvco trig v(CKP) val='supply*0.8' td=0.1us rise=100
+ targ v(CKP) val='supply*0.8' td=0.1us rise=111
.meas tran fvco param=('10/tvco')

what's wrong ?

Thanks!

You have swept the differential voltage. Just plot the results in awaves.

old version may not display measure results.
In new version, find fvco through results browser->types->measure->fvco

version is ok, 2003.03
I can find the measure using single-ended control voltage type VCO
differential type as my netlist above cannot find it.
syntax error?

jxzhang said:
version is ok, 2003.03
I can find the measure using single-ended control voltage type VCO
differential type as my netlist above cannot find it.
syntax error?

Oh, I see.
Please change vdif to dif or _vdif or anything don't begin with letter v or i. Hspice treats names beginning with v as voltage source's instance name.

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