REV. C

AD824

–12–

APPLICATIONS

Single Supply Voltage-to-Frequency Converter

The circuit shown in Figure 4 uses the AD824 to drive a low

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,

the overall feedback loop.

1/4

AD824

C5

0.1 F

NOTES

*

= 1% METAL FILM, <50ppm/ C TC

**

= 10%, 20T FILM, <100ppm/ C TC

U4

REF02

2

6

5

4

3

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

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

2

ms

±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

0.1 F

R1

90k

R2

9k

R3

1k

R4

1k

R5

9k

R6

90k

G = 10

G = 100

G = 10

G = 100

OHMTEK

PART # 1043

1/4

AD824

2

1

3

6

7

5

1k

1k

11

R6

R4 + R5

R5 + R6

R4

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

1/4

AD824

Figure 5b. A Single Supply Programmable

Instrumentation Amplifier