Datasheet

+
V
OUT
+
-
-
R
A
C
F
V
IN
= KI
+
-
IR RADIATION
INTENSITY, I
V
OUT
R
A
K(R
A
+ R
B
)
I =
IR SENSOR
R
B
10k
100k 1M 10M
FREQUENCY (Hz)
60
70
80
90
100
110
120
GAIN (dB)
C
IN
= 50 pF
C
F
= 4.5 pF
+
-
+
-
792B
792A
C
IN
= 50 pF
47 k:
4.5 pF
1 k:
0.1 PF
10 k:
+
-
V
OUT
I
IN
V
OUT
I
IN
= 470,000
A
TI
=
LMV791, LMV792
www.ti.com SNOSAG6F –SEPTEMBER 2005–REVISED MARCH 2013
Figure 62. 1.5 MHz Transimpedance Amplifier, with A
TI
= 470000
Figure 63. 1.5 MHz Transimpedance Amplifier Frequency Response
SENSOR INTERFACES
The low input bias current and low input referred noise of the LMV791 and LMV792 make them ideal for sensor
interfaces. These circuits are required to sense voltages of the order of a few μV, and currents amounting to less
than a nA, and hence the op amp needs to have low voltage noise and low input bias current. Typical
applications include infra-red (IR) thermometry, thermocouple amplifiers and pH electrode buffers. Figure 64 is
an example of a typical circuit used for measuring IR radiation intensity, often used for estimating the
temperature of an object from a distance. The IR sensor generates a voltage proportional to I, which is the
intensity of the IR radiation falling on it. As shown in Figure 64, K is the constant of proportionality relating the
voltage across the IR sensor (V
IN
) to the radiation intensity, I. The resistances R
A
and R
B
are selected to provide
a high gain to amplify this voltage, while C
F
is added to filter out the high frequency noise.
Figure 64. IR Radiation Sensor
Copyright © 2005–2013, Texas Instruments Incorporated Submit Documentation Feedback 21
Product Folder Links: LMV791 LMV792