ep1s25 Altera Corporation, ep1s25 Datasheet - Page 111
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ep1s25
Manufacturer Part Number
ep1s25
Description
Stratix Device Family Data Sheet
Manufacturer
Altera Corporation
Datasheet
1.EP1S25.pdf
(276 pages)
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Altera Corporation
July 2005
VCO period from up to eight taps for individual fine step selection. Also,
each clock output counter can use a unique initial count setting to achieve
individual coarse shift selection in steps of one VCO period. The
combination of coarse and fine shifts allows phase shifting for the entire
input clock period.
The equation to determine the precision of the phase shifting in degrees
is: 45° ÷ post-scale counter value. Therefore, the maximum step size is
45° , and smaller steps are possible depending on the multiplication and
division ratio necessary on the output counter port.
This type of phase shift provides the highest precision since it is the least
sensitive to process, supply, and temperature variation.
Clock Delay
In addition to the phase shift feature, the ability to fine tune the Δt clock
delay provides advanced time delay shift control on each of the four PLL
outputs. There are time delays for each post-scale counter (e, g, or l) from
the PLL, the n counter, and m counter. Each of these can shift in 250-ps
increments for a range of 3.0 ns. The m delay shifts all outputs earlier in
time, while n delay shifts all outputs later in time. Individual delays on
post-scale counters (e, g, and l) provide positive delay for each output.
Table 2–21
delay buffer mode where Δt
The t
delay shift difference between any two PLL outputs, however, must be
less than ±3 ns. For example, shifts on two outputs of –1 and +2 ns is
allowed, but not –1 and +2.5 ns because these shifts would result in a
difference of 3.5 ns. If the design uses external feedback, the Δt
remove delay from outputs, represented by a negative sign (see
Table
feedback loop.
Note to
(1)
Δt
Δt
Δt
Table 2–21. Output Clock Delay for Enhanced PLLs
Normal or Zero Delay Buffer Mode
eOUTPUT
gOUTPUT
lOUTPUT
Δt
OUTPUT
2–21). This effect occurs because the Δt
e
Table
removes delay from outputs in external feedback mode.
= Δt
= Δt
= Δt
shows the combined delay for each output for normal or zero
for a single output can range from –3 ns to +6 ns. The total
n
2–21:
n
n
− Δt
− Δt
− Δt
m
m
m
+ Δt
+ Δt
+ Δt
l
e
g
e
, Δt
g
, or Δt
Δt
Δt
Δt
l
eOUTPUT
gOUTPUT
lOUTPUT
Stratix Device Handbook, Volume 1
is unique for each PLL output.
External Feedback Mode
e
= Δt
delay is then part of the
= Δt
= Δt
n
n
n
− Δt
− Δt
− Δt
m
m
m
Stratix Architecture
+ Δt
− Δt
+ Δt
e
l
g
(1)
e
delay will
2–97