OPAX140 datasheet(21/56 Pages) TI2

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7.3.9 EMI Rejection

The electromagnetic interference (EMI) rejection ratio, or EMIRR, describes the EMI immunity of operational

amplifiers. An adverse effect that is common to many op amps is a change in the offset voltage as a result of

RF signal rectification. An op amp that is more efficient at rejecting this change in offset as a result of EMI has

a higher EMIRR and is quantified by a decibel value. Measuring EMIRR can be performed in many ways, but

this section provides the EMIRR IN+, which specifically describes the EMIRR performance when the RF signal is

applied to the noninverting input pin of the op amp. In general, only the noninverting input is tested for EMIRR for

the following three reasons:

• Op amp input pins are known to be the most sensitive to EMI, and typically rectify RF signals better than the

supply or output pins.

• The noninverting and inverting op amp inputs have symmetrical physical layouts and exhibit nearly matching

EMIRR performance

• EMIRR is easier to measure on noninverting pins than on other pins because the noninverting input terminal

can be isolated on a PCB. This isolation allows the RF signal to be applied directly to the noninverting input

terminal with no complex interactions from other components or connecting PCB traces. Figure 7-6

Frequency (MHz)

100

120

100

10k

PRF = -10 dbm

VS = r12 V

VCM = 0 V

Figure 7-6. OPA2140 EMIRR

The EMIRR IN+ of the OPA2140 is plotted versus frequency as shown in .If available, any dual and quad op

amp device versions have nearly similar EMIRR IN+ performance. The OPA2140 unity-gain bandwidth is

11 MHz. EMIRR performance below this frequency denotes interfering signals that fall within the op amp

bandwidth.

For more information, see the EMI Rejection Ratio of Operational Amplifiers Application Report, available for

download from www.ti.com.

www.ti.com

OPA140, OPA2140, OPA4140

SBOS498F – JUNE 2010 – REVISED MARCH 2023

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OPAX140 Datasheet(PDF) 21 Page - Texas Instruments