Data Sheet
APPLICATIONS INFORMATION
SINGLE SUPPLY VOLTAGE-TO-FREQUENCY
CONVERTER
The circuit shown in Figure 32 uses the
to drive a low
power timer, which produces a stable pulse of width, t
1
. The
positive going output pulse is integrated by R1 and C1 and used
as one input to the
which is connected as a differential
integrator. The other input (nonloading) is the unknown
voltage, V
IN
. The
output drives the timer trigger input,
closing the overall feedback loop.
10V
C5
0.1µF
U4
REF02
2
6
3
4
5
V
REF
= 5V
R
SCALE
**
10kΩ
CMOS
74HCO4
OUT2
AD824
Table 6.
In Amp Performance
Parameter
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
V
S
= 3 V, 0 V
74 dB
−0.2 V to +2 V
180 kHz
18 kHz
2 μs
5 μs
270 nV/√Hz
2.2 μV/√Hz
270 nV/√Hz
2.2 μV/√Hz
V
S
= ±5 V
80 dB
−5.2 V to +4 V
180 kHz
18 kHz
C3
0.1µF
4
U3B
3
U3A
2
1
U2
CMOS 555
5µs
OUT1
100
90
R2
499kΩ
1%
R1
499kΩ
1%
U1
C1
0.01µF
2%
1/4
R3*
116kΩ
4
R
6 THR
2 TR
8
V+
OUT
CV
3
5
10
0%
00875-033
AD824
C6
390pF
5%
(NPO)
7 DIS
GND
1
0V TO 2.5V
FULL SCALE
C2
0.01µF
2%
C4
0.1µF
1V
Figure 33. Pulse Response of In Amp to a 500 mV p-p Input Signal;
V
S
= 5 V, 0 V; Gain = 10
R1
90kΩ
V
REF
R2
9kΩ
R3
1kΩ
R4
1kΩ
R5
9kΩ
R6
90kΩ
NOTES
f
OUT
= V
IN
/(V
REF
× t
1
), t
1
= 1.1 × R3 × C6 = 25kHz f
S
AS SHOWN.
00875-032
* = 1% METAL FILM, <50ppm/°C TC
** = 10%, 20T FILM, <100ppm/°C TC
t
1
= 33µs FOR f
OUT
= 20kHz @ V
IN
= 2.0V
OHMTEK
PART #1043
Figure 32. Single Supply Voltage-to-Frequency Converter
Typical
bias currents of 2 pA allow MΩ range source
impedances with negligible dc errors. Linearity errors 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.
G = 10
+V
S
G = 100
G = 100
G = 10
0.1µF
2
R
P
1kΩ
R
P
1kΩ
(G = 10) V
OUT
= (V
IN1
– V
IN2
)(1 +
(G = 10) V
OUT
= (V
IN1
– V
IN2
)(1 +
R6
)+V
REF
R4 + R5
00875-034
6
1/4
SINGLE SUPPLY PROGRAMMABLE GAIN
INSTRUMENTATION AMPLIFIER
The
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.
FET inputs bias
currents of 2 pA 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
V
IN2
3
AD824
1
5
1/4
AD824
11
7
V
OUT
R5 + R6
)+V
REF
R4
FOR R1 = R6, R2 = R5 AND R3 = R4
Figure 34. A Single Supply Programmable Instrumentation Amplifier
Rev. E | Page 13 of 16
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