“…On the contrary, since the noise from VCDL is located behind the filter capacitor, so it presents a highpass behaviour, allowing the extension of the loop bandwidth for suppressing high-frequency noise. Particularly, since the reference clock noise is almost simultaneously injected to the PD and the VCDL, it exhibits nearly all pass characteristics, indicating that all the clock jitter is fully transported to the output; therefore, a highquality reference clock is definitely beneficial to depress the output noise [12][13][14][15]. In practical, the baseband noise dominant in the low-and medium-frequency region should be seriously restricted, so the upper bound of loop bandwidth is limited for reducing the output jitters mainly coming from PD and CP noises, while the low limit of loop bandwidth is restricted for reducing the output jitters mainly coming from VCDL and input clock noise.…”