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 Measureing INPUT impedance of the Passive Switching Mixer 

Last post Tue, Sep 6 2011 11:38 AM by Tawna. 4 replies.
Started by RFQuery 20 Jul 2011 11:16 AM. Topic has 4 replies and 4894 views
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  • Wed, Jul 20 2011 11:16 AM

    • RFQuery
    • Top 75 Contributor
    • Joined on Wed, Jul 20 2011
    • Posts 89
    • Points 1,270
    Measureing INPUT impedance of the Passive Switching Mixer Reply

     Hi All,

    I want to plot the input impedance ( in RF Port side) of a passive switching Mixer [2-Phase i.e. 2- 180 degree out of phase non-over lapping LOs with rise and fall time of 1 fs & Two switches Loaded with   Resistors of  50 Ohm at the IF ports] with respect to Frequency.

    LO frequency was kept 1 GHz and the RF input frequency is swept from 0 to 5 GHz. The RF port impedance is kept at 50 ohm. Also I used analogLib delay element to generate 180 degree out-of pahse 2nd LO.

    From theory I know this input impeadnce at the RF port will be a Frequency translated version of the IF side Impedance. But since I am using simple resistor at the IF side the RF side impedance will be the same resistor i.e 50 Ohm

    I did PSS and PSP analysis and then I plotted the S11 but I got 0dB across  the frequency instead of getting a very large -ve value !!

    Can anybody please tell me Where I am going wrong in doing the simulation ?

    My Netlist is as Below:--

    // Library name: PASSIVE_MIXER
    // Cell name: IN_IMPEDANCE
    // View name: schematic
    V0 (net7 0) vsource type=pulse pacmag=1 pacphase=0 val0=1 val1=0 period=1n \
            delay=0 rise=1f fall=1f width=500.0p
    PORT0 (net1 0) port r=50 num=1 type=sine freq=frf dbm=prf fundname="rf"
    DELAY0 (net033 0 net7 0) delay td=500.0p gain=1.0
    R1 (IF_N 0) resistor r=50
    R0 (IF_P 0) resistor r=50
    SW1 (IF_N net1 0 net033) relay vt1=0 vt2=1 ropen=1T rclosed=1.0
    SW2 (IF_P net1 0 net7) relay vt1=0 vt2=1 ropen=1T rclosed=1.0

    simulatorOptions options reltol=1e-3 vabstol=1e-6 iabstol=1e-12 temp=27 \
        tnom=27 scalem=1.0 scale=1.0 gmin=1e-12 rforce=1 maxnotes=5 maxwarns=5 \
        digits=5 cols=80 pivrel=1e-3 ckptclock=1800 \
        sensfile="../psf/sens.output" checklimitdest=psf
    pss  pss  fund=500M  harms=51  errpreset=moderate  annotate=status
    psp  psp  sweeptype=absolute  start=0  stop=5G  step=100M
    +    portharmsvec=[0]  ports=[PORT0]  donoise=no  annotate=status
    modelParameter info what=models where=rawfile
    element info what=inst where=rawfile
    outputParameter info what=output where=rawfile
    designParamVals info what=parameters where=rawfile
    primitives info what=primitives where=rawfile
    subckts info what=subckts  where=rawfile
    saveOptions options save=allpub

     

    • Post Points: 20
  • Mon, Jul 25 2011 1:30 AM

    Re: Measureing INPUT impedance of the Passive Switching Mixer Reply

    Wasn't quite complete - don't know what your parameter values were. Anyway, there's something a little odd here - I would have expected PORT0 to be a dc source  - you don't want it to be time varying. Also the fact that the LO had pacmag set on it threw me a bit.

    I would suggest not using delay - this can be problematic with PSS simulation; instead either add a second pulse source which is inverted, or use an ideal balun maybe.

    Andrew.

    • Post Points: 20
  • Sat, Sep 3 2011 11:14 PM

    • RFQuery
    • Top 75 Contributor
    • Joined on Wed, Jul 20 2011
    • Posts 89
    • Points 1,270
    Re: Measureing INPUT impedance of the Passive Switching Mixer Reply

     Thanks Andrew

    I wanted to give the attachemts of Schematic and the LOG file but unfortunately this forum does NOT have option to attach files.

    Finally I found what is the issue. It turns out that My IDEAL switch parameters settings were wrong. So they were always OFF.I did the proper setting of the switches and got 50 Ohm at the RF side.

    As suggested by you PSS has some issues with delay elements. If I want to have N-path (say 8 paths) switches and all are driven by multiphase (delayed) pulse sources, don't you think it is also a problem for PSS analysis as it has to Handle 8 driven Large Signal Sources.

    If it is a problem, then in this scenario what can be done to have multiphase/delayed clocks in the simulation.

    Thanks-

     

    • Post Points: 35
  • Sat, Sep 3 2011 11:32 PM

    Re: Measureing INPUT impedance of the Passive Switching Mixer Reply
    Actually the forum _does_ have the ability to attach files. Go to the "options" tab when posting or replying to a post.

    If you have 8 pulse sources with the same frequency but different values of the "delay" parameter, then that should work perfectly OK. That would be much better than trying to use separate "delay" components. The sources themselves don't cause hidden state problems, and whilst the "delay" component does work these days (I think, if my memory is correct - it may not be, because I'm not sure I've ever tried it) it's considerably more complicated for PSS.

    Regards,

    Andrew
    • Post Points: 5
  • Tue, Sep 6 2011 11:38 AM

    • Tawna
    • Top 25 Contributor
    • Joined on Thu, Jul 10 2008
    • Snohomish, WA
    • Posts 212
    • Points 5,625
    Re: Measureing INPUT impedance of the Passive Switching Mixer Reply

    Hi all,

     

    I'm pretty sure that the delay will have hidden state issues with PSS analysis.

     

    best regards,

    Tawna

    Best regards, Tawna Wilsey Staff Support AE, Global Customer Support Cadence Design Systems, Inc.
    • Post Points: 5
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Started by RFQuery at 20 Jul 2011 11:16 AM. Topic has 4 replies.