I am looking for an explanation on how the .bode directives is solved in Qspice? is there any difference compared to the .meas fra directive?
Because I found a different result when I apply .bode directive in FRA_SMPS.qsch example file.
is it based on some fancy technique such as multitone or the like?
In case I want to ensure best accuracy, do I need to implement the bode plot using .meas fra + .step?
Frequency Response Analysis
If the SMPS reference voltage is not at AC ground, specify which node to use as the reference via with the command .options boderef=
This is a computationally intensive task. In the interest of getting a complete Bode plot in under one minute, a number of original numerical methods are used. The Bode plot can be left with artifacts due to spectral leakage, aperture diffraction, and even stochastic noise, If concerned about the reliability of the result, individual points, such as the phase and gain margins of the Bode plot, can easily checked via the .measure command .meas NAME fra FREQ INPUT OUTPUT […]. This .meas command is irrefutably the most reliable way of obtaining frequency domain response from a SMPS that’s ever been used in any simulator.