Question about ltspice .measure
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Posted by Svenn Are Bjerkem on July 29, 2007, 3:31 pm
Please log in for more thread options Hi, I simulate a passive high-pass filter with a 1 pF capacitor and a 50 Ohm resistor. I simulate reom 10 to 100 GHz With the waveform tool I measure the -3 dB frequency to be 3.19 GHz and then I tried to measure with a .measure statement from a file. The measure statement I took from the manual: .MEAS AC tmp max mag(V(out)); find the peak response .MEAS AC meas_3db trig mag(V(out))=3Dtmp/sqrt(2) The measure report windos tell me: tmp: MAX(V(out))=3D(-0.0043981dB,1.82317=B0) FROM 10 TO 1e+011 meas_3db=3D9.68205e+010 FROM 3.17955e+009 TO 1e+011 What is the number directly behind the =3D? (9.68205e+010) -- Svenn | ||||||||||||||||
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Posted by Helmut Sennewald on July 29, 2007, 4:04 pm
Please log in for more thread options > Hi,
> I simulate a passive high-pass filter with a 1 pF capacitor and a 50
> Ohm resistor. > I simulate reom 10 to 100 GHz > With the waveform tool I measure the -3 dB frequency to be 3.19 GHz > and then I tried to measure with a .measure statement from a file. The > measure statement I took from the manual: > .MEAS AC tmp max mag(V(out)); find the peak response
> .MEAS AC meas_3db trig mag(V(out))=tmp/sqrt(2) > The measure report windos tell me:
> tmp: MAX(V(out))=(-0.0043981dB,1.82317°) FROM 10 TO 1e+011 > meas_3db=9.68205e+010 FROM 3.17955e+009 TO 1e+011 > What is the number directly behind the =? (9.68205e+010)
Maybe the last before last frequency point in the AC-simulation. > Svenn#
Hello Svenn, The following command will do what you want. .ac dec 100 10k 100g .MEAS AC tmp max mag(V(out)); find the peak response .MEAS AC meas_3db when mag(V(out))=(tmp/sqrt(2)) --- output in the .log file tmp: MAX(mag(v(out)))=(-0.0043981dB,0°) FROM 10 TO 1e+011 meas_3db: mag(v(out))=(tmp/sqrt(2)) AT 3.18011e+009 Best regards, Helmut LTspice user group: http://tech.groups.yahoo.com/group/LTspice/ | ||||||||||||||||
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