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i'm looking at an impedance curve of a non-ideal tantalum capacitor in LTSpice. The test circuit and impedance curve is seen in this screengrab:

http://www.apspektakel.com/bilder/tantal.png"

The spice file is here http://www.apspektakel.com/bilder/tantal.asc".

So, the imdpedance curve shows the expected impedance minimum, but also an unexpected maximum at about 100MHz, where there is also a polarity switch in phase. This feature does not show up if I do an impedance plot in octave:

Which result in these plotsCode (Text):octave:1> f = [1000:1000:1e9];

octave:2> C = 2e-3

C = 0.0020000

octave:3> R = 2e-3

R = 0.0020000

octave:4> L = 1e-9

L = 1.0000e-09

octave:5> z = R + f.*2*pi*j*L-1./(f.*2*pi*j*C)

octave:6> loglog(f,abs(z))

octave:7> semilogx(f,atand(imag(z)./real(z)))

http://www.apspektakel.com/bilder/tantal.svg"

http://www.apspektakel.com/bilder/phase.svg"

The parameters in the octave code are the same as in LTSpice component. Anyone know where this comes from? The phases look pretty different, is there something wrong with the test circuit?

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# Strange impedance curve in LTSpice

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