AD9516-4 Datasheet, PDF (33/84 Pages) Analog Devices – 14-Output Clock Generator with Integrated 1.6 GHz VCO

Phase-Locked Loop (PLL)
REF_SEL VS GND
RSET
REFMON
REFERENCE
SWITCHOVER
DIST
REF
REFIN (REF1)
REFIN (REF2)
BYPASS
REF1
REF2
STATUS
STATUS
R DIVIDER
LOW DROPOUT
REGULATOR (LDO)
N DIVIDER
P, P + 1
A/B
PRESCALER COUNTERS
PROGRAMMABLE
R DELAY
PROGRAMMABLE
N DELAY
CPRSET VCP
LOCK
DETECT
PLL
HOLD
REF
PHASE
FREQUENCY
DETECTOR
CHARGE PUMP
LF
CLK
CLK
VCO
DIVIDE BY
2, 3, 4, 5, OR 6
10
VCO STATUS
0
1
Figure 45. PLL Functional Blocks
AD9516-4
LD
CP
STATUS
The AD9516 includes an on-chip PLL with an on-chip VCO.
The PLL blocks can be used either with the on-chip VCO to
create a complete phase-locked loop, or with an external VCO
or VCXO. The PLL requires an external loop filter, which
usually consists of a small number of capacitors and resistors.
The configuration and components of the loop filter help to
establish the loop bandwidth and stability of the operating PLL.
The AD9516 PLL is useful for generating clock frequencies
from a supplied reference frequency. This includes conversion
of reference frequencies to much higher frequencies for subsequent
division and distribution. In addition, the PLL can be exploited to
clean-up jitter and phase noise on a noisy reference. The exact
choices of PLL parameters and loop dynamics is very application
specific. The flexibility and depth of the AD9516 PLL allows the
part to be tailored to function in many different applications
and signal environments.
Configuration of the PLL
The AD9516 allows flexible configuration of the PLL,
accomodating various reference frequencies, PFD comparison
frequencies, VCO frequencies, internal or external VCO/VCXO,
and loop dynamics. This is accomplished by the various settings
that include the R divider, the N divider, the PFD polarity (only
applicable to external VCO/VCXO), the antibacklash pulse
width, the charge pump current, the selection of internal VCO
or external VCO/VCXO, and the loop bandwidth. These are
managed through programmable register settings (see Table 51
and Table 53) and by the design of the external loop filter.
Successful PLL operation and satisfactory PLL loop performance
are highly dependant upon proper configuration of the PLL
settings. The design of the external loop filter is crucial to the
proper operation of the PLL. A thorough knowledge of PLL
theory and design is helpful.
ADIsimCLK™ (V1.2 or later) is a free program that can help
with the design and exploration of the capabilities and features
of the AD9516, including the design of the PLL loop filter. It is
available at www.analog.com/clocks.
Phase Frequency Detector (PFD)
The PFD takes inputs from the R counter and N counter and
produces an output proportional to the phase and frequency
difference between them. The PFD includes a programmable
delay element that controls the width of the antibacklash pulse.
This pulse ensures that there is no dead zone in the PFD
transfer function and minimizes phase noise and reference
spurs. The antibacklash pulse width is set by 0x17<1:0>.
An important limit to keep in mind is the maximum frequency
allowed into the PFD. The maximum input frequency to the
PFD is a function of the antibacklash pulse setting, as specified
in the Phase/Frequency Detector section of Table 2.
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