AD9518-2 Analog Devices, Inc., AD9518-2 Datasheet - Page 37

• Manufacturer Part Number: AD9518-2
• Description: 6-output Clock Generator With Integrated 2.2 Ghz Vco
• Manufacturer: Analog Devices, Inc.

Table 34. Duty Cycle with VCO Divider, Input Duty Cycle Is X%
VCO
Divider
Even
Odd = 3
Odd = 5
Even
Odd = 3
Odd = 3
Odd = 5
Odd = 5
Table 35. Channel Divider Output Duty Cycle When the
VCO Divider Is Not Used
Input Clock
Duty Cycle
Any
Any
50%
X%
The internal VCO has a duty cycle of 50%. Therefore, when the
VCO is connected direct to output, the duty cycle is 50%. If the
CLK input is routed direct to output, the duty cycle of the output is
the same as the CLK input.
Phase Offset or Coarse Time Delay (0, 1, and 2)
Each channel divider allows for a phase offset, or a coarse time
delay, to be programmed by setting register bits (see Table 36).
These settings determine the number of cycles (successive
rising edges) of the channel divider input frequency by which to
offset, or delay, the rising edge of the output of the divider. This
delay is with respect to a nondelayed output (that is, with a
phase offset of zero). The amount of the delay is set by five bits
loaded into the phase offset (PO) register plus the start high
(SH) bit for each channel divider. When the start high bit is set,
the delay is also affected by the number of low cycles (M)
programmed for the divider.
It is necessary to use the SYNC function to make phase offsets
effective (see the Synchronizing the Outputs—SYNC Function
section).
N + M + 2
1 (divider
bypassed)
1 (divider
bypassed)
1 (divider
bypassed)
Even
Odd
Even
Odd
Even
Odd
N + M + 2
1
Even
Odd
Odd
D
X
D
X
DCCOFF = 1
50%
33.3%
40%
(N + 1)/
(N + M + 2)
(N + 1)/
(N + M + 2)
(N + 1)/
(N + M + 2)
(N + 1)/
(N + M + 2)
(N + 1)/
(N + M + 2)
(N + 1)/
(N + M + 2)
DCCOFF = 1
1 (divider
bypassed)
(N + 1)/
(M + N + 2)
(N + 1)/
(M + N + 2)
(N + 1)/
(M + N + 2)
Output Duty Cycle
Output Duty Cycle
DCCOFF = 0
50%
(1 + X%)/3
(2 + X%)/5
50%,
requires M = N
50%,
requires M = N + 1
50%,
requires M = N
(3N + 4 + X%)/(6N + 9),
requires M = N + 1
50%,
requires M = N
(5N + 7 + X%)/(10N + 15),
requires M = N + 1
DCCOFF = 0
Same as input
duty cycle
50%, requires M = N
50%, requires
M = N + 1
(N + 1 + X%)/(2 × N + 3),
requires M = N + 1
Rev. 0 | Page 37 of 64
Divider
0
1
2
Table 36. Setting Phase Offset and Division for Divider 0,
Divider 1, and Divider 2
Let
Δ
Δ
T
(in seconds).
Φ =
16 × SH<4> + 8 × PO<3> + 4 × PO<2> + 2 × PO<1> + 1 × PO<0>
The channel divide-by is set as N = high cycles and M = low cycles.
Case 1
For Φ ≤ 15,
Δ
Δ
Case 2
For Φ ≥ 16,
Δ
Δ
By giving each divider a different phase offset, output-to-output
delays can be set in increments of the channel divider input
clock cycle. Figure 38 shows the results of setting such a coarse
offset between outputs.
DIVIDER 0
DIVIDER 1
DIVIDER 2
Synchronizing the Outputs—SYNC Function
The AD9518 clock outputs can be synchronized to each other.
Outputs can be individually excluded from synchronization.
Synchronization consists of setting the nonexcluded outputs to
a preset set of static conditions and subsequently releasing these
outputs to continue clocking at the same instant with the preset
conditions applied. This allows for the alignment of the edges of
two or more outputs or for the spacing of edges according to the
coarse phase offset settings for two or more outputs.
DIVIDER INPUT
X
t
c
t
c
t
c
= delay (in seconds).
= Φ × T
= (Φ − 16 + M + 1) × T
= delay (in cycles of clock signal at input to D
= Δ
= Δ
= period of the clock signal at the input of the divider, D
CHANNEL
t
t
/T
/T
PO = 0
PO = 1
PO = 2
SH = 0
SH = 0
SH = 0
X
X
Start
High (SH)
0x191<4>
0x194<4>
0x197<4>
X
= Φ
Figure 38. Effect of Coarse Phase Offset (or Delay)
0
1
Tx
2
Phase
Offset (PO)
0x191<3:0>
0x194<3:0>
0x197<3:0>
3
X
1 × Tx
2 × Tx
4
5
6
7
Low Cycles
M
0x190<7:4>
0x193<7:4>
0x196<7:4>
8
9 10 11 12 13 14 15
X
AD9518-2
).
High Cycles
N
0x190<3:0>
0x193<3:0>
0x196<3:0>
X