AD9520-4SLASHPCBZ datasheet(46/84 Pages) AD

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AD9520-4

Rev. 0 | Page 46 of 84

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

Output Duty Cycle

N + M + 2

Disable Divider

DCC = 1

Disable Div

DCC = 0

Even

Channel

divider

bypassed

50%

Odd = 3

Channel

divider

bypassed

33.3%

50%

Odd = 5

Channel

divider

bypassed

40%

50%

Even, odd

Even

(N + 1)/(N + M + 2)

50%; requires

M = N

Even, odd

Odd

(N + 1)/(N + M + 2)

50%; requires

M = N + 1

Table 36. Channel Divider Output Duty Cycle with VCO

Divider ≠ 1 and Input Duty Cycle Is X%

VCO

Divider

Output Duty Cycle

N + M + 2

Disable Div

DCC = 1

Disable Div DCC = 0

Even

Channel

divider

bypassed

50%

Odd = 3

Channel

divider

bypassed

33.3%

(1 + X%)/3

Odd = 5

Channel

Divider

bypassed

40%

(2 + X%)/5

Even

(N + 1)/

(N + M + 2)

50%, requires M = N

Even

Odd

(N + 1)/

(N + M + 2)

50%, requires M = N + 1

Odd = 3

Even

(N + 1)/

(N + M + 2)

50%, requires M = N

Odd = 3

Odd

(N + 1)/

(N + M + 2)

(3N + 4 + X%)/(6N + 9),

requires M = N + 1

Odd = 5

Even

(N + 1)/

(N + M + 2)

50%, requires M = N

Odd = 5

Odd

(N + 1)/

(N + M + 2)

(5N + 7 + X%)/(10N + 15),

requires M = N + 1

Table 37. Channel Divider Output Duty Cycle When the

VCO Divider is Enabled and Set to 1

Input

Clock

Duty Cycle

Output Duty Cycle

N + M + 2

Disable Div

DCC = 1

Disable Div DCC = 0

Any

Even

(N + 1)/

(M + N + 2)

50%, requires M = N

50%

Odd

(N + 1)/

(M + N + 2)

50%, requires M = N + 1

Odd

(N + 1)/

(M + N + 2)

(N + 1 + X%)/(2 × N + 3),

requires M = N + 1

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

Output Duty Cycle

N + M + 2

Disable Div

DCC = 1

Disable Div DCC = 0

Any

Chanel

divider

bypassed

Same as input

duty cycle

Same as input duty

cycle

Any

Even

(N + 1)/

(M + N + 2)

50%, requires M = N

50%

Odd

(N + 1)/

(M + N + 2)

50%, requires M = N + 1

Odd

(N + 1)/

(M + N + 2)

(N + 1 + X%)/(2 × N + 3),

requires M = N + 1

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

Divider

Start

High (SH)

Phase

Offset (PO)

Low Cycles

High Cycles

0x191[4]

0x191[3:0]

0x190[7:4]

0x190[3:0]

0x194[4]

0x194[3:0]

0x193[7:4]

0x193[3:0]

0x197[4]

0x197[3:0]

0x196[7:4]

0x196[3:0]

0x19A[4]

0x19A[3:0]

0x199[7:4]

0x199[3:0]

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