Datasheet

AD822
REV. A
–15–
APPLICATIONS
Single Supply Voltage-to-Frequency Converter
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.
2
6
53
4
+10V
0.1µF
C5
R
SCALE
**
10k
R1
499k, 1%
V
IN
R2
499k, 1%
0V TO 2.5V
FULL SCALE
C1
0.01µF, 2%
C2
0.01µF, 2%
U4
REF-02
U1
43
U3B
21
U3A
C6
390pF
5%
C3
0.1µF
THR
TR
DIS
RV+
OUT
CV
GND
48
6
2
7
1
3
5
(NPO)
C4
0.01µF
R3*
116k
U2
CMOS 555
OUT2
OUT1
NOTES:
f
OUT
= V
IN
/(VREF*t
1
), t
1
= 1.1*R3*C6
* = 1% METAL FILM, <50ppm/°C TC
** = 10%, 20T FILM, <100ppm/°C TC
t
1
= 33µs FOR f
OUT
= 20kHz @ V
IN
= 2.0V
= 25kHz f
S
AS SHOWN.
V
REF
= 5V
CMOS
74HCO4
1/2
AD822B
Figure 44. Single Supply Voltage-to-Frequency Converter
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
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.
Table I. AD822 In Amp Performance
Parameters V
S
= 3 V, 0 V V
S
= 65 V
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 = 10 180 kHz 180 kHz
G = 100 18 kHz 18 kHz
t
SETTLING
2 V Step (V
S
= 0 V, 3 V) 2 µs
5 V (V
S
= ±5 V) 5 µs
Noise @ f = 1 kHz, G = 10 270 nV/√
Hz 270 nV/√Hz
G = 100 2.2 µV/√
Hz 2.2 µV/√Hz
I
SUPPLY
(Total) 1.10 mA 1.15 mA
10
90
100
0%
5µs
1V
Figure 45a. Pulse Response of In Amp to a 500 mV p-p
Input Signal; V
S
= +5 V, 0 V; Gain = 10
(G =10) V
OUT
= (V
IN1
–V
IN2
) (1+ ) +V
REF
R6
R4 + R5
(G =100) V
OUT
= (V
IN1
–V
IN2
) (1+ ) +V
REF
FOR R1 = R6, R2 = R5, AND R3 = R4
R5 + R6
R4
R1 R2 R3 R4 R5 R6
90k9k1k1k9k90k
V
OUT
V
IN1
0.1µF
8
1/2
AD822
1/2
AD822
V
IN2
R
P
1kΩ
1
2
3
6
5
4
7
OHMTEK
PART # 1043
V
REF
G =10 G =100
R
P
1kΩ
G =100 G =10
+V
S
Figure 45b. A Single Supply Programmable
Instrumentation Amplifier