AD824
APPLICATIONS
Table I. AD824 In Amp Performance
VS = 3 V, 0 V VS = ꢂ5 V
74 dB 80 dB
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 t1. 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,
VIN. The AD824 output drives the timer trigger input, closing
the overall feedback loop.
Parameters
CMRR
Common-Mode
Voltage Range
3 dB BW, G = 10
G = 100
–0.2 V to +2 V –5.2 V to +4 V
180 kHz
18 kHz
180 kHz
18 kHz
tSETTLING
2 V Step (VS = 0 V, 3 V)
5 V (VS = ±5 V)
Noise @ f = 1 kHz, G = 10
2 ms
10V
U4
5 ms
270 nV/÷Hz
2.2 mV/÷Hz
REF02
C5
270 nV/÷Hz
0.1ꢀF
2
V
= 5V
G = 100 2.2 mV/÷Hz
REF
6
5
CMOS
R
10kꢃ
**
OUT2
OUT1
3
SCALE
74HCO4
C3
0.1ꢀF
5µs
4
U3B
U3A
2
4
3
1
100
90
U2
CMOS 555
0.01ꢀF, 2%
4
8
R2
U1
R3*
C1
R
V+
499kꢃ, 1%
116kꢃ
6
THR
OUT
3
5
1/4
2
7
TR
10
AD824
R1
CV
0%
DIS
499kꢃ, 1%
C6
390pF
5%
1V
GND
0VTO 2.5V
1
C4
FULL SCALE
(NPO)
C2
0.1ꢀF
Figure 5a. Pulse Response of In Amp to a 500 mV p-p
Input Signal; VS = 5 V, 0 V; Gain = 10
0.01ꢀF, 2%
NOTES
=V /(VREF ꢄ t1), t1 = 1.1 ꢄ R3 ꢄ C6
f
OUT
IN
= 25kHz f AS SHOWN.
S
R1
R2
R3
R4
R5
R6
OHMTEK
* = 1% METAL FILM, <50ppm/ꢁC TC
** = 10%, 20T FILM, <100ppm/ꢁC TC
PART # 1043
V
90kꢃ
9kꢃ
1kꢃ
1kꢃ
9kꢃ
90kꢃ
REF
t1 = 33ꢀs FOR f
= 20kHz @V = 2.0V
IN
OUT
G = 10
G = 100
G = 100
G = 10
Figure 4. Single Supply Voltage-to-Frequency Converter
+V
S
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.
0.1ꢀF
2
3
6
1/4
1
1/4
AD824
7
AD824
R
P
V
V
5
OUT
IN1
11
1kꢃ
R
P
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.
V
IN2
1kꢃ
R6
R4 + R5
(G = 10)V
= (V
IN1
–V ) (1+
IN2
) +V
REF
OUT
R5 + R6
R4
(G = 100)V
= (V
IN1
–V ) (1+
IN2
) +V
REF
OUT
FOR R1 = R6, R2 = R5 AND R3 = R4
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.
Figure 5b. A Single Supply Programmable
Instrumentation Amplifier
–12–
REV. C
ADI [ ADI ]
