ALTPLL (Phase-Locked Loop) IP Core User Guide

ID 683732
Date 6/16/2017
Document Table of Contents

Programmable Bandwidth

The PLL bandwidth is defined as the ability of the PLL to track the input clock and jitter. The bandwidth is measured by the -3 dB frequency of the closed-loop gain in the PLL, or approximately the unity gain point of the PLL open loop response. Altera devices provide a programmable PLL bandwidth feature that allows you to configure the characteristics of the PLL loop filter. Most loop filters contain only passive components, such as resistors and capacitors, which consumes board space. Altera FPGAs already contain these components, and by using the programmable bandwidth feature, you can control how the components affect the PLL bandwidth. This includes controlling the charge pump current, loop filter resistance, and high frequency capacitance values. The charge pump current affects the PLL bandwidth directly. The higher the charge pump current, the higher the PLL bandwidth.