Datasheet

AD9513
Rev. 0 | Page 20 of 28
Table 16. OUT0 Divide or OUT2 Divide
S9 S10
OUT0
Divide (Duty Cycle
1
)
S2 ≠ 2/3
OUT2
Divide (Duty Cycle
1
)
S2 = 2/3
0 0 1 7 (43%)
1/3 0 2 (50%) 11 (45%)
2/3 0 3 (33%) 13 (46%)
1 0 4 (50%) 14 (50%)
0 1/3 5 (40%) 17 (47%)
1/3 1/3 6 (50%) 19 (47%)
2/3 1/3 8 (50%) 20 (50%)
1 1/3 9 (44%) 21 (48%)
0 2/3 10 (50%) 22 (50%)
1/3 2/3 12 (50%) 23 (48%)
2/3 2/3 15 (47%) 25 (48%)
1 2/3 16 (50%) 26 (50%)
0 1 18 (50%) 27 (48%)
1/3 1 24 (50%) 28 (50%)
2/3 1 30 (50%) 29 (48%)
1 1 32 (50%) 31 (48%)
1
Duty cycle is the clock signal high time divided by the total period.
DIVIDER PHASE OFFSET
The phase offset of OUT1 and OUT2 can be selected (see Table 13
to
Table 15). This allows the relative phase of the outputs to be set.
After a SYNC operation (see the
Synchronization section), the
phase offset word of each divider determines the number of
input clock (CLK) cycles to wait before initiating a clock output
edge. By giving each divider a different phase offset, output-to-
output delays can be set in increments of the fast clock period, t
CLK
.
Figure 24 shows four cases, each with the divider set to divide = 4.
By incrementing the phase offset from 0 to 3, the output is
offset from the initial edge by a multiple of t
CLK
.
014123 5 9678 10 1411 12 13 5
t
CLK
CLOCK INPUT
CLK
DIVIDER OUTPUT
DIV = 4
PHASE = 0
PHASE = 1
PHASE = 2
PHASE = 3
t
CLK
2 × t
CLK
3 × t
CLK
05595-024
Figure 24. Phase Offset—Divider Set for Divide = 4, Phase Set from 0 to 2
For example:
CLK = 491.52 MHz
t
CLK
= 1/491.52 = 2.0345 ns
For Divide = 4:
Phase Offset 0 = 0 ns
Phase Offset 1 = 2.0345 ns
Phase Offset 2 = 4.069 ns
Phase Offset 3 = 6.104 ns
The outputs can also be described as:
Phase Offset 0 = 0°
Phase Offset 1 = 90°
Phase Offset 2 = 180°
Phase Offset 3 = 270°
Setting the phase offset to Phase = 4 results in the same relative
phase as Phase = 0° or 360°.
The resolution of the phase offset is set by the fast clock period
(t
CLK
) at CLK. The maximum unique phase offset is less than the
divide ratio, up to a phase offset of 15.
Phase offsets can be related to degrees by calculating the phase
step for a particular divide ratio:
Phase Step = 360°/Divide Ratio
Using some of the same examples:
Divide = 4
Phase Step = 360°/4 = 90°
Unique Phase Offsets in Degrees Are Phase = 0°, 90°,
180°, 270°
Divide = 9
Phase Step = 360°/9 = 40°
Unique Phase Offsets in Degrees Are Phase = 0°, 40°, 80°,
120°, 160°, 200°, 240°, 280°, 320°