Reconfigurable Bandwidth
The charge pump current directly affects the PLL bandwidth. The higher
the charge pump current, the higher the PLL bandwidth. You can choose
from a fixed set of values for the charge pump current. Figure 1–31 shows
the loop filter and the components that can be set through the Quartus II
software. The components are the loop filter resistor, R, and the high
frequency capacitor, CH, and the charge pump current, IUP or IDN
.
Figure 1–31. Loop Filter Programmable Components
IUP
PFD
R
Ch
IDN
C
Software Support
The Quartus II software provides two levels of bandwidth control.
Megafunction-Based Bandwidth Setting
The first level of programmable bandwidth allows you to enter a value
for the desired bandwidth directly into the Quartus II software using the
altpllmegafunction. You can also set the bandwidth parameter in the
altpllmegafunction to the desired bandwidth. The Quartus II software
selects the best bandwidth parameters available to match your
bandwidth request. If the individual bandwidth setting request is not
available, the Quartus II software selects the closest achievable value.
Advanced Bandwidth Setting
An advanced level of control is also possible using advanced loop filter
parameters. You can dynamically change the charge pump current, loop
filter resistor value, and the loop filter (high frequency) capacitor value.
1–50
Stratix II Device Handbook, Volume 2
Altera Corporation
July 2009
ALTERA [ ALTERA CORPORATION ]
