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.