TS615 ST Microelectronics, Inc., TS615 Datasheet - Page 24

• Manufacturer Part Number: TS615
• Description: Dual Wide Band Operational Amplifier
• Manufacturer: ST Microelectronics, Inc.

TS615
CHOICE OF THE FEEDBACK CIRCUIT
Table 71 : Closed-Loop Gain - Feedback Compo-
nents
INVERTING AMPLIFIER BIASING
In this case a resistance is necessary to achieve a
good input biasing, as R on (fig.30).
This resistance is calculated by assuming the neg-
ative and positive input bias current. The aim is to
make the compensation of the offset bias current
which could affect the input offset voltage and the
output DC component. Assuming Ib-, Ib+, R
and a zero volt output, the resistance R comes: R
= R
Figure 72 : Compensation of the Input Bias
Current
24/27
Ib-
Ib-
in
// R
fb
R
R
V
±2.5
Ib+
Ib+
CC
.
in
in
±6
(V)
R
R
_
_
+
+
TS615
TS615
Gain
+1
+2
+4
+8
+1
+2
+4
+8
-1
-2
-4
-8
-1
-2
-4
-8
R
R
Vcc+
Vcc+
Vcc-
Vcc-
fb
fb
R
Output
Output
1.1k
fb
750
680
620
510
680
680
620
510
910
680
910
680
1k
1k
1k
( )
Load
Load
in
, R
fb
ACTIVE FILTERING
Figure 73 : Low-Pass Active Filtering. Sallen-Key
The resistors R
the filter as a classical non-inverting amplification
configuration :
Assuming the following expression as the re-
sponse of the system:
the cutoff frequency is not gain dependent and it
comes:
the damping factor comes:
The higher the gain the more sensitive the damp-
ing factor is. When the gain is higher than 1 it is
preferable to use some very stable resistors and
capacitors values.
In the case of R1=R2:
IN
IN
=
R
R
1
1
T
1
-- - c C 1 R 1
2
j
=
Vout
-------------------
fb
R
R
Vin
A V
2
2
c
and R
=
=
j
=
j
+
2C
----------------------------------- -
R
R
------------------------------------- -
C 1 R 2
G
G
g
C
C
2 C 1 C 2
R1R2C 1C2
C
C
=
2
1
1
G
2
2
=
–
---------------------------------------------
1
give directly the gain of
1
C
+
1
+
+
+
_
_
+
1
2
C 2 R 1 C 1 R 1 g
R fb
--------- -
R
--------- -
R
TS615
TS615
R g
------ -
j
910
910
fb
g
R
R
g
c
fb
fb
+
–
------------- -
j
c
2
2
OUT
OUT
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