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https://designers-guide.org/forum/YaBB.pl Simulators >> RF Simulators >> sp analysis with one port https://designers-guide.org/forum/YaBB.pl?num=1196459940 Message started by wakizashi on Nov 30th, 2007, 1:58pm |
Title: sp analysis with one port Post by wakizashi on Nov 30th, 2007, 1:58pm Hello, I have a question concerning 1 port sp analysis with spectrerf. I would like to use sp analysis to calculate a node capacitance. Therefore I have created a simple circuit first. It is a port component and say 1pF capacitor (ideal). I would like to run sp analysis and calculate c as following: C=imag(y11)/(2*pi*freq) At least this is how I could do it in ADS. In spectre however it doesnt work. I get 0 for all the frequency sweep range. Does anyone know how to prepare test bench and calculate it in spectre? Thank you for your help. Regards. |
Title: Re: sp analysis with one port Post by pancho_hideboo on Nov 30th, 2007, 8:25pm Your question is not design issue but usage of EDA tool. Please post to "The Designer's Guide Community Forum ≫ Simulators ≫ RF Simulators". Quote:
This is because ADS saves frequency as "freq" in dataset. Quote:
Spectre doesn't save frequency as "freq" in PSF data. So "freq" is not available in PSF. Instead of "freq" you have to use "xval(y11)". This is true for RFDE(ADSsim) if you convert ADS dataset to PSF. The following is example. http://www.designers-guide.org/Forum/YaBB.pl?num=1133858081/1#1 |
Title: Re: sp analysis with one port Post by wakizashi on Dec 1st, 2007, 2:37am Hi, Thanks for the answer. I'm not so familiar with ocean but got your script to work somehow. However, I still get strange results from it even for inductor case like in your example. For example: Q1@1kHz=-1.2833e+09 L1@1kHz=-2.53303e+14[nH] I use an Rs Ls series connection and Cp (in parallel). Ideal elements. L=1nH. Could you show your setup for the mentioned ocean script? Do you configure anything special in sp analysis except for AC magnitude in port = 1V? Thank you. |
Title: Re: sp analysis with one port Post by pancho_hideboo on Dec 1st, 2007, 2:43am Sorry my example is for floating inductor. port1 >---Inductor ----< port2 L1 is inductance evaluated with port2=gnd. L2 is inductance evaluated with port1=gnd. L1 = imag(1/y11)/(2*pi*xval(y11)) L2 = imag(1/y22)/(2*pi*xval(y22)) Q1 = imag(1/y11)/real(1/y11) Q2 = imag(1/y22)/real(1/y22) Quote:
Your DUT is grounded. So it is natural that L1 = imag(1/y11)/(2*pi*xval(y11)) doesn't match to your Ls=1nH. Quote:
In sp analysis, AC magnitude in port is meaningless. The following script for capacitance from grounded Y11. Code:
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Title: Re: sp analysis with one port Post by wakizashi on Dec 2nd, 2007, 11:00am Hello, Thank you for the answer. Ok, now I have used the same setup as yours and I get new problems. In CIW I get: *Error* ("error" 10 t nil ("*Error* gausex: Equations may be dependent (row 0)\n")) when trying to plot YP(1 1). Im lost here. My netlist is like this for reference: L0 (net5 0) inductor PORT0 (net5 0) port num=1 dc=0 type=sine 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" sp sp ports=[PORT0] start=1k stop=10G annotate=status Its just a port and inductor connected together. Do you see any problem here? Thank you for the reply. Regards. |
Title: Re: sp analysis with one port Post by Ken Kundert on Dec 2nd, 2007, 12:53pm I tried your netlist in my version of Spectre and it ran fine. It computes s11 to be -1 over all frequencies, which is as I expect because you gave no value for the inductance of L0, and the default is 0. So the inductor is simply acting like a short circuit. -Ken |
Title: Re: sp analysis with one port Post by wakizashi on Dec 2nd, 2007, 1:15pm Hello, Thank you for spotting this. I have manually updated the netlist with an inductance value and now sp computes correctly the same value. Regards. |
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