For best operational performance, use good PCB
layout practices, including:
- Noise can propagate into
analog circuitry through the power pins of the circuit as a whole and op amp
itself. Bypass capacitors are used to reduce the coupled noise by providing
low-impedance power sources local to the analog circuitry.
- Connect low-ESR,
0.1µF ceramic bypass capacitors between each supply pin and ground,
placed as close to the device as possible. A single bypass capacitor
from V+ to ground is applicable for single-supply applications.
- Separate grounding for analog
and digital portions of circuitry is one of the simplest and most-effective
methods of noise suppression. One or more layers on multilayer PCBs are
usually devoted to ground planes. A ground plane helps distribute heat and
reduces EMI noise pickup. Physically separate the digital and analog grounds
paying attention to the flow of the ground current.
- To reduce parasitic coupling,
run the input traces as far away from the supply or output traces as
possible. If these traces cannot be kept separate, then crossing the
sensitive trace perpendicular is much better as opposed to in parallel with
the noisy trace.
- Place the external components
as close to the device as possible. As shown in Figure 7-5, keeping RF and RG close to the inverting input minimizes parasitic
capacitance.
- Keep the length of input
traces as short as possible. Always remember that the input traces are the
most sensitive part of the circuit.
- Consider a driven,
low-impedance guard ring around the critical traces. A guard ring can
significantly reduce leakage currents from nearby traces that are at
different potentials.
- Cleaning the PCB following
board assembly is recommended for best performance.
- Any precision integrated
circuit can experience performance shifts due to moisture ingress into the
plastic package. Following any aqueous PCB cleaning process, baking the PCB
assembly is recommended to remove moisture introduced into the device
packaging during the cleaning process. A low temperature, post cleaning bake
at 85°C for 30 minutes is sufficient for most circumstances.