Chapter 5: Clock Networks and PLLs in Cyclone IV Devices
5–41
Spread-Spectrum Clocking
October 2012
Altera Corporation
shows the dynamic phase shifting waveform.
The
PHASESTEP
signal is latched on the negative edge of
SCANCLK
(a,c) and must remain
asserted for at least two
SCANCLK
cycles. Deassert
PHASESTEP
after
PHASEDONE
goes low.
On the second
SCANCLK
rising edge (b,d) after
PHASESTEP
is latched, the values of
PHASEUPDOWN
and
PHASECOUNTERSELECT
are latched and the PLL starts dynamic
phase-shifting for the specified counters, and in the indicated direction.
PHASEDONE
is
deasserted synchronous to
SCANCLK
at the second rising edge (b,d) and remains low
until the PLL finishes dynamic phase-shifting. Depending on the VCO and
SCANCLK
frequencies,
PHASEDONE
low time may be greater than or less than one
SCANCLK
cycle.
You can perform another dynamic phase-shift after the
PHASEDONE
signal goes from
low to high. Each
PHASESTEP
pulse enables one phase shift.
PHASESTEP
pulses must be
at least one
SCANCLK
cycle apart.
f
For information about the ALTPLL_RECONFIG MegaWizard
Plug-In Manager
,
ALTPLL_RECONFIG Megafunction User Guide
.
Spread-Spectrum Clocking
Cyclone IV devices can accept a spread-spectrum input with typical modulation
frequencies. However, the device cannot automatically detect that the input is a
spread-spectrum signal. Instead, the input signal looks like deterministic jitter at the
input of the PLL. PLLs of Cyclone IV devices can track a spread-spectrum input clock
as long as it is in the input jitter tolerance specifications and the modulation frequency
of the input clock is below the PLL bandwidth, that is specified in the fitter report.
Cyclone IV devices cannot generate spread-spectrum signals internally.
PLL Specifications
f
For information about PLL specifications, refer to the
chapter.
Figure 5–26. PLL Dynamic Phase Shift
PHASEDONE goes low
synchronous with SCANCLK
SCANCLK
PHASESTEP
PHASEUPDOWN
PHASECOUNTERSELECT
PHASEDONE
a
b
c
d
Summary of Contents for Cyclone IV
Page 10: ...x Chapter Revision Dates Cyclone IV Device Handbook March 2016 Altera Corporation Volume 1...
Page 14: ...I 2 Section I Device Core Cyclone IV Device Handbook March 2016 Altera Corporation Volume 1...
Page 274: ...vi Contents Cyclone IV Device Handbook February 2015 Altera Corporation Volume 2...
Page 440: ...iv Contents Cyclone IV Device Handbook December 2016 Altera Corporation Volume 3...
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