AD9518-1A/PCBZ Analog Devices Inc, AD9518-1A/PCBZ Datasheet - Page 26

• Manufacturer Part Number: AD9518-1A/PCBZ
• Description: 6-Output Clock Generator With 2.8GHz
• Manufacturer: Analog Devices Inc

Specifications of AD9518-1A/PCBZ

• Main Purpose: Timing, Clock Generator
• Embedded: No
• Utilized Ic / Part: AD9518-1A
• Primary Attributes: 2 Inputs, 6 Outputs, 2.5GHz VCO
• Secondary Attributes: LVPECL Output Logic
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD9518-1
Phase-Locked Loop (PLL)
The AD9518 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 AD9518 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 are application
specific. The flexibility and depth of the AD9518 PLL allow the
part to be tailored to function in many different applications
and signal environments.
Configuration of the PLL
The AD9518 allows flexible configuration of the PLL,
accommodating 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
REFIN (REF1)
REFIN (REF2)
BYPASS
CLK
CLK
LF
REGULATOR (LDO)
LOW DROPOUT
REF1
REF2
VCO
REF_SEL
SWITCHOVER
REFERENCE
STATUS
STATUS
1
2, 3, 4, 5, OR 6
DIVIDE BY
VS
PRESCALER
0
P, P + 1
GND
N DIVIDER
RSET
DIST
COUNTERS
REF
R DIVIDER
A/B
Figure 30. PLL Functional Blocks
Rev. A | Page 26 of 64
0
1
VCO STATUS
REFMON
PROGRAMMABLE
PROGRAMMABLE
R DELAY
N DELAY
managed through programmable register settings (see Table 42
and Table 44) and by the design of the external loop filter.
Successful PLL operation and satisfactory PLL loop performance
are highly dependent 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 AD9518, 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 Register 0x017[1:0].
An important limit to keep in mind is the maximum frequency
allowed into the PFD, which in turn determines the correct
antibacklash pulse setting. The antibacklash pulse setting is
specified in the phase/frequency detector parameter of Table 2.
FREQUENCY
DETECTOR
DETECT
LOCK
PHASE
CPRSET
REF
PLL
CHARGE PUMP
VCP
HOLD
LD
CP
STATUS