ADA4311-1

Rev. 0 | Page 12 of 16

BOARD LAYOUT

As is the case with all high speed applications, careful attention

to printed circuit board (PCB) layout details prevents associated

board parasitics from becoming problematic. Proper RF design

technique is mandatory. The PCB should have a ground plane

covering all unused portions of the component side of the

board to provide a low impedance return path. Removing the

ground plane on all layers from the area near the input and

output pins reduces stray capacitance, particularly in the area of

the inverting inputs. Signal lines connecting the feedback and

gain resistors should be as short as possible to minimize the

inductance and stray capacitance associated with these traces.

Termination resistors and loads should be located as close as

possible to their respective inputs and outputs. Input and

output traces should be kept as far apart as possible to minimize

coupling (crosstalk) though the board. Wherever there are

complementary signals, a symmetrical layout should be provided

to the extent possible to maximize balanced performance.

When running differential signals over a long distance, the

traces on the PCB should be close. Doing this reduces the

radiated energy and makes the circuit less susceptible to RF

interference. Adherence to stripline design techniques for long

signal traces (greater than about 1 inch) is recommended.

For more information on high speed board layout, see A

Practical Guide to High-Speed Printed-Circuit-Board Layout

.

POWER SUPPLY BYPASSING

The ADA4311-1 operates on supplies from 6 V to 12 V. The

ADA4311-1 circuit should be powered with a well-regulated

power supply. Careful attention must be paid to decoupling the

power supply. High quality capacitors with low equivalent series

resistance (ESR), such as multilayer ceramic capacitors (MLCCs),

should be used to minimize supply voltage ripple and power

dissipation. In addition, 0.1 μF MLCC decoupling capacitors

should be located no more than ⅛-inch away from each of the

power supply pins. A large, usually tantalum, 10 μF capacitor is

required to provide good decoupling for lower frequency signals

and to supply current for fast, large signal changes at the

ADA4311-1 outputs. Bypassing capacitors should be laid out

in such a manner as to keep return currents away from the

inputs of the amplifiers, which minimizes any voltage drops that

can develop due to ground currents flowing through the ground

plane. A large ground plane also provides a low impedance path

for the return currents.