ADA4937-1/ADA4937-2

Data Sheet

Rev. F | Page 22 of 28

LAYOUT, GROUNDING, AND BYPASSING

As high speed devices, the ADA4937-1/ADA4937-2 are sensitive

to the PCB environment in which they operate. Realizing their

superior performance requires attention to the details of high

speed PCB design. This section shows a detailed example of

how the design issues of the ADA4937-1 is addressed.

The first requirement is a solid ground plane that covers as

much of the board area around the ADA4937-1 as possible.

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

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

must be cleared of all ground and power planes (see Figure 61).

Clearing the ground and power planes minimizes any stray capa-

citance at these nodes and prevents peaking of the response of

the amplifier at high frequencies.

The thermal resistance, θJA, is specified for the device, including

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

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

Figure 61. Ground and Power Plane Voiding in Vicinity of RF and RG

Bypass 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 capaci-

tors (1000 pF and 0.1 μF) be used for each supply with the 1000 pF

capacitor placed closer to the device; further away, provide low

frequency bypassing using 10 μF tantalum capacitors from each

supply to ground.

Signal routing must be short and direct to avoid parasitic

effects. Wherever complementary signals exist, provide a sym-

metrical layout to maximize balanced performance. When

routing differential signals over a long distance, keep PCB

traces close together and twist any differential wiring to mini-

mize loop area. Doing this reduces radiated energy and makes

the circuit less susceptible to interference.

1.30

0.80

0.80

1.30

Figure 62. Recommended PCB Thermal Attach Pad Dimensions (mm)

0.30

PLATED

VIA HOLE

1.30

GROUND PLANE

POWER PLANE

BOTTOM METAL

TOP METAL

Figure 63. Cross-Section of 4-layer PCB Showing Thermal Via Connection to Buried Ground Plane (Dimensions in mm)