OPA189IDBVT datasheet(21/48 Pages) TI1

21 / 48 page

Digital

Multimeter

Ambient temperature: 25Û&

Sample /

Averaging

V+

V±

Not shown: 0.1 µF and 10 µF supply decoupling

RF Source

DC Bias: 0 V

Modulation: None (CW)

Frequency Sweep: 201 pt. Log

Low-Pass

Filter

OPA189, OPA2189

www.ti.com

SBOS830E – SEPTEMBER 2017 – REVISED MAY 2019

Product Folder Links: OPA189 OPA2189

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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 more simple 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 may result in adverse

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

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

transient voltages, or other unknown behavior. Take care to properly shield and isolate sensitive analog nodes

from noisy radio signals and digital clocks and interfaces.

The EMIRR +IN of the OPAx189 is plotted versus frequency as shown in Figure 42. If available, any dual and

quad op amp device versions have nearly similar EMIRR +IN performance. The OPAx189 unity-gain bandwidth

is 14 MHz. EMIRR performance below this frequency denotes interfering signals that fall within the op amp

bandwidth.

8.3.5 EMIRR +IN Test Configuration

Figure 43 shows the circuit configuration for testing the EMIRR +IN. An RF source is connected to the op amp

noninverting input terminal using a transmission line. The op amp is configured in a unity-gain buffer topology

with the output connected to a low-pass filter (LPF) and a digital multimeter (DMM). A large impedance mismatch

at the op amp input causes a voltage reflection; however, this effect is characterized and accounted for when

determining the EMIRR IN+. The multimeter samples and measures the resulting DC offset voltage. The LPF

isolates the multimeter from residual RF signals that may interfere with multimeter accuracy.

Figure 43. EMIRR +IN Test Configuration

OPA189IDBVT Datasheet(PDF) 21 Page - Texas Instruments

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