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To test the INA 155 I gave a sine wave of amplitude 0.2 V p-p 100Hz. It was operated at 5 V single supply. The reference pin was connected to 2.5 V from an op amp buffer. There seems to be no offset in the output whatever voltage the reference pin is given to. The gain was set at 10 with the pins 1 and 8 open circuited.

Schematic:

The circuit is working fine in simulation.

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    \$\begingroup\$ You can't just float the input voltages and expect it to work- the input has to be maintained within the input common mode range. \$\endgroup\$ – Spehro Pefhany May 31 '16 at 12:32
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    \$\begingroup\$ Does your test circuit ac source have a DC return path to the power for the amplifier? \$\endgroup\$ – Peter Smith May 31 '16 at 12:34
  • \$\begingroup\$ The common mode voltage range is from 0.3v to 5.2v. But i want to use this amplifier for emg data acquisition which is of very less magnitude. Is there any single supply In amp which can be used for emg acquisition \$\endgroup\$ – spider May 31 '16 at 12:56
  • \$\begingroup\$ @spider - I take your comment to mean that your signals are less than 0.3 volts, but you want to use a single-supply amplifier. Build your own x10 difference amplifier (4 resistors) using a rail-to-rail op amp. \$\endgroup\$ – WhatRoughBeast May 31 '16 at 14:03
  • \$\begingroup\$ @Peter Smith - there is a dc return path from the source. I missed it in the simulation. \$\endgroup\$ – spider May 31 '16 at 14:14
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The INA555's common mode range is affected by the gain and the reference voltage. Since you are running a simulation, you can see this clearly by replacing the INA555 with the two op amps and resistors as represented on the INA555 data sheet. The output of the first internal amplifier must not be saturated (go to either rail) or the part won't work properly.

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  • \$\begingroup\$ The problem of common mode input voltage is eliminated now by adding 0.5 v to both the input signals. The non inverting input is a sine wave with 0.5 v offset and inverting terminal is given a constant 0.5 v. Now the mean of the output signal keeps increasing. It initially is 1.8 v and is increasing continuously. The reference pin is given 2.5 v from a low impedance op amp buffer which means the mean of the output should actually be 2.5 v. But it increases beyond that. \$\endgroup\$ – spider Jun 1 '16 at 4:21
  • \$\begingroup\$ I was using NI Virtual bench initially when the problem was there. Now when the circuit is battery powered, it is working fine. Why does the mean increase when the circuit is powered from NI Virtual bench? \$\endgroup\$ – spider Jun 1 '16 at 10:38

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