Datasheet > AD8236ARMZ-RL1

AD8236ARMZ-RL1

更新时间： 2022-05-24 12:28:28

品牌	Logo	应用领域
亚德诺 - ADI		仪表放大器
页数	文件大小	规格书
20页	514K
描述
40 Î¼A Micropower Instrumentation Amplifier with Zero Crossover Distortion

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数据手册

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AD8236ARMZ-RL1 数据手册

AD8236

This circuit was designed and tested using the AD8609, low

LOW POWER HEART RATE MONITOR

power, quad op amp. The fourth op amp is configured as a Schmitt

trigger to indicate if the right arm or left arm electrodes fall off

the body. Used in conjunction with the 953 kΩ resistors at the

inputs of the AD8236, the resistors pull the inputs apart when

the electrodes fall off the body. The Schmitt trigger sends an

active low signal to indicate a leads off condition.

The low power and small size of the AD8236 make it an

excellent choice for heart rate monitors. As shown in Figure 42,

the AD8236 measures the biopotential signals from the body.

It rejects common-mode signals and serves as the primary gain

stage set at G = 5. The 4.7 μF capacitor and the 100 kΩ resistor

set the −3 dB cutoff of the high-pass filter that follows the

instrumentation amplifier. It rejects any differential dc offsets

that may develop from the half-cell overpotential of the electrode.

The reference electrode (right leg) is set tied to ground. Likewise,

the shield of the electrode cable is also tied to ground. Some

portable heart rate monitors do not have a third electrode. In

such cases, the negative input of the AD8236 can be tied to GND.

A secondary gain stage, set at G = 403, amplifies the ECG signal,

which is then sent into a second-order, low-pass, Bessel filter

with −3 dB cutoff at 48 Hz. The 324 Ω resistor and 1 ꢁF capacitor

serve as an antialiasing filter. The 1 μF capacitor also serves as a

charge reservoir for the ADC’s switched capacitor input stage.

Note that this circuit is shown, solely, to demonstrate the capability

of the AD8236. Additional effort must be made to ensure

compliance with medical safety guidelines.

+2.5V

–2.5V

20kꢀ

1kꢀ

+2.5V

5kꢀ

AD8609

LEADS OFF DETECTION

+2.5V

0.1µF

953kꢀ

INTERRUPT

LEADS OFF

680nF

+2.5V

0.1µF

AD8236

24.9kꢀ

4.02kꢀ

IN-AMP

AD8609

324ꢀ

AD8609

0.1µF

10-BIT ADC

MCU + ADC

100kꢀ

953kꢀ

1kꢀ

402kꢀ

220nF

1µF

0.1µF

4.7µF

–2.5V

+2.5V

AD8609

1kꢀ

–2.5V

Figure 42. Example Low Power Heart Rate Monitor Schematic

Rev. 0 | Page 19 of 20

1...16 17 181920

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