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https://designers-guide.org/forum/YaBB.pl Simulators >> RF Simulators >> Error: Periodic signal in autonomous circuits https://designers-guide.org/forum/YaBB.pl?num=1117624513 Message started by Terence on Jun 1st, 2005, 4:15am |
Title: Error: Periodic signal in autonomous circuits Post by Terence on Jun 1st, 2005, 4:15am Hi, I got an error during PSS in SpectreRF 5.033. "Ixx.V0 is a periodic input signal, which is inconsistent with autonomous circuits." This error is just a warning in IC4.4.6, however, IC5.033 stop it by error. Ixx.V0 is a baseband signal which must be included in modulator simulation. Does anyone advise how to do PSS simulation w/o error in IC5033? ??? Many thanks. Terence |
Title: Re: Error: Periodic signal in autonomous circuits Post by Andrew Beckett on Jun 2nd, 2005, 2:07pm What was happening was that in IC446, it was not checking for this situation, and as a result, your PSS solution was not properly taking into account the driven input signal when in autonomous mode. The most common cause of this was people who used pulse sources to kick-start an oscillator - and made those sources periodic (albeit with a very long period). In most cases the solution was to make that source a one-shot by omitting the period. If you've got an autonomous circuit, and want to simulate the effect with a driven input as well, you can't - and never have been able to (it may have given the appearance of working in the past, but it wasn't doing the right thing; usually it wouldn't have converged - so the fact that it did was probably luck - perhaps bad luck?). If this is an oscillator with a mixer (say), and you need to have a large signal input (i.e pac or pxf won't do), then what you can do is characterize the oscillator's performance, and then replace it with a verilog-a model of the oscillator (such as that in rfLib, which models noise properly if I remember rightly). Then the oscillator becomes a driven circuit, and so you can then simulate it together with the large signal input using PSS or QPSS (depending on the frequencies involved). Best Regards, Andrew. |
Title: Re: Error: Periodic signal in autonomous circuits Post by Terence on Jun 6th, 2005, 8:36am Hi Andrew, Thanks for the answer. I am simulating a modulator including an oscillator and a mixer. There is not any driven input for the oscillator. Ixx.V0 in the error message is actually the 5MHz baseband signal for mixer input. For such case, we are used to PSS and PNoise to simulate phase noise of modulated output. But IC5033 cannot allow such configuration in PSS. Do you have any suggestion ? Thanks. Terence |
Title: Re: Error: Periodic signal in autonomous circuits Post by Ken Kundert on Jun 6th, 2005, 9:52am This error message indicates that Ixx.V0 has been supplied parameter values that direct it to produce a periodic signal. To avoid the error, simply visit that source and configure it so that it does not attempt to generate a periodic signal. -Ken |
Title: Re: Error: Periodic signal in autonomous circuits Post by Terence on Jun 6th, 2005, 5:24pm Hi Ken, Actually, I need to simulate the phase noise of a modulator including a VCO and mixer. Baseband signal must be input of the mixer. Do you have suggestions about such simulation? Thanks. Terence |
Title: Re: Error: Periodic signal in autonomous circuits Post by Andrew Beckett on Jun 7th, 2005, 9:28am Please read the previous posts (particularly my posting on 2nd June). I was not talking (necessarily) about having a driven input to the oscillator (unless it was a kick-start), but having a driven input to the mixer, as well as a free-running oscillator. You either don't really need the large signal input to the mixer to be there, or if you do (you're driving the mixer into compression, say), you'll need to separately characterize the oscillator and replace it with a behavioural model, as I said before. Ken was quite right. The source that is being referenced has some parameters on it which are making it a periodic source - which you cannot do if you're simulating in autonomous mode. Regards, Andrew. |
Title: Re: Error: Periodic signal in autonomous circuits Post by Ken Kundert on Jun 7th, 2005, 2:55pm To add just a bit of detail to what Andrew is saying, if you really don't need the driven signal to be large, then you can apply it as a small signal and use a PAC or PXF analysis. This is possible if you are just computing a transfer function. It is not possible if the circuit is expected to react in a nonlinear fashion to the driven signal, as would be the case if the signal were a blocker and you were trying to measure reciprocal mixing. In this case, you would need to build a behavioral model of the oscillator that appears driven but exhibits phase noise, and then use QPSS. -Ken |
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