# using variables in calculator (cadence spectre)

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#### bharathr87

##### Member level 1

i need to find the rise time in cadence spectre.....I have been using the calculator in wavescan to find it...now i have to test the circuit under different vdd conditions for which the expression for risetime also changes...is there any way by which i can use a variable as an argument in calculator so that i dont have to painstakingly change the expression for risetime everytime i run it for a different vdd.....

#### saro_k_82

##### Full Member level 6

Result browser --> variables-->middle click on the required variable and get expression--> use this expression for the variable in the output setup.

dfleisch

Points: 2

### dfleisch

Points: 2

#### analog_match

##### Member level 2

Bharath,

Looks like you have an expression which uses VDD in it and VDD is your variable, correct? You can just select the VDD net by clicking Vt and then the net in the schematic which should put something like VT("netxx") into your calculator expression field.

Hope his helps.

#### saro_k_82

##### Full Member level 6
use design variables in cadence calculator

VT stands for Transient voltage., so this trick will work here (VDC will be better)., but it won't work for any design variable., for example you have set a variable for rise time, frequency, capacitance, transistor width, etc...

#### JoannesPaulus

calculator variables

If VDD is a parameter, you can use it in an expression as VAR("VDD"), for example: cross(VT("/net0"),VAR("VDD")/2,1,"either",nil,nil) will give you the time when the voltage on net0 crosses VDD/2.

JitterJaw

### JitterJaw

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#### bharathr87

##### Member level 1
how to put variables in calculator

use the results browser found under tools....

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