• 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 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.

• To reduce parasitic coupling, run the input traces as far away from the supply or output traces as possible. If it

is not possible to keep them separate, it is much better to 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.

7.3.2 Layout Example

+

RIN

RG

RF

VOUT

VIN

Figure 7-5. Operational Amplifier Schematic for Noninverting Configuration

OUT1

OUT2

IN1

í

IN1+

VCC

í

VCC+

IN2

í

IN2+

RG

RIN

RF

GND

VIN

VS-

GND

VS+

GND

Run the input traces as far

away from the supply lines

as possible

Only needed for

dual-supply

operation

Place components close to

device and to each other to

reduce parasitic errors

Use low-ESR, ceramic

bypass capacitor

(or GND for single supply)

Ground (GND) plane on another layer

Figure 7-6. Operational Amplifier Board Layout for Noninverting Configuration

RC4580

SLOS412E – APRIL 2003 – REVISED NOVEMBER 2024

www.ti.com

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