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    Interpreting NF Circle ang Gain circle for matching network

    Hello,i have built a circuit shownbellow,from the S-param simulation i got the Gain circle and NF circle
    how to know from the circles to what input impedance network should i use and to what output impedance network should i use?
    Thanks.
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    - - - Updated - - -

    update:

    Why the point we take on the smith chart in the Gamma_s and not the Gamma_L?
    Thanks

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    Last edited by yefj; 26th March 2020 at 18:20.

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    Re: Interpreting NF Circle ang Gain circle for matching network

    NFmin is a single point and NF Circles are rounding this point by sacrificing NF value.So the best NF can be obtained at that point only, then first circle covers more points ( impedance values ) by cost of degradation of NF by xdB ( more flexibility but more NF ) so on..
    Gain circles are also interpreted as such that way,,
    Noise is a function of Source Impedance which is seen by active device so Gamma_S is used.Gamma_L has very little contribution onto this.



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    Re: Interpreting NF Circle ang Gain circle for matching network

    for whar kind of circle Gamma_L is used?
    Thanks.



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    Re: Interpreting NF Circle ang Gain circle for matching network

    Quote Originally Posted by yefj View Post
    for whar kind of circle Gamma_L is used?
    Thanks.
    Gamma_L is used for Power Gain ..



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    Re: Interpreting NF Circle ang Gain circle for matching network

    Hello, i am trying to produce a gain circles on a simple transistor as shown bellow.

    i have defined the range from 1 til 30 dB and i dont get any circle just dots in infinity?

    Where did i go wrong?
    Thanks.

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    Re: Interpreting NF Circle ang Gain circle for matching network

    Is it a joke ?? Everything is short circuited..
    Read on simulation techniques much.There are millions app notes and papers about it.



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    Re: Interpreting NF Circle ang Gain circle for matching network

    Hello , yes i had a little biasing problem where i put Vdc in port 0.8 and for some reason it biased 1.6V on the gate as shown bellow.
    i Have succseeded building those circles and i picked a point in between the NF circle an GAIN circle and the GAMMA is GAMMA_S(as you said)
    Next i calculate from GAMMA_S yo GAMMA_L extract the impedance using the following matlab code

    My question is, what is the best tool you reccomend for building a matching network from 50 to the load impedance and source impedance we calculated?
    gamma=0.548*exp(deg2rad(-159.05)*i);
    z=gamma2z(gamma,50)/50;

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    - - - Updated - - -

    I have calculated the Zs and ZL as shown bellow so i need to do a matching network from 50 to Zs and ZL to 50 so i will get minimum S11 and minimum S22?


    Updated matlab code:
    gamma_s=75.8966*exp(deg2rad(280.88)*i);
    z_s=gamma2z(gamma_s,50);
    s11=0.99875-0.03202*i
    s12=721.33*10^(-6)+8.622*10^(-3)*i
    s21=-188.37*10^(-3)+30.611*10^(-3)*i
    s22=875.51*10^(-3)-100.72*10^(-3)*i
    gamma_L=conj((s22+(s12*s21*gamma_s)/(1-s11*gamma_s)))
    z_L=gamma2z(gamma_L,50)

    - - - Updated - - -

    Do i need to build the network to the conjugate value of Zs and ZL
    ?



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    Re: Interpreting NF Circle ang Gain circle for matching network




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