Datasheet
Table Of Contents
- Features
- Applications
- General Description
- Functional Block Diagram
- Revision History
- Specifications
- Power Supply Requirements
- PLL Characteristics
- Clock Inputs
- Clock Outputs
- Timing Characteristics
- Clock Output Additive Phase Noise (Distribution Only; VCO Divider Not Used)
- Clock Output Absolute Phase Noise (Internal VCO Used)
- Clock Output Absolute Time Jitter (Clock Generation Using Internal VCO)
- Clock Output Absolute Time Jitter (Clock Cleanup Using Internal VCO)
- Clock Output Absolute Time Jitter (Clock Generation Using External VCXO)
- Clock Output Additive Time Jitter (VCO Divider Not Used)
- Clock Output Additive Time Jitter (VCO Divider Used)
- Delay Block Additive Time Jitter
- Serial Control Port
- PD, RESET, and SYNC Pins
- LD, STATUS, and REFMON Pins
- Power Dissipation
- Timing Diagrams
- Absolute Maximum Ratings
- Pin Configuration and Function Descriptions
- Typical Performance Characteristics
- Terminology
- Detailed Block Diagram
- Theory of Operation
- Operational Configurations
- High Frequency Clock Distribution—CLK or External VCO > 1600 MHz
- Internal VCO and Clock Distribution
- Clock Distribution or External VCO < 1600 MHz
- Phase-Locked Loop (PLL)
- Configuration of the PLL
- Phase Frequency Detector (PFD)
- Charge Pump (CP)
- On-Chip VCO
- PLL External Loop Filter
- PLL Reference Inputs
- Reference Switchover
- Reference Divider R
- VCXO/VCO Feedback Divider N—P, A, B, R
- Digital Lock Detect (DLD)
- Clock Distribution
- Reset Modes
- Power-Down Modes
- Operational Configurations
- Serial Control Port
- Thermal Performance
- Register Map Overview
- Register Map Descriptions
- Applications Information
- Outline Dimensions
Data Sheet AD9516-1
Rev. C | Page 79 of 80
CMOS CLOCK DISTRIBUTION
The AD9516 provides four clock outputs (OUT6 to OUT9)
that are selectable as either CMOS or LVDS level outputs.
When selected as CMOS, each output becomes a pair of CMOS
outputs, each of which can be individually turned on or off and
set as noninverting or inverting. These outputs are 3.3 V CMOS
compatible.
Whenever single-ended CMOS clocking is used, some of the
following general guidelines should be used.
Point-to-point nets should be designed such that a driver has
only one receiver on the net, if possible. This allows for simple
termination schemes and minimizes ringing due to possible
mismatched impedances on the net. Series termination at the
source is generally required to provide transmission line
matching and/or to reduce current transients at the driver.
The value of the resistor is dependent on the board design and
timing requirements (typically 10 Ω to 100 Ω is used). CMOS
outputs are also limited in terms of the capacitive load or trace
length that they can drive. Typically, trace lengths less than
3 inches are recommended to preserve signal rise/fall times and
preserve signal integrity.
CMOS CMOS
10Ω
60.4Ω
(1.0 INCH)
MICROSTRIP
06420-076
Figure 75. Series Termination of CMOS Output
Termination at the far-end of the PCB trace is a second option.
The CMOS outputs of the AD9516 do not supply enough
current to provide a full voltage swing with a low impedance
resistive, far-end termination, as shown in Figure 76. The far-
end termination network should match the PCB trace impedance
and provide the desired switching point. The reduced signal
swing may still meet receiver input requirements in some
applications. This can be useful when driving long trace
lengths on less critical nets.
CMOS
CMOS
10Ω
50Ω
100Ω
100Ω
VS
06420-077
Figure 76. CMOS Output with Far-End Termination
Because of the limitations of single-ended CMOS clocking,
consider using differential outputs when driving high speed
signals over long traces. The AD9516 offers both LVPECL and
LVDS outputs that are better suited for driving long traces
where the inherent noise immunity of differential signaling
provides superior performance for clocking converters.