CDCE62005 Datasheet, PDF (47/76 Pages) Texas Instruments – Five/Ten Output Clock Generator/Jitter Cleaner With Integrated Dual VCOs

CDCE62005
www.ti.com........................................................................................................................................................................................... SCAS862 – NOVEMBER 2008
Digital Phase Adjust
Figure 31 provides an overview of the Digital Phase Adjust feature. The output divider includes a coarse phase
adjust that shifts the divided clock signal that drives the output buffer. Essentially, the Digital Phase Adjust timer
delays when the output divider starts dividing; thereby shifting the phase of the output clock. The phase adjust
resolution is a function of the divide function. Coarse phase adjust parameters include:
• Number of Phase Delay Steps – the number of phase delay steps available is equal to the divide ratio
selected. For example, if a Divide by 4 is selected, then the Digital Phase Adjust can be programmed to
select when the output divider changes state based upon selecting one of the four counts on the input.
Figure 31 shows an example of divide by 16 in which there are 16 rising edges of Clock IN at which the
output divider changes state (this particular example shows the fourth edge shifting the output by one fourth
of the period of the output).
• Phase Delay Step Size – the step size is determined by the number of phase delay steps according to the
following equations:
Stepsize(deg)
=
360 degrees
OutputDivideRatio
(3)
1
Stepsize(sec)
=
f_ClockIN
OutputDivideRatio
(4)
Clock
IN
(from Smart MUX )
Digital Phase Adjust (7-bits)
Start Divider
/1 - /80
To Output Buffer
Clock IN
Output Divider (no adjust )
Output Divider (phase adjust )
Figure 31. CDCE62005 Phase Adjust
Phase Adjust example
Given:
Output Frequency: 30.72 MHz
VCO Operating Frequency: 1966.08 MHz
Prescaler Divider Setting: 2
Output Divider Setting: 32
Stepsize(deg) = ³⁶⁰ = 11.25° / Step
32
(5)
The tables that follow provide a list of valid register settings for the digital phase adjust blocks.
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