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This question is software related. I just wanted to know if it was possible to get the time at which my circuit reaches a certain value without just running the cursor and getting a approximate value. For example if I have a RC circuit , plot the time at which the voltage across resistor reaches 1/2 * Vdd. Is there someway to do code it and get the exact answer? if yes can you please explain how it can be done?

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  • \$\begingroup\$ Yes, it's called circuit analysis. For simple circuits- you can derive an equation representing the time domain response; then simply solve that equation for your conditions, e.g. time at Vout = Vdd/2. \$\endgroup\$
    – user16324
    Commented Jun 30, 2021 at 16:37
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    \$\begingroup\$ For sure you can do it try to read here ltwiki.org/LTspiceHelp/LTspiceHelp/… and here youtube.com/watch?v=GtRaEHhMeCE \$\endgroup\$
    – G36
    Commented Jun 30, 2021 at 16:44
  • \$\begingroup\$ Aagh? I want to get it solved with LTSPICE not pen and paper. From my simulation results I want to find the time taken to reach a certain point @user_1818839 \$\endgroup\$ Commented Jun 30, 2021 at 16:45
  • \$\begingroup\$ @HariKrishna What do you mean by "plot the time at which the voltage across resistor reaches 1/2 * Vdd"? A .TRAN simulation is done in a range of time, anything plotted will be a function of that whole timespan. Did you mean that you wanted your simulation to stop when it reaches that value? Otherwise, this might help. \$\endgroup\$ Commented Jun 30, 2021 at 16:54
  • \$\begingroup\$ You want to use the .measure statement to automate such measurements. You should be able to search for examples using that keyword. \$\endgroup\$ Commented Jun 30, 2021 at 17:26

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Use a .meas statement.

.MEAS TRAN res4 FIND V(out) WHEN V(x)=3*V(y) rise=last

Print the value of V(out) the last time the condition V(x)=3V(y) is met when approached as V(x) increasing wrt 3V(y). This will be labeled res4. Source: LT wiki

If I wanted to find the time when a node was at 0.5V, I would use a statement like this:

.meas TRAN newsignal2 FIND time WHEN 0.5=V(vout)

The results will show up in the spice error log, also if it says "Measurement [nameofsignal] FAIL'ed" that means the statement didn't find anything OR the syntax is wrong so this can make it difficult to debug.

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