Preliminary Technical Data

ADA4938-1

Rev. PrD | Page 13 of 14

LAYOUT, GROUNDING, AND BYPASSING

As a high speed device, the ADA4938-1 is sensitive to the

PCB environment in which it operates. Realizing its superior

performance requires attention to the details of high speed

PCB design.

The first requirement is a solid ground plane that covers as

much of the board area around the ADA4938-1 as possible.

cleared of all ground and power planes (see Figure 8). This

minimizes any stray capacitance at these nodes and prevents

peaking of the response of the amplifier at high frequencies.

The power supply pins should be bypassed as close to the device

as possible and directly to a nearby ground plane. High frequency

ceramic chip capacitors should be used. 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, low frequency bypassing should be

provided, using 10 μF tantalum capacitors from each supply

to ground.

Signal routing should be short and direct to avoid parasitic

effects. Wherever complementary signals exist, a symmetrical

layout should be provided to maximize balanced performance.

When routing differential signals over a long distance, PCB

traces should be close together, and any differential wiring

should be twisted such that loop area is minimized. This

reduces radiated energy and makes the circuit less susceptible

to interference.