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Passive switching mixer volatge conversion gain calculation and its varition with frequency

lahsivece

Hi All,

I am trying to do a passive switching mixer volatge conversion gain simulation. The circuit consists of a MOS transistor driving a resistive load. The gate of MOS is driven by a rail to rail square pulse. 

I tried the steps given in the Application note "Mixer design using Spectre RF " , but it didn't give meaningful results.

Is there any application note that deals specifically with passive switching mixers with LO being driven by a rai to rail signal or a similar situation ?

Best Regards

Vishal

  • Vishal,

    There are some challenges with measuring IP3 with passive mixers due to limitations of certain device models (e.g. bsim3v3 and bsim4) - there are a number of academic papers on this problem. But I'm not sure whether this is what you mean by "didn't give meaningful results". That's a rather open statement...

    Kind Regards,

    Andrew.

  • Hi Andrew,

    Sorry for not specifying the problem correctly. I am not getting correct gain (loss) out of the passive mixer . My test bench looks like following:

    c1=500fF

    Conversion gain was calculated using pss+swept pac. For pss analysis , # of harmonics set to 0 . Port0 is dc type (based Spectre RF simulation manual)  . In Swept pac # of sidebands  was set to 2. The input.scs looks like following:

    // Library name: MIXER_CHARACTERIZATION
    // Cell name: RX_MIXER_FUNDAMENTAL_RZ_MOS_PSF_PXF
    // View name: schematic
    PORT0 (RF 0) port r=50 dc=600m type=dc freq=frf dbm=vrf pacmag=1
    V1 (LO 0) vsource type=pulse val0=0 val1=1 period=tlo width=d*tlo
    M0 (IF LO RF 0) N_12_RF wf=5u lf=120.0n nf=4 m=1
    R0 (IF 0) capacitor c=c1
    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 sensfile="../psf/sens.output" \
        checklimitdest=psf
    pss  pss  fund=500M  harms=100  errpreset=moderate  annotate=status
    pac  pac  start=1K  stop=500M  maxsideband=2  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

    The conversion gain for h=-1 is shown below. I am getting a positive gain whcih doesn't make any sense to me .

    Please advise what is wrong with this way of simulating mixer conversion gain.

    The gain at 10MHz If calculated by using pss analysis followed by a dB20 peak measurement comes as  -4.7dB. Test bench looks like (c1=500f)

     // Library name: MIXER_CHARACTERIZATION
    // Cell name: RX_MIXER_FUNDAMENTAL_RZ_MOS_SW
    // View name: schematic
    R0 (IF 0) capacitor c=c1
    M0 (IF LO RF 0) N_12_RF wf=5u lf=120.0n nf=4 m=1
    V1 (LO 0) vsource type=pulse val0=0 val1=1 period=tlo width=d*tlo
    V0 (RF 0) vsource dc=600.0m type=sine ampl=vrf freq=frf
    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 sensfile="../psf/sens.output" \
        checklimitdest=psf
    dcOp dc write="spectre.dc" maxiters=150 maxsteps=10000 annotate=status
    dcOpInfo info what=oppoint where=rawfile
    pss  pss  fund=10M  harms=200  errpreset=conservative
    +    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
                                         

    Thanks

    With Best Regards

    Vishal
  • Hi Andrew ,

    Sorry for not being clear. I am not getting a correct voltage gain from passive swictging mixer . The test bench looks like following :

    The input.scs file is :

    // View name: schematic
    PORT0 (RF 0) port r=50 dc=600m type=dc freq=frf dbm=vrf pacmag=1
    V1 (LO 0) vsource type=pulse val0=0 val1=1 period=tlo width=d*tlo
    M0 (IF LO RF 0) N_12_RF wf=5u lf=120.0n nf=4 m=1
    R0 (IF 0) capacitor c=c1
    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 sensfile="../psf/sens.output" \
        checklimitdest=psf
    pss  pss  fund=500M  harms=100  errpreset=moderate  annotate=status
    pac  pac  start=1K  stop=500M  maxsideband=2  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
     

    c1=500f

    The simulated gain curve from pss+swept pac is

    I belive that this is wrong.

    I also calculated gain as VIF/VRF from PSS analysis  which at 10MHz IF comes to be -4.6dB. The input.scs looks like folowing :

    // Cell name: RX_MIXER_FUNDAMENTAL_RZ_MOS_SW
    // View name: schematic
    R0 (IF 0) capacitor c=c1
    M0 (IF LO RF 0) N_12_RF wf=5u lf=120.0n nf=4 m=1
    V1 (LO 0) vsource type=pulse val0=0 val1=1 period=tlo width=d*tlo
    V0 (RF 0) vsource dc=600.0m type=sine ampl=vrf freq=frf
    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 sensfile="../psf/sens.output" \
        checklimitdest=psf
    dcOp dc write="spectre.dc" maxiters=150 maxsteps=10000 annotate=status
    dcOpInfo info what=oppoint where=rawfile
    pss  pss  fund=10M  harms=200  errpreset=conservative
    +    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

    Please advise as to what is going wrong with a pss+swept pac simulation.

     Thanks,

    With Best Regards

    Vishal

  • Vishal,

    There are no pictures in your posts. You can attach pictures via the Options tab when posting a reply.

    Regards,

    Andrew.

  • Hi Andrew,

    Pictures were attached . Any way here is the whole post again

    Hi Andrew ,

    Sorry for not being clear. I am not getting a correct voltage gain from passive swictging mixer . The test bench looks like following :

     Please refer to image

    The input.scs file is :

    // View name: schematic
    PORT0 (RF 0) port r=50 dc=600m type=dc freq=frf dbm=vrf pacmag=1
    V1 (LO 0) vsource type=pulse val0=0 val1=1 period=tlo width=d*tlo
    M0 (IF LO RF 0) N_12_RF wf=5u lf=120.0n nf=4 m=1
    R0 (IF 0) capacitor c=c1
    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 sensfile="../psf/sens.output" \
        checklimitdest=psf
    pss  pss  fund=500M  harms=100  errpreset=moderate  annotate=status
    pac  pac  start=1K  stop=500M  maxsideband=2  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
     

    c1=500f

    The simulated gain curve from pss+swept pac is

    Please refer to gain_curve.png image.

    I belive that this is wrong.

    I also calculated gain as VIF/VRF from PSS analysis  which at 10MHz IF comes to be -4.6dB. The input.scs looks like folowing :

    // Cell name: RX_MIXER_FUNDAMENTAL_RZ_MOS_SW
    // View name: schematic
    R0 (IF 0) capacitor c=c1
    M0 (IF LO RF 0) N_12_RF wf=5u lf=120.0n nf=4 m=1
    V1 (LO 0) vsource type=pulse val0=0 val1=1 period=tlo width=d*tlo
    V0 (RF 0) vsource dc=600.0m type=sine ampl=vrf freq=frf
    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 sensfile="../psf/sens.output" \
        checklimitdest=psf
    dcOp dc write="spectre.dc" maxiters=150 maxsteps=10000 annotate=status
    dcOpInfo info what=oppoint where=rawfile
    pss  pss  fund=10M  harms=200  errpreset=conservative
    +    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

    Please advise as to what is going wrong with a pss+swept pac simulation.

     Thanks,

    With Best Regards

    Vishal

  •  The pictures were not attached. If you paste the pictures in the post, it doesn't work - because they don't get uploaded to the forum server. So in your last post there was only one picture (the PAC output response) - but I think the text talks about a picture of the testbench too.

    Regards,

    Andrew.

  • I'd suggest you contact customer support. I'm a bit pushed for time this week to take a look - maybe somebody else on the forum can try it.

    Regards,

    Andrew.

  • Hi Andrew,

    It's not an issue.

    I will  contact customer support for the same.

    Regards

    Vishal

     

     

  • Looks like my earlier post didn't make it onto the forum...

    I agree with Andrew - this sort of question is best handled by Customer Support - they can dedicate more time and energy to answer questions.

    There is an existing Solution on Cadence Online Support that you may want to look at:

    http://support.cadence.com/wps/mypoc/cos?uri=deeplinkmin:ViewSolution;solutionNumber=11454704

     

    Also, if you are using BSIM transistor models in your circuit, see this paper:

    LINFET: A BSIM Class FET Model with Smooth Derivatives at Vds=0

    by Lawrence F. Wagner, C. Michael Olsen.  

    IBM Systems & Technology Group, Global Engineering Solutions.

    http://www.nsti.org/procs/Nanotech2007v3/7/W79.604

    best regards,

    Tawna

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