Datasheet

LT1996
16
1996f
Figure 10. Difference Amplifier Using the LT1996. Gain Is Set
Simply by Connecting the Correct Resistors or Combinations of
Resistors. Gain of 27 Is Shown, with Dashed Lines Modifying It
to Gain of 2.7. Noise Gain Is Optimal
Difference Amplifiers
The resistors in the LT1996 allow it to easily make differ-
ence amplifiers also. Figure 10 shows the basic 4-resistor
difference amplifier and the LT1996. A difference gain of
27 is shown, but notice the effect of the additional dashed
connections. By connecting the 50k resistors in parallel,
the gain is reduced by a factor of 10. Of course, with so
many resistors, there are many possible gains. Table 4
shows the difference gains and how they are achieved.
Note that, as for inverting amplifiers, the noise gain is 1
more than the signal gain.
Table 4. Connections Giving Difference Gains for the LT1996
Gain V
IN
+
V
IN
–
Output GND (REF)
0.083 P9 M9 M27, M81 P27, P81
0.110 P9 M9 M81 P81
0.297 P27 M27 M9, M81 P9, P81
0.321 P9 M9 M27 P27
0.329 P27 M27 M81 P81
0.439 P9, P27 M9, M27 M81 P81
2.189 P81 M81 M9, M27 P9, P27
2.700 P27 M27 M9 P9
2.893 P81 M81 M27 P27
3.214 P9, P81 M9, M81 M27 P27
8.1 P81 M81 M9 P9
9 P9 M9
10.8 P27, P81 M27, M81 M9 P9
27 P27 M27
36 P9, P27 M9, M27
81 P81 M81
90 P9, P81 M9, M81
108 P27, P81 M27, M81
117 P9, P27, P81 M9, M27, M81
APPLICATIO S I FOR ATIO
WUU
U
4pF
4pF
–
+
R
F
R
G
R
G
V
IN
+
V
IN
+
V
IN
–
V
IN
–
V
OUT
V
OUT
V
OUT
= GAIN • (V
IN
+
– V
IN
–
)
GAIN = R
F
/R
G
–
+
1996 F10
450k
450k
8
6
5
9
10
1
2
3
LT1996
CLASSICAL DIFFERENCE AMPLIFIER USING THE LT1991
CLASSICAL DIFFERENCE AMPLIFIER IMPLEMENTED
WITH LT1991. R
F
= 450k, R
G
= 16.7k, GAIN = 3.
ADDING THE DASHED CONNECTIONS CONNECTS THE
TWO 450k RESISTOR IN PARALLEL, SO R
F
IS REDUCED
TO 45k. GAIN BECOMES 45k/16.7k = 2.7.
R
F
PARALLEL
TO CHANGE
R
F
, R
G
450k/81
450k/27
450k/9
450k/81
450k/27
450k/9
4pF
4pF