LTC1992 Family
37
1992fb
Figure 7. Asymmetrical Feedback Application Circuits (Most Suitable in Applications with Dual,
Split Supplies (e.g., ±5V), Ground Referenced Single-Ended Input Signals and V
OCM
Connected to Ground)
once the V
OCM
voltage is set to zero, the gain formula is the
same as a standard noninverting op amp circuit multiplied
by two to account for the complementary output. Taking
R
FB
to zero (i.e., taking β to one) gives the same formula
as the top circuit. As in the top circuit, this circuit is also
useful as a single-ended output, high input impedance
inverting gain block (this time with gain). The input com-
mon mode considerations are similar to the top circuit’s,
but are not nearly as constrained since there is now gain
in the noninverting amplifier path. This circuit, with V
OCM
at ground, also permits a rail-to-rail output swing in most
applications.
The bottom circuit is another circuit that utilizes a standard
op amp configuration with a complementary output. In this
case, the standard op amp circuit has an inverting con-
figuration. With V
OCM
at zero volts, the gain formula is the
same as a standard inverting op amp circuit multiplied by
two to account for the complementary output. This circuit
does not have any common mode level constraints as the
inverting input voltage sets the input common mode level.
This circuit also delivers rail-to-rail output voltage swing
without any concerns.
APPLICATIONS INFORMATION
–
–
+
+
+V
OUT
V
OUTDIFF
= 2(+V
IN
– V
OCM
)
SETTING V
OCM
= 0V
V
OUTDIFF
= 2V
IN
–V
OUT
V
IN
V
OCM
V
OCM
LTC1992
–
–
+
+
+V
OUT
R
FB
R
IN
V
OUTDIFF
= 2
SETTING V
OCM
= 0V
V
OUTDIFF
= 2V
IN
–V
OUT
V
IN
V
OCM
R
IN
R
FB
()
+V
IN
; B =
= 2V
IN
1 +
– V
OCM
1
B
()
1
B
()
R
IN
R
IN
+ R
FB
R
FB
R
IN
–
–
+
+
+V
OUT
V
OUTDIFF
= 2
SETTING V
OCM
= 0V
V
OUTDIFF
= 2V
IN
–V
OUT
1992 F07
V
IN
V
OCM
()
+V
IN
; B =
= 2V
IN
+ V
OCM
1 – B
B
()
1 – B
B
()
R
IN
R
IN
+ R
FB
R
FB
R
IN
V
OCM
LTC1992
V
OCM
LTC1992
