Data Sheet

ADA4927-1/ADA4927-2

Rev. B | Page 23 of 25

LAYOUT, GROUNDING, AND BYPASSING

As a high speed device, the ADA4927 is sensitive to the PCB

environment in which it operates. Realizing the superior

performance requires attention to the details of high speed

PCB design. This section shows a detailed example of how the

ADA4927-1 was addressed.

The first requirement is a solid ground plane that covers as

much of the board area around the ADA4927-1 as possible.

However, clear the area near the feedback resistors (RF), gain

resistors (RG), and the input summing nodes (Pin 2 and Pin 3) of

all ground and power planes (see Figure 55). Clearing the ground

and power planes minimizes any stray capacitance at these nodes

and prevents peaking of the response of the amplifier at high

frequencies. Whereas ideal current feedback amplifiers are

insensitive to summing node capacitance, real-world amplifiers

can exhibit peaking due to excessive summing node capacitance.

the exposed pad, soldered to a high thermal conductivity 4-layer

circuit board, as described in EIA/JESD 51-7.

Figure 55. Ground and Power Plane Voiding in Vicinity of RF AND RG

Bypassed the power supply pins as close to the device as

possible and directly to a nearby ground plane. Use high

frequency ceramic chip capacitors. It is recommended that two

parallel bypass capacitors (1000 pF and 0.1 µF) be used for each

supply. The 1000 pF capacitor should be placed closer to the

device. Further away, provide low frequency bulk bypassing,

using 10 µF tantalum capacitors from each supply to ground.

Make signal routing short and direct to avoid parasitic effects.

Wherever complementary signals exist, provide a symmetrical

layout to maximize balanced performance. When routing

differential signals over a long distance, place PCB traces close

together, and twist any differential wiring such that the loop

area is minimized. Doing this reduces radiated energy and

makes the circuit less susceptible to interference.

1.30

0.80

0.80

1.30

Figure 56. Recommended PCB Thermal Attach Pad Dimensions (Millimeters)

0.30

PLATED

VIA HOLE

1.30

GROUND PLANE

POWER PLANE

BOTTOM METAL

TOP METAL

Figure 57. Cross-Section of 4-Layer PCB Showing Thermal Via Connection to Buried Ground Plane (Dimensions in Millimeters)