The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl Simulators >> Circuit Simulators >> Frequency versus control voltage in VCO https://designers-guide.org/forum/YaBB.pl?num=1052924112 Message started by vakilia on May 14th, 2003, 7:55am |
Title: Frequency versus control voltage in VCO Post by vakilia on May 14th, 2003, 7:55am I have designed this ring VCO and the time domain analysis shows me how the frequency (Frq) changes with the control voltage (Vctrl), which is not a linear behavior actually. To find the VCO gain I would like to be able to find the transfer function (Frq/Vctrl) in frequency domain but I am not sure if Spectre will take care of the non-linear behavior of the VCO and even if it is possible to do so?! Thanks Babak |
Title: Re: Frequency versus control voltage in VCO Post by Eugene on May 14th, 2003, 12:12pm You mention a frequency domain transfer function and nonlinearity in the same inquiry. Exactly what do you mean by frequency domain transfer function? Do you mean the static relationship between VCO tuning voltage and the VCO's steady state operating frequency? Or do you mean the small signal transfer function about an operating point (which would be proportional to 1/s)? Or do you mean something like a describing function, which is essentially the linear transfer function that best approximates the large signal response? |
Title: Re: Frequency versus control voltage in VCO Post by vakilia on May 14th, 2003, 3:51pm I actully mean the static relationship between VCO tuning voltage and the VCO's steady state operating frequency. |
Title: Re: Frequency versus control voltage in VCO Post by Eugene on May 14th, 2003, 8:32pm I don't believe you can easily generate this curve using the basic Spectre. However, I have generated such curves with relative ease using SpectreRF. If memory serves, I ran a swept autonomous PSS analysis and plotted "beat frequency" against the sweep variable. The sweep variable was of course the VCO tuning voltage. |
Title: Re: Frequency versus control voltage in VCO Post by Andrew Beckett on May 15th, 2003, 7:00am Another way you can do this is to do a transient and then sweep the control voltage. At the output of the VCO, put a freq_meter component (in ahdlLib under <instdir>/tools/dfII/samples/local/artist/ahdlLib at the output. This is a verilog-a model which captures the instantaneous frequency. However, in order to allow it to settle you probably need to sweep the control voltage slowly, or perhaps use a pwl source to step the control voltage up so you can leave it steady for a few cycles. Best is to use the autonomous PSS method described previously in this thread, though. Regards, Andrew. |
Title: Re: Frequency versus control voltage in VCO Post by vakilia on May 16th, 2003, 4:25pm Eugene and Andrew; I actually used the freq_meter component in ahdlLib and changed the Vctl to pwl with approperiate slope and ran the transient simulation. In the results window I plotted output frequency versus control voltage by changing the x-axis to Vctr net name and it showed the static frequency responce perfectly. I will try the other way as well. Thanks for your helpful comments, Babak |
The Designer's Guide Community Forum » Powered by YaBB 2.2.2! YaBB © 2000-2008. All Rights Reserved. |