Datasheet
16
LT1995
1995fb
Using the LT1995 as an AC-coupled inverting gain stage,
the REF pin and the relevant P inputs may all be driven from
a V
BIAS
source as depicted in the example of Figure 6, thus
establishing the quiescent voltage on the input and output
pins. The V
BIAS
signal will only have to source the bias
current (I
B
) of the noninverting input of the internal op amp
(0.6µA typically), so a high V
BIAS
source impedance (R
S
)
will cause the quiescent level of the amplifier output to
deviate from the intended V
BIAS
level by I
B
• R
S
.
In operation as a noninverting gain stage, the P and REF
inputs may be configured as a “supply splitter,” thereby
providing a convenient mid-supply operating point. Fig-
ure 7 illustrates the three attenuation configurations that
generate 50% mid-supply biasing levels with no external
components aside from the desired coupling capacitors.
As with the DC-coupled input attenuation ratios, A, a
compound output function including the feedback gain
parameter G is given by:
V
OUT
= A • G • V
IN
APPLICATIO S I FOR ATIO
WUUU
M4
M2
M1
P1
P2
P4
8
9
10
1
2
3
V
OUT
C
OUT
V
BIAS
V
IN
–
+V
6
4
5
1995 F06
7
LT1995
REF
C
IN
Figure 6. AC-Coupled Inverting Gain Amplifier
General Configuration (G = 5 Example)
M4
M2
M1
P1
P2
P4
8
9
10
1
2
3
V
OUT
C
OUT
C
IN
V
IN
*
+V
6
4
*CONFIGURE M INPUTS FOR DESIRED G PARAMETER; REFER TO FIGURE 2 FOR CONNECTIONS. ANY M
INPUTS SHOWN GROUNDED IN FIGURE 2 SHOULD INSTEAD BE CAPACITIVELY COUPLED TO GROUND
5
7
LT1995
A = 0.750
REF
M4
M2
M1
P1
P2
P4
8
9
10
1
2
3
V
OUT
1995 F07
C
OUT
C
IN
V
IN
*
+V
6
4
5
7
LT1995
A = 0.500
REF
M4
M2
M1
P1
P2
P4
8
9
10
1
2
3
V
OUT
C
OUT
C
IN
V
IN
*
+V
6
4
5
7
LT1995
A = 0.667
REF
Figure 7. AC-Coupled Noninverting Amplifier Input Attenuation Configurations (Supply Splitting)
M4
M2
M1
P1
P2
P4
8
9
10
1
2
3
V
OUT
C
OUT
V
BIAS
V
IN
+
V
IN
–
+V
6
4
5
1995 F05
7
LT1995
REF
C
IN
C
IN
Figure 5. AC-Coupled Difference Amplifier
General Configuation (G = 5 Example)