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  1. #21
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    Re: S11 inductance measurement

    [QUOTE=BradtheRad;1606574]
    If a default RLC resonant circuit appears, then click the Circuits menu, and go to Op Amps >> Gyrator.

    https://tinyurl.com/yah5tp4t

    I wonder why your tinyurl fails?

    http://tinyurl.com/y983s4bo
    A good design question lists your overall requirements™ The best question deserves a better answer. ™
    ... Tony Stewart EE since 1975



    •   Alt21st February 2018, 02:59

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  2. #22
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    Re: S11 inductance measurement

    Quote Originally Posted by SunnySkyguy View Post
    Thanks, Tony. Your tinyurl link works fine. It displays the gyrator circuit.

    My link was produced by Falstad's version 1.5n which is no longer up-to-date with the website version. I suspected it would misbehave. I use the older version because it allows me to rearrange scope traces by editing the file directly in the Export window.



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    Re: S11 inductance measurement

    Quote Originally Posted by promach View Post
    Have anyone used S11 result to calculate inductance value of active inductor as decribed in https://www.ieee.li/pdf/essay/s_para...nts.pdf#page=5 ?

    Attachment 144460

    Attachment 144459
    I must confess I've never computed L from s11.

    From your datasheet. 50 Ohms @ 100MHz has s11 =0.333, 30 degrees which is a VSWR of 2.0 and return loss of 9.6 dB

    Z = Zo * ((1 + Γ) / (1 - Γ))
    Γ = (Z - Zo) / (Z + Zo)
    S11 = 20 * Log10(mag)

    Reflected power is the square of reflection coefficient or 1/9th or 11.1% in this example.



    same example
    Z= 82.9Ω +j30.7Ω

    L=Z_Im/2πf
    L= 30.7/(2π*1e8Hz) = 49 nH

    have fun.
    Last edited by SunnySkyguy; 21st February 2018 at 04:01.
    A good design question lists your overall requirements™ The best question deserves a better answer. ™
    ... Tony Stewart EE since 1975


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  4. #24
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    Re: S11 inductance measurement

    Why do "denominator addition" and "numerator addition" ?

    Click image for larger version. 

Name:	S11_inductance.png 
Views:	8 
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ID:	144801



    •   Alt22nd February 2018, 00:35

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  5. #25
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    Re: S11 inductance measurement

    Z_denominator_im =S.11_im*(-1)
    Do you guys have any idea how the author arrived at this expression exactly ?



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    Re: S11 inductance measurement

    Quote Originally Posted by promach View Post
    Do you guys have any idea how the author arrived at this expression exactly ?
    Surely learn and study very basic things.

    Z=(1+S.11)/(1-S.11)

    Z_numerator=1+S.11=(1+S.11_re) + j*S.11_im
    Z_denominator=1-S.11=(1-S.11_re) + j*(-S.11_im)

    Z_numerator_re=1+S.11_re
    Z_numerator_im=S.11_im

    Z_denominator_re=1-S.11_re
    Z_denominator_im=-S.11_im


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  7. #27
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    Re: S11 inductance measurement

    Could anyone tell me why I am not getting Leq to be 1nH ?

    Click image for larger version. 

Name:	Screenshot from 2018-03-01 00-05-01.png 
Views:	8 
Size:	125.3 KB 
ID:	145000

    Click image for larger version. 

Name:	Screenshot from 2018-03-01 00-00-36.png 
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ID:	144999

    - - - Updated - - -

    The following is the netlist for the test circuit :

    Code:
    * gnetlist -g spice-noqsi -o test_active_inductor.net test_active_inductor.sch
    * SPICE file generated by spice-noqsi version 20130710
    * Send requests or bug reports to jpd@noqsi.com
    RZ1 Vtest Ltest 50      
    Vtest Vtest GND dc 1
    +ac 1
    .GLOBAL Vdd Vss
    .PARAM SUPPLY=3.3v
    .options TEMP=25
    .MODEL n1 NMOS
    .MODEL p1 PMOS
    .INCLUDE CMOS_Inverter.net
    .INCLUDE Gm2.net
    Vd Vdd GND 'SUPPLY'
    Vs Vss GND 0V
    Ltest Ltest GND 1n  
    .control
    set noaskquit
    AC LIN 1000 100Meg 200Meg
    run
    let S11=(2*v(Ltest)/v(Vtest)-1)
    settype s-param S11
    
    let S11db=db(S11)
    settype decibel S11db
    
    let P11=180*ph(s11)/pi
    settype phase P11
    
    plot s11db ylimit -0.5 0
    plot P11
    
    print S11 > S11.log
    *plot smithgrid S11
    *wrs2p s3046.s2p $ write touchstone vers. 1 file s3046.s2p
    .endc
    Last edited by promach; 28th February 2018 at 17:12.



  8. #28
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    Re: S11 inductance measurement

    Found the root cause for the miscalculation.

    I forgot to multiply by Zo which is 50ohm



    •   Alt2nd March 2018, 11:32

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  9. #29
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    Re: S11 inductance measurement

    Quote Originally Posted by BradtheRad View Post
    Thanks, Tony. Your tinyurl link works fine. It displays the gyrator circuit.

    My link was produced by Falstad's version 1.5n which is no longer up-to-date with the website version. I suspected it would misbehave. I use the older version because it allows me to rearrange scope traces by editing the file directly in the Export window.

    You can still do that with this version
    http://tinyurl.com/y946spno
    http://tinyurl.com/y72hdnj6 without current trace
    A good design question lists your overall requirements™ The best question deserves a better answer. ™
    ... Tony Stewart EE since 1975



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