To achieve the levels of
high-frequency performance of the THS402x, follow
proper printed-circuit board (PCB), high-frequency design techniques. The following
is a general set of guidelines. In addition, a THS402x
evaluation board is available to use as a guide for layout or for evaluating the
device performance.
- Ground planes—make sure
that the ground plane used on the board provides all components with a
low-inductive ground connection. However, in the areas of the amplifier inputs
and output, the ground plane can be removed to minimize stray capacitance.
- Proper power-supply
decoupling—use a 6.8-μF tantalum capacitor in parallel with a 0.1-μF
ceramic capacitor on each supply pin. Sharing the tantalum capacitor among
several amplifiers is possible depending on the application, but always use a
0.1-μF ceramic capacitor on the supply pin of every amplifier. In addition,
place the 0.1-μF capacitor as close as possible to the supply pin. As this
distance increases, the inductance in the connecting trace makes the capacitor
less effective. Strive for distances of less than 0.1 inch (2.54 mm) between the
device power pins and the ceramic capacitors.
- Short trace runs or compact
part placements—optimum high-frequency performance is achieved when
stray series inductance has been minimized. To realize this, make the circuit
layout as compact as possible, thereby minimizing the length of all trace runs.
Pay particular attention to the inputs of the amplifier, keeping the trace
lengths as short as possible. This layout helps to minimize stray capacitance at
the input of the amplifier.