ADA4930-1_17 Datasheet, PDF (23/25 Pages) Analog Devices – Ultralow Noise Drivers for Low Voltage ADCs

Data Sheet
LAYOUT, GROUNDING, AND BYPASSING
The ADA4930-1/ADA4930-2 are high speed devices. Realizing
their superior performance requires attention to the details of
high speed PCB design.
The first requirement is to use a multilayer PCB with solid ground
and power planes that cover as much of the board area as possible.
Bypass each power supply pin directly to a nearby ground plane, as
close to the device as possible. Use 0.1 µF high frequency ceramic
chip capacitors.
Provide low frequency bulk bypassing, using 10 µF tantalum
capacitors from each supply to ground.
Stray transmission line capacitance in combination with package
parasitics can potentially form a resonant circuit at high
frequencies, resulting in excessive gain peaking or possible
oscillation.
Signal routing should be short and direct to avoid such parasitic
effects. Provide symmetrical layout for complementary signals
to maximize balanced performance.
ADA4930-1/ADA4930-2
Use radio frequency transmission lines to connect the driver
and receiver to the amplifier.
Minimize stray capacitance at the input/output pins by clearing
the underlying ground and low impedance planes near these pins
(see Figure 56).
If the driver/receiver is more than one-eighth of the wavelength
from the amplifier, the signal trace widths should be minimal.
This nontransmission line configuration requires the underlying
and adjacent ground and low impedance planes to be cleared
near the signal lines.
The exposed thermal paddle is internally connected to the ground
pin of the amplifier. Solder the paddle to the low impedance
ground plane on the PCB to ensure the specified electrical
performance and to provide thermal relief. To reduce thermal
impedance further, it is recommended that the ground planes
on all layers under the paddle be connected together with vias.
1.30
0.80
1.30 0.80
Figure 56. ADA4930-1 Ground and Power Plane Voiding
in the Vicinity of RF and RG
TOP METAL
GROUND PLANE
Figure 57. Recommended PCB Thermal Attach Pad Dimensions (Millimeters)
1.3 mm
0.8 mm
POWER PLANE
BOTTOM METAL
Figure 58. Cross-Section of 4-Layer PCB Showing Thermal Via Connection to Buried Ground Plane (Dimensions in Millimeters)
Rev. C | Page 23 of 25