Matlab - Add reference line in a bode plot

# Add reference line in a bode plot Sometimes, adding a reference line can explain a lot in a plot. For PLL noise transfer functions, the reference noise transfer function has a low pass characteristic. The VCO noise transfer function has a high pass characteristic. The PLL bandwidth splits the noise plot into two regions: - phase noise of VCO dominates the high frequencies because its noise transfer function have no effect in this region - phase noise of references and phase detector dominates the low frequency region > noise transfer functions of the reference and VCO Therefore, it is useful to show the PLL bandwidth in the plot. New version Matlab provides a 'xline' function, vertical line with constant x-value, to plot a line in a plot. If you don't have the new version of Matlab, you can use another m function ([Link](https://wwem.lanzouq.com/iSonk1hpecmh)) to add a reference line. Example code is shown below: