PLLs in Stratix II and Stratix II GX Devices
The parameters for these changes are: charge_pump_current,
loop_filter_r, and loop_filter_c. Each parameter supports the
specific range of values listed in Table 1–16.
Table 1–16. Advanced Loop Filter Parameters
Parameter
Values
Resistor values (k)
(1)
(1)
(1)
High-frequency capacitance values (pF)
Charge pump current settings (
Note to Table 1–16:
(1) For more information, see AN 367: Implementing PLL Reconfiguration in
Stratix II Devices.
f
For more information about Quartus II software support of
reconfigurable bandwidth, see the Design Example: Dynamic PLL
Reconfiguration section in volume 3, Verification, of the Quartus II
Development Software Handbook.
PLLs use several divide counters and different VCO phase taps to
perform frequency synthesis and phase shifts. In Stratix II and
Stratix II GX enhanced and fast PLLs, the counter value and phase are
configurable in real time. In addition, you can change the loop filter and
charge pump components, which affect the PLL bandwidth, on the fly.
You can control these PLL components to update the output clock
frequency, PLL bandwidth, and phase-shift variation in real time, without
the need to reconfigure the entire FPGA.
PLL
Reconfiguration
f
For more information about PLL reconfiguration, see AN 367:
Implementing PLL Reconfiguration in Stratix II Devices.
Digital clocks are square waves with short rise times and a 50% duty
cycle. These high-speed clocks concentrate a significant amount of energy
in a narrow bandwidth at the target frequency and at the higher
frequency harmonics. This results in high energy peaks and increased
electromagnetic interference (EMI). The radiated noise from the energy
peaks travels in free air and, if not minimized, can lead to corrupted data
and intermittent system errors, which can jeopardize system reliability.
Spread-
Spectrum
Clocking
Traditional methods for limiting EMI include shielding, filtering, and
multi-layer printed circuit boards (PCBs). However, these methods
significantly increase the overall system cost and sometimes are not
Altera Corporation
July 2009
1–51
Stratix II Device Handbook, Volume 2
ALTERA [ ALTERA CORPORATION ]
