OPAX189 datasheet(22/52 Pages) TI

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8.3.3 Input Bias Current Clock Feedthrough

Zero-drift amplifiers such as the OPAx189 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.

8.3.4 EMI Rejection

The OPAx189 uses 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 OPAx189

benefits 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 OPAx189. Table 8-1 lists the EMIRR +IN values for the

OPAx189 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.

100

120

10M

100M

10G

Frequency (Hz)

C005

Figure 8-2. EMIRR Testing

Table 8-1. OPAx189 EMIRR IN+ for Frequencies of Interest

FREQUENCY

APPLICATION AND ALLOCATION

EMIRR IN+

400 MHz

Mobile radio, mobile satellite, space operation, weather, radar, ultra-high frequency

(UHF) applications

48.4 dB

900 MHz

Global system for mobile communications (GSM) applications, radio

communication, navigation, GPS (to 1.6 GHz), GSM, aeronautical mobile, UHF

applications

52.8 dB

1.8 GHz

GSM applications, mobile personal communications, broadband, satellite, L-band

(1 GHz to 2 GHz)

69.1 dB

2.4 GHz

802.11b, 802.11g, 802.11n, Bluetooth®, mobile personal communications,

industrial, scientific and medical (ISM) radio band, amateur radio and satellite,

S-band (2 GHz to 4 GHz)

88.9 dB

3.6 GHz

Radiolocation, aero communication and navigation, satellite, mobile, S-band

82.5 dB

5 GHz

802.11a, 802.11n, aero communication and navigation, mobile communication,

space and satellite operation, C-band (4 GHz to 8 GHz)

95.5 dB

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

OPA189, OPA2189, OPA4189

SBOS830I – SEPTEMBER 2017 – REVISED OCTOBER 2021

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