AD822
SINGLE-SUPPLY PROGRAMMABLE GAIN
INSTRUMENTATION AMPLIFIER
OHMTEK
PART # 1043
R1
90kΩ
R2
9kΩ
R3
1kΩ
R4
1kΩ
R5
9kΩ
R6
90kΩ
+
–
V
REF
The AD822 can be configured as a single-supply instrumenta-
tion amplifier that is able to operate from single supplies down
to 3 V or dual supplies up to ±±5 Vꢀ Using only one AD822 rather
than three separate op amps, this circuit is cost and power efficientꢀ
The 2 pA bias currents of the AD822 FET inputs minimize
offset errors caused by high unbalanced source impedancesꢀ
G = 10
G = 100
G = 100
G = 10
V+
0.1µF
2
3
6
5
–
–
1/2
AD822
1/2
7
+
–
1
R
P
An array of precision thin film resistors sets the in-amp gain to
be either ±0 or ±00ꢀ These resistors are laser trimmed to ratio
match to 0ꢀ0±% and have a maximum differential TC of 5 ppm/°Cꢀ
AD822
1kΩ
+
+
V
OUT
V
V
IN1
4
R
P
1kΩ
IN2
R6
R4 + R5
Table 6. In-Amp Performance
Parameters
(G = 10) V
OUT
= (V
IN1
– V
IN2
)
+V
1+
REF
(
)
VS = 3 V, 0 V
VS = 5 V
R5 + R6
R4
(G = 100) V
OUT
= (V
IN1
– V
IN2
)
+V
REF
1+
(
)
CMRR
74 dB
80 dB
Common-Mode Voltage Range −0.2 V to +2 V −5.2 V to +4 V
3 dB BW
G = 10
G = 100
tSETTLING
2 V Step
5 V Step
Noise @ f = 1 kHz
G = 10
G = 100
ISUPPLY (Total)
Figure 49. A Single-Supply Programmable Instrumentation Amplifier
LOW DROPOUT BIPOLAR BRIDGE DRIVER
180 kHz
18 kHz
180 kHz
18 kHz
The AD822 can be used for driving a 350 Ω Wheatstone bridgeꢀ
Figure 50 shows one-half of the AD822 being used to buffer the
AD589, a ±ꢀ235 V low power referenceꢀ The output of 4ꢀ5 V can
be used to drive an analog-to-digital converter (ADC) front endꢀ
The other half of the AD822 is configured as a unity-gain inverter
and generates the other bridge input of −4ꢀ5 Vꢀ Resistor R± and
Resistor R2 provide a constant current for bridge excitationꢀ The
AD620 low power instrumentation amplifier is used to condition
the differential output voltage of the bridgeꢀ The gain of the AD620
is programmed using an external resistor RG and determined by
2 μs
5 μs
270 nV/√Hz
2.2 μV/√Hz
1.10 mA
270 nV/√Hz
2.2 μV/√Hz
1.15 mA
5µs
49ꢀ9 k
100 . . . . . . . .
. . . .
. . . . . . . . . . . .
. . . . . . . . . . .
. . .
G
±
RG
90
V+
49.9kꢀ
+1.235V
+
8
R1
20ꢀ
3
+
1/2
AD822
1
TO A/D CONVERTER
REFERENCE INPUT
AD589
2
–
–
10
. . . . . . . . . . . . . . . .
. . . . . . . . . . . .
. . . .
. . . . . . . .
+V
S
0%
25.4kꢀ 1%
10kꢀ 1%
350ꢀ
1V
7
350ꢀ
350ꢀ
2
3
–
6
R
AD620
350ꢀ
G
Figure 48. Pulse Response of In-Amp to a 500 mV p-p Input Signal;
VS = 5 V, 0 V; Gain = 0
+
5
4
10kꢀ 1%
V
REF
–V
S
6
5
–
1/2
7
10kꢀ 1%
V+
0.1μF
GND
0.1μF
V–
+5V
–5V
–4.5V
+
+
+
AD822
1μF
1μF
+
4
R2
20ꢀ
+
V–
Figure 50. Low Dropout Bipolar Bridge Driver
Rev. I | Page 20 of 24
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