AD9520-4 Analog Devices, Inc., AD9520-4 Datasheet - Page 46

• Manufacturer Part Number: AD9520-4
• Description: 12 Lvpecl/24 Cmos Output Clock Generator With Integrated 1.6 Ghz Vco
• Manufacturer: Analog Devices, Inc.

AD9520-4
Duty-cycle correction requires the following channel divider
conditions:
• An even division must be set as M = N
• An odd division must be set as M = N + 1
When not bypassed or corrected by the DCC function, the duty
cycle of each channel divider output is the numerical value of
(N + 1)/(N + M + 2) expressed as a percent.
The duty cycle at the output of the channel divider for various
configurations is shown in Table 35 to Table 38.
Table 35. Channel Divider Output Duty Cycle with VCO
Divider ≠ 1, Input Duty Cycle Is 50%
VCO
Divider
Even
Odd = 3
Odd = 5
Even, odd
Even, odd
Table 36. Channel Divider Output Duty Cycle with VCO
Divider ≠ 1 and Input Duty Cycle Is X%
VCO
Divider
Even
Odd = 3
Odd = 5
Even
Even
Odd = 3
Odd = 3
Odd = 5
Odd = 5
N + M + 2
Channel
divider
bypassed
Channel
divider
bypassed
Channel
Divider
bypassed
Even
Odd
Even
Odd
Even
Odd
N + M + 2
Channel
divider
bypassed
Channel
divider
bypassed
Channel
divider
bypassed
Even
Odd
D
X
D
X
Disable Div
DCC = 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)
Disable Divider
DCC = 1
50%
33.3%
40%
(N + 1)/(N + M + 2)
(N + 1)/(N + M + 2)
Output Duty Cycle
Output Duty Cycle
Disable Div DCC = 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
Disable Div
DCC = 0
50%
50%
50%
50%; requires
M = N
50%; requires
M = N + 1
Rev. 0 | Page 46 of 84
Divider
0
1
2
3
Table 37. Channel Divider Output Duty Cycle When the
VCO Divider is Enabled and Set to 1
Input
Clock
Duty Cycle
Any
50%
X%
Note Channel Divider must be enabled when VCO Divider = 1.
Table 38. Channel Divider Output Duty Cycle When the
VCO Divider Is Bypassed
Input
Clock
Duty Cycle
Any
Any
50%
X%
The internal VCO has a duty cycle of 50%. Therefore, when the
VCO is connected directly to the output, the duty cycle is 50%.
If the CLK input is routed directly to the output, the duty cycle of
the output is the same as the CLK input.
Phase Offset or Coarse Time Delay
Each channel divider allows for a phase offset, or a coarse time
delay, to be programmed by setting register bits (see Table 39).
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.)
Table 39. Setting Phase Offset and Division
Start
High (SH)
0x191[4]
0x194[4]
0x197[4]
0x19A[4]
N + M + 2
Even
Odd
Odd
N + M + 2
Chanel
divider
bypassed
Even
Odd
Odd
D
D
X
X
0x19A[3:0]
Phase
Offset (PO)
0x191[3:0]
0x194[3:0]
0x197[3:0]
Disable Div
DCC = 1
(N + 1)/
(M + N + 2)
(N + 1)/
(M + N + 2)
(N + 1)/
(M + N + 2)
Disable Div
DCC = 1
Same as input
duty cycle
(N + 1)/
(M + N + 2)
(N + 1)/
(M + N + 2)
(N + 1)/
(M + N + 2)
Output Duty Cycle
Output Duty Cycle
Low Cycles
M
0x190[7:4]
0x193[7:4]
0x196[7:4]
0x199[7:4]
Disable Div DCC = 0
50%, requires M = N
50%, requires M = N + 1
(N + 1 + X%)/(2 × N + 3),
requires M = N + 1
Disable Div DCC = 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
0x199[3:0]
High Cycles
N
0x190[3:0]
0x193[3:0]
0x196[3:0]