To achieve the levels of
high-frequency performance of the OPAx892, follow
proper printed-circuit board (PCB), high-frequency design techniques. The following
is a general set of guidelines. In addition, a OPAx892
evaluation board is available to use as a guide for layout or for evaluating the
device performance.
- Ground planes—ensure 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—optimized 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.