LT1991 Linear Technology, LT1991 Datasheet - Page 16

• Manufacturer Part Number: LT1991
• Description: Precision / 100uA Gain Selectable Amplifier
• Manufacturer: Linear Technology

APPLICATIONS INFORMATION
LT1991
Inverting Confi guration
The inverting amplifi er, shown in Figure 8, is another
classical op amp confi guration. The circuit is actually
identical to the noninverting amplifi er of Figure 4, except
that V
able gains is shown in Table 3, and some of the circuits
are shown in Figure 9. Noise gain is 1+|Gain|, as is the
usual case for inverting amplifi ers. Again, for the best DC
performance, match the source impedance seen by the
op amp inputs.
16
(DRIVE)
V
Figure 8. The LT1991 as a Classical Inverting Op Amp.
Note the Circuit Is Identical to the Noninverting Amplifi er,
Except that V
IN
IN
and GND have been swapped. The list of avail-
CLASSICAL INVERTING OP AMP CONFIGURATION IMPLEMENTED
WITH LT1991. R
GAIN IS ACHIEVED BY GROUNDING, FLOATING OR FEEDING BACK
THE AVAILABLE RESISTORS TO ARRIVE AT DESIRED R
WE PROVIDE YOU WITH <0.1% RESISTORS.
V
IN
10
8
9
1
2
3
CLASSICAL INVERTING OP AMP CONFIGURATION.
YOU PROVIDE THE RESISTORS.
IN
R
150k
450k
450k
150k
50k
50k
and Ground Have Been Swapped.
G
F
= 225k, R
–
+
G
450k
= 50k, GAIN = –4.5.
R
–
+
F
4pF
V
GAIN = – R
450k
4pF
OUT
5
= GAIN • V
F
LT1991
/R
V
G
OUT
IN
F
6
AND R
G
1991 F08
V
.
OUT
Table 3. Confi guring the M Pins for Simple Inverting Gains
–0.077
–0.273
–0.25
–2.25
Gain
–0.1
–0.3
–0.4
–1.5
–1.8
–2.5
–4.5
–10
–12
–13
–1
–3
–4
–6
–9
Output
Output
Output
Output
Output
Drive
Drive
Drive
Drive
Drive
Drive
Drive
Drive
Drive
Float
Float
Float
Float
Float
M9
M9, M3, M1 Connection
Output
Output
Output
Output
Output
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Drive
Drive
Drive
Drive
Drive
Drive
Drive
Drive
Drive
Float
Float
Float
Float
Float
M3
Output
Output
Output
Output
Output
Drive
Drive
Drive
Drive
Drive
Drive
Drive
Drive
Drive
Float
Float
Float
Float
Float
M1
1991fg