Datasheet
AD620
REV. D
–12–
≈
3kΩ
+5V
DIGITAL
DATA
OUTPUT
ADC
REF
IN
AGND
20kΩ
10kΩ
20kΩ
AD620B
G=100
1.7mA
1.3mA
MAX
0.10mA
0.6mA
MAX
499Ω
3kΩ
3kΩ3kΩ
4
AD705
2
1
8
3
7
6
5
Figure 33. 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 suited for higher resistance pres-
sure sensors powered at lower voltages where small size and low
power become more significant.
Figure 33 shows a 3 kΩ 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 sig-
nal 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 34) where high source resistances of 1 MΩ or
higher are not uncommon. The AD620’s low power, low supply
voltage requirements, and space-saving 8-pin 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.
7
8
1
2
3
5
6
G = 7
AD620A
0.03Hz
HIGH
PASS
FILTER
OUTPUT
1V/mV
+3V
–3V
R
G
8.25kΩ
24.9kΩ
24.9kΩ
AD705J
G = 143
C1
1MΩ
R4
10kΩ
R1
R3
R2
4
OUTPUT
AMPLIFIER
PATIENT/CIRCUIT
PROTECTION/ISOLATION
Figure 34. A Medical ECG Monitor Circuit