op22002 Analog Devices, Inc., op22002 Datasheet - Page 8

• Manufacturer Part Number: op22002
• Description: Dual Micropower Operational Amplifier
• Manufacturer: Analog Devices, Inc.

OP220
INSTRUMENTATION AMPLIFIER APPLICATIONS OF
THE OP220
Two Op Amp Configuration
The excellent input characteristics of the OP220 make it ideal for
use in instrumentation amplifier configurations where low-level
differential signals are to be amplified. The low-noise, low input
offsets, low drift, and high gain combined with excellent CMRR
provide the characteristics needed for high-performance instru-
mentation amplifiers. In addition, the power supply current
drain is very low.
The circuit of Figure 4 is recommended for applications where
the common-mode input range is relatively low and differential
gain will be in the range of 10 to 1,000. This two op amp instrumen-
tation amplifier features independent adjustment of common-mode
rejection and differential gain. Input impedance is very high since
both inputs are applied to noninverting op amp inputs.
10k
INPUT
INPUT
Figure 2. Small-Signal Transient Response
Figure 3. Large-Signal Transient Response
100
90
0%
10
100
0%
90
10
OP220
2V
5V
OP220
50mV
20mV
40k
25k
R
25k
2 s
L
200 s
100pF
C
100pF
OUTPUT
L
OUTPUT
–8–
V
The input voltages are represented as a common-mode input
V
to the ratio R2/R, to reject the common-mode input V
differential signal V
Note that gain can be independently varied by adjusting R
From considerations of dynamic range, resistor tempco match-
ing, and matching of amplifier response, it is generally best to
make RX, R2, R3, and R4 approximately equal. Designating
R1, R2, R3, and R4 as RN allows the output equation to be
further simplified:
Dynamic range is limited by A1 as well as A2; the output of A1 is:
If the instrumentation amplifier were designed for a gain of 10
and maximum V
and V
have a maximum output of ± 5 V plus 2 V
±10 V on the output of A1 would imply a limit of ±2.5 V on V
A nominal value of 100 kW for R
tions. A range of 200 W to 25 kW for R
range of 10 to 1,000. The current through R
amplifiers must supply ± 10 mV/200 W when the gain is at the
maximum value of 1,000 and V
Rejecting common-mode inputs is most important in accurately
amplifying low-level differential signals. Two factors determine
the CMR of this instrumentation amplifier configuration (assuming
infinite gain):
1. CMRR of the op amps
2. Matching of the resistor network (R3/R4 = R2/R1)
If
O
CM
R
=
1
V
V
Configuration
V
plus a differential input V
Figure 4. Two Op Amp Instrumentation Amplifier
CM
CM
O
R
R
=
V
O
4
O
– 1/2 V
+ 1/2 V
3
R
would be a maximum of ± 10 V. Amplifier A1 would
=
2
È
Í
Î
=
1
2 1
=
+
Ê
Á
Ë
R
R
D
D
R
V
4
3
1
2
D
+
3
–
+
Ê
Á
Ë
Ê
Á
Ë
D
1
R
=
R
V
R
R
+
of ± 1 V, then R
N
O
R1
R
2
1
D
1
4
R
R
ˆ
˜
¯
+
is then amplified according to:
= -
1/2
OP220
,
4
V
3
then
R
R
D
+
Ê
Á
Ë
4
3
1
, where
ˆ
˜ +
¯
R
A1
R2
+
V
2
O
R
R
R
R0
+
D
R
R3
O
N
O
D
=
. The ratio R3/R4 is made equal
R
2
N
ˆ
˜
¯
R
R
is at ± 10 mV.
2 1
3
+
N
V
is suitable for most applica-
V1
Ê
Á
Ë
0
N
/R
ˆ
˜
¯
D
R
V
+
=
O
3
+
O
D
˘
˙
˚
R
GAIN
ADJ
R
would need to be four
R
will then provide a gain
2
V
, where
1
1
0
CM
V
D
ˆ
˜
¯
=
CM
V
, thus a limit of
+
O
R
R4
D
is V
R
R
2
A2
4
3
R
R
=
1/2
OP220
Ê
Á
Ë
D
4
3
R
/R
R
R
3
=
3
4
O
CM
=
R
R
, so the
-
R
REV. A
2
1
. The
V
R
R
4
O
O
2
1
.
CM
ˆ
˜
¯
V
.
CM