AD822
APPLICATIONS
Single Supply Voltage-to-Frequency Converter
Table I. AD822 In Amp Performance
The circuit shown in Figure 44 uses the AD822 to drive a low
power timer, which 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, which 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
REF-02
2
6 V
REF
= 5V
5
4
4
R
SCALE
**
10k
CMOS
74HCO4
U3B
3
U3A
2
1
U2
CMOS 555
R3
*
116k
4
6
2
7
C6
390pF
5%
(NPO)
NOTES:
f
OUT
= V
IN
/(VREF*t
1
), t
1
= 1.1*R3*C6
= 25kHz f
S
AS SHOWN.
R
THR
TR
DIS
GND
1
CV
8
V+
OUT
3
5
OUT2
C3
0.1µF
OUT1
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
V
S
=
80 dB
5V
–0.2 V to +2 V –5.2 V to +4 V
180 kHz
180 kHz
18 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
3
5µs
100
90
0.01µF, 2%
R2
499k, 1%
U1
1/2
AD822B
C1
R1
V
IN
499k, 1%
0V TO 2.5V
FULL SCALE
C2
0.01µF, 2%
C4
0.01µF
10
0%
1V
*
= 1% METAL FILM, <50ppm/
°
C TC
**
= 10%, 20T FILM, <100ppm/
°
C TC
t
1
= 33µs FOR f
OUT
= 20kHz @ V
IN
= 2.0V
Figure 45a. Pulse Response of In Amp to a 500 mV p-p
Input Signal; V
S
= +5 V, 0 V; Gain = 10
Figure 44. Single Supply Voltage-to-Frequency Converter
R1
V
REF
90k
R2
9k
R3
1k
R4
1k
R5
9k
R6
90k
OHMTEK
PART # 1043
Typical AD822 bias currents of 2 pA allow megaohm-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 volt single supply which
delivers less than 1 mA to the entire circuit.
Single Supply Programmable Gain Instrumentation Amplifier
G =10
+V
S
G =100
G =100
G =10
0.1µF
2
R
P
1kΩ
V
IN2
1kΩ
(G =10)
(G =100)
R6
V
OUT
= (V
IN1
–V
IN2
) (1+
) +V
REF
R4 + R5
V
OUT
= (V
IN1
–V
IN2
) (1+
R5 + R6
) +V
REF
R4
R
P
6
1
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. 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
IN1
1/2
8
3
AD822
1/2
5
AD822
4
7
V
OUT
FOR R1 = R6, R2 = R5, AND R3 = R4
Figure 45b. A Single Supply Programmable
Instrumentation Amplifier
REV. A
–15–
AD [ ANALOG DEVICES ]
