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https://designers-guide.org/forum/YaBB.pl Simulators >> Circuit Simulators >> Weird Z11 https://designers-guide.org/forum/YaBB.pl?num=1382435929 Message started by ywguo on Oct 22nd, 2013, 2:58am |
Title: Weird Z11 Post by ywguo on Oct 22nd, 2013, 2:58am Hi Guys, I got weird Z11 parameter with SP analysis of spectre simulator. That is a 50 Ω microstrip. So I simulated with a n2port and read the S-parameter file. I got weird Z11 if I put two port cells at both ports. But Z11 looks good if the port cell at the second port is replaced with a 50 Ω resistor. The schematics and the Z11 vs. frequency are shown below. I read Kundert's The Designer's Guide to Spice & Spectre. For SP analysis, only the AC magnitude at one port is set to non-zero at any time. So I think both configuration should give correct result. Who can explain the weird Z11? Best Regards, Yawei |
Title: Re: Weird Z11 Post by ywguo on Oct 22nd, 2013, 3:02am That is Z11 vs. frequency if I simulate with two port cells. |
Title: Re: Weird Z11 Post by ywguo on Oct 22nd, 2013, 3:07am The schematic of one port cell on the first port and one 50 Ω resistor on the second port. |
Title: Re: Weird Z11 Post by ywguo on Oct 22nd, 2013, 3:12am That is Z11 vs. frequency of one 50 Ω resistor on the second port. |
Title: Re: Weird Z11 Post by ywguo on Oct 22nd, 2013, 3:21am Furthermore, for the schematic two_port_cell, Z11 looks good if only one port is selected for SP analysis. Code:
But Z11 is weird if both port cells are selected for SP analysis. Code:
Thanks for any comments. Yawei |
Title: Re: Weird Z11 Post by raja.cedt on Oct 22nd, 2013, 9:51am Dear ywguo, You can't find input impedance with Z(1,1) because you have to find input impedance with 50ohm loading, where as real(Z(1,1)) with open circuit in the second port. I normally Load 2nd port with 50ohm(or what) and find the impedance by ac source at port 1. or there is a built in function in cadence called Zm. Hope this helps... |
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