OPA140 Datasheet, PDF (22/44 Pages) Texas Instruments – 11-MHz JFET Op Amp

OPA140, OPA2140, OPA4140
SBOS498B – JULY 2010 – REVISED NOVEMBER 2015
www.ti.com
Feature Description (continued)
7.3.9 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 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 easier 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. Figure 38
The EMIRR IN+ of the OPA2140 is plotted versus frequency as shown in .If available, any dual and quad op
amp device versions have nearly similar EMIRR IN+ performance. The OPA2140 unity-gain bandwidth is
11 MHz. EMIRR performance below this frequency denotes interfering signals that fall within the op amp
bandwidth.
See the application report, EMI Rejection Ratio of Operational Amplifiers (SBOA128), available for download
from www.ti.com.
120
P_RF = -10 dbm
V_S = r12 V
100 _{VCM = 0 V}
80
60
40
20
0
10
100
1k
10k
Frequency (MHz)
Figure 38. OPA2140 EMIRR
22
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