Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

How i can find the optimom value of load impedance?

Status
Not open for further replies.

rezaee

Full Member level 2
Joined
Jul 3, 2009
Messages
129
Helped
4
Reputation
8
Reaction score
1
Trophy points
1,298
Activity points
2,117
Hi
i have designed a power amplifier circuit now i want to find the optim load impedance because of the maximum power transfer to the load and give the most PAE .
in one way i sweep the load impedance between two point with step size and i see which impedance give me best result ( for example Z1) in other way I use S-parameter simulation in ADS software ( all of supply short circuit and i add 50Ω terms in input and output) and with the equation of: Zout=50*(1+S(2,2))/(1-S(1,1)) i calculate output impedance of circuit ( for example Z2) Is it true that for transfer maximum power to load the load impedance must be complex conjugate of Z2??
If the answer to this question is YES then why Z1 isnt equal to complex conjugate of Z2 ???
 

One thing to note is that Power Amps are not good to simulate with S-parameters.
S-params are for small signal systems. The best/easiest way is to get the
impedance from the PA Vendor, if you are the IC designer then you might need to
get a high power load pull line and find out the Pmax Load empirically.

PA's put out more power because they have low output impedance.

P=V²/Z !
If your Vdd= 3V then the best way to get more MAX power is to let Z get smaller!

3²/50Ω << 3²/5Ω
22.dBm 32.5dBm

Cheers
 

    rezaee

    Points: 2
    Helpful Answer Positive Rating
thanks Element_115 for your reply

Im beginner in designing RF circuits now i design a class-E PA in 0.18um at2.4GHz and i simulated it in ADS , from your reply i understand that i can find the optimum load impedance with load-pull or on the other hand with sweeping load impedance.

OK , But now i have a question : If S-param dont give me correct output impedance in PA then How i can caculate the output impedance correctly in ADS?

If I calculate the correct output impedance of circuit , Is it true that i tell the optim load impedance is complex conjugate of this?

Ofcourse i have same problem for calculate input impedance of my designed PA because of i want to match the input and output to standard 50Ω.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top