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# Beat frequency in SpectreRF PSS simulation

Last post Thu, Dec 7 2006 9:19 PM by archive. 2 replies.
 Started by archive 07 Dec 2006 09:19 PM. Topic has 2 replies and 3904 views
• #### Thu, Dec 7 2006 9:19 PM

• archive
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Beat frequency in SpectreRF PSS simulation
 Hi all,While doing pss setup, the simulator asks for "beat frequency". Please explain what is "Beat frequency in SpectreRF PSS simulation". I'm doing a ring-oscillator simulation and the expected output frequency is 384MHz. In this case, what value of beat frequency should I feed and why?RegardsOriginally posted in cdnusers.org by vj
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• #### Thu, Dec 7 2006 9:34 PM

• archive
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RE: Beat frequency in SpectreRF PSS simulation
 In a driven system, the beat frequency would be the greatest common divisor of all the input tones in the circuit (or the divided down frequencies if there are dividers in the circuit). PSS needs to solve a periodic waveform - and so you need to have an integer number of cycles of all the frequencies in the circuit.In an autonomous system (e.g. an oscillator), you turn on the "oscillator" checkbox, and the beat frequency is then the estimated frequency, which gives PSS a starting point to solve for the oscillator frequency. It's important when in oscillator mode to select the outputs of the circuit, which include any subharmonics. In other words, if you have an oscillator followed by a divider, point at the divider output, and give the estimated divided frequency as the beat frequency. Again, this is because you need to solve an integer number of cycles of all the frequencies in the circuit. Note, don't use oscillator mode for circuits which aren't oscillators, since you're then trying to get the simulator to solve for an unknown which is not unknown, which may lead to convergence problems.So in your specific case, enter 384M, and turn on the oscillator checkbox, and point at the output of the oscillator.Regards,Andrew.Originally posted in cdnusers.org by adbeckett
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• #### Thu, Dec 7 2006 10:30 PM

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RE: Beat frequency in SpectreRF PSS simulation
 Thanks Andrews for the detailed explanation.Originally posted in cdnusers.org by vj
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