OPA227 Datasheet, PDF (21/46 Pages) Burr-Brown (TI) – High Precision, Low Noise OPERATIONAL AMPLIFIERS

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Feature Description (continued)
R₁
2MΩ
R₂
2MΩ
R₈
402kΩ
OPA227, OPA2227, OPA4227
OPA228, OPA2228, OPA4228
SBOS110B – MAY 1998 – REVISED JUNE 2015
R₁₁
178kΩ
R₃
1kΩ
C₁
C₂
1μF
1μF
Input from
Device
Under
Test
R₄
9.09kΩ
R₆
R₇
40.2kΩ 97.6kΩ
U1
(OPA227)
C₃
0.47μF
R₅
634kΩ
C₄
22nF
C₆
10nF
2
6
U2
3
(OPA227)
R₉
178kΩ
R₁₀
226kΩ
2
6
U3
C₅
3
0.47μF
(OPA227)
V_OUT
Figure 41. 0.1 Hz to 10 Hz Bandpass Filter Used to Test Wideband Noise of the
OPAx22x Series
22pF
100kΩ
10Ω
2
6
OPA227
3
V_OUT
Device
Under
Test
Figure 42. Noise Test Circuit
Figure 41 shows the 0.1 Hz 10 Hz bandpass filter used to test the noise of the OPA227 and OPA228. The filter
circuit was designed using Texas Instruments’ FilterPro software (available at www.ti.com). Figure 42 shows the
configuration of the OPA227 and OPA228 for noise testing.
7.3.8 EMI Rejection Ratio (EMIRR)
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.
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Product Folder Links: OPA227 OPA2227 OPA4227 OPA228 OPA2228 OPA4228