AD620

REV. E

–12–

3k

+5V

DIGITAL

DATA

OUTPUT

ADC

REF

IN

AGND

20k

10k

20k

AD620B

G=100

1.7mA

0.10mA

0.6mA

MAX

499

3k

3k

3k

2

1

8

3

7

6

5

4

1.3mA

MAX

AD705

Figure 35. A Pressure Monitor Circuit which Operates on a +5 V Single Supply

Pressure Measurement

Although useful in many bridge applications such as weigh

scales, the AD620 is especially suitable for higher resistance

pressure sensors powered at lower voltages where small size and

low power become more significant.

Figure 35 shows a 3 k

Ω pressure transducer bridge powered

from +5 V. In such a circuit, the bridge consumes only 1.7 mA.

Adding the AD620 and a buffered voltage divider allows the

signal to be conditioned for only 3.8 mA of total supply current.

Small size and low cost make the AD620 especially attractive for

voltage output pressure transducers. Since it delivers low noise

and drift, it will also serve applications such as diagnostic non-

invasive blood pressure measurement.

Medical ECG

The low current noise of the AD620 allows its use in ECG

monitors (Figure 36) where high source resistances of 1 M

Ω or

higher are not uncommon. The AD620’s low power, low supply

voltage requirements, and space-saving 8-lead mini-DIP and

SOIC package offerings make it an excellent choice for battery

powered data recorders.

Furthermore, the low bias currents and low current noise

coupled with the low voltage noise of the AD620 improve the

dynamic range for better performance.

The value of capacitor C1 is chosen to maintain stability of the

right leg drive loop. Proper safeguards, such as isolation, must

be added to this circuit to protect the patient from possible

harm.

G = 7

AD620A

0.03Hz

HIGH

PASS

FILTER

OUTPUT

1V/mV

+3V

–3V

8.25k

24.9k

24.9k

AD705J

G = 143

C1

1M

R4

10k

R1

R3

R2

OUTPUT

AMPLIFIER

PATIENT/CIRCUIT

PROTECTION/ISOLATION

Figure 36. A Medical ECG Monitor Circuit