# Choosing PLL Loop Filter Bandwidth and Phase Margin for Frequency Ramp Generation

I am new to PLLs and am trying to use one to generate a frequency ramp between 5.725 GHz and 5.875 GHz. I have found tools online that help design loop filters for PLLs, and all of these tools require that the user know the desired loop filter bandwidth and phase margin. I have not been able to find suggestions for choosing filter bandwidth. Also, I understand that filter bandwidth and phase margin are related, but I don't know how to choose appropriate values for them for this application.

• What experiences and skill sets do you bring to the table, regarding nearly $6\:\text{GHz}$ signals? (You may want to include some discussion of the reason why you need this and some of your thoughts.) – jonk Aug 30 '19 at 1:54
• Can you define slew rate MHz/ms tracking rate or capture time or LPF BW of clock noise or BW output of signal and BW of noise, then any performance features you expect? Anything? – Tony Stewart Sunnyskyguy EE75 Aug 30 '19 at 2:00
• I am a total beginner with PLLs, so no. PLL is for FMCW radar. Specifically, I am trying to understand a project I found online. Unsure of how designer made decisions like this one. In most sources I have found nebulous recommendations for choosing bandwidth like "increase loop bandwidth for more rapid loop response." – Saunders Aug 30 '19 at 2:24
• I understand you need to read more to ask a better question. Use the key words like this. scholar.google.ca/…. Then when U hit a paywall, search the title.. try again... researchgate.net/profile/Frank_Herzel/publication/… – Tony Stewart Sunnyskyguy EE75 Aug 30 '19 at 4:56
• to achieve a clean phase trajectory, you may need a higher-order loop – analogsystemsrf Aug 30 '19 at 14:43

A PLL uses integration to eliminate steady state phase error in a stable input. Whereas with a ramp f input, there is a gain-dependant fixed phase-error ( as well as other variables)

Not having done FMCW RADAR before, may I refer to an excellent article.

It defines all the variables that affect BW , settling time and fixed phase error which is an indicator of Spectral Density noise BW that contributes (error and ) has both 1st and 2nd order sensitivity.