Datasheet

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