Data Sheet

AD824

APPLICATIONS INFORMATION

SINGLE SUPPLY VOLTAGE-TO-FREQUENCY

CONVERTER

The circuit shown in Figure 32 uses the AD824 to drive a low

positive going output pulse is integrated by R1 and C1 and used

as one input to the AD824, which is connected as a differential

integrator. The other input (nonloading) is the unknown

closing the overall feedback loop.

1/4

AD824

U4

REF02

10kΩ

2

6

5

4

3

CMOS

74HCO4

4

3

2

1

U3B

U3A

OUT2

OUT1

10V

U1

2

6

5

3

7

1

4

8

U2

CMOS 555

TR

THR

DIS

CV

OUT

R

V+

GND

0V TO 2.5V

FULL SCALE

C3

0.1µF

C4

0.1µF

C6

390pF

5%

(NPO)

R2

499kΩ

1%

R3*

116kΩ

C2

0.01µF

2%

C1

0.01µF

2%

C5

0.1µF

R1

499kΩ

1%

NOTES

* = 1% METAL FILM, <50ppm/°C TC

** = 10%, 20T FILM, <100ppm/°C TC

Figure 32. Single Supply Voltage-to-Frequency Converter

Typical AD824 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.

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 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.

Table 6. AD824 In Amp Performance

Parameter

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

2 μs

5 μs

Noise @ f = 1 kHz

G = 10

270 nV/√Hz

270 nV/√Hz

G = 100

2.2 μV/√Hz

2.2 μV/√Hz

10

0%

100

90

1V

5µs

Figure 33. Pulse Response of In Amp to a 500 mV p-p Input Signal;

0.1µF

R6

90kΩ

R5

9kΩ

R4

1kΩ

R3

1kΩ

R2

9kΩ

R1

90kΩ

G = 10

G = 10

G = 100

G = 100

OHMTEK

PART #1043

2

1

3

6

7

5

11

1/4

AD824

1/4

AD824

1kΩ

1kΩ

R6

R4 + R5

FOR R1 = R6, R2 = R5 AND R3 = R4

R5 + R6

R4

Figure 34. A Single Supply Programmable Instrumentation Amplifier

Rev. E | Page 13 of 16