Figure 6 shows an active control loop that adjusts the output
offset voltage to zero. A
2
, R, and C form an integrator that
produces an offsetting voltage applied to one input of the
INA103. This produces a –6dB/octave low frequency roll-
off like the capacitor input coupling in Figure 5.
COMMON-MODE INPUT RANGE
For proper operation, the combined differential input signal
and common-mode input voltage must not cause the input
amplifiers to exceed their output swing limits. The linear
input range is shown in the typical performance curve
“Maximum Common-Mode Voltage vs Output Voltage.”
For a given total gain, the input common-mode range can be
increased by reducing the input stage gain and increasing the
output stage gain with the circuit shown in Figure 7.
OUTPUT SENSE
An output sense terminal allows greater gain accuracy in
driving the load. By connecting the sense connection at the
load, I•R voltage loss to the load is included inside the
feedback loop. Current drive can be increased by connect-
ing a current booster inside the feedback loop as shown in
Figure 11.
I
B–
≈
I
B+
≈
2.5µA
16
15
13
∆
V
IN
14
6
2
1
OPA27
INA103
11
7
10
Gain = 1V/V
(0dB)
–In
I
B–
16
15
13
Gain = 100V/V
(40dB)
V
OUT
V+
100µA
(1)
11
INA103
7
10
V
OUT
14
6
–
+
10kΩ
150Ω
+In
(1)
50kΩ
I
B+
2
1
Offset Adjustment
Range = ±15mV
100µA
(1)
NOTE: (1)
1/2 REF200
150Ω
50kΩ
100kΩ
(1)
(1)
NOTE: (1) 50k
Ω
R, 100k
Ω
pot is
max recommended value. Use
smaller values in this ratio if possible.
V–
FIGURE 4. Output Offsetting.
FIGURE 5. Input Offset Adjustment for AC-Coupled Inputs.
16
–In
15
13
14
6
2
+In
100kΩ
(1)
Gain = 100V/V
(40dB)
11
INA103
7
C
1µF
(1)
f
–3dB
=
10
V
OUT
R
100kΩ
Gain
12π RC
1
100kΩ
10kΩ
A
2
1/2 OPA1013
–
+
2kΩ
NOTE: (1) 100k
Ω
is max recommended
value. Use smaller value if possible.
FIGURE 6. Automatic DC Restoration.
®
INA103
10
BURR-BROWN [ BURR-BROWN CORPORATION ]
