Datasheet

TIME (0.5s/DIV)
V
OUT
(0.5V/DIV)
Typical Opamp
LMV852
+
-
R
1
50:
RFin
C
1
22 pF
C
2
10 µF
100 pF
V
DD
V
SS
Out
+
C
3
100 pF
10 µF
+
C
4
C
5
LMV851, LMV852, LMV854
www.ti.com SNOSAW1A –OCTOBER 2007–REVISED MARCH 2013
be a 50Ω stripline in order to match the RF impedance of the cabling and the RF generator. On the PCB a 50Ω
termination is used. This 50Ω resistor is also used to set the bias level of the IN+ pin to ground level. For
determining the EMIRR, two measurements are needed: one is measuring the DC output level when the RF
signal is off; and the other is measuring the DC output level when the RF signal is switched on. The difference of
the two DC levels is the output voltage shift as a result of the RF signal. As the op amp is in the unity gain
configuration, the input referred offset voltage shift corresponds one-to-one to the measured output voltage shift.
Figure 53. Circuit for Coupling the RF Signal to IN
+
Cell Phone Call
The effect of electromagnetic interference is demonstrated in a setup where a cell phone interferes with a
pressure sensor application (Figure 55). This application needs two op amps and therefore a dual op amp is
used. The experiment is performed on two different dual op amps: a typical standard op amp and the LMV852,
EMI hardened dual op amp. The op amps are placed in a single supply configuration. The cell phone is placed
on a fixed position a couple of centimeters from the op amps.
When the cell phone is called, the PCB and wiring connected to the op amps receive the RF signal.
Subsequently, the op amps detect the RF voltages and currents that end up at their pins. The resulting effect on
the output of the second op amp is shown in Figure 54.
Figure 54. Comparing EMI Robustness
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