OPA145IDBVT datasheet(21/44 Pages) TI1

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100

120

140

10M

100M

1000M

Frequency (Hz)

C004

±200

±150

±100

±50

100

10k

100k

Frequency (Hz)

C006

V± Supply

V+ Supply

OPA145

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SBOS427C – JUNE 2017 – REVISED JULY 2018

Product Folder Links: OPA145

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Feature Description (continued)

7.3.8 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.

High-frequency signals conducted or radiated to any pin of the operational amplifier result in adverse effects,

as the amplifier would not have sufficient loop gain to correct for signals with spectral content outside its

bandwidth. Conducted or radiated EMI on inputs, power supply, or output may result in unexpected DC

offsets, transient voltages, or other unknown behavior. Be sure to properly shield and isolate sensitive analog

nodes from noisy radio signals and digital clocks and interfaces. Figure 43 shows the effect of conducted

EMI to the power supplies on the input offset voltage of OPA145.

The EMIRR IN+ of the OPA145 is plotted versus frequency as shown in Figure 42. The OPA145 unity-gain

bandwidth is 5.5 MHz. EMIRR performance below this frequency denotes interfering signals that fall within

the op amp bandwidth.

See EMI Rejection Ratio of Operational Amplifiers, available for download from www.ti.com.

Figure 42. OPA145 EMIRR IN+

Figure 43. OPA145 EMI-Induced Input Offset Voltage

(Power Supplies)

OPA145IDBVT Datasheet(PDF) 21 Page - Texas Instruments

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