AD620_04 AD [Analog Devices], AD620_04 Datasheet - Page 15

• Manufacturer Part Number: AD620_04
• Description: Low Cost Low Power Instrumentation Amplifier
• Manufacturer: AD [Analog Devices]

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 40 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
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
noninvasive blood pressure measurement.
1.7mA
3k Ω
3k Ω
5V
3k Ω
3k Ω
PROTECTION/ISOLATION
G = 100
PATIENT/CIRCUIT
499 Ω
C1
Figure 40. A Pressure Monitor Circuit that Operates on a 5 V Single Supply
AD705J
1M Ω
R4
10k Ω
R1
8
1
3
2
1.3mA
MAX
AD620B
Figure 41. A Medical ECG Monitor Circuit
4
R3
24.9k Ω
7
R2
24.9k Ω
5
Rev. G | Page 15 of 20
8.25k Ω
R
0.10mA
G
6
20k Ω
10k Ω
AD620A
20k Ω
Medical ECG
The low current noise of the AD620 allows its use in ECG
monitors (Figure 41) 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-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
–3V
+3V
AD705
0.6mA
MAX
FILTER
0.03Hz
HIGH-
PASS
REF
IN
AGND
ADC
AMPLIFIER
G = 143
OUTPUT
DIGITAL
DATA
OUTPUT
OUTPUT
1V/mV
AD620