Datasheet

REV. C
AD824
–12–
APPLICATIONS
Single Supply Voltage-to-Frequency Converter
The circuit shown in Figure 4 uses the AD824 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 AD824, which is connected as a differential
integrator. The other input (nonloading) is the unknown voltage,
V
IN
. The AD824 output drives the timer trigger input, closing
the overall feedback loop.
1/4
AD824
C5
0.1F
NOTES
f
OUT
= V
IN
/(VREF  t
1
), t
1
= 1.1  R3  C6
= 25kHz f
S
AS SHOWN.
* = 1% METAL FILM, <50ppm/C TC
** = 10%, 20T FILM, <100ppm/C TC
t
1
= 33s FOR f
OUT
= 20kHz @ V
IN
= 2.0V
U4
REF02
2
6
5
4
3
V
REF
= 5V
R
SCALE
**
10k
CMOS
74HCO4
4
U3B U3A
32 1
C3
0.1F
OUT2
OUT1
10V
R2
499k, 1%
U1
0.01F, 2 %
C1
R3*
116k
2
6
5
3
7
1
48
U2
CMOS 555
TR
THR
DIS
CV
OUT
RV+
GND
C4
0.1F
C6
390pF
5%
(NPO)
C2
0.01F, 2 %
R1
499k, 1%
0V TO 2.5V
FULL SCALE
Figure 4. Single Supply Voltage-to-Frequency Converter
Typical AD824 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 V single supply, which
delivers less than 3 mA to the entire circuit.
Single Supply Programmable Gain Instrumentation Amplifier
The AD824 can be configured as a single supply instrumenta-
tion amplifier that is able to operate from single supplies down
to 5 V or dual supplies up to ±15 V. AD824 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. AD824 In Amp Performance
Parameters V
S
= 3 V, 0 V V
S
= 5 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 ms
5 V (V
S
= ±5 V) 5 ms
Noise @ f = 1 kHz, G = 10 270 nV/÷Hz 270 nV/÷Hz
G = 100 2.2 mV/÷Hz 2.2 mV/÷Hz
10
0%
100
90
1V
5µs
Figure 5a. Pulse Response of In Amp to a 500 mV p-p
Input Signal; V
S
= 5 V, 0 V; Gain = 10
V
REF
V
OUT
V
IN1
V
IN2
0.1F
+V
S
R1
90k
R2
9k
R3
1k
R4
1k
R5
9k
R6
90k
G = 10 G = 100 G = 10G = 100
OHMTEK
PA R T # 1043
1/4
AD824
2
1
3
6
7
5
R
P
1k
R
P
1k
11
(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
R5 + R6
R4
FOR R1 = R6, R2 = R5 AND R3 = R4
1/4
AD824
Figure 5b. A Single Supply Programmable
Instrumentation Amplifier