ADA4927-1/ADA4927-2

Rev. 0 | Page 22 of 24

LAYOUT, GROUNDING, AND BYPASSING

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

environment in which it operates. Realizing its 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)