AD822
APPLICATIONS
SINGLE-SUPPLY VOLTAGE-TO-FREQUENCY
CONVERTER
The circuit shown in Figure 47 uses the AD822 to drive a low
power timer that produces a stable pulse of width t
1
. The
positive going output pulse is integrated by R1 − C1 and used as
one input to the AD822 that is connected as a differential
integrator. The other input (nonloading) is the unknown
voltage, V
IN
. The AD822 output drives the timer trigger input,
closing the overall feedback loop.
10V
C5
0.1µF
U4
REF02
V
REF
= 5V
R
SCALE
**
10kΩ
CMOS
74HCO4
U3B
3
4
0.01µF, 2%
Table 6. In-Amp Performance
Parameters
CMRR
Common-Mode Voltage
Range
3 dB BW, G = 10
G = 100
t
SETTLING
2 V Step (V
S
= 0 V, 3 V)
5 V (V
S
= ±5 V)
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
270 nV/√Hz
2.2 μV/√Hz
1.10 mA
5 μs
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
2
6
5
3
4
U3A
2
C3
0.1µF
1
U2
CMOS 555
4
6
2
7
R
THR
OUT2
OUT1
100
90
5µs
.... .... .... .... ...
... .... .... .... ....
R2
499kΩ
1%
R1
499kΩ
1%
U1
C1
R3*
116kΩ
8
V+
AD822B
–
+ 1/2
OUT
CV
3
5
TR
DIS
GND
1
V
IN
Figure 47. Single-Supply Voltage-to-Frequency Converter
00874-047
NOTES
1. f
OUT
= V
IN/
(V
REF ×
t
1
), t
1
= 1.1
×
R3
×
C6.
= 25kHz F
S
AS SHOWN.
2. *
= 1% METAL FILM <50ppm/°C TC.
3. **
= 10% 20T FILM <100ppm/°C TC.
4. t
1
= 33µF FOR f
OUT
= 20kHz @ V
IN
= 2.0V.
Figure 48. Pulse Response of In-Amp to a 500 mV p-p Input Signal; V
S
= 5 V,
0 V; Gain = 0
R1
90kΩ
R2
9kΩ
R3
1kΩ
R4
1kΩ
R5
9kΩ
R6
90kΩ
OHMTEK
PART # 1043
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 AD822 FET inputs’ 2 pA bias currents
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.
V
IN2
R
P
1kΩ
(G = 10) V
OUT
= (V
IN1
– V
IN2
) 1+
(G = 100) V
OUT
= (V
IN1
– V
IN2
) 1+
R5 + R6
R4
+V
REF
Figure 49. A Single-Supply Programmable Instrumentation Amplifier
Rev. G | Page 22 of 28
00874-049
(
(
R6
R4 + R5
)
)
+V
REF
–
V
IN1
+
+
3
AD822
5
AD822
4
+
R
P
1kΩ
1/2
1
–
–
SINGLE-SUPPLY PROGRAMMABLE GAIN
INSTRUMENTATION AMPLIFIER
–
Typical AD822 bias currents of 2 pA allow MΩ range source
impedances with negligible dc errors. Linearity errors on the
order of 0.01% full scale can be achieved with this circuit. This
performance is obtained with a 5 V single supply that delivers
less than 1 mA to the entire circuit.
V
REF
G = 10
G = 100
+V
S
G = 100
G = 10
2
0.1µF
6
1/2
7
V
OUT
00874-048
C2
0.01µF
2%
0V TO 2.5V
FULL SCALE
C4
0.01µF
10
0%
.... .... .... .... .... .... .... .... .... ....
1V
+
AD [ ANALOG DEVICES ]
