AD822
+
V
REF
V
IN1
V
IN2
SINGLE-SUPPLY PROGRAMMABLE GAIN
INSTRUMENTATION AMPLIFIER
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 ±15 V. Using only one AD822 rather
than three separate op amps, this circuit is cost and power efficient.
The 2 pA bias currents of the AD822 FET inputs minimize
offset errors caused by high unbalanced source impedances.
An array of precision thin film resistors sets the in-amp gain to
be either 10 or 100. These resistors are laser trimmed to ratio
match to 0.01% and have a maximum differential TC of 5 ppm/°C.
Table 6. In-Amp Performance
Parameters
CMRR
Common-Mode Voltage Range
3 dB BW
G = 10
G = 100
t
SETTLING
2 V Step
5 V Step
Noise @ f = 1 kHz
G = 10
G = 100
I
SUPPLY
(Total)
V
S
= 3 V, 0 V
74 dB
−0.2 V to +2 V
180 kHz
18 kHz
2 μs
5 μs
270 nV/√Hz
2.2 μV/√Hz
1.10 mA
270 nV/√Hz
2.2 μV/√Hz
1.15 mA
V
S
= ±5 V
80 dB
−5.2 V to +4 V
180 kHz
18 kHz
R1
90kΩ
R2
9kΩ
R3
1kΩ
R4
1kΩ
R5
9kΩ
R6
90kΩ
OHMTEK
PART # 1043
R
P
1kΩ
(G = 10) V
OUT
= (V
IN1
– V
IN2
) 1+
(G = 100) V
OUT
= (V
IN1
– V
IN2
) 1+
(
(
R6
R4 + R5
R5 + R6
R4
)
)
+V
REF
+V
REF
00874-049
Figure 49. A Single-Supply Programmable Instrumentation Amplifier
LOW DROPOUT BIPOLAR BRIDGE DRIVER
The AD822 can be used for driving a 350 Ω Wheatstone bridge.
a 1.235 V low power reference. The output of 4.5 V can
be used to drive an analog-to-digital converter (ADC) front end.
The other half of the AD822 is configured as a unity-gain inverter
and generates the other bridge input of −4.5 V. Resistor R1 and
Resistor R2 provide a constant current for bridge excitation. The
low power instrumentation amplifier is used to condition
the differential output voltage of the bridge. The gain of the AD620
is programmed using an external resistor R
G
and determined by
5µs
100
90
.... .... .... .... ...
... .... .... .... ....
G
½
49.9 k
R
G
1
V+
49.9kΩ
+1.235V
3
8
10
0%
1/2
+
AD589
AD822
2
–
–
.... .... .... .... .... .... .... .... .... ....
1V
00874-048
+
R1
20Ω
1
TO A/D CONVERTER
REFERENCE INPUT
25.4kΩ 1%
10kΩ 1%
+V
S
350Ω
R
G
3
10kΩ 1%
10kΩ 1%
V–
1μF
–5V
V–
Figure 50. Low Dropout Bipolar Bridge Driver
Rev. I | Page 20 of 24
00874-051
+
5
–
6
1/2
4
AD822
7
–4.5V
R2
20Ω
V+
+
0.1μF
GND
+
0.1μF
+
Figure 48. Pulse Response of In-Amp to a 500 mV p-p Input Signal;
V
S
= 5 V, 0 V; Gain = 0
350Ω
350Ω
–
350Ω
2
7
6
AD620
5
4
V
REF
–V
S
+
+
+5V
1μF
–
+
+
3
AD822
5
AD822
4
+
R
P
1kΩ
1/2
1
–
–
–
G = 10
V+
0.1µF
2
6
G = 100
G = 100
G = 10
1/2
7
V
OUT
AD [ ANALOG DEVICES ]
