To achieve the levels of
high-frequency performance of the THS413x
devices, follow proper
printed-circuit board (PCB) high-frequency design techniques. Following is a general
set of guidelines. In addition, a THS413x
evaluation board is available to use as a guide
for layout or for evaluating device performance.
- Ground planes—Use a ground plane
on the board to provide 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 the 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 among several amplifiers is
possible depending on the application; however, 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 inches between the device power pin and
the ceramic capacitors.
- Short trace runs or compact part
placements—to optimize high-frequency performance, minimize stray series
inductance. The best method is to 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; keep the length as short as possible.
This short length helps minimize stray capacitance at the input of the
amplifier.