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Simulators >> RF Simulators >> simulating a differential mixer
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Message started by zxhelinor on Feb 24^th, 2005, 9:05am

Title: simulating a differential mixer
Post by zxhelinor on Feb 24^th, 2005, 9:05am

Dear Ken,

I read your article about simulating differential circuits, say Mixer. I have some questions related to LO differential input. I put an ideal balun from Cadence analoglib, with one input connecting to port of sine source(pLd) with port impedance(100ohm for example), another input to a port of DC source (pLc) with V=0.9volt with the port impedance of 25ohm. When I run the DC analysis, I found out that the DC node voltage of the pLc is 1.8V which is twice of the DC voltage I set. Could you explain what it means?

Title: Re: simulating a differential mixer
Post by Ken Kundert on Feb 24^th, 2005, 10:30am

It means that the common mode impedance looking into the LO port is much higher than 25 Ohms. A port component produces the specified voltage only when properly terminated.

-Ken

Title: Re: simulating a differential mixer
Post by zxhelinor on Feb 24^th, 2005, 12:17pm

Dear Ken,

Thanks a lot for your reply. In order to understand the test bench for differential input circuit, I construct a simple circuit: an ideal balun from Cadence Analoglib, two input ports to balun are:
1.Pld(differential mode, sine type, amplitude=1.8V): f=5G with source impedance of 100ohm;
2.Plc(common mode, DC type, Vdc=1V): with source impedance of 25ohm;
The balun's two outputs are connected to ground through 50ohm resistors respectively. So the differential input impedance is 100ohm, and the common mode input impedance is 25ohm. Then I run a DC and PSS simulation, this time the DC node voltage is correct, but the PSS voltage at the input(Pld) of balun is 1.8V with phase of 270degree. This result surprised me, the expected value observed at input(Pld) should be 1.8V with phase=0 since the port is perfectly matched.
Am I wrong in the set up?

Thanks a lot.

zxhelinor

Title: Re: simulating a differential mixer
Post by Mighty Mouse on Feb 24^th, 2005, 1:57pm

Are you using a recent version of SpectreRF? I believe that originally the time reference for phase in PSS was chosen to be the start of the shooting interval, which would mean that the reported phase was dependent on things like tstab. I thought they had fixed that in more recent versions.

- MM -