
Altera Corporation
1–5
July 2009
Stratix II Device Handbook, Volume 2
PLLs in Stratix II and Stratix II GX Devices
Figure 1–2. Stratix II GX PLL Locations
Enhanced PLLs
Stratix II and Stratix II GX devices contain up to four enhanced PLLs with
advanced clock management features. The main goal of a PLL is to
synchronize the phase and frequency of an internal and external clock to
an input reference clock. There are a number of components that
comprise a PLL to achieve this phase alignment.
Enhanced PLL Hardware Overview
Stratix II and Stratix II GX PLLs align the rising edge of the reference
input clock to a feedback clock using the phase-frequency detector (PFD).
The falling edges are determined by the duty-cycle specifications. The
PFD produces an up or down signal that determines whether the VCO
needs to operate at a higher or lower frequency.
FPLL7CLK
FPLL8CLK
CLK[3..0]
7
1
2
8
5
11
6
12
CLK[7..4]
CLK[15..12]
PLLs