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    How to know Proper Values for ZL and ZS , Load Pull and Source Pull in ADS

    Hi everyOne!
    first things first: I'm new to this stuff!

    I'm trying to design an amplifer with a GaAs Design kit.
    CAD : ADS
    frequency = 1 tone 10.7 GHz
    tried to bias it for Class A operation.
    stabilized it.
    now I'm trying to do load pull and source pull.
    I'm just wondering to know the proper range for ZL and ZS?! I mean , I'm getting something from source pull to place at source. but it seems unusual!

    please take a look at the procedure :

    1-DCIV simulation => class A : VD = 8 & VG = -.5 has been selected.
    Click image for larger version. 

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    2- Stability Check , and making it stable with L&S stabling circles : push 9GHz circle back.
    Click image for larger version. 

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    3- Load Pull and then load pull and getting 52 +j*52 for the Z-Source which made me think that HOW SHOULD I KNOW THAT THIS IS WOULD BE FINE? for a 150um Gate (UG = 75um and NOF = 2) GaAs Transistor?!!
    Click image for larger version. 

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    Thank you for Your time!
    Surely let me know what basic things I should learn

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    Re: How to know Proper Values for ZL and ZS , Load Pull and Source Pull in ADS

    Load Pull and Source Pull Analysis is done for those design metrics..

    -Max. Efficiency for Power Amplifiers OR
    -Max. Gain for an Amplifier OR
    -Max. Delivered Power for Power Amplifiers

    They cannot generally be obtained simultaneously.You have to decide which is more important for you then you analyze in regard of these three..



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    Re: How to know Proper Values for ZL and ZS , Load Pull and Source Pull in ADS

    Yeah, I’m aiming for best PAE possible and the values that I talked about are all based On best PAE. My question is wheter the values are normal or not? 52 ohm for 75um device?



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    Re: How to know Proper Values for ZL and ZS , Load Pull and Source Pull in ADS

    For max PAE, the I would think that the gain needs to be as high as possible and therefore you need to conjugately match at the input. With the source impedance you are getting from source pull, check your s11. It should be very low.



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    Re: How to know Proper Values for ZL and ZS , Load Pull and Source Pull in ADS

    Quote Originally Posted by Amir.Sk View Post
    Yeah, I’m aiming for best PAE possible and the values that I talked about are all based On best PAE. My question is wheter the values are normal or not? 52 ohm for 75um device?
    Nobody knows it..We don't have enough information about your semiconductor devices and their characteristics..
    But I think you make some serious mistakes while simulating the circuit.I cannot say 52 Ohm is not proper value but seems weird.
    Power Amplifiers have generally low Optimum Load Impedances in order to drive with higher currents due to low supply voltage.
    For instance a PA may have 2+j*3 Ohm or similar values for Optimum PAE or Pload. You ought to double-check your simulating environment.



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    Re: How to know Proper Values for ZL and ZS , Load Pull and Source Pull in ADS

    I used to get values like 20-25 ohms at 28GHz for a SiGe transistor (after layout). Most of it used to come from the internal base resistance. I have no idea about GaAs devices though.



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    Re: How to know Proper Values for ZL and ZS , Load Pull and Source Pull in ADS

    You were right guys. Something is seriously wrong!
    I have tried S-params simulation and I got terrible results with that ZL and ZS in hand! Hence I'd tried a somehow tricky simulation: changed the terminations Impedance on both side of the circuit till I get a notch on both S11 and S22 in the desired frequency.

    Click image for larger version. 

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    I came with these 2 values in hands: Zs= 15.352 + j*44.738 and ZL=55.393 + j*164 which are far from what ADS Load-Pull gave me : ZS = 52 + j*52 and ZL=165.282 + J*96.46
    which seemed to be correct: (e.g load-pull)
    Click image for larger version. 

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    also I think its important to mention that I am setting my number of harmonics in load-pull and source-pull to 1 ! because setting them to 2 or 3 made so much confusion and I could not get a single contour on data set page!

    someone please help this young lost guy who wanna be a designer!



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    Re: How to know Proper Values for ZL and ZS , Load Pull and Source Pull in ADS

    Quote Originally Posted by Amir.Sk View Post
    You were right guys. Something is seriously wrong!
    I have tried S-params simulation and I got terrible results with that ZL and ZS in hand! Hence I'd tried a somehow tricky simulation: changed the terminations Impedance on both side of the circuit till I get a notch on both S11 and S22 in the desired frequency.
    The load impedance that gives you a notch for s22 will probably not be the same as the one where you get your maximum PAE. Your optimum impedances for maximum power, maximum gain and maximum PAE will be close, but in general the impedances cannot be same always. s22 is typically never that great for any practical amplifier (because you almost always match for maximizing output power or maximizing power added efficiency).



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