OPA192 datasheet(23/51 Pages) TI

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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 8-2. 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 8-3 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.

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

Figure 8-3. EMIRR +IN Test Configuration

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OPA189, OPA2189, OPA4189

SBOS830G – SEPTEMBER 2017 – REVISED APRIL 2021

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