LT1996 Linear Technology, LT1996 Datasheet - Page 16

• Manufacturer Part Number: LT1996
• Description: 100uA Gain Selectable Amplifier
• Manufacturer: Linear Technology

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LT1996
APPLICATIO S I FOR ATIO
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
16
4
0.083
0.110
0.321
0.297
0.329
0.439
2.189
2.700
2.893
3.214
Gain
10.8
108
117
8.1
27
36
81
90
9
P9, P27, P81 M9, M27, M81
P27, P81
P27, P81
P9, P27
P9, P81
P9, P27
P9, P81
V
P27
P27
P81
P27
P81
P81
P27
P81
P9
P9
P9
P9
IN
+
U
M27, M81
M27, M81
M9, M27
M9, M81
M9, M27
M9, M81
U
V
M27
M27
M81
M27
M81
M81
M27
M81
M9
M9
M9
M9
IN
–
W
M27, M81
M9, M81
M9, M27
Output
M81
M27
M81
M81
M27
M27
M9
M9
M9
U
GND (REF)
P27, P81
P9, P81
P9, P27
P81
P27
P81
P81
P27
P27
P9
P9
P9
TO CHANGE
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
PARALLEL
R
F
, R
V
V
IN
G
IN
–
+
CLASSICAL DIFFERENCE AMPLIFIER IMPLEMENTED
WITH LT1991. R
ADDING THE DASHED CONNECTIONS CONNECTS THE
TWO 450k RESISTOR IN PARALLEL, SO R
TO 45k. GAIN BECOMES 45k/16.7k = 2.7.
CLASSICAL DIFFERENCE AMPLIFIER USING THE LT1991
V
V
IN
IN
10
8
9
1
2
3
–
+
450k/81
450k/27
450k/27
450k/81
450k/9
R
R
450k/9
G
G
F
= 450k, R
–
+
G
R
R
= 16.7k, GAIN = 3.
–
+
F
F
V
GAIN = R
450k
450k
OUT
4pF
4pF
4pF
4pF
= GAIN • (V
F
F
IS REDUCED
/R
LT1996
G
V
OUT
IN
+
– V
5
6
IN
–
)
V
1996 F10
1996f
OUT