Jitter Man
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Am I? Or am I so sane that u just blew your mind?
Posts: 50
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Oreke, The sweeptype parameter specifies how the output frequency range relates to the sweep range. If sweeptype=absolute then fout = f and if sweeptype=relative then fout = f + relharmnum*ffund. So if you were to set sweeptype=absolute and leave sideband=[-1] then you would be computing the transfer function from (1kHz->1MHz)-2GHz to (1kHz->1MHz). This is a down conversion term. It the the transfer function from the lower sideband of the fundamental to baseband.
With the setup you described (with sweeptype=relative) , you were computing the up-conversion term (from baseband to the upper sideband of the fundamental). To get this same transfer function with sweeptype=absolute you would have to change the sweep range. Rather than sweeping from 1kHz->1MHz, you would sweep from 1kHz+2GHz to 1MHz+2GHz. However, this is problematic for several reasons. First, you set the sweep parameters before the simulation occurs, and at that point you really don't know the oscillation frequency precisely. Second, you can no longer plot the results with a logrithmic x-axis. Finally, it is more difficult to resolve the offset frequency from the plot.
The freqaxis parameter does not affect the transfer functions that are computed by SpectreRF, it only affects how they are plotted. Remember that the transfer functions computed by SpectreRF include frequency conversion, so the input and output frequencies may be different. freqaxis allows you to specify whether you want the results plotted versus input frequency or output frequency.
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