OPA182 datasheet(19/43 Pages) TI

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8.3 Feature Description

The OPAx182 operational amplifiers have several integrated features that help maintain a high level of precision

throughout all operating conditions. These features include phase-reveral protection, input bias current clock

feedthrough and MUX-friendly inputs.

8.3.1 Phase-Reversal Protection

The OPAx182 have an internal phase-reversal protection. Many op amps exhibit a phase reversal when the

input is driven beyond the linear common-mode range. This condition is most often encountered in noninverting

circuits when the input is driven beyond the specified common-mode voltage range, causing the output to

reverse into the opposite rail. The OPAx182 input prevents phase reversal with excessive common-mode

voltage. Instead, the output limits into the appropriate rail. This performance is shown in Figure 8-1.

Time (1 ms/div)

Vout (V)

Vin (V)

C017

Figure 8-1. No Phase Reversal

8.3.2 Input Bias Current Clock Feedthrough

Zero-drift amplifiers such as the OPAx182 use switching on the inputs to correct for the intrinsic offset and drift

of the amplifier. Charge injection from the integrated switches on the inputs can introduce short transients in

the input bias current of the amplifier. The extremely short duration of these pulses prevents the pulses from

amplifying; however, the pulses may be coupled to the output of the amplifier through the feedback network.

The most effective method to prevent transients in the input bias current from producing additional noise at the

amplifier output is to use a low-pass filter such as an RC network.

8.3.3 EMI Rejection

The OPAx182 use integrated electromagnetic interference (EMI) filtering to reduce the effects of EMI

interference from sources such as wireless communications and densely-populated boards with a mix of analog

signal chain and digital components. EMI immunity can be improved with circuit design techniques; the OPAx182

benefit from these design improvements. Texas Instruments has developed the ability to accurately measure and

quantify the immunity of an operational amplifier over a broad frequency spectrum extending from 10 MHz to 6

GHz. Figure 8-2 shows the results of this testing on the OPAx182. Table 8-1 lists the EMIRR +IN values for the

OPAx182 at particular frequencies commonly encountered in real-world applications. Applications listed in Table

8-1 may be centered on or operated near the particular frequency shown. Detailed information can also be found

in the EMI Rejection Ratio of Operational Amplifiers application report, available for download from www.ti.com.

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:

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OPA182, OPA2182, OPA4182

SBOS936D – DECEMBER 2019 – REVISED DECEMBER 2021

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