What is the purpose of the resistors(470 and 100k) at the input pins 3 and 2 of the instrumentation amplifier and what diffenter image description hereerence does it make if i do away with them?

  • \$\begingroup\$ No faint idea. What is the source of your schematic, and what was it trying to do? \$\endgroup\$ – WhatRoughBeast Mar 5 '17 at 17:27
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    \$\begingroup\$ i think it's to have a connection to the high-impedance inputs in case the connector is disconnected from the source. so the op-amp inputs don't float. maybe the 470 ohms is to isolate the source a little from the electronics of the instrumentation amp. \$\endgroup\$ – robert bristow-johnson Mar 5 '17 at 17:34
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    \$\begingroup\$ @WhatRoughBeast Its an ecg signal. It's(instrumentation amplifier) suppose to amplify the ecg by a gain of 5 +(85k/R1) \$\endgroup\$ – TosinAl Mar 5 '17 at 17:58

The series 470R offers additional limited ESD current limit protection of device to internal shunt diodes from cable to body capacitance discharges. It reduces the rise time of avalanche ESD effects so the protection diode can respond faster than the sub-nanosecond events.

The 100K shunt values provide a CM shunt impedance of 100K to shunt galvanic electrode CM offsets but mainly a reference ground for shielding CM noise as well.

Electrode coupling resistance are expected to be 1~10k.


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