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sp modelling of differential amplifier

aaamin

 I need to extract s parameters of a differential linear equalizer (high pass filter) using spectre.

I do not have spectre RF.  How do I do four port analysis? 

  • Assuming you want basic differential and not mixed-mode S-parameters, then you can attach a  "balun" component (from the "rfLib" library)  to both the differential input and output of your amplifer. One would then attach a "port" component (from the "analogLib") library to single-ended terminals of the balun. The port should configured with the correct impedance (e.g 50Ohms) and assigned a port number (1 and 2). Depending on your design you may also need to add DC blocking and biasing to the amplifier inputs, etc.

     The "rfLib " library is available in the cadence installation directory: $CDS_INSTALL_DIR/tools/dfII/samples/artist/rfLib

     You should now be ready to simulate the design in spectre using ADE. Setup an "sp" analysis and sweep over the desired frequencies. After the simulation completes, select "Results->Direct Plot->Main Form..." You can also use the calculator to plot S12.

    You may also want to check the RF Design Forum for addition help and suggestions.

     Jim

  •  Jim,

    Thank you for pointing to right direction. The challenge is that I do not have rfLib.

    So I tried to create balun using two xfmr elements. But cant define rout and rin of balun.

    I am not sure what port impedance to use. Considering the ckt as blakcbox, how do I select

    port imepdance?

     

  • You should also be able to get it to work using the xfrm. The port impedance can be set by changing the port resistance parameter. The default is 50Ohms.

     Jim

  • in reply to aaamin

    Transformer impedance is related to the square of turn ratio.  Say you have a transformer with turn ratio of 1:n  That is the primary is 1 times and the secondary is n times of turns.  Now say you connect the secondary to say Zout  Then the impedance seen from primary is Zout/SQR(n)  and if you connect the primary to Zin the output impedance seen by the output connection is: 

    Zin/SQR(1/n)

    or

    Zin X SQR(n) = Zin X n^2

    SQRT(Zin/Zout) =1/n

    or

    Zin/Zout =SQR(1/n)= (1/n)^2

    Regards,

    Babak

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