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?

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