200 Ps/DIV

VOUT

VIN

VS = 5V

Figure 7-2. Step Response

7.1.2 EMI Suppression

The near-ubiquity of cellular, Bluetooth®, and Wi-Fi® signals and the rapid rise of sensing systems incorporating

wireless radios make electromagnetic interference (EMI) an evermore important design consideration for

precision signal paths. Though RF signals lie outside the op-amp band, RF carrier switching can modulate the

dc offset of the op amp. Also some common RF modulation schemes can induce down-converted components.

The added dc offset and the induced signals are amplified with the signal of interest and thus corrupt the

measurement. The LPV521 uses on-chip filters to reject these unwanted RF signals at the inputs and power

supply pins, thereby preserving the integrity of the precision signal path.

Twisted pair cabling and the active front-end common-mode rejection provide immunity against low-frequency

noise (for example, 60Hz or 50Hz mains) but are ineffective against RF interference. Even a few centimeters of

printed circuit board (PCB) trace and wiring for sensors located close to the amplifier can pick up significant

1GHz RF. The integrated EMI filters of the LPV521 reduce or eliminate external shielding and filtering

requirements, thus increasing system robustness. A larger EMIRR means more rejection of the RF interference.

For more information on EMIRR, see the AN-1698 A Specification for EMI Hardened Operational Amplifiers

application report.

LPV521

SNOSB14E – AUGUST 2009 – REVISED JULY 2024

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