For best operational performance of the device,
use good PCB layout practices, including:
- Noise can propagate into analog
circuitry through the power pins of the circuit as a whole and the operational
amplifier. 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 a simple and effective method of noise
suppression. One or more layers on multilayer PCBs are typically devoted to
ground planes. A ground plane helps distribute heat and reduces EMI noise
pickup. Make sure to physically separate 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
keeping the input traces separate from the supply or output traces is not
possible, cross the sensitive trace perpendicular as opposed to in parallel with
the noisy trace.
- Place the external components as
close to the device as possible. Keeping RF and RG close to the inverting input
minimizes parasitic capacitance, as shown in Layout Example.
- 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.