AD822
APPLICATIONS
SINGLE-SUPPLY VOLTAGE-TO-FREQUENCY
CONVERTER
Table 6. In-Amp Performance
Parameters
VS = 3 V, 0 V
VS = 5 V
CMRR
74 dB
80 dB
The circuit shown in Figure 47 uses the AD822 to drive a low
power timer that produces a stable pulse of width t1. 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, VIN. The AD822 output drives the timer trigger input,
closing the overall feedback loop.
Common-Mode Voltage
Range
3 dB BW, G = 10
G = 100
−0.2 V to +2 V
180 kHz
18 kHz
−5.2 V to +4 V
180 kHz
18 kHz
tSETTLING
2 V Step (VS = 0 V, 3 V)
5 V (VS = 5 V)
Noise @ f = 1 kHz, G = 10
G = 100
2 μs
5 μs
10V
270 nV/√Hz
2.2 μV/√Hz
1.10 mA
270 nV/√Hz
2.2 μV/√Hz
1.15 mA
U4
REF02
= 5V
C5
0.1µF
ISUPPLY (Total)
V
REF
2
4
6
5
CMOS
74HCO4
OUT2
OUT1
R
**
C3
0.1µF
3
SCALE
10kΩ
U3A
2
U3B
5µs
3
1
4
U2
CMOS 555
100 . . . . . . . .
. . . .
. . . . . . . . . . . .
. . . . . . . . . . .
. . .
R2
499kΩ
1%
0.01µF, 2%
C1
90
8
4
R3*
116kΩ
U1
R
V+
6
3
THR
+
OUT
CV
R1
1/2
2
7
499kΩ
1%
TR
AD822B
5
V
–
DIS
IN
GND
C2
0.01µF
2%
1
10
C4
0.01µF
. . . . . . . . . . . . . . . .
. . . . . . . . . . . .
. . . .
. . . . . . . .
0%
0V TO 2.5V
FULL SCALE
1V
NOTES
1. f
= V /(V × t ), t = 1.1 × R3 × C6.
IN REF 1 1
OUT
= 25kHz F AS SHOWN.
= 1% METAL FILM <50ppm/°C TC.
= 10% 20T FILM <100ppm/°C TC.
S
Figure 48. Pulse Response of In-Amp to a 500 mV p-p Input Signal; VS = 5 V,
0 V; Gain = 0
2. *
3. **
4. t
= 33µF FOR f
= 20kHz @ V = 2.0V.
1
OUT
IN
Figure 47. Single-Supply Voltage-to-Frequency Converter
OHMTEK
PART # 1043
R1
90kΩ
R2
9kΩ
R3
1kΩ
R4
1kΩ
R5
9kΩ
R6
90kΩ
+
–
V
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.
REF
G = 10
G = 100
G = 100
G = 10
+V
S
0.1µF
1
2
3
6
5
–
–
SINGLE-SUPPLY PROGRAMMABLE GAIN
INSTRUMENTATION AMPLIFIER
1/2
AD822
1/2
7
+
–
R
P
AD822
1kΩ
+
+
V
OUT
V
V
IN1
4
R
P
1kΩ
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.
IN2
R6
(G = 10) V
OUT
= (V
– V
IN2
)
+V
1+
IN1
REF
(
)
)
R4 + R5
R5 + R6
R4
(G = 100) V
OUT
= (V
IN1
– V
IN2
)
+V
REF
1+
(
Figure 49. A Single-Supply Programmable Instrumentation Amplifier
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.
Rev. G | Page 22 of 28
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