OPA211_15 Datasheet, PDF (23/45 Pages) Texas Instruments – Low Power, Precision Operational Amplifier

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OPA211, OPA2211
SBOS377H – OCTOBER 2006 – REVISED NOVEMBER 2015
Application Information (continued)
9.1.5 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 operational amplifiers is a change in the offset voltage as a
result of RF signal rectification. An operational amplifier 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 operational amplifier. In general, only the noninverting
input is tested for EMIRR for the following three reasons:
1. Operational amplifier input pins are known to be the most sensitive to EMI, and typically rectify RF signals
better than the supply or output pins.
2. The noninverting and inverting operational amplifier inputs have symmetrical physical layouts and exhibit
nearly matching EMIRR performance.
3. EMIRR is easier to measure on noninverting pins than on other pins because the noninverting input terminal
can be isolated on a printed-circuit-board (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.Figure 46
The EMIRR IN+ of the OPA211 is plotted versus frequency as shown in Figure 46. If available, any dual and
quad operational amplifier device versions have nearly similar EMIRR IN+ performance. The OPA211 unity-gain
bandwidth is 45 MHz. EMIRR performance below this frequency denotes interfering signals that fall within the
operational amplifier bandwidth.
Detailed information can also be found in the application report EMI Rejection Ratio of Operational Amplifiers,
SBOA128, available for download from www.ti.com.
140
P_RF = -10 dbm
120 ^{VS = r12 V}
V_CM = 0 V
100
80
60
40
20
0
10M
100M
1G
10G
Frequency (Hz)
Figure 46. OPA211 EMIRR
Table 1 shows the EMIRR IN+ values for the OPA211 at particular frequencies commonly encountered in real-
world applications. Applications listed in Table 1 may be centered on or operated near the particular frequency
shown. This information may be of special interest to designers working with these types of applications, or
working in other fields likely to encounter RF interference from broad sources, such as the industrial, scientific,
and medical (ISM) radio band.
FREQUENCY
400 MHz
900 MHz
1.8 GHz
Table 1. OPA211 EMIRR IN+ For Frequencies of Interest
APPLICATION OR ALLOCATION
Mobile radio, mobile satellite, space operation, weather, radar, ultra-high frequency (UHF)
applications
Global system for mobile communications (GSM) applications, radio communication, navigation,
GPS (to 1.6 GHz), GSM, aeronautical mobile, UHF applications
GSM applications, mobile personal communications, broadband, satellite, L-band (1 GHz to 2 GHz)
EMIRR IN+
48.4 dB
34.6 dB
46.0 dB
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